***Stringway Machine Users Club***

[Jacklondon00]

Add me to the club

My ML 100 arrived last week. I haven't had the chance to use it yet.

I do have a question, does anyone know what socket is used to tighten the perpendicular side bars/table top stand legs? There are two holes, one on each side, with a little nut inside. 3/8 is too small, but 7/16 is too big. Do these even need tightening?

https://flic.kr/p/qSTn4m

 

[oble]

Welcome to the club, oble! Perhaps your rabbit will become the new Stringway club mascot.

Thanks Oh yeah, I think that'll be a great career for him. :lol:

You have to start teaching your assistant how to string and you're all set

Heh.. I'll have to make sure he doesn't start gnawing at the strings. He has an affinity towards soft plasticky things. :-?

 

[Peppershaker]

My ML 100 arrived last week. I haven't had the chance to use it yet.

I do have a question, does anyone know what socket is used to tighten the perpendicular side bars/table top stand legs? There are two holes, one on each side, with a little nut inside. 3/8 is too small, but 7/16 is too big. Do these even need tightening?

https://flic.kr/p/qSTn4m

All components on the Stringway machines are I believe metric. On my machine the two nuts are 10mm; however, I doubt that there should be any reason to adjust these. There may be other purposes but I believe they are there to hold the legs on both ends of the machine.

Enjoy your machine.....they are very nice builds.

 

[Jacklondon00]

Hmmm, that's going to be tricky, these are not tightened all the way, so there is some movement in the legs when trying to move them by hand, otherwise it stands firm. Would be nice to get everything nice and tight.

 

[oble]

Hmm... mine are also nice and snug but I agree that it would be nice to get everything nice and tight, especially with the legs. Not sure if you can find metric sockets where you're located? 10mm is right in between 3/8" and 7/16" lol.

Gotta love the metric/imperial unit discrepancies when it comes to tools and fittings. :-?

 

[oble]

I have a question regarding the situation shown in the picture above. Is that fine for the main string's tension if it gets tensioned while being in contact with the throat?

I read some older comments in this thread suggesting placing a business card or something similar between the string and the throat before pulling tension. There were also some comments about tensioning the next string through the head instead and use some tugging and string pitch tuning to get the tension right for the preceding string? Is one way better than the other or does it not matter much at all?

Another similar issue I had was for a couple of the holes just outside of the throat around 4T~6T and 4H~6H, where the natural angle between the grommet and the tension head causes the string to rub a little against the white plastic bit of the racquet support post (the thing at the bottom-middle of the same picture above) when tension is applied. Is this also a non-issue in general? If my description is not clear, I'll take a picture the next time I string a racquet.

 

[Maui19]

I read some older comments in this thread suggesting placing a business card or something similar between the string and the throat before pulling tension. There were also some comments about tensioning the next string through the head instead and use some tugging and string pitch tuning to get the tension right for the preceding string? Is one way better than the other or does it not matter much at all?

I have tried it both ways, and I don't find a noticeable difference in the stringbed tension, playability or longevity. I prefer pulling everything from the head because my mains are gut and I don't like them rubbing against the frame. I also find it to be faster when stringing.

 

[Jacklondon00]

I finally got some AAA batteries for my tension scale and decided to test the accuracy of the "automatic drop weight" component of the machine. I placed the scale inside the frame so the friction component is taken into account. When the bar is perfectly horizontal, the tension is right on, it's scary how accurate it is.

However, when the bar is not perfectly horizontal, I am getting a noticeable difference in tension, 2 lb higher when the bar is above horizontal, and 2 lb lower when the bar is below horizontal, and these are not on the very extremes of the above/below range. The below horizontal would be normal for a stretchy string like Monogut ZX.

Not sure how this accuracy relates to lets say your regular drop weight, where you always shoot for horizontal, and with a ratchet system it's easier to adjust for that. But the whole point of this machine is to have exactly the same tension at every angle. It's not easy to adjust that if you have a very stretchy string, there is no ratchet system, and you can only pull on the string so much prior to clamping and lowering the arm.

Any advice?

I uploaded a video here:

http://youtu.be/mXfuGnvVsHg

 

[Jacklondon00]

When using the concorde system for the first 2 mains, the difference +-5lb on the extremes when the reference tension is 60 lb, and +- 3 lb when the arm is a reasonable distance above and below horizontal.

 

[volusiano]

I finally got some AAA batteries for my tension scale and decided to test the accuracy of the "automatic drop weight" component of the machine. I placed the scale inside the frame so the friction component is taken into account. When the bar is perfectly horizontal, the tension is right on, it's scary how accurate it is.

However, when the bar is not perfectly horizontal, I am getting a noticeable difference in tension, 2 lb higher when the bar is above horizontal, and 2 lb lower when the bar is below horizontal, and these are not on the very extremes of the above/below range. The below horizontal would be normal for a stretchy string like Monogut ZX.

Not sure how this accuracy relates to lets say your regular drop weight, where you always shoot for horizontal, and with a ratchet system it's easier to adjust for that. But the whole point of this machine is to have exactly the same tension at every angle. It's not easy to adjust that if you have a very stretchy string, there is no ratchet system, and you can only pull on the string so much prior to clamping and lowering the arm.

Any advice?

I uploaded a video here:

http://youtu.be/mXfuGnvVsHg

I have an MS200 DX (using the spring system along the leg instead of the drop weight). So I couldn't perform the exact same test you did, but I performed a similar test on mine.

When setting mine to 60 lbs, I get about 61 on the high end and 58 on the low end. My high end means I pull the string as tight as I can and it doesn't stretch much at all (or I repull again if it stretches until I get minimum stretching). My low end means I give the string enough slack so that the head goes far back as it can just before the red button pops. The MS200 DX has a red button which pops out when the head goes too far back out of range for accurate tension.

So I think my result is not too far off from yours.

I don't know what angles you had in your experiment exactly, but if it's about plus and minus 20 degrees, you can take the cosine of 20 degrees and multiply it by 60 lbs, which will give you about 56.4 lbs. This would be how far off in tension a normal drop weight would be if you let it drop 20 degrees below horizontal.

