Manually Measuring Swingweight
- Thread starter TennisLogic
- Start date
Power Player
Bionic Poster
Yeah but im not sure what could be off. Ive been measuring tw on frames for an hour. Lol.
Adding weight exactly at 12 should not affect the twistweight at all. Obviously if you are adding the weight in the form of a lead strip 'in the 12 o'clock area' rather than at exact 12-point ten that is a different story.
Power Player
Bionic Poster
Well yeah thats what im doing. Im adding 3 grams of lead across the top. Its just how most ppl describe adding lead at the top area.
Addxyz
Hall of Fame
You subtract SW from rotated 90degree SW right? If you increase SW, and the rotated 90degree SW doesn't increase, the difference increases right?
snoflewis
Hall of Fame
wouldn't both increase if you add lead at 12?
Addxyz
Hall of Fame
Would both increase at the same rate? They should if it doesn't increase TW. But that's not what PP is getting.
Irvin
Talk Tennis Guru
Left and right depends on how you look at it. I do use the default. Each calibrate rod can be different mine is 324.3 and 167.6 respectively. Not sure I would go in and change the calibration to any other value unless I had good reason to believe the values on the rod weren't correct.
Another thing I used to do is check to make sue the iPhone is sitting at 45 degrees in the cradle. I downloaded a level app to do that. Not sure it is makes a difference ot not. But I don't check the level any more.
Irvin
Talk Tennis Guru
Actually all 3 increase spin weight, swing weight, and twist weight. If you add a 3 grams at 12 there will have to be some length to the mass in contrast to a point mass. 2 leads strips of 1/4" lead tape will have to be 15.5 cm long each. That width adds and extra 0.24 kgcm to TW and 9.75 to SW. So spin weight goes up 10 points. Not sure if SW1 is accurate enough to consistently measure 0.01 inertia.
Question - does it matter if the racquet is swung say with the logo on the butt cap facing both ways?
For me, until now, when I measure the weight and balance, I always make sure I measure with the logo in the butt cap in the upright position, same for when I mount the racquet on the stringing machine.
When I measure the swingweight, I always make sure the bottom of the logo is closest to the homemade rig, so the racquet is always swung the same way when I measure the SW.
don’t know if I have over think this, but I thought I’d be as “consistent” as possible. Lol
For me, until now, when I measure the weight and balance, I always make sure I measure with the logo in the butt cap in the upright position, same for when I mount the racquet on the stringing machine.
When I measure the swingweight, I always make sure the bottom of the logo is closest to the homemade rig, so the racquet is always swung the same way when I measure the SW.
don’t know if I have over think this, but I thought I’d be as “consistent” as possible. Lol
Irvin
Talk Tennis Guru
It matters if you measure a racket take it off and mount the racket is the exact same orientation. It matter is there is a breeze blowing. It matter if you don’t let the spring warm up a little bit. It matters if the level is off. It matters if you SW1 is not on a stable surface. Everything matters.
I measure SW with the logo facing the phone and spin weight with the logo upright.
EDIT: I usually take 5 readings and use the mean result, not individual results. They will never all be the same.
Power Player
Bionic Poster
Yeah the Sws are super accurate but i need to dial in the spin weight. I added lead to 2 and 10 on my vcore pro and the sw was accurately measured at 328.
The twistweight though, had actually gone down (?). So thats where i have to dial things in a bit somehow.
Just having accurate sw is amazing in itself. So im just trying to maximize the machine now.
The twistweight though, had actually gone down (?). So thats where i have to dial things in a bit somehow.
Just having accurate sw is amazing in itself. So im just trying to maximize the machine now.
TennisLogic
Semi-Pro
I am glad about the way this thread is going. It's things to hold racquet manufacturers to a higher level of tolerance standards. Especially when I am hearing pro staffs will cost around $300 per frame
yep - i agree.
up until the recent times, the manufactures probably thinks us general customer have very little access to a RDC (or even a calibrated RDC)... so for them to hold their SW QC isnt as important...
now that there is an affordable, easy to setup/use, and accurate (lets assume/agree it is for now) device on the market... i hope the manufactures will start paying attention and realise we can and will measure the SW and TW of our racquets... so hopefully they will improve their QC.... one day.
bfroxen
Rookie
Measuring just swingweight to useful precision/accuracy is relatively easy. Measuring both swingweight and spinweight well enough to determine twistweight with useful precision is more difficult.
There's a page in the guide that talks about some, but certainly not all, of the factors that an affect accuracy.
I also created a blog post in response to a question about the effects of twist orientation. If you're just measuring swingweight, being 5° off vertical isn't that big of a deal, but when determining twistweight, it is.
It's also important to get the racquet positioned against the back wall of the cradle. A gap of 0.5 mm would increase swingweight by ~0.75 kg·cm² for a typical racquet. I have a racquet with a damaged butt cap (sweaty hands and serving aren't a good combination), so it's a problem to position that racquet the same in any orientation. Even if a but cap just isn't stapled squarely, it might have a small effect.
