[YZF]

You just need enough margin with steppers so you don't lose steps. Particularly during accelerations. That margin shouldn't need to be x10. It also depends on what screws you're using and whether there's any other reduction. You can get huge linear forces from a relatively tiny stepper. You're also going to need margins with a closed loop DC brushless/servo system otherwise while you won't lose your position you will get a position error.

There's also systems with steppers and encoders.

A common issue though is that the steppers are driven at too low of a voltage. You also want the right kind of driver that PWMs a high enough voltage to maintain the current at speed. That's because as the speed goes up the motor has higher back-EMF voltage that the driver needs to overcome. Constant voltage drive really suffers as the motor speeds up.

But sure, DC brushless + servos are nice, more expensive, and require more expensive controllers.

[PragmaticPulp]

Agreed. High powered servos and associated controllers are great with an infinite budget, but properly sized steppers are perfectly fine for hobby CNC machines.

The forces involved can be estimated ahead of time with simple math. It's easy to verify stepper motor holding torque with a common kitchen scale. Cutting forces can be estimated with readily-available calculators online.

[imtringued]

What's wrong with a kit like this? https://www.omc-stepperonline.com/closed-loop-stepper-kit/ye...

[PragmaticPulp]

Those are great if they’re in your overall budget. Depending on machine layout you could need 4 of those. Spending $400 on motors alone puts this firmly in the very expensive end of the hobby CNC spectrum.

The closed loop functionality will never come into play with properly sized motors, though.

If the machine gets to the point where the closed loop function is trying to make up for lost steps, it’s almost certainly because something has gone wrong (crashed machine into workpiece, for example). At that point, it’s actually better to halt the machine and alert the operator, which is what a lot of people end up using closed loop stepper feedback for.

New Trinamic stepper drivers have some built in functionality to detect stalled steppers, which can be used for the same effect.

Closed loop steppers definitely aren’t bad, but they’re not a must-have for hobby machines.

[jacquesm]

Nothing, technically that's a servo system using a stepper motor as the actuator, which is fine.