Geckos as Ray says are set to 128 counts so how much that is will depend on your encoder count, any reduction and pitch of screws. The drives I use can be set to any following error I wish. The thing is you want to get it as tight as you can as that means your machine is where its meant to be, no point in having the machine capable of being off when machining as you will end up with scrap.
Hood

BTW - Mine typically run less than 20 counts error (0.001") on all axes in actual use.

Regards,
Ray L.

That makes sense.  With my steppers if they ever stall they usually stall by a lot, so I keep things conservative.  It's usually because of junk on the ballscrew, hitting the limit without limit switches, rapids that are too fast, or just cutting too hard (happens on Z all the time while drilling).  I sort of assumed that servos would be able to read this error, even if it's like 1/2", and correct for it.  Good to know!

John

Servos don't "correct" errors.  They can simply make you aware of them.  But a properly designed and operated stepper system should never be off-position.  This is not an inherent characteristic of steppers, but rather an indicator that the stepper system (motors, drivers, power supplies) were either poorly matched to the requirements, or are being operated outside their capabilities.  Under those conditions, servos will fare no better.  How would you "correct" for a 1/2" position error anyway?  The part is long since scrap by the time that happens.

Regards,
Ray L.

Yeah the part would be scrap but at least you wouldn't have to re-zero, I make lots of identical parts on fixtures.  Thanks for clearing it up for me guys!

Yeah the part would be scrap but at least you wouldn't have to re-zero, I make lots of identical parts on fixtures.  Thanks for clearing it up for me guys!

That's where accurate home switches and fixture offsets come in handy.  If you lose position, you simply toss the part, re-home the machine, and get back to work, losing only a few seconds.  If you don't have home switches, then I suggest using probing to zero the machine - also takes just a few seconds per axis.  You just have to make sure you always have appropriate reference surfaces, on the part, fixture, or vice, to zero to, even if the part has been partially machined.

Regards,
Ray L.