What to believe??

[Moppet52]

Hi, I have a question regarding measuring string bed tension. I am using an Alpha Revo 4000 lockout machine and in my quest to understand how "well" I am doing in my string jobs I have used 3 different methods to measure / calibrate each of my string jobs. My goals include the ability to consistently understand the result of each string job and understand how different techniques or events during a string job affect the end result. My latest string job was a full bed of Volkl Cyclone 18 on a Head Microgel Prestige Pro MP @ 42lbs. Here are the results from the various methods I use:

- Calibrated machine with digital scale at 40, 50, and 60 lbs. Used tension at lockout to calibrate the machine
- ERT 300 reading of DT = 34. According to the conversion chart, the string bed tension was 49lbs.
- Racquettune iPhone app measured the result @ 46 lbs. I used generic Polyester 1.20mm string in a 95in head size racquet. I believe

I am concerned that my machine is incorrectly calibrated. Any thoughts on the level of confidence I should have in each of the ways I am attempting to get the desired tension?

Thank you,

 

[Joonas]

Ert-300 and racquet tune are affected by the string type. Ert-300 conversion chart is really just rough view. Also other frames string higher than others with similar tension and string type.

Best way to monitor your consistency is to follow your readings with same racquet and same string over time. I check every job with Ert300 and racquet tune. Racquet tune provides me a library/history and I always enter ert DT value in the comments.

 

[diredesire]

There's no real simple answer to this question. The experienced guys will generally default to the answer of "absolute isn't that important, reference is important."

This is true to a certain extent, but this is the case because absolute is extremely difficult to measure. If we had perfect knowledge and tools, both would be important, of course.

Ask yourself this question: What's the difference between constant pull and a lockout? What's the rule of thumb for a CP vs crank machine? (Hint: Rule of thumb is ~10%) What does this mean when you measure a crank stringbed vs a CP?

If you had a CP frame tensioned at 54 lbs and a crank stringjob @ 60 lbs, would you EXPECT the same reading on RT or ERT?

My point here is that there are a lot of variables, and chasing down every last variable and trying to put a number to it is extremely challenging, especially when you live in the real world, and you have other systems and work to compare against.

If you're happy living in a vacuum, you can make your product extremely repeatable and consistent, but you will always have that "absolute" term that is going to haunt you.

If you want to quantify how 'well' you're stringing, compare each job historically against your previous work. String X frame at Y tension with Z string and do it again in the future. Track the tension loss as you hit with similar conditions (or even in isolation) and see how the frames compare. Consistency to yourself is important!

TL;DR: Focus less on absolute because you will go insane trying to do it right -- the right tools don't exist yet to give high confidence in absolute measurements. Understand the limitations of the tools you're using, otherwise they're useless. A hammer isn't that useful if all you've got is nuts and bolts.

 

[Moppet52]

There's no real simple answer to this question. The experienced guys will generally default to the answer of "absolute isn't that important, reference is important."

This is true to a certain extent, but this is the case because absolute is extremely difficult to measure. If we had perfect knowledge and tools, both would be important, of course.

Ask yourself this question: What's the difference between constant pull and a lockout? What's the rule of thumb for a CP vs crank machine? (Hint: Rule of thumb is ~10%) What does this mean when you measure a crank stringbed vs a CP?

If you had a CP frame tensioned at 54 lbs and a crank stringjob @ 60 lbs, would you EXPECT the same reading on RT or ERT?

My point here is that there are a lot of variables, and chasing down every last variable and trying to put a number to it is extremely challenging, especially when you live in the real world, and you have other systems and work to compare against.

If you're happy living in a vacuum, you can make your product extremely repeatable and consistent, but you will always have that "absolute" term that is going to haunt you.

If you want to quantify how 'well' you're stringing, compare each job historically against your previous work. String X frame at Y tension with Z string and do it again in the future. Track the tension loss as you hit with similar conditions (or even in isolation) and see how the frames compare. Consistency to yourself is important!