Cosine of 45 degrees is 0.707.
Cosine of 20 degrees is 0.94.
Cosine of 10 degrees is 0.985.

So as you can see, in a normal drop weight, if you're only about 10 degrees off from horizontal, you're only 1.5% off. If you're 20 degrees off, that's about 6% off. At 45 degrees, you're almost 30% off.

So it looks like the Stringway head is not so exact in tension at any angle like advertised based on your and my experiments. But it seems like it's still a little better than the regular drop weight (if you angle of experiment is 20 degrees per my eye balling).

In terms of the theory why the Stringway head in theory should give the same tension at any angle, check out the equation below:

As to why your (and my) experiment does not yield the same result as the theory? I'm guessing it's because of manufacturing variances in the tension head design such that the leverage bar is not 100% perpendicular to the line between the pivot point and the tension head's mouth, resulting in tension deviation because angle A on the drop weight (left) side (as seen on the pic above) is not really the same as angle A on the tension head (right) side as assumed.

What would be interesting is if you allow 45 degrees off and see whether the tension is a lot less than 30% off or not. If a lot less than 30% (as 30% would be the case of a normal drop weight), then you know that the head design on the Stringway performs more accurately when the drop weight is grossly non-horizontal, even though not exactly at any angle as advertised in theory due to manufacturing variances.

 

[Jacklondon00]

Thanks for the detailed reply and the number crunching effort. I can definitely confirm that the variance in tension is much better than one would expect from a regular drop weight, based on your calculations. I don't have a way to measure the angle, but the difference between perfectly horizontal and close to the bottom is 4% at 60 lb, and I think that this is definitely more than a 20 degree angle. I would need to run more test to see if the percentage increases at lower tensions.

Since I was already used to this system from using an M50, I am able to place the string and adjust is with one hand so that the arm falls almost perfectly horizontal on most occasions. Being a perfectionist I was doing this on my old machine because that one had the same issue, which I attributed to being an old machine. On my old M50, the ruler was not as well correlated to the actual tension pulled, I had to use the digital scale to mark my own tension points along the metal arm. Thus I thought it was a mechanical issue that was causing the variance, so I was surprised to see it with this brand new machine, especially since the tension is spot on when using the ruler when the arm is horizontal.

Still, if I was Stringway I would be more sensitive to the quality control/calibration of that mechanism. Although I realize that most people never probably test this. If there is indeed a small variance in this mechanism, their advertising should reflect this, because the end result is that there is a small difference in tension, so the tension is not the same in every position as they claim.

It would be nice to know if this is the case with most Stringways, or did I just get a badly calibrated machine.

 

[tball]

Does anybody know if such inaccuracies are also present in the foot-operated version of this machine? It has the same jaws, but the pulling force is generated by the pedal, not by the weight on a stick.

 

[volusiano]

Does anybody know if such inaccuracies are also present in the foot-operated version of this machine? It has the same jaws, but the pulling force is generated by the pedal, not by the weight on a stick.

Yes, that's the one I have -> the MS200 DX foot-pedal operated with a spring inside. I see about the same variation.

 

[Jacklondon00]

Ok, so after running a few more tests, here are a few things I learned that might help everyone (assuming that this is not just an issue with my machine)

1. The concorde system creates much greater variance.

So if you have the concorde system, make sure the lever is horizontal or slightly above horizontal when stringing those first several mains. In my tests at 50 lb, using the concorde system, when the lever was close to bottoming out, it only pulled 45.5 lb of tension. This would be pretty important to those stringing with stretchy multis or natural gut mains. This is because the string enters the jaws at a different angle than usual, so makes perfect sense.

2. When not using the concorde system, the difference is actually pretty minor, and the lower the reference tension the smaller the difference. At 40 lb I was getting +- 1.5 lb when the lever was above/below horizontal towards the extreme ends, so less than 1 lb above/below on most occasions. At 50 lb it was +- 2 lb towards the more extreme ends.

3. On most occasions if the lever is within reasonable distance from horizontal, so not on the extremes, it was basically 1 lb to 1.5 lb difference, so 51.5 lb vs 48.5 lb. And since you can always adjust the lever to fall at horizontal or below, we are talking about a range of about 1 lb, so pretty accurate, but not perfect.

4. At 60 lb reference tension, when the lever is close to bottoming out, the actual tension is 57 lb. This is something to consider when stringing with a stretchy string.

So to sum this up, as long as the lever is not at the extremes, (as in not close to bottoming out), I am getting within 1 lb to 1.5 lb of reference tension with a pretty wide range above and bellow horizontal. At lower tensions (low 40s), the difference is basically within 1 lb. And it's very easy to get the arm to fall horizontal with some practice, and if it's slightly off it makes almost no difference in tension.

My main concern is having to string stretchy strings at high tensions, and especially on the first several mains when using the concorde system.

If someone can please post and tell me that their machine gives them EXACTLY the same tension at every angle, or at least EXACTLY the same tension with the arm slightly above or below horizontal, please post it here. This would mean that I need to get my machine adjusted somehow because mine definitely does not give "perfect" reference tension at every angle, but I suspect that most of these machines are similar, whereby they are pretty accurate but far from "prefect."

 

[Jacklondon00]

How to mod your Strigway to be more accurate

Here is a video of a modification I invented that improved the accuracy of my brand new Stringway ML100 from a variance of 4 lbs to virtually zero variance. With this modification to your machine, it will now function as advertised:

The tension is the same for every angle of the lever, which has 3 advantages:

1) The accuracy of the system is very reliable.
2) The stringer does not have to pay attention to the angle of the drop weight lever.
3) The tension is maintained during the slow elongation of the string.

I plan to patent this system and sell it to Stringway. Best of all, no tools required!

http://youtu.be/PZJBhmjV3og

 

[volusiano]

Here is a video of a modification I invented that improved the accuracy of my brand new Stringway ML100 from a variance of 4 lbs to virtually zero variance. With this modification to your machine, it will now function as advertised:

The tension is the same for every angle of the lever, which has 3 advantages:

1) The accuracy of the system is very reliable.
2) The stringer does not have to pay attention to the angle of the drop weight lever.
3) The tension is maintained during the slow elongation of the string.

