Edited to say that the post below does not apply to servo motors, and does not apply for stepper motors driven with coarse pulses
Maybe I can describe the resolution issue
in practical end-result terms.... (and bring the thread back to table size)
If you are engraving the faces of medals and coins, you need a very fine resolution and lots of gearing (lots of pulses per inch).
If you are cutting background props for a Wild West movie set then you absolutely don't need any gearing!
Gearing is expensive, complicated. So, the natural question is, "How good can one cut without gearing
?" I have lots of experience with a biggish (8'x4') router running 600 oz.in steppers directly to 1" diam pinions running on open racks. (The drives are 1/8 microstepping.) This combination makes a rather good machine for cutting up MDF and Plywood sheets with typically a 3/8" cutter.
When cutting rectangles out of boards (eg. Kitchen
cupboard doors), the "low" resolution of the direct motor/pinion/rack drive has no noticeable effect - the edges are smooth and free of chatter marks. When cutting curved counter tops, a tiny "chatter" can be seen on the edge - still far
better than a jigsaw or bandsaw. These "chatters" are easily sanded out by hand. We do cutting on a job-shop basis and the boatbuilders and shopfitters have no problems with the edge quality. www.camcraftsa.com
But we won't do small plastic parts for glossy promotional gifts. (A larger cutter also gives a much smoother finish). If you are willing to apply a little sandpaper afterwards, you can also do the high-gloss smaller artsy stuff
So, I guess what I want say is that one can build a productive CNC router with direct drive stepper motors, but this is for big cutters, big sheets of wood, big space, big income
Anyway, this is a table size thread
and I thought I needed to colour in the big table, low resolution end of the scale. The "tractor" end versus the "sports car" end - they both have their place, and they are not interchageable. You could drive to church on your tractor, but you can't plough a field with your sports car!
All the best