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View Full Version : How to calibrate a crank machine...


federermcenroeagassi
12-24-2006, 03:20 PM
Hey everyone,

I'm completely confused about how to do this. I'm planning on buying an Alpha Revo 4000 (crank machine), but i know about the crank machines being 10% looser than a constant pull machine due to the spring when it brakes. So i've read that you must calibrate the machine every once in a while.

So i searched on the forums, but got more confused. I read how some people do it with a frame, some without (because different frames cause different frictions, thus messing up your results), so i plan on doing it without a racket. Let's just say im using a plain calibrator (not a fish scale, or any other scale of sorts, just one for tennis stringing), how would i go about calibrating?

thanks a lot

dancraig
12-24-2006, 05:41 PM
Hey everyone,

I'm completely confused about how to do this. I'm planning on buying an Alpha Revo 4000 (crank machine), but i know about the crank machines being 10% looser than a constant pull machine due to the spring when it brakes. So i've read that you must calibrate the machine every once in a while.

So i searched on the forums, but got more confused. I read how some people do it with a frame, some without (because different frames cause different frictions, thus messing up your results), so i plan on doing it without a racket. Let's just say im using a plain calibrator (not a fish scale, or any other scale of sorts, just one for tennis stringing), how would i go about calibrating?

thanks a lot

Insert and knot a piece of string, preferably poly or kevlar, into each end of the calibrator.
Place one end in a locked clamp and the other end into the string gripper on the tension head. You may find that you need to lock the turntable into place. You also may need to experiment a little to get alignment correct.
Set the tension head to 50 or 60 pounds. Pull tension and check the reading on the calibrator. If it is close you may want to pull several times, cranking the handle at different speeds and pressures. You may find that different cranking speeds will give slightly different results.
If you decide to recalibrate, release tension. Many machines have two hex screws on the gripper assembly for calibrating. One is a set screw and one actually adjusts the tension pulled. On my machine, one hex screw is of a slightly different size than the other. I suggest you make sure to use the correct size wrench for each screw. You might want to check with the owner's manual, or someone that owns a Revo, to determine which is which. If you round off one of these screws, you could have a real problem.
You must first loosen the set screw and then turn the adjusting screw. On my machine, counterclockwise increases tension.
Now you must use the trial and error method to calibrate. Make an adjustment and check tension being pulled as above. When you are satisfied with the calibration, retighten the set screw.
My calibrations remains correct through dozens, even a hundred racquets.

NOTE:
You may need to loosen and tighten the set screw with each "trial and error" adjustment. I'm not sure since I don't own a Revo.