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Ramon
04-16-2012, 05:53 PM
So far, I'm very happy with my new APDC+. It's smooth, rock solid, and the tension mechanism is so easy to use I don't really see the need for a crank.

The only issue I have at this point is the tension accuracy. I've been tracking tension on my racquets with the RacquetTune app, and my machine seems to be at least 8-10 pounds higher than other machines, and my subjective evaluation confirms this. To add to the confusion, I bought the Alpha Tension Calibrator with the machine and it actually says my machine is 1-2 pounds low when I test it at 50 and 60 pounds. The other places that strung my racquets include 2 internet retailers (including TW) and a friend's machine. I suspect the internet retailers were fairly accurate, while my friend's machine was probably too loose.

I suspect that one reason could be constant pull vs. lockout, but setting the machine to 52 to get 60-62 pounds seems to be abnormal. Has anyone else had a similar experience? Is the difference between constant pull and lockout really that much?

gotwheels
04-16-2012, 06:43 PM
Ramon, RacquetTune is a relative measure, not truly quantitative. Is your tension calibrator a mechanical or electronic device? The electronic unit stands a better chance to be a more accurate measure. I have never cared for the mechanical gauge type due to accuracy and resolution. I would recommend testing the calibration of any tension gauge to a known measure (I would even want to measure the test weights used for the check). The calibration should be checked over your tensioning range.

There is a real difference between the stringbed tension of constant pull vs lockout machines, because of tensioning/clamping differences.

Several years ago, I checked the calibration of an Alpha Pioneer DC Plus over an ~ 40-70 lb. range with a calibrated measure and the unit was very accurate/repeatable, with the linear gripper in a consistent position. I guess that the bar scale decal can be offset (I have not seen), but the tension offset should be linear.

Good luck - keep stringin!

Ramon
04-16-2012, 06:57 PM
Ramon, RacquetTune is a relative measure, not truly quantitative. Is your tension calibrator a mechanical or electronic device? The electronic unit stands a better chance to be a more accurate measure. I have never cared for the mechanical gauge type due to accuracy and resolution. I would recommend testing the calibration of any tension gauge to a known measure (I would even want to measure the test weights used for the check). The calibration should be checked over your tensioning range.

There is a real difference between the stringbed tension of constant pull vs lockout machines, because of tensioning/clamping differences.

Several years ago, I checked the calibration of an Alpha Pioneer DC Plus over an ~ 40-70 lb. range with a calibrated measure and the unit was very accurate/repeatable, with the linear gripper in a consistent position. I guess that the bar scale decal can be offset (I have not seen), but the tension offset should be linear.

Good luck - keep stringin!

My reference to RacquetTune's measure is relative to the other places that strung my racquets. I have a scientific background in QC, so you don't have to explain to me the elementary differences between absolute and relative. I'm absolutely positive that my machine is pulling at least 8-10 pounds more tension than those other machines at my normal tension range. If my machine is accurate then the internet retailer's machines are 8-10 pounds loose and my friend's machine is about 15 pounds loose at my normal tension range.

I'm a bit disappointed with the readability of the Alpha mechanical calibration device. If it's accurate, then the other machines are even 1-2 pounds looser than I described.

Ramon
04-22-2012, 01:15 PM
I think I found the answer. I've been pulling the mains for at least 5 seconds and the crosses for at least 20 seconds because that is recommended for the JET technique. I'm also following the same string pattern and increasing the tension at the tie-offs by 6 lbs.

http://tt.tennis-warehouse.com/showpost.php?p=6326493&postcount=37

For the JET technique, the set tension is supposed to be 7-10 lbs lower. I'm basically using a modification of that technique, which would explain why I'm off by that same amount.

Whew! I'm glad that's solved.

shamaho
06-04-2012, 01:18 PM
Ahhh! well spotted!

I felt the very same thing you did (but only subjectively since I could not compare to any other reference - but it felt way more tension than what I'm used to for that same amount of 25Kg) after doing my very first self-stringing job on a brand new drop-weight machine (Tyger eco-45).

However I also left the pull on mains and crosses for quite some time (after reading up on JET :-)

SwankPeRFection
06-04-2012, 10:32 PM
I always wait for my DC to pretty much stop stretching the string out before clamping the string. It's usually 5-10 seconds or so. My measured tension is right what I had the machine set to within a few 10ths of a pound. Last two jobs were set to 56 and came off at 55.xx after sitting for 5 minutes.