[geokon]

The grad students in the lab next door have to sit meticulously for hours/days with dental drills drilling out samples from rocks. I was hoping to be able to automate it with an affordable CNC machine (and an attached scanner bed) – but I seem to not be able to find any clear information about step sizes. Here it says microstepping is bad....

I also don't really need to do any milling, just adjust to the right x-y position and punch a tiny hole and collect the dust. Milling rocks in any case is a no-no from what I understand. Maybe someone could suggest some ideas for my .. unconventional requirements :)

The samples are pretty small (maybe 20cm^2 at the most) and I don't need to do it fast... And I prolly don't have a huge budget

[YZF]

I tend to disagree with the author there. Microstepping isn't "bad". The biggest issue with hobbyist setups is that they have problems with the higher step frequencies required. If you have a good controller and driver you should probably go for higher micro stepping resolution. It will give you smoother motion (less vibrations/unintended frequencies) and better positional accuracy.

Anyways, for your use case it sounds like that isn't relevant. What positional accuracy do you need? What screws are you planning to use? Start there. Most likely a full or half step setup is more than enough for your purposes and just make sure you set the motion parameters right... The cheapest solution for X/Y positioning is going to be something like fixed voltage (just using some transistors to switch the stepper motor phases) and stepping via software at slow speeds.

What's your budget? What's your more precise requirements? (working area, accuracy, speed etc.?) What can you build yourself vs. buy? Depending on what you need and what you're comfortable building it's either a trip to your local hardware store or just buy a cheap off-the-shelf 3-axis CNC kit.

[KaiserPro]

I would personally save your self a bunch of effort and get a openbuilds/ooznest workbee.

Its a kit, should be ~$1700 all in. Its repeatability is rather good (0.05mm something like that) the firmware and software are all tuned for that machine (assuming you use a kit)

sure you can just do it all yourself, but if you've never done it before its going to cost months of your time

[jbay808]

Microstepping isn't bad. The author says it reduces torque, but it does not. That is a myth.

As long as you are below the maximum pulse frequency that your controller can process, there's no penalty at all to microstepping.

[throwaway9d0291]

> Microstepping isn't bad. The author says it reduces torque, but it does not. That is a myth.

It's more complicated than that [0,1] and characterising it as a myth is dismissive and wrong.

[0]: https://www.faulhaber.com/fileadmin/user_upload_global/suppo...

[1]: https://www.njr.com/electronic_device/PDF/application_notes/...

[jbay808]

It's not more complicated than that. There is a confusion between incremental torque, which does get reduced (as correctly noted in the above) but only because the increments get reduced, and stall torque or holding torque, which in almost all cases do not. The latter are the ones that people generally care about, but because they read about a reduced incremental torque, they get the misconception microstepping creates some torque compromise.

But a full-stepping motor also has bad incremental torque for small displacements; by disabling microstepping you're just forfeiting the option to command them.

If anything, microstepping lets you run even closer to the motor's torque envelope, because you're less likely to induce a dynamic stall by either exciting a resonance or letting the stator's magnetic field get too far away from the rotor angle.

[fest]

I recall reading some hobbyist experiments that show that not all drivers implement microstepping equally: some have very bad angular linearity.

I can now find this article, but I think the one I remember reading also tested the torque in microstepping vs full step mode: https://hackaday.com/2016/08/29/how-accurate-is-microsteppin...

[jbay808]

Definitely, if your driver is bad there might be no improvement from microstepping, either.

[craftinator]

Bad microstepping timing in either the controller and the driver will definitely reduce torque.

[imtringued]

stepcraft has cheap kits (https://shop.stepcraft-systems.com/stepcraft-2-300-construct...) and also offers them preassembled for a reasonable price.