Linear scales on CNC?

[dogma]

I love magnetic linear scales. I use 1 micron resolution units on my machines. They are pretty much impervious to chips, coolant, and oils. Keep magnets and acetone away from them. I have been using magnetic scales since about 2014 and have had very good luck with them.

That sounds great. By any chance do you have rough BOM that you could share? There number of options is bewildering and cheap nema17 servo motors for small scale experiments don't seem to exist.

 

[JimDawson]

I think (I need to confirm) that the lead on the ball screws is 4mm, which would make the driving rpm range something like 6-600rpm. I'm pretty sure that a conventional bldc motor has almost no torque at 6 rpm. Relacement drive would be bldc motor + gear box + encoder + brake + scale?

A BLDC motor normally has a pretty flat torque curve from 0 to rated RPM. Stepper motor torque drops off pretty fast as the speed increases.

 

[dogma]

Linear scales can be used with steppers depending on the controller used.

The back of the envelope plan is linuxcnc + a mesa board (possibly 7i76E).

 

[JimDawson]

That sounds great. By any chance do you have rough BOM that you could share? There number of options is bewildering and cheap nema17 servo motors for small scale experiments don't seem to exist.

A NEMA 17 BLDC servo is not common. NEMA 23 BLDC servos are very available.
https://www.automationtechnologiesinc.com/products-page/dc-brushless-motor

I have been buying Ditron DMR 200 scales directly from Ditron in China. sales@dcoee.com

Old prices, but are still pretty close
Read Head DMR200 1um 90USD
Magnetic Tape MS200-2M 2+2 56USD (2 meters tape)

The back of the envelope plan is linuxcnc + a mesa board (possibly 7i76E).

That could work.

 

[dogma]

I'm not sure where to put a magnetic tape for the Y axis. The only [accessible] machined surface is the top of the Y axis rail but then tje encoder would then reduce the available travel and be at risk of being smashed. Chips also pile up on top of the rail. I think a magnetic scale assembly would probably be less work.