[fyffe555]

Phil,

maybe a dumb question but is the motor dropping off at 240rpm or is it the driver? If it's the driver then for the cost of those drive screws maybe it's worth upgrading the drivers first? Wouldn't the 3977 drive this faster?


One of my machines (first one) is a 12x12" moving gantry mdf special. It's pretty light and uses cheap 3/8-16 allthread, gas pipe/rollerskate on X, pacsci 118oz motors and IMS 483 drivers @ 38vdc and 3.5a ea. That runs up to 70 ipm or 1120rpm quarter stepping the driver. In fact it does run faster but the gantry jumps up and down as the X screw starts to whip.....

For the McMasterCarr stuff The leadscrew and the nut you've listed are not quite the same profile...The leadscrew is 'precision acme' the nut is 'precision modified'.

I'm using similar screws in 1/2-10 acme and the MMC wear compensating nuts on a stiffer 28" x 28". Similar 118oz pacsci motors and same drivers. I started off with cheaper Enco 1/2-10 and delrin but the Lead accuracy was way off over the length. The MMC wear commpensating nuts didn't fit the enco acme, got some leadscrew from a surpls store locally which still has a slightly different profile but works well if a little tight at first. Inertia of the heavier screws limits rpm to about 900 on the 118oz motors @ 48v and 4a so that's ~90ipm or about 22 seconds end to end G00 rapid factoring accel.. With hindsight I would have got something in the 6 or 4 lead per inch range and kept the motors more in their torque range but I'd already bought the nuts.... one or more starts really depends upon where in the torque curve you want to gear your motors.

If you're going to go with Acme the quality and price of the MMC stuff is pretty good. The wear compensating nut isn't quite backlash free but over 28" I've struggled to measure the deviance after some ten months of intermittant hobby use at fairly high rpms...

hth

Andrew