1. A slight correction.
Old-tech type servos, dc brushed servos like geckodrive 320, of which I have 7, used to dither.
The geckos are not in use anymore.

New ac brushless servos find the position commanded, and lock.
Zero dither.
They are "live" about 0.5 secs, and then lock solid.

I have 2 brands, about 15 total in use and in stock, all are the same.
From 400W / 60V, 750W/220, 2.5 kW/220V.


The bigger servos mostly have a led display, you can configure, as std it shows the error count.
So you can see the error on the led, which always goes to zero, and then the servo locks.

The moral:
A 1.3 Nm (400W) servo is the same size as a Nema 23 stepper.

A full set costs == 290€ EU 22% VAT.
A Nema 23 new stepper set == 40 + 50 + cables ==100 €.
A servo is about 200€ more / cheap small nema23 stepper, per axis.

But a Nema 34 stepper system, high voltage, with a 150€ driver, is about 250€ all-in.
The modern ac servo system is vastly better.

So the steppers are very cheap, pretty accurate, but have low dynamic range.
This means stepper systems are either accurate, fast, powerful, but not all 3.

Vast numbers of excellent routers have been made with steppers.
Including mechmate-sized 10k$ systems for workshop use.

I am not a servo-zealot by any means.
For one, you must have hw limit switches, imo.
Unlike with steppers.

Likewise, almost all lathe conversions I see are with steppers direct coupled.
This is a terrible idea. Imo. Ime.
And I tried 2000 hours.

Quote Originally Posted by m_c View Post
1.
Servos are rarely perfectly held on position.

They will normally always be dithering at least an encoder count or two, especially if they're subjected to any kind of varying load. Under normal use, even with perfect tuning, they will always be out a few counts, however compared with a stepper motor, servos should produce near continuous torque at any point in their rotation, and produce near constant torque over their entire rated speed range.

However, you don't really need to know any of this. If you design the system around rated torques (in the case of steppers, look at the torque/speed graph, to get the torque at the maximum speed you think you'll be machining), then you shouldn't have any problems.

Don't rely on servo peak torques, as they're more to allow for rapid acceleration.