Almost there on the CNC lathe

Joined: January 1st, 1970, 12:00 am

November 27th, 2017, 3:32 am #1

About two weeks ago I took a few minutes to nail some of my recently-obtained electronics rather unceremoniously to an old hunk of plywood, and tried once again to get my CNC lathe up and running.

Turns out one of my then-brand-new stepper drivers was DOA, out of the box. I returned it and got a refund, and went to pick up another. I wound up, instead, splurging a bit, and bought a set of "hybrid" steppers with built-in encoders, to make a "closed loop" with their included drives.

A typical home-shop build CNC like this generally uses stepper motors as they're cheap, simple and generally reliable. Higher end equipment, and virtually all industrial stuff, use servos, which are generally more powerful and can be considerably faster. The problem there is they require encoders to feed back the shaft position to the controller.

The stepper systems are usually "open loop", meaning the controller can send out signals for the motor (or axis) to move X far, but if something jams it, or the acceleration rate is too fast for the motor, etc, it can "skip" steps, and thus get out of position. The controller has no idea, as there's no feedback.

Servos, and this kind of "hybrid" stepper, have an encoder to feed the shaft position back to the controller, so it can compensate for heavy loads, slow acceleration, or other problems.

I didn't really "need" these, but since I'm ultimately planning on using this machine to make short run production parts- it might be fun, but I'm not just doing this conversion for the giggles - so I figured it was worth the extra $200 for the extra accuracy and security.

Anyway, I finally got 'em in on Friday, and took a few minutes here and there over the weekend to get 'em installed and wired.



That's two more cables bolted to my wall o' insanity...




But it works. I wasn't particularly thrilled with the short cables supplied with the motors (something like 18" or so) but once wired and booted up, it works great. They sound both quieter and a bit 'smoother' than the old motors, and should work just fine.

Over the course of this week, if and when I have a few minutes, I hope to get the axes calibrated and at least one limit switch on each installed. After which I should be able to pick out a suitable tool, and try the turning demo program that Centroid included.

And if that works, it'll just be a bit more detail work and I can start cutting real parts with this thing!

... Or rather, learning how to cut real parts with it.

Doc.
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Joined: September 16th, 2014, 7:01 am

November 27th, 2017, 8:54 pm #2

It has to be said - cover that belt and pulley on the stepper, or chips will make a mess and shred the belt.

Did you ever make a Vacuform table? A sheet of 1/8" or 3/32" clear Lucite would be perfect for that, and a simple wood block form to drape it over.

And hang a sheet of Visqueen in front of the drivers and power supplies on the temporary backboard of insanity, at least till you lock down the design and start on a proper enclosure. Same thing, major havoc if the chips fling Just Right...
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Joined: January 1st, 1970, 12:00 am

November 28th, 2017, 9:36 am #3

If you read the full write-up of the build, you'll see I made a just such a cover for the X-axis drive pulley.



I had it off to swap the drives, and left it off so I can see the pulley turn as I'm testing the new motors.

No, I've never done vacuum forming- at least, not outside of high school art class.

My only real concern at the moment is coolant. The Y-axis screw is pretty well protected, and the cross-slide itself is wider than the saddle casting so it acts as it's own drip rail. But the stepper and drive, while "enclosed" is not necessarily water-tight, and there's no particularly easy way to make it so.

I do plan on making production-run parts on this thing, so coolant and at least a rudimentary splash enclosure is almost a requirement, but I'll have to figure out some way to seal the drive to keep water out of the belt, bearings and motor.

As for the electronics, as noted in the earlier post and in the write-up pages, the plywood is just temporary- I figured I'd be moving things around, and didn't want to keep drilling and tapping a bunch of semi-random holes in a box or aluminum mounting plate.

I have a suitable enclosure now, and apart from possibly swapping one power supply (one unit that takes the place of the two smaller ones) I believe that's pretty much the final configuration. I'll be swapping it all over before too long.

Doc.
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Joined: September 11th, 2014, 4:35 pm

November 28th, 2017, 4:46 pm #4

Find a tupperware or similar of sufficient size, mill shallow slots into the side and top of the mounting block for the stepper, cut a matching hole out of the end of the tupperware, mount it upside-down over the stepper, pulley, belt, etc., then seal the slots liberally with caulk. Leave the bottom open for access, or put the lid on the tupperware to close it off (punch holes for cable access as needed.)
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Joined: August 16th, 2016, 11:47 am

November 28th, 2017, 4:49 pm #5

If you read the full write-up of the build, you'll see I made a just such a cover for the X-axis drive pulley.



I had it off to swap the drives, and left it off so I can see the pulley turn as I'm testing the new motors.

No, I've never done vacuum forming- at least, not outside of high school art class.

My only real concern at the moment is coolant. The Y-axis screw is pretty well protected, and the cross-slide itself is wider than the saddle casting so it acts as it's own drip rail. But the stepper and drive, while "enclosed" is not necessarily water-tight, and there's no particularly easy way to make it so.

I do plan on making production-run parts on this thing, so coolant and at least a rudimentary splash enclosure is almost a requirement, but I'll have to figure out some way to seal the drive to keep water out of the belt, bearings and motor.

As for the electronics, as noted in the earlier post and in the write-up pages, the plywood is just temporary- I figured I'd be moving things around, and didn't want to keep drilling and tapping a bunch of semi-random holes in a box or aluminum mounting plate.

I have a suitable enclosure now, and apart from possibly swapping one power supply (one unit that takes the place of the two smaller ones) I believe that's pretty much the final configuration. I'll be swapping it all over before too long.

Doc.
I expect your answer to fluid proofing will be better than some I've worked with. Their answer seemed to be MORE RTV!
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