For those whose machines fitted with ECP, did anyone actually measure the actual tension compared to the set tension? For example, if you string a racket at 26 lbs, is it actually pulling 26 lbs and not more? I am asking because rackets strung with ECP machines usually feels tighter than calibrated drop weight or crank machine. Does the pre-stretch function got any thing to do with it?
Calibrated ECP machines pull at the exact tension that you set them at. The reason that it feels tighter is indeed partly because of the pre stretch function, but also because it pulls at the right tension and keeps pulling at that tension. Crank machines pull at the right tension, but block there, so the string stretches and loses tension. Drop weight machines also pull at the right tension, but only if your lever ends up perfectly horizontal. Any angle causes a slight tension loss.
pre-stretch attempt to get rid of any slack or tension loss in the string by pulling a higher than the pre-set tension, and then eases back to the preset. this way the rate of tension loss is lower after the racket is strung. but at the end of the pull, it will always go back to the preset. ECP when properly calibrated will always give a more true tension than crank/lock-out machine, and with pre-stretch on will help maintain that true tension better than drop weight. so yes it will feel tighter but that's because it is more "real" of a tension. on a crank if you ask for 26lbs, you might actually get 24 or 23.
I am using a drop weight machine. As long as the lever is within 10 degs from horizontal, the difference in tension loss is negligible (less than 0.3 lbs). I use a digital fishing scale to confirm this.
Then, it should produce the "actual" final tension. But it still feels tighter compared to a drop weight machine. That is why I am wondering if ECP machine do intentionally add certain percentage of tension to compensate the presumed tension lost for a particular string job.
No, ECP machines pull right on the spot. They are not different from other types of machines on this matter, you still have to calibrate them. So unless all calibrators intentionally show lower tensions so you over calibrate the machine, they dont "add a certain % of tension" The big difference is the prestretch function and the drop weight angle (.3 lbs is still .3 lbs, and it's possible that sometimes the angle is greater during stringing if one doesn't mind or pay attention). Pre stretch plays a major role depending on the string. The string bed can end up as low as 10% lower tension if the strings are not pre stretched. This is particularly true with BG65 and most Victor strings.
Pre-stretch is the major factor then. Come to think about it, BG65 shows the biggest difference. I guess I need to add 10% on my drop machine if I'm stringing with BG65. Thanks for clearing this up.
You could also pre stretch the string manually before you string. It doesn't take that much time and is pretty efficient.