I plan to patent this system and sell it to Stringway. Best of all, no tools required!

http://youtu.be/PZJBhmjV3og

I thought about this issue some more and I think it has to do with mechanical variances that cause your drop weight bar to be not perfectly perpendicular with the line between the pivot point to the tip of the tension head mouth where the string is grabbed. If you look at the picture and theoretical calculation below, if that relationship of the actual head and bar is not perfectly perpendicular due to slight manufacture variances, the angle A on the drop weight (left side) won't be exactly the same as the angle A on the tension head (right) side as assumed in the calculation. The slight variation from the 90 degree assumption will result in the variances you see in the tension pulled.

For some reason, when you elevate the tension head end of the stringer with books, it helps make the drop weight bar closer to being perpendicular, therefore the result falls more inline with the theory. That's the only thing I can think of because the other 2 values a and b in the equation remains the same whether you elevate the stringer end with books or not.

As to why you get perfectly 60 lbs on the dot when the bar is horizontal, that's simply due calibration to 60lbs at the horizontal position. But any variance from the 90 degree angle relationship will for sure result in tension variances when the bar is above or below horizontal. The bigger this angle variance, the bigger the tension variance. You can almost replace the angle A in the equation below with A1 and A2 and go through the math backward and calculate this variance based on your actual tension variance result. As long as A1 is not equal to A2, the torque variance will be proportional to the angle variance.

As to why elevating the stringer end helps make the drop weight bar more perpendicular, maybe there's a little play on the bar somehow that cause it to droop down a little more when flat but the elevation reduces this slight drooping? So maybe this is an adjustment issue after all, because I think the bar can be taken off when moving if desired, right? I don't know whether there's anything to tighten when you reinsert the bar back in for operation, though.

Anyhow, that's the only logical thing I can think of that would explain what you observed. Hope this helps.

By the way, just out of curiosity, I tried to elevate my tension head side of my MS200 machine like you did to see if that makes a difference on my machine but it didn't. I still see about a +/- 1.5 lbs variation (totalling 3 lbs variation from one extreme to the other) on my machine like before. But since my machine is the spring-based foot-pedal operated design, I think there's a lot more variables at play than the simple drop weight design. The spring may not provide the exact force at various points like the static mass of the weight in the drop weight does. Also, my tension head design may also suffer the same fate of not having a perfectly perpendicular 90% angle between the (very short) leverage bar and the pivot point and the tension head mouth either. Except in your case you can correct your variance with the elevation for some reason, but I can't apply the same correction on mine with the same success.

 

[Jacklondon00]

I think this confirms your theory?

http://youtu.be/-QYQ2LJHlEg

I actually made this video first, which gave me the idea to put the books under the tension head.

I have had a long email discussion with Fred Timmer from Stringway about this. He watched the videos and has been patient and kind enough to explain the issues in his emails.

Basically it comes down to manufacturing tolerances. They don’t calibrate their machines individually post production, so the accuracy comes down to the design and the quality of the manufacturing process.

He said that having this small variance is normal. He doesn’t consider the variance at extreme angles as practically relevant while stringing, and I would have to agree with him on this. So basically the variance is not really -+2 lbs at 60 lbs, but closer to around 1.25 lbs over/under with quite a large deviation from the horizontal position. With a regular drop weight, this angle would cause a much greater variance of over 30 lbs.

While I am still happy with my machine because it’s giving me exactly spot on tension at horizontal position, I would definitely like to see Stringway calibrate each machine individually or have some sort of adjustment option. It is obvious from my tests that the design allows for much less variance.

In my head I always considered these machines equivalent to high end luxury automobiles, and at this price point I would have expected that they would do some individual calibration, so I was surprised to find out that they don't. So this experience has been a little disappointing for me. I think that they might come up with a solution in the future that might allow for an adjustment, these guys make a lot of innovative stuff, but it will be too late for my machine.

I am quite surprised that nobody besides volusiano posted about their views on this issue or about their experience with their machine. Over 20 people have seen my videos, so it would be nice to hear peoples opinion on this issue. Do you think I am being too picky with the variance +- 2 lbs from what I expected?

I realize that we all love our Stringways, but maybe if people tested them out years earlier and said something the current version of the machine would be either individually calibrated or had an adjustment option to eliminate the variance and make these machines absolutely perfect.

 

[volusiano]

I think this confirms your theory?

http://youtu.be/-QYQ2LJHlEg

While this video doesn't confirm my theory about the right angle not being really 90 degrees, causing the 2 angles A on the left and A on the right not being the same, it made me think of another (more obvious) theory.

Going back to the picture/calculation below again, another assumption (beside the right angle assumption above), is that the Te (tension on the string) is applied to a perfectly horizontal string. For the equation W*H=Te*V to hold true (same torque on both sides of the equation), W is assumed to be perfectly vertical, and Te to be perfectly horizontal.

V = b * cos(A) assumes that V is the vertical perpendicular height to the horizontal Te, or else the equation using cos(A) would not work.

So if your string is not perfectly horizontal to line up with the calculated Te, then the resulting Te on the string will deviate.

Maybe your normal string angle is pointing upward and by either elevating the tension head end or lowering the racket frame head end, it helps make your string more horizontal? Do you have a small bubble level that you can put on the string to see if the string is horizontal after your adjustment or not? It's worth checking that out.

In reality, when you have a racket on there, the string may not be perfectly straight through and through from the racket head to the tension head's mouth. The racket throat may cause a slight deflection point and it is from there to the tension head's mouth that will determine how horizontal that section of the string will be. So your experiment here will be tainted by that variation as well in real life.

One small comment about the picture below: The distance "a" in the picture is not exactly correct. It needs to extend out to the center of the big black dot on the left.

 

[10SDad]

I am quite surprised that nobody besides volusiano posted about their views on this issue or about their experience with their machine. Over 20 people have seen my videos, so it would be nice to hear peoples opinion on this issue. Do you think I am being too picky with the variance +- 2 lbs from what I expected?

Hey Jacklondon00.

While there haven't been additional responses, I'm sure others, like me, are reading your posts with interest. Math has never been my strongest trait, so I've refrained from trying to calculate an explanation for your testing. I think Volusiano has done a great job in providing some feasible explanations, and the responses from Fred at Stringway provide good info as well.

