Spindle encoder, but encoder is on the motor, 2:1 ratio

Hello, I believe I read that I can do this for my mill but wanted to be sure. I am currently using a Centroid Acorn and I know I cannot use the encoder that is on the servo driving the spindle unless it is 1:1. I want to switch to a 2:1 ratio so I can get up to a 10k RPM speed. I want Linux CNC to report the RPM accurately, so when the servo is at 5,000 RPM, in software it knows to report that as 10,000. I believe this would be self evident if I played with it but want to be sure before ripping out the Acorn. 

If its just for RPM readout, its simply a scaling issue.

For spindle synchronized motion (at least with LinuxCNC),
you need an index that only occurs once per spindle rotation.
 This may be doable with a proximity sensor on the spindle
that either functions as and index or as index mask for the
actual encoder index.
 

RB211 wrote:

Hello, I believe I read that I can do this for my mill but wanted to be sure. I am currently using a Centroid Acorn and I know I cannot use the encoder that is on the servo driving the spindle unless it is 1:1. I want to switch to a 2:1 ratio so I can get up to a 10k RPM speed. I want Linux CNC to report the RPM accurately, so when the servo is at 5,000 RPM, in software it knows to report that as 10,000. I believe this would be self evident if I played with it but want to be sure before ripping out the Acorn. 
 

Yeah I do this on my mill. I have a 5000rpm servo and a 1:2 and 1:1 pulley. You have to scale the commands and the feedbacks which is more complicated than it sounds but I've had this going for years, rigid tapping and all. There's a gearchange hal component now, might be worth using. I did it before that was available so it can be done without and I think gearchange is missing feedback.

Here is my mill's hal file. My spindle is setup as a 2:1 reduction so you're obviously have to scale it the other way. I have a custom panel on Gmoccapy to switch from high to low gear so you'll have to figure that out but this should show you how to do it.

 

Thank you for spending the time to send me the hal, I will study it.