Good morning.
This geared stepper motor (https://www.oyostepper.com/category-26- ... Motor.html) is running under high-speed loads, causing the gearbox to heat up quickly. Recently, the closed-loop accuracy has started to drift. After removing the motor's back cover, I found a very thin oil film on the encoder disc.
Following the oil trail, I found that the base oil in the grease added to the gearbox had separated at high temperatures, thinned, and slowly seeped along the output shaft gap to the encoder at the rear of the motor. Cleaning the code disc restored the grease, but the seepage soon returned.
Could I use a synthetic grease that doesn't separate at high temperatures, or add an oil-proof retaining ring between the motor and the gearbox? This oil stain is so well hidden; it took me two days to find the root cause.
Thank you all for your help.