I wouldn't say your pursuit of understanding your particular machine's capabilities is picky, but is rather an indication of your enthusiasm for your craft. I think it's important to remember that while the mathematical calculations upon which this tensioning system functionality is based are theoretically correct, there will always be variables introduced in actual application that will impact the final results. (Just like Economic Theory.) Different frame widths/sizes, grommets/locations, clamp pressures/locations, pull angles, manufacturing tolerances, and especially the human component can all impact final results, if even just slightly. Knowing our machines, and then working them like a craftsman is what allows us to be as proficient as possible. The adjustments you have discovered/are making will help you do your best stringing with your particular machine.

I appreciate the efforts you've taken and your willingness to share them. I plan to test my own machine, not because I am not happy with its performance, but to see if I can learn to use it better.

 

[onehandbh]

I don't have a digital tensior calibrator (mine is manual), but I'll test my stringway machine later today to see how much variance I get.

Overall, I've been pretty happy with it. I seem to get more consistent string jobs doing it myself versus having a shop do it. Could be the stringer rather than the machine, though.

 

[Joonas]

I opened a thread about this topic awhile ago. http://tt.tennis-warehouse.com/showthread.php?t=484949
I also talked with Fred about it and like 10sdad above said it is good way to undrstand your machine rather than something to worry about.

As always in stringing being constant in your ways of working is also very true with Stringway machine.

I string alot for many junior players and I measure DT of the stringbed everytime with ERT300. And the DT is always the same for each players racket time after time. That says quite much about the consistency of the machine.

EDIT: Fred pointed out that measurements should always be taken inside of the racquet sonthat the angle to tension head is as it is in reaity. By doing that there was less variation in results between lever being up or down.

 

[onehandbh]

I have a Gamma XST lockout machine and also a stringway.

A racquet strung at 50lbs by the stringway feels tighter than a racquet strung at 50lbs with the XST. I only use the stringway now.

 

[lew750]

Wouldn't a racket strung on any drop weight feel tighter than one strung on a lockout?

 

[Joonas]

Wouldn't a racket strung on any drop weight feel tighter than one strung on a lockout?

It is more about the machine being a constant pull or lock out.
There are electronic contstant pulls and electronic lock outs.

Stringway is a constant pull and most other drop weights are lock outs as they have the ratchet mechanism.

It is only natural that stringbed strung with constant pull should feel tighter.

 

[Irvin]

There are fixed clamps and flying clamps that have a lot to do the the end result for string bed stiffness. Where tension is pull ot 60# on a CP machine or 60# on a LO makes no difference what so ever. When pulling on CP machine the tension is constant and as the string stretches it is continuously at 60#. On a LO machine if you pull more than once you effectively have the same end result except for the fact that is LO is more accurate than a CP.

 

[Rabbit]

^^^^^^^
I know there's a video on this, allegedly proving it, but I disagree with the premise. Pulling tension twice on a LO doesn't equal results on a constant pull.

 

[Irvin]

I'm not saying it does but you can increase the string bed stiffness by pulling slower or by pulling more than one time. Whether a racket is strung on a CP or LO machine does not necessarily determine which one will have the higher tension. More often than not a LO tensioner will produce a lower tension though.

 

[onehandbh]

I'm not saying it does but you can increase the string bed stiffness by pulling slower or by pulling more than one time.

I also found that pulling slowly on the lockout machine resulted in higher stringbed stiffness. If I pulled very quickly I could string faster but it felt like the tension was lower.

I got the stringway because it fit the following criteria:
- manual & does not need electricity
- durable
- easy to disassemble and put away
- fairly accurate /consistent

I love the stringway clamps. They seem to work much easier and better than the clamps that came with my gamma xst. With the gamma clamps it was much easier to accidentally make them too tight and crush the strings a bit.

I also liked the idea that someone designed a dropweight that did not require the bar to be perfectly parallel. I used to occasionally string with a klippermate years ago and the parallel bar thing drove me nuts.

 

[Joonas]

I would suggest not to make this another cp/lo thread. Irvin has point.

For this topic "onehandbh" put it in good way. Stringway mechanics make life for stringer easier and speeds up things as you don't have to waste time to make sure bar is horzontal.

Keep things constant, have your rhytm when stringing and Stringway machine won't stand in your way to achieve perfectly constant results.

 

[Irvin]

...For this topic "onehandbh" put it in good way. Stringway mechanics make life for stringer easier and speeds up things as you don't have to waste time to make sure bar is horzontal...

Unless I'm mistaken someone not long ago came up with readings that were off depending on whether the bar was high or low (see post 258 on.) That tells me the autmatic feature of the Stringway does not work.

 

[Joonas]

Unless I'm mistaken someone not long ago came up with readings that were off depending on whether the bar was high or low (see post 258 on.) That tells me the autmatic feature of the Stringway does not work.

Irvin, check the thread by me which I pasted few posts ago. We are talking about few % differences.

And I repeat myself. I ALWAYS end up in same DT with each player. For notion ERSA (likely USRSA as well) as well has the tolerance in certification tests of +-1 DT units.

So again. Stringway machine won't stand in between you and consisten results.

 

[volusiano]

Unless I'm mistaken someone not long ago came up with readings that were off depending on whether the bar was high or low (see post 258 on.) That tells me the autmatic feature of the Stringway does not work.

This is jumping to the wrong conclusion, IMHO.

The constant pull feature of the Stringway, even if there's some slight deviation of a pound or two in tension from the reference 60 lbs when the drop weight is not horizontal, is still much more accurate than a regular drop weight at the same angles from being horizontal.

So the constant pull feature of the Stringway at non-horizontal levels does work. Even if it doesn't work "perfectly" as advertised, it still does work much better than the regular drop weight.

The complaint is that it's not "perfect" as advertised. But by making some minor adjustment, the OP CAN get it to work almost perfectly as advertised.

So the theory holds, it's just that the OP wishes Stringway scales back their marketing from portraying it as being "perfect" to something more "realistic" (due to mfg variations) to set better expectation with buyers.