There's a page in the guide that talks about some, but certainly not all, of the factors that an affect accuracy.
I also created a blog post in response to a question about the effects of twist orientation. If you're just measuring swingweight, being 5° off vertical isn't that big of a deal, but when determining twistweight, it is.
It's also important to get the racquet positioned against the back wall of the cradle. A gap of 0.5 mm would increase swingweight by ~0.75 kg·cm² for a typical racquet. I have a racquet with a damaged butt cap (sweaty hands and serving aren't a good combination), so it's a problem to position that racquet the same in any orientation. Even if a but cap just isn't stapled squarely, it might have a small effect.
tim-ay
Hall of Fame
i use a small level when measuring TW to at least make sure the racket face is oriented consistently. this helps and i’ve been able to pull fairly consistent TW numbers over a few days on the same racket.
if someone asked me about my doppios, for example, i would tell them removing any of my previous mods has SW at 328, 330, and 331 for the 3 frames. i’ve pulled those number over and over after multiple calibrations. TW - i would just say seems close to target around 13.5.
i really am impressed with this machine. that we are even talking about TW is incredible. and to think SW is almost too easy, lol. insane.
just a great product - hats off to bfroxen
if someone asked me about my doppios, for example, i would tell them removing any of my previous mods has SW at 328, 330, and 331 for the 3 frames. i’ve pulled those number over and over after multiple calibrations. TW - i would just say seems close to target around 13.5.
i really am impressed with this machine. that we are even talking about TW is incredible. and to think SW is almost too easy, lol. insane.
just a great product - hats off to bfroxen
Power Player
Bionic Poster
Ok good to know. I will use a level when I measure Twistweights.
I have the same situation as Tim with the PK Doppios except mine aren't 330. All 4 are around 322-325 strung and one is 294 unstrung. Really nice QC from PK there. Of course his string may be heavier than mine. I think Element is a lighter string than other polys in it's gauge.
PrinceYonex
Semi-Pro
I received my sw1 yesterday, expecting the calibration rod tomorrow. I’ve now even downloaded a leveling app on my phone. I’m too excited to start getting frustrated with my own difficulties in getting precise measurements!
Does it do anything different to the one that's included with iOS? It's part of the Measure app.
PrinceYonex
Semi-Pro
No idea. I didn't know about the one included on the iphone. Thanks for the heads up.
Power Player
Bionic Poster
I used the level for twist weight and it helps with consistency for sure. I still get some bizarre numbers, like a twist weight of 4 for an XL Pk that I have. Meanwhile the other XL PK I have seemed to measure pretty dead on.
The Swingweights though - wow incredibly accurate. Like this thing is the same reading every day with minimal variance. Real happy with it.
The Swingweights though - wow incredibly accurate. Like this thing is the same reading every day with minimal variance. Real happy with it.
tim-ay
Hall of Fame
Yeah, the level helps for TW, but you have to make sure to calibrate, then level, then just be a little lucky to get the TW’s consistently.
But yeah, the SW is dead on. Also, I think you are right about string weight. I’m going to restring Doppio’s this week and will check unstrung and strung. That has to be it. Or….. just thought of this…. On the PK handles, I also put the overgrip right up on the edge because I find them a little sharp compared to Wilson. That could easily kick me out a mm or two which Brian notes could add .75 per 1/2mm, so maybe 3SW ? I don’t have any issues on my Wilsons or Prince frames as I don’t put the overgrip up over the edge and they are much closer to spec. I’ll pull off the overgrip on the PK’s and recheck everything, guessing I’ll find they are really 325 / 326 range.
PrinceYonex
Semi-Pro
Turns out, it is already on your iPhone.
Irvin
Talk Tennis Guru
I’m not using my level and more and I think my SW and TW readings are accurate. Most of the TW numbers I get are in the 12-14 range. I don’t think I’ve seen any bizarre numbers that I remember. I don’t understand where anything that is not close to level wouldn’t be good enough. How can a slight deviation from level throw TW off but not SW?
tim-ay
Hall of Fame
It throws off SW too, but it’s just not a significant error. I’ve had some measurements of TW that were .3-.5 off, which is in the ignore range for SW. After triple checking, the TW made more sense. Ex - 13.1 vs. 13.5 on a Q+5 Pro.
Irvin
Talk Tennis Guru
@Power Player @bfroxen @tim-ay here is an example of SW and TW measurements I made with my SW1. First I made 3 swing weight measurements then rotated the racket 180 degrees and made 3 more all in the same group for a swing weight of 338.77. Then I rotated the racket 90 degrees and made 3 spin weight measurements and rotated 180 again to make the final 3 spin weight measurements resulting in spin weight of 352.38 and twist weight of 13.61.
i feel confident my SW is 339 and TW is 13.6. do You guys not get readings as consistent as this?
EDIT: After calibrating my SW1 the measurements did change a little see post #180. Seems like the SW1 being so light and portable may be a disadvantage.
i feel confident my SW is 339 and TW is 13.6. do You guys not get readings as consistent as this?
