Almost there on the CNC lathe

by Doc Nickel

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 happy.gif - 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.

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

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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. happy.gif


Posted on Nov 26, 2017, 6:32 PM

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