 

[onehandbh]

You bring up an interesting question, though. How much of a difference does the stringway mechanism make vs a regular dropweight machine?

My gamma string calibrator only has scale markings in increments of 5 lbs, but I'll try a test later today or tomorrow where I make the tension arm near the bottom, at the middle and also near the top to see how much of a difference it makes.

I haven't had a chance to look into the physics/math calculations of how it works, but I'll try to when I get some more free time. I usually trying to squeeze in playing some tennis during my free time, though.

The constant pull feature of the Stringway, even if there's some slight deviation of a pound or two in tension from the reference 60 lbs when the drop weight is not horizontal, is still much more accurate than a regular drop weight at the same angles from being horizontal.

So the constant pull feature of the Stringway at non-horizontal levels does work. Even if it doesn't work "perfectly" as advertised, it still does work much better than the regular drop weight.

 

[volusiano]

You bring up an interesting question, though. How much of a difference does the stringway mechanism make vs a regular dropweight machine?

My gamma string calibrator only has scale markings in increments of 5 lbs, but I'll try a test later today or tomorrow where I make the tension arm near the bottom, at the middle and also near the top to see how much of a difference it makes.

I haven't had a chance to look into the physics/math calculations of how it works, but I'll try to when I get some more free time. I usually trying to squeeze in playing some tennis during my free time, though.

The math of the regular drop weight is very simple, actually. The deviation is basically the cosine of the deviated angle. For example (I showed this in an earlier post):

Cosine of 45 degrees is 0.707.
Cosine of 20 degrees is 0.94.
Cosine of 10 degrees is 0.985.

So as you can see, in a normal drop weight, if you're only about 10 degrees off from horizontal, you're only 1.5% off. If you're 20 degrees off, that's about 6% off. At 45 degrees, you're almost 30% off.

Let's use 60 lbs as the horizontal reference, at 45 degrees, 30% off is 18 lbs lower. At 20 degrees, 6% off is 3.6 lbs lower.

In Jacklondon00's videos, his angles above or below sure looks like he was more than 20 degrees off horizontal, and he was only a couple of lbs off from 60 lbs, not 3.6 lbs or more like with the drop weight. I don't think he was quite at 45 degrees off. But let's just say by an eyeballing guess, he was roughly 30 degrees off, the cosine(30)=0.866 or 13% off or 7.8 lbs off from 60 lbs. This is considerably more than the couple of lbs off that Jacklondon00 was seeing.

 

[Jacklondon00]

Wow, lots of great posts in the last few days. And thanks for adding the link to the old thread about this issue. Reading it was interesting to say the least.

I did a few more tests, including some while using my iphone to measure the angle of the string going into the gripper. The string does not enter the gripper perfectly horizontal, and even when I set it up to do so, the results don't improve much. The angle of the string changes based on the angle of the lever. Even when the machine is set up with books and gives the same tension at every angle, the string enters the gripper at different angles. The only thing that remained constant was that when the angle of the string entering the gripper was negative, (that is the slope was from high to low), the inacuracy was much greater even if the slope was only between -0.5 and -1.5 degrees. However, when the slope was positive, (that is from low to high), I was getting exactly the same tension when the string angle was between +4.6 and +5.6 degrees.

Not sure what conclusions I can draw from this, seems like the string should go into the gripper from low to high at arounf 5 degrees on my machine. I feel like if the gripper was a few inches higher on my machine, I could get accurate tension at every angle of the lever.

For now, I am content with adding a thin book to one side, which doesn't tilt the machine too much, and I can reduce the varience to within 1 lb, above/below, so I am fine with that. Perhaps I might invest in some custom rubber legs that raise that side by an inch or two instead of using a book.

Thanks for the great posts, and I hope if some of you decide to test your machine, or figure out why raising the gripper helps improve accuracy, post the results here and let us know.

 

[OccasionalStringer]

So looking at this theoretical calculation presented in the drawings found also in this thread.

They are of course correct provided:

1) The string comes exactly horizontally to the gripper
2) The tension head is perpendicular to the weight bar (= line drawn from the string gripping point to the tension head pivot point makes 90 degree angle with the weight bar)

The inaccuracy Jaclondon00 has detected comes directly from point 2 above. In the real implementation the tension head angle is not exactly 90 degrees. This is affected not only by the manufacturing tolerances but also by the string thickness. So if you measure this angle with and without string in the gripper you can easily detect a difference of a few degrees.

So if the tension angle differs from 90 degree by B degrees then the balance equation becomes (assuming that the string comes horizontally to the gripper)

W * a * cos (A) = Te *b* cos(A+B)

And then the equation for string tension is

Te = cos(A)/Cos(A+B) * W * a / b.

i.e the tension depends on the weight bar angle. I think that the error in tension head angle varies between machines due to the manufacturing tolerances. In my ML100 it is about +3 degrees with 1.25 mm string.

So if you analyse this error factor cos(A)/cos(A+B) with B=3 degrees you notice that it is very close 1 to when A is zero (weight bar horizontal) and the error increases as angle A increases or decreases (goes below zero)

Assuming positive B and negative A (=bar below horizontal) the error factor is less than 1 so string tension is also below the intended reference.

And with positive B and positive A the error factor is greater than 1 and thus the string tension is higher than the intended reference.

Assuming B = 3 degrees then the error factor and error -% with certain different angles A

A /Error Factor /Error-%
-30 0,972 -2,80
-20 0,983 -1,74
-10 0,992 -0,78
0 1,0014 0,14
10 1,0107 1,07
20 1,0208 2,08
30 1,0326 3,26
40 1,0474 4,74


So concerning the experiment with books done by Jacklondon. If you tilt the machine so that you increase the angle of the weight bar by B degrees (assuming positive B) then you basically eliminate the error factor as A is now actually A+B and thus the error factor is 1.

Analysis of the error when the string is not horizontal is also pretty straightforward. When the string comes from a mounted racket the string comes quite close to horizontal and the error caused by this quite small except when you go over or under the throat. Anyway I would go over the the throat because the string tension is higher when the string comes from high to low so this thus compensates the extra friction.