TL;DR: Focus less on absolute because you will go insane trying to do it right -- the right tools don't exist yet to give high confidence in absolute measurements. Understand the limitations of the tools you're using, otherwise they're useless. A hammer isn't that useful if all you've got is nuts and bolts.

Really well thought out and helpful response. Appreciate the experience and thoughts of all (okay... most) on the boards :-?

Anyway, I think your thought process is spot on. I am starting to take more meticulous notes on each string job. Since I am only stringing for myself at this point, I have rarely done the same exact string job in the same frame (in search of the "perfect" string setup... for me that is).

 

[PCS_Super]

great post dire desire... a DT of 34 on 42lbs is perhaps slightly high but then again cyclone is a stiffish string... joonas is right conversion chart could be easily off by 7 or 8 lbs and your racquet tune result i would discount because a prestige pro is a 98 sq in frame you entered 95 on racquet tune so that could have brought your racquet tune result down a few lbs... forget the tension the machine says and find what DT reading works best for you then find the tension setting on the machine that achieves your desired DT reading, then it doesnt matter unless your a pro shop or stringing for dozens of clients

 

[Irvin]

If you'd like to use RacquetTune to track how well you're doing why not measure frequency. We have all heard that the tension from one of these apps/ERTs is not absolute so why trust it in the first place. They all work on frequency to begin with. Why let something you're not so sure about run through it algorithms based solely on a string factor and gauge that may or may not be accurate anyway?

 

[OccasionalStringer]

If you'd like to use RacquetTune to track how well you're doing why not measure frequency. We have all heard that the tension from one of these apps/ERTs is not absolute so why trust it in the first place. They all work on frequency to begin with. Why let something you're not so sure about run through it algorithms based solely on a string factor and gauge that may or may not be accurate anyway?

This is exactly true. The tension in the racket is directly proportional to the square of the frequency.

So in order track the tension loss over time it is sufficient to record frequency immediately after stringing (or some other reference point). Then later on to check the remaining tension you just need to measure the tension at that moment.

The remaining tension in percentages is 100 * ( CurrentFrequency / ReferenceFrequency) ^ 2

For example, if straight after stringing the ReferenceFrequency is 590 Hz and after a few days (weeks) you measure 530 Hz then you have left 100 * (530/590) *(530/590) % = 80,69 % , i.e. the tension loss has been about 20 %

You need a calculator though

 

[Irvin]

Don't need a calculator if all you're concerned about if frequency.

 

[Moppet52]

great post dire desire... a DT of 34 on 42lbs is perhaps slightly high but then again cyclone is a stiffish string... joonas is right conversion chart could be easily off by 7 or 8 lbs and your racquet tune result i would discount because a prestige pro is a 98 sq in frame you entered 95 on racquet tune so that could have brought your racquet tune result down a few lbs... forget the tension the machine says and find what DT reading works best for you then find the tension setting on the machine that achieves your desired DT reading, then it doesnt matter unless your a pro shop or stringing for dozens of clients

Just to confirm, I had thought it was accepted that an IG Prestige Pro is 95 sq in, even though it is marketed as 98. Or if more accurate, it compares to other manufacturer's 95 sq in models. Incidentally enough, I have picked up a IG Prestige S and comparing it side by side, I think it is a "true" 98 sq. in.

Can anyone help confirm my super unscientific findings?

As a follow-up to my original post, I have started taking ERT and RacquetTune readings after every string job and hitting session. What I have noted is that RacquetTune is extremely accurate when it comes to establishing the DT based on frequency. It is always within decimal points of the ERT computer reading. That gives me a sense of comfort, which is great.

No longer stressed about finding the absolute, but finding comfort that my string jobs are consistent to my expectations. Tension loss happens faster than I had expected. But any information is good information.

 

[Irvin]

Pie are square. Measure and add together the inside height and weight and divide by 4. Square the result and multiply by PI.

 

[Perrotoro]

Add the Height and Weight???...

No disrespect intended Irvin but I think you meant:

1) (Height + Width)/2 = Average Diameter

2) Square this number

3) Then divide by 4

4) Then Muitiply by PI

 

[Irvin]

Thank you Perrotoro I corrected it.