[PragmaticPulp]

I think he's exaggerating for effect. Properly sized steppers have more than enough margin for rapid movement on hobby machines without losing steps ( Video example at 1000ipm: https://www.instagram.com/p/B1wSmXfnm6C/ ).

Skipped steps are only a problem if the machine is tuned wrong, like you said, or the steppers are too undersized to keep up.

People tend to underestimate the strength of common NEMA23 steppers while overestimating the cutting forces they need. Most hobby machines don't have enough rigidity or spindle power to require more than a few pounds of lateral cutting force.

[YZF]

To be precise, it's not the strength of the stepper, it's the gearing through the screw that converts the torque of the stepper into the force on the tool.

[jacquesm]

And that will give you slop which will translate into imprecise workpieces and surfaces that aren't flat.

[PragmaticPulp]

At the hobby CNC level (what’s being discussed in this article), the rigidity of the machine is far more of an issue.

I think your advice is spot-on if someone was designing a 5000lb vertical mill out of steel, but hobbyists building DIY bench top machines face a different set of problems.

Hobby level machines are almost always limited by rigidity, not movement motor torque.

[jacquesm]

I've built a whole pile of CNC machinery, both lightweight and heavyweight. If you don't actually care about what you produce, fine, go with open loop steppers. If you want to control a device that produces accurate work products that do not need extensive rework (or to be tossed) then use something with a feedback mechanism.

I'm fine with you advocating for steppers for non-contact or drawing work (laser cutters, engraving and so on). But if you care about your tools, you don't want to wait for hours for what should be a small job then add the bit of money for a servo or a hybrid solution, on the total cost of the machine it won't make a lot of difference and the machine will be so much more reliable and faster that you'll end up using it much more frequently.

Right tool for the job and all that, bench top CNC with small servos is a very powerful tool in the hobbyists arsenal, and if you scrounge ebay you'll find they can be quite affordable. Note that anything that cuts has a stand-time, and if you move slower or make many passes because you can't really cut then you will end up spending a fortune in tooling which at some point will easily outweigh the price of the feedback mechanism, which automatically compensates for increased load and toolbit wear.

[jacquesm]

> I think he's exaggerating for effect.

I wasn't. You'll never make it through your first resonance point without current feedback, and a good stepper driver can easily go into very large multiples of that frequency.

Then there is microstepping.

> Most hobby machines don't have enough rigidity or spindle power to require more than a few pounds of lateral cutting force.

This is true, but a different problem.

[PragmaticPulp]

I think you’re approaching this discussion from a commercial/industrial scale.

Hobbyist CNC machines simply don’t have the same issues as large commercial-grade CNC mills. None of the popular hobby CNCs use closed loop motor control. Skipped steps are simply not an issue at this scale.