And finally, I also agree that Stringway marketing considering the accuracy of this machine has been way too much! I think that Stringway web pages used to have a reference directly to this thread but I can't find it anymore!

 

[lew750]

Interesting discussion about the accuracy of the Stringway. Here are my thoughts about it.

My opinion is based on the following assumptions. When a drop weight machine's bar is level, the tension is usually very accurate. This goes for the Stringway as well as my old Eagnas & Klippermate. When the bar is not level, the tension is less accurate, although more accurate on the Stringway. Other drop weight machines correct for this by having some kind of mechanism to easily move the bar back to level. Based on videos I've seen, Stringways don't have a mechanism for this. Stringway claims you don't need it. Bottom line, most drop weight machines are very accurate but string jobs take longer because of the extra time taken leveling the bar after each pull. Stringway machines are faster and more convenient because you don't have to level the bar, but your tensions may be off a little depending on the angle of the bar.

I'm happy with my P200, but it's 30 years old and parts are hard to come by. I try to know as much about other machines as I can so I can recognize a deal if it drops in my lap. Most of you love your Stringways and are happy with the results you get. I would probably be happy too, but learning they are not as accurate as advertised makes me wonder if I wouldn't be happier with something like a Pioneer DC Plus.

 

[marco forehand]

My two cents on the accuracy issue.
I can understand the attempt to use a gauge and then project that the differences measured using a gauge will translate to X in a string bed. I say have at it for those who want to explore things in that way.
For me the final result is the most important consideration. So I prefer analysing the string bed after it comes off the machine.
I had three string machines in my house for about 18 months. A Stringway ML 100, a Stringway EM450 and an Ektelon H (with a lockout and a Wise 2086 tension head).
I tested the string bed with a variety of tools. A Babolat RDC, an ERT 300, and a Stringmeter.My favorite device has ended up being the Stringmeter. It allows me to test individual mains and crosses and I trust it's readings more then the ERT 300 (were I could get different readings within minutes of each other)
I string mostly "players" frames, rarely anything over 100 sq", no fly patterns. Poly,poly hybrids, some gut and some syn gut, very little in the way of multifilaments.
With all that as a qualifier, I get my most consistent results (based on using the various test equipment I described above) with the ML 100.
I was able to get good results with all the machines. I now do almost all my stringing on the ML 100. I sold the EM 450 (not because it wasn't a good machine, I didn't think it was appropriate for a home based stringer) and I still have the Ektelon H even though I rarely use it.
I am a fan of Stringway but that is based on my experience with their product.
As an aside, I don't find stringing on my stand mounted ML 100 to be slower then any other machine I have worked with. In fact I think it is faster. But I have never kept a log of my stringing times so I will allow that is just an impression.

 

[volusiano]

So looking at this theoretical calculation presented in the drawings found also in this thread.

They are of course correct provided:

1) The string comes exactly horizontally to the gripper
2) The tension head is perpendicular to the weight bar (= line drawn from the string gripping point to the tension head pivot point makes 90 degree angle with the weight bar)

The inaccuracy Jaclondon00 has detected comes directly from point 2 above. In the real implementation the tension head angle is not exactly 90 degrees. This is affected not only by the manufacturing tolerances but also by the string thickness. So if you measure this angle with and without string in the gripper you can easily detect a difference of a few degrees.

So if the tension angle differs from 90 degree by B degrees then the balance equation becomes (assuming that the string comes horizontally to the gripper)

W * a * cos (A) = Te *b* cos(A+B)

And then the equation for string tension is

Te = cos(A)/Cos(A+B) * W * a / b.

i.e the tension depends on the weight bar angle. I think that the error in tension head angle varies between machines due to the manufacturing tolerances. In my ML100 it is about +3 degrees with 1.25 mm string.

I think it's established here that the variation B degree introduced here is a fixed variation due to manufaturing variation (and string thickness).

For clarity, I'll call this Bf (for B fixed).

So concerning the experiment with books done by Jacklondon. If you tilt the machine so that you increase the angle of the weight bar by B degrees (assuming positive B) then you basically eliminate the error factor as A is now actually A+B and thus the error factor is 1.

I'm not quite sure here how the introduction of a temporary B degree variation from raising the end with a book actually takes away the error factor.

I'll call this new B Bt (for B temporary).

Your hypothesis is that the equation becomes:

Te = (cos(A+Bt)/cos(A+Bf))*W*a/b, so if Bt=Bf, Bt cancels out Bf.

But I contend that Bt is introduced on both sides, not just 1 side. The equation becomes

Te = (cos(A+Bt)/cos(A+Bf+Bt)*W*a/b.

Here Bf doesn't get cancelled out by Bt. If you add a book and raise the weight bar higher by Bt on the left side, the hard/fixed angle between the weight bar and the line to the grip is still (90+Bf) just the same, so if Bt is added to the left side to yield cos(A+Bt), I contend that Bt is added to the right side just the same to yield cos(A+Bf+Bt).

The bottom line is that Bt doesn't cancel out Bf because Bt gets introduced to both side when raised by the book.

I really wanted to believe with your hypothesis initially because it would work out the math so well and explain everything. But then I just couldn't visualize how introducing Bt on the left side could NOT ALSO add Bt to the right side as well, hence this post here.

I don't have any explanation myself at this point as to why raising with the book helps. So I'm still all ears for a plausible explanation.

 

[TennisCJC]

I have been playing over 35 years. I have laserfibre model like stringway table top ml90 with 2 action fixed clamps.

I don't know the formulas but know the results are damn good. When I string at 58 lbs, it feels like 58 lbs. When I string at 50 lbs, it feels like 50 lbs. After 35+ years, I think I have pretty good feel for tension. My string jobs are certainly as good as the local tennis shop that uses all usrsa certified stingers. Personally, I think my string jobs are better.

I have never even calibrated the machine.

I only string for friends and only string 2 - 3 dozen rackets per year other than mine. But, over 8+ years, no one has ever complained or even questioned tension.

I believe Stringway is pretty much spot on with tension and I really like the true constant pull feature.

 

[volusiano]

It looks like we've gotten a lot of reminders from folks here to look at the 'big picture" that the Stringway machine is still a pretty darn good and accurate machine overall. And not to let the few percent in tension variation taint the good name of the machine, but instead focus on the end result, which is not going to be greatly affected by a few percent variation.

