Wednesday, April 26, 2006


Godzilla z-axis turns properly...

I haven't had time in some days to work at debugging the bigger NEMA 17 controller board prototype due to pressure of billable hour work.

That said, my sister was dropping by this morning and hadn't seen a NEMA 17 actually running so I cranked up the single 754410 chip board and set it to running for her. No problems.

After she left, I left it on. After a while it developed a bit of a whine with a period of about a second. It was laying on my worktable and vibrating, no big deal. The NEMA was near the back end of the z-axis stage where the threaded drive rod protrudes so I idly just let the coupling that I'd made some time ago just thread itself onto the rod and begin to turn it. At a setting of 250 (just over 1 rps) it happily turned the rod while I held the motor in my hand... for a while until the bearings got out of alignment. I tightened the bearings onto the rod and noticed that the motor nestled nicely onto the baseboard of the housing for the rear of the z-axis and at a setting of 240 ran the drive rod happily.

What I had was what amounted to a floating motor mount, something that I've been trying to design in my head for the better part of a month. The drive rod alignment is determined by the lock nuts set on the bearings. I'd been trying to create a rigid stepper mounting system and, because of my crude fabrication capabilities with the hand tools I have wasn't able to get the tolerances close enough to make things work properly.

Turns out that I didn't need close tolerances. :-D

The NEMA has about 2 degrees float in the motor mounting. With the 24 threads/inch drive rods that I'm using that means that the motor float introduces about .005 mm of periodic inaccuracy into z-axis

I think that I can live with that. :-)

I tested the thrust that the NEMA put into the drive rod by hanging onto one of the nuts I'd threaded onto it. It appears that there should be enough thrust to move the vertical y-axis stage back and forth across the work table.

I think that if I shim the threaded drive rod into the bearings with some electrical tape I should be able to get rid of most of the 2 degree float. The holes in the 3/8-in bearings are slightly bigger than 3/8-inch.

I'll try to see if I can kluge up a housing on the y-axis stage to hold the z-axis thrust nut this evening. Wish me luck.

Rather than machining things, it might pay to hold them in position and fix them in place with CAPA.

Vik :v)
Already did that with the connector between the stepper and the threaded drive rod. Mind, I packed a little warm capa into a connecting bolt rather than using a big wad of it. Worked nicely. :-)
Post a Comment

<< Home

This page is powered by Blogger. Isn't yours?

Subscribe to
Posts [Atom]