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

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14 Dec 2023 02:16 #288089 by RB211
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. 

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14 Dec 2023 03:22 #288092 by PCW
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.
 
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14 Dec 2023 07:57 #288109 by blazini36

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.
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15 Dec 2023 07:59 #288196 by blazini36
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.

 

File Attachment:

File Name: PM25MV_7i7...2-15.hal
File Size:20 KB
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19 Dec 2023 02:44 #288538 by RB211
Thank you for spending the time to send me the hal, I will study it.

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