help tuning Ahren's screw/coupler for faster rapids

[groomden]

Hi,

For the life of me, I can't seem to get Ahren's system to rapid at more than 100in/min consistently. I can rapid along stretches of my x or y axis at 150, but i invariably run into some sort of bind and can hear steps missing. I'm know that my screws are somewhat warped but they aren't 'that' bad -- maybe 3/16's of an inch along the length. I have 5 start screws and they are 48 and 53 inches respectively. I'm driving with the Probotix 4 axis Monster stepper kit with 400oz/in steppers, ProboStep VX Uni-Polar Stepper Motor Drivers, and the2 4Volt 6.5Amp Switching Power Supply.

If I turn the screw by hand with the power off, it feels pretty easy to rotate the shaft... i'm out of ideas here, help.

[jsheerin]

With 1/2-10 5 start screws, I rapid at 200ipm with no problems. 300ipm is possible as well, but the screws start to get into whipping. So there are two possible issues. One is that your screws are whipping earlier because of the bend - they start off in an unstable condition. The other is that your low power supply voltage is limiting your speed and you are running out of torque at high speeds. I'm using 425oz motors from Keling and a 48V supply with a G540 for comparison. If you happen to have smaller diameter screws than 1/2 inch or they have more threads per inch, then that would also limit your speed more.

[groomden]

okay, this is exciting. i finally fully disassembled the entire y axis and rolled the screw around on my bench. interestingly, it wasn't warped at all... that seemed odd. so i then reassembled the axis only to discover that where the gantry attached to the anti backlash nut no longer lined up by about 3/16's of an inch. hmmm.... so out of kicks i didn't force the alignment and instead used vise grips as a temporary attachment and voila, I can now easily rapid at 200 inches a minute with no missed steps and the screw turns true. so yes, i am not only traveling with stupid, i am stupid. but i'm thrilled! now to do the same on the x axis....

[jsheerin]

That would do it as well. When I built mine, I used oversized holes to mount the antibacklash nuts to the router. I left it unbolted until it was all assembled, then tightened it down after making sure it was all aligned.