On 11/23/23 14:26, Chris Albertson wrote:
On Nov 22, 2023, at 1:06 PM, gene heskett <ghesk...@shentel.net> wrote:
I'd have to agree Andy. I need to design a disk brake for my A axis as there's
half a degree of slop in the worm drive which if it gets to the motor will be
held, but the slop in the worm makes for sloppy looking holes, but the
activation method is still in my head. Even that is only important when
drilling a hole for the handle. I'll come up with something.
Would a simple disk brake work? I think it might clamp the part any place
within that 1/2 degree of slop range. Ideally, you would have an index plate
and some way to place a pin in a hole to lock the table. But you could only
have a few holes and not enough holes for one at every place you might want to
stop.
What if the disk had “V” slots cut in the edge. Like a very large US Quarter
Dollar, but with maybe 360 grooves. Then you could wedge a shape (like a tiny
axe head?) into the slot and force the disk to stop on an even degree. You
could use more than one wedge, space them around the disk.
A wedge would need a lot less clamp force than a brake disk pad because it is a
mechanical lock almost like an index pin
If you still want a “disk brake” why not use an actual disk brake from a
bicycle? They are about the right size, have huge holding power, and don’t
cost all that much. The ones you would want to use are hydraulic so the
electric actuator could be a couple feet from the rotating table. They still
make cheaper ones that use cable but avoid those, they are too hard to adjust.
Or maybe both, Use the slot and wedge to aligh the table to the nearest degree
and then clamp it with a hydraulic disk brake. Cost is under $100.
This A drive is a 3 phase stepper/servo driving a 5/1 worm. It the slop
in the worm its driving, but the overall accuracy, ignoring the worm
backlash is 5000 individual stops in a 360 degree turn. Or about 0.0225
degrees a step once the drivers /16 microstepping is figured in. Plenty
good enough for the girls I might go with.
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Cheers, Gene Heskett.
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