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Comment by DannyBee | Hacker News Reader

This could be greatly simplified (at higher cost) by using linear motors for the cross-slides.

It may even be more rigid than what is there now (though nowhere near rigid enough to do anything real)

The design is actually not unique at all - you can buy much better versions of it (at higher cost, obviously).

Most positioning actuators you can buy are literally built to be attached to each other in a cross-slide configuration, and to have a rotary table attached to it. They also directly sell pre-built cross-slide actuators.

If you just google "cross-slide stepper" or "cross-slide servo", you can see this (servo/stepper just gets rid of the manual ones, which also exist).

The normal reason the configuration is not used is because it has no meaningful rigidity.

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Are you talking about products like this? https://www.amazon.com/Electric-Sliding-Ballscrew-SFU1605-Wo...

I'm not sure what you mean by "linear motor", I think these cross-slides typically use steppers or steppers with feedback.

A linear motor is essentially a stepper motor that has been unrolled. The Stator and rotor are flat. Kern uses them in really high end VMCs and the result is better position control and better rigidity.

do you have a pointer to a reasonably accessible device I can buy? I work with CNC and 3D printers and other motion stuff a lot and always want to find better products than the cheap steppers I'm using.

Here you go:

https://www.kollmorgen.com/en-us/products/motors/direct-driv...

and their page on success in CNC seems fairly impressive.

https://www.kollmorgen.com/en-us/service-and-support/knowled...

Edit: I'm not sure how accessible these are, but they have a life sales rep chat, so they seem to want to get them to you quickly...

Generally, if a product requires talking to a sales rep, it's not marketed towards my interests (hobbyist automated microscopy and astronomy), and the product will be too expensive.

Ah yes, at that level, you've probably found lots of reasonable linear actuators - rotary motors paired with a screw drive - but I don't recall seeing any low-cost ones either. Maybe eBay is the best bet, but it's hit or miss. It does seem there would be a market for some low-cost options.

I used to work at Kollmorgen — they really are top-notch for this kind of work, but there is a relatively large used market available on eBay. No need to buy direct from them, unless you want brand new stuff at a markup.

My uncle uses Kollmorgen drives and servos on his homemade CNC, all sourced from second-hand machines and people, so it's totally possible to do!

I recommend that you use Clearpath servos. It is a step up in budget, but the motion is much smoother and there is no vibrations which are somewhat inherent in steppers.

Linear motors are great, but are overkill unless you are concerned with the lost motion inherent in any screw, r&p, or belt. servos and double nut ball screws are adequate for almost everyone (including Mazak, DMG, HAAS, etc).

What is your budget?

I'd like to build this: https://www.thorlabs.com/thorproduct.cfm?partnumber=PT3-Z8 but for about $500 or less. I don't think those Z8s are linear motors, though. They mean "linear translation", but using DC servos.

It doesn't need to be nearly as precise,

Well said.

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