losing counts on BOSS8 encoders

[jmelson]

I thought I was about done with my R2E3 retrofit project. But, doing some testing, I found it was losing a little bit of position when moving. Every axis shows this, but it is worst on the Y axis. I have a program that moves Y 3" back and then returns to the indicator. It seems like at 12IPM or below, it doesn't seem to lose position, but above that speed it loses from a half to a full thousandth on each repeat. I've looked at the A and B quadrature signals with a scope, and they look good, the differential complements look like complements. I am using my own CNC interface that is a manufactured product, and I've never seen this on my older Bridgeport using the same hardware.

This retrofit is using the Pico Systems PPMC interface, LinuxCNC, and AMC 30A20AC servo amps, and the original motors. I reterminated the original Bridgeport encoder cables to the PPMC encoder board, and have checked all that wiring.
Anybody have any suggestions? I'm strongly considering replacing all the encoders, there are some nice ones on eBay right now, but I would have to make shaft and mounting adapters.
Thanks for any comments,
Jon

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[MillMan97]

Taking a long shot, are you by any chance using the original encoders from the R2E3.We had a BOSS 9 R2E3 (or E4 - not sure which), not all that different from the BOSS 8, with Powertron Servo motors and Contraves encoders. Let me put it as politely as I can after 30 years. THEY SUCKED! The encoders became unreliable after a few months of use and started mis-positioning. Only a little at first, then by whopping amounts, or they sometimes caused a shutdown for no feedback signal. The entire servomotor/encoder setup had to be sent out for very expensive repairs. The entire machine was essentially an abortion that Bridgeport rushed out in order to get one of the first CNC Knee mills with servo motors instead of steppers. After a few years of repeated breakdowns and problems, we had a Centroid retrofit put in that has been highly reliable ever since (with a couple exceptions, but that is not the subject of this post). In the event that your retrofit retained the original servo encoders, I would strongly suggest replacing them. Even if they weren't retained, the encoders could still be the issue..

[jmelson]

Crazy problem! It was the knock-off indicol dial test indicator holder that I was using. It was slipping just a little each time I did a back and forth move. I did have one encoder that was dirty, I tore the whole thing apart and cleaned the encoder disc with alcohol, and now it is working fine. I did buy some 10X higher resolution encoders online, but will have to make adapters to mount them in the motors.
Thanks,
Jon

[steevgg]

Crazy problem! It was the knock-off indicol dial test indicator holder that I was using. It was slipping just a little each time I did a back and forth move. I did have one encoder that was dirty, I tore the whole thing apart and cleaned the encoder disc with alcohol, and now it is working fine. I did buy some 10X higher resolution encoders online, but will have to make adapters to mount them in the motors.
Thanks,
Jon

Do you ever replace the encoders ? I’m looking Into replacing mine but don’t know what to go with