I think this is a good point because we've seen some folk jumping into conclusion already that the accuracy of this machine "doesn't work", which is not true.

But I think there's still intellectual value in wanting to understand better why the machine doesn't perform like in theory, if only to understand where the deviation comes from in case there are easy ways to adjust for it.

Apparently Jacklondon00 has stumbled upon an easy adjustment step for his machine's variation, although we may not have been able to explain why the adjustment helps yet. But more importantly, his finding validates that once the right adjustment is made, the accuracy of the machine can be as close to theory as you can measure it.

I think this is the most important conclusion here: the theory works and the design works when adjustment for manufacturing variation can be made. And even with no adjustment, the variation is not too far off and the end result is still pretty darn good.

 

[lew750]

Not disagreeing with anyone; I would take a Stringway and not worry about the slight variance. Still, I wonder how many people who don't think Stringway's +/- 5% variance is a big deal would give the same pass to an Eagnas machine with the same variance?

 

[Tennisist]

-- Great discoveries by JackLondong00 and great discussion.

A little variance in pulling seems unavoidable. Luckily, this variance seems to be too small to matter in practice. ( I was hoping the foot operated version would not have it, but alas. ).

I am far more concerned with the losses/variations introduced by the clamps. I have the dual-action ones. Sometimes, I get zero pullback. Other times, I see the clamp move back 1/4 inch or so. I would not mind it this pullback was repeatable and consistent. But it is not. The pullback seems to be particularly bad and inconsistent on crosses.

Anybody else noticed this? concerned about it?

If there is anything I would improve about this machine, that would be the clamps.

Also adjustments of the clamps: some machines have a wheel to adjust tension for various gauges. I have to use an allen wrench. There is no "feel" if gripping is too tight or too loose.

 

[Tennisist]

I have another curiosity, and no equipment to test it: I tried stringing crosses top to bottom regular (a), top-to-bottom progressive (b), and start from center (c). The response of the stringbed seems very different. Has anyone measured the actual stringbed tension for these cases, and how did it come out?

 

[OccasionalStringer]

I think it's established here that the variation B degree introduced here is a fixed variation due to manufaturing variation (and string thickness).

For clarity, I'll call this Bf (for B fixed).



But I contend that Bt is introduced on both sides, not just 1 side. The equation becomes

Te = (cos(A+Bt)/cos(A+Bf+Bt)*W*a/b.

Here Bf doesn't get cancelled out by Bt. If you add a book and raise the weight bar higher by Bt on the left side, the hard/fixed angle between the weight bar and the line to the grip is still (90+Bf) just the same, so if Bt is added to the left side to yield cos(A+Bt), I contend that Bt is added to the right side

Yes, I simplified this too much. But what happens is that when tilting the machine angle (relative to horizontal ) at which the string comes from racket to gripper changes as well.

Assuming that the machine is not tilted the balance equation when the string angle deviates from Horizontal by angle Bh is

W*a*cos(A) = Te * b * cos (A + Bf - Bh )

where sign for Bh is selected so that it is positive when the string comes from low to high from racket to gripper.

So when tilting the machine so you increase Bh and the error factor approaches 1 with certain tilt angle Bt.

I agree that you can get consistent results with ML100 as with any machine having good clamps and racket support. To me the question here is if ML100 pulling accuracy at any angle is as good as advertised.

 

[Jacklondon00]

-- Great discoveries by JackLondong00 and great discussion.

A little variance in pulling seems unavoidable. Luckily, this variance seems to be too small to matter in practice. ( I was hoping the foot operated version would not have it, but alas. ).

I am far more concerned with the losses/variations introduced by the clamps. I have the dual-action ones. Sometimes, I get zero pullback. Other times, I see the clamp move back 1/4 inch or so. I would not mind it this pullback was repeatable and consistent. But it is not. The pullback seems to be particularly bad and inconsistent on crosses.

Anybody else noticed this? concerned about it?

If there is anything I would improve about this machine, that would be the clamps.

Also adjustments of the clamps: some machines have a wheel to adjust tension for various gauges. I have to use an allen wrench. There is no "feel" if gripping is too tight or too loose.

I used to have this issue with my M50, but with some practice, I managed to eliminate most of the drawback. Granted, I had single action clamps, but the drawback was still quite large, probably the same as you have. All you have to do is preload the clamps before clamping.

So I would press the clamps in the direction that the string tension is going to pull after you release the string from the tension head. With my single action clamps it worked best when I pressed the bottom of the clamp towards the tension head, and the top of the clamp away from the tension head (so in the direction the string was going to pull after the release). I believe that Irvin has a video on Youtube on how to mitigate drawback.

 

[Jacklondon00]

I have another curiosity, and no equipment to test it: I tried stringing crosses top to bottom regular (a), top-to-bottom progressive (b), and start from center (c). The response of the stringbed seems very different. Has anyone measured the actual stringbed tension for these cases, and how did it come out?

Sorry, I don't have experience stringing my crosses from the center. I have only done this once (with a Prince O racket) because I did not have a another way of strinign it on that machine at the time. Not sure how the stringbed fehlt because it was not for me.

Perhaps you can open a new thread in the general forum, and I am sure that there are losts of people who have experimented with this and who will post, I would be curious to read what they say.

 

[Jacklondon00]

Not disagreeing with anyone; I would take a Stringway and not worry about the slight variance. Still, I wonder how many people who don't think Stringway's +/- 5% variance is a big deal would give the same pass to an Eagnas machine with the same variance?

Well, it's actually closer to 2% to 3% on most occasions, and 0% when the bar is horizontal. I think the machine has so many other redeeming qualities, like the mounting system and solid build quality, which make up for this.

As people already mentioned, the "big picture" is that the overall quality of the string jobs on these machines is still excellent. I am in agreement, especially now that I know how to adjust things. But I do want to point out that had I not known what I now know about my machine, that might not have been the case. For example, the concorde system allows for friction free pulling, and is likely much more accurate that on the machines where the string has to go around the throat. However, had I not known about the tension variance, and let the bar drop below horizontal, I would have lost 3 lb to 4 lb of tension on the center mains! That really adds up when you take all the center mains into account. Probably would have made my string jobs feel better due to the extra sweet spot.

