I have got a question/comment about drop weight stringing machines. The fact is these type of machines are fairly accurate and provide constant pull on the string under tension. The physics about its working principle is also clear. But so far I did not see any discussion about the friction, which occurs in the rotational tensioner, which is attached to the housing by a bolt and two nuts. Any friction reduces the torque, which is exerted by the mass (weight), meaning that the pull force will be smaller.
I did some experiments with my Premium Stringer 3600 using the calibrator (force gauge). I found that the tightening the nuts on each side of the bolt affects the force by which the string is pulled (it decreases) and besides no constant pull effect can be observed (the tension is not readjusted and slowly falls). Even slight tightening of the nuts introduces significant differences to the exerted stringing tension (more than 2 kg). However, if the nuts are untightened, the tension increases and matches the tension indicated on the bar. In such case the force is also kept more or less constant (constant pull effect). The problem is that without the calibrator it is very hard to tell when the nuts are tightened too much (you can be sure they are, if the bar cannot be moved anymore) and also over the time (a couple of months - 50 rackets strung) the readjustment was needed, because the tension dropped. I also saw this time drift by looking at the trend of the measured tension/frequency of the strung racket stringbed (test were made for the same racket, the same string, same stringing time and using Racket Tune app); the stringbed tension of freshly restrung racket dropped for about 1,0 kg over 3 months (the racket was restrung approx. every two weeks during this period).
I guess the described might also be the reason that the rackets strung using drop weight machines are usually slightly softer (cca. 1 kg) compared to those strung on electronic machines.
I am really interested if anybody had similar problems or observations. Is there any rule (guidance) how to properly tighten the nuts? How it is done in service - are machines always recalibrated?
Thanks for your comments.
Cheers,
Greg
I did some experiments with my Premium Stringer 3600 using the calibrator (force gauge). I found that the tightening the nuts on each side of the bolt affects the force by which the string is pulled (it decreases) and besides no constant pull effect can be observed (the tension is not readjusted and slowly falls). Even slight tightening of the nuts introduces significant differences to the exerted stringing tension (more than 2 kg). However, if the nuts are untightened, the tension increases and matches the tension indicated on the bar. In such case the force is also kept more or less constant (constant pull effect). The problem is that without the calibrator it is very hard to tell when the nuts are tightened too much (you can be sure they are, if the bar cannot be moved anymore) and also over the time (a couple of months - 50 rackets strung) the readjustment was needed, because the tension dropped. I also saw this time drift by looking at the trend of the measured tension/frequency of the strung racket stringbed (test were made for the same racket, the same string, same stringing time and using Racket Tune app); the stringbed tension of freshly restrung racket dropped for about 1,0 kg over 3 months (the racket was restrung approx. every two weeks during this period).
I guess the described might also be the reason that the rackets strung using drop weight machines are usually slightly softer (cca. 1 kg) compared to those strung on electronic machines.
I am really interested if anybody had similar problems or observations. Is there any rule (guidance) how to properly tighten the nuts? How it is done in service - are machines always recalibrated?
Thanks for your comments.
Cheers,
Greg