EDIT: After calibrating my SW1 the measurements did change a little see post #180. Seems like the SW1 being so light and portable may be a disadvantage.
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tim-ay
Hall of Fame
I do if I’m super careful if I’m going to also check TW. then it’s very repeatable and I get similar consistency to your numbers. Your numbers are really tight though - you may have a built in level in your head, haha. In fairness i have an ear infection right now that is driving me nuts….
Irvin
Talk Tennis Guru
I measured the same racket again and noticed a difference in both SW and TW, but I had moved the SW1 without recalibrating it. The SW1 was in the same general area but moved. So I re-calibrated my SW1 without bothering to level it. I measured SW and TW again with the same procedures but about 30 minutes apart and made sure the SW1 machine stayed in the same place.
My mean SW measurements were within 0.03 kgcm^2 of each other and my mean TW measurements were within 0.02 kgcm^2 of each other.
EDIT: I do not see any significant difference between SW or TW measurements. I did not level the SW1 or check the angle of my iPhone or the racket for any of the measurements. I was measuring a racket with no grip on it. Maybe the square fit between a bare pallet and the SW1 makes a difference.
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Power Player
Bionic Poster
Exact same specs on mine. To the T.
bfroxen
Rookie
@Irvin, I get similarly consistent results. I think your method is a good one to account for any non-squareness of the butt cap.
Calibration can compensate pretty well if the SW1 is not quite level. I expect that if the SW1 is not level, it will affect linearity of the results. Thus, measurements near to the calibration values will still be accurate, but measurements far from the calibration values will be off. It might need to be very non-level to matter, but I haven't yet attempted to quantify that.
Calibration can compensate pretty well if the SW1 is not quite level. I expect that if the SW1 is not level, it will affect linearity of the results. Thus, measurements near to the calibration values will still be accurate, but measurements far from the calibration values will be off. It might need to be very non-level to matter, but I haven't yet attempted to quantify that.
Irvin
Talk Tennis Guru
That’s like getting a new bike on Christmas but not getting the wheels until New Year. Unless the SW1 is calibrated I’m not sure if the SW measurements are accurate or not.Received the main unit on Saturday, and the calibration rod is arriving later today! Super excited to spend hours measuring SW and TW values
Yeah, it was pretty brutal, but I managed to hold it together - I haven't bothered trying to do anything without calibration, figuring that it would be pointless.... I will get it set up tonight.
Power Player
Bionic Poster
Ill do unstrung measurements when I string up my frames next. No OG as well.
PrinceYonex
Semi-Pro
lol, i'm in the same situation -- received the main unit on Saturday, waiting with great excitement for the bloody rod today!
Irvin
Talk Tennis Guru
I measured 2 RF97As for a client I just strung using my method of making 3 measurements then rotation the racket 180 for 3 more measurements in the same group. In the snapshot below the bottom 2 groups are for a red RF97A and the top 2 groups are for a black RF97A. 2 different version models. When switching from the first 3 measurements in each group to the second all 4 time I seen a significant change in the deviation from the mean. So I think there could be a difference in the squareness of the butt caps.
Also these rackets had had new OGs on them so I did not talk them off. I noticed after rotating the first racket the racket twisted a few degrees (did not measure) so I repositioned it before readings. Something to be careful of. Make sure racket is square before and after mounting. The measurements above include a #64 rubber band from the 4th main on left to 4th main on right just below the bottom cross so I could not take it out without stringing it again.
Notice the swing weight of the red PS is almost equal to the spin weight of the second. Big difference from one model to another.
Yeah. It makes sense. I won’t do the unstrung measurement for others I string for, unless they ask nicely, or I know he/she will be going through a journey of different string setups/experiments. Lol
But… does it really matter, at the end of the day? It’s like using the same stringer and during the same stringing machine again and again. All these are good for getting a reference for yourself or your circle of mates/customers.
I am sure even the RDC machines can vary between shops, when they can be calibration dependent.
I only have access to my own stringing machines and home made balance board/SW setup. I always try to be as consistent as possible, so at least my reference measurement/figures can be used and compared, until I change the setup/get new machine(s).
i wouldn’t be surprised if your measurements differs to Brian’s.
Irvin
Talk Tennis Guru
I think it could. If someone had a calibration rod of 150.0 & 300.0 and I had a calibration rod of 160 & 310 who’s to say either is correct. I could fool my SW1 by telling my SW1 the rod was 165 and 325 in stead of using the values on the rod of 167.6 & 324.3. This would mess up my calibration but if I could match 2 rackets to the same value it would be good because they would both be the same whether they are the right actual SW or not.
That’s right, and I agree.
now, when do you think it is a good time to nudge Brian again to see if he has sorted the SW1 packing abd international shipping challenges? Lol
Irvin
Talk Tennis Guru
One of the issues he had was shipping the SW1 and the calibration rod. The SW1 comes in about a 6x6x8 box and the rod comes in a long rectangular box. Send 2 boxes was more expensive. I suggested to home to send instruction for those overseas to build their own calibration rod. Not sure what will happen.