I would like to make three points of why this discussion is important.

1. The advertised exact tension at every angle, meaning that the stringer doesn't have to worry about the angle, which is a huge time saver and the main selling point of the machine. I think people have the right to know that they are getting something that due to manufacturing tolerances may not give them exact tension. However, I don't see Stringway changing this anytime soon, as I said, this is the main selling point of the machine. As someone already mentioned, the Pioneer DC Plus is looking a whole lot better at its price points, especially when one can pick up a used one for a few hundred.

2. Thanks to some very intelligent people on here that really know their math, looks like we are getting to the bottom of what seems to be the cause of this variance. Fred Timmer tried to explain this to me after I send him the video demonstrating that I was getting exact same tension when the angle of the string entered the tension head from below the level of the mounting platform. I told him that something inside my tension head was not calibrated to the level of the platform. He said it had nothing to do with calibration, but I could not understand what he meant, maybe his explanation will help those who are better at seeing the theoretical aspects of this. Fred wrote:

"The basis idea about our tensioner is that it pulls the string through the grommet as horizontal as possible. This means that the gripper pushes the string down wards in the situation that the lever is above horizontal. Because of the angle the horizontal lever of the string gets smaller so the tension goes up when the lever is far above horizontal. In your test you compensate for this angle by moving the fixed point of the string downwards and therefore changing the angle of the string coming out of the gripper. This results in longer lever so the tension goes down.
But it is not possible to combine this situation when the tensioner is on the level of the stringbed what we want. It has nothing to do with the calibration of the machine.

When I sent him the video with books, he also seemed to undestand what was happening, and gave me a good explanation, but again I am just not really sure what he meant.

"Why do the books have influence? The importance of the tensioner is the relation between the angle of the lever and the angle “with the earth” and of the out going string.

* For the angle of the lever the angle in relation to the horizontal line is important. The driving force of the system is maximum when the lever is horizontal creating the maximum torque.

* For the outgoing string the angle in relation to the frame of the machine is important. With the books you rotate the angle of the out going string and the frame. But the angle of the lever “with the earth” stays the same. So you actually rotate the tension head compared to the angles that were used before. This means that the push down effect in the above horizontal range, which is caused by the large radius of the upper jaw, is less."

So as you can see Fred has been pretty patient with me, and he seems to understand the issues (even so I don't undersatnd his explanations), so I am sure if it was within his capacity to fix this he probably would. Seems like the required precision would be too much for the manufacturing tolerances, afterall, he is not making thigs for NASA.

Still, I do wonder if they could introduce some sort of individual calibration process, or add some user adjustments, that would be able to correct this issue, since they currently rely solely on the integrity of the design. I think that the advertising by Stringway and the high price of their machines should warrant somthing like this.

3. Finally, the last point is that everyone should test their machine and know what it is capable of and what are its weakneses, this is unique to every machine. This way you can get the most out of it.

 

[volusiano]

Yes, I simplified this too much. But what happens is that when tilting the machine angle (relative to horizontal ) at which the string comes from racket to gripper changes as well.

Assuming that the machine is not tilted the balance equation when the string angle deviates from Horizontal by angle Bh is

W*a*cos(A) = Te * b * cos (A + Bf - Bh )

where sign for Bh is selected so that it is positive when the string comes from low to high from racket to gripper.

So when tilting the machine so you increase Bh and the error factor approaches 1 with certain tilt angle Bt.

I don't think you can insert Bh into the cosine calculation like you show above because A and Bf are angles of the 2 lines whose common point of origin is the pivot on the tension head.

Meanwhile, Bh described by you as the deviation from the horizontal vector Te on the string is the angle between the horizontal string line and the slanted string after adjustment, whose common point of origin is not the same as the pivot point of the tension head.

If they don't share the same point of original, Bh can't be part of that cos(A+Bf) calculation.

 

[volusiano]

Fred Timmer tried to explain this to me after I send him the video demonstrating that I was getting exact same tension when the angle of the string entered the tension head from below the level of the mounting platform. I told him that something inside my tension head was not calibrated to the level of the platform. He said it had nothing to do with calibration, but I could not understand what he meant, maybe his explanation will help those who are better at seeing the theoretical aspects of this. Fred wrote:

"The basis idea about our tensioner is that it pulls the string through the grommet as horizontal as possible. This means that the gripper pushes the string down wards in the situation that the lever is above horizontal. Because of the angle the horizontal lever of the string gets smaller so the tension goes up when the lever is far above horizontal. In your test you compensate for this angle by moving the fixed point of the string downwards and therefore changing the angle of the string coming out of the gripper. This results in longer lever so the tension goes down.
But it is not possible to combine this situation when the tensioner is on the level of the stringbed what we want. It has nothing to do with the calibration of the machine.

When I sent him the video with books, he also seemed to undestand what was happening, and gave me a good explanation, but again I am just not really sure what he meant.

"Why do the books have influence? The importance of the tensioner is the relation between the angle of the lever and the angle “with the earth” and of the out going string.

* For the angle of the lever the angle in relation to the horizontal line is important. The driving force of the system is maximum when the lever is horizontal creating the maximum torque.

* For the outgoing string the angle in relation to the frame of the machine is important. With the books you rotate the angle of the out going string and the frame. But the angle of the lever “with the earth” stays the same. So you actually rotate the tension head compared to the angles that were used before. This means that the push down effect in the above horizontal range, which is caused by the large radius of the upper jaw, is less."

So as you can see Fred has been pretty patient with me, and he seems to understand the issues (even so I don't undersatnd his explanations), so I am sure if it was within his capacity to fix this he probably would. Seems like the required precision would be too much for the manufacturing tolerances, afterall, he is not making thigs for NASA.

I'm sure Fred knows what he's talking about, but like you, I can't make head to tail of his explanation to understand what he's trying to say either.

But I can't fault him because it's not easy to explain using plain words, unless you do it within the context of a clear drawing and mathematical equations for reference to help make the explanation perfectly precise.