Losing Position in Z

[matt_r]

Greetings! It's been a while since I've been on this site, but it's always nice to come back.

I have a circa 2004 PRT96. My control box is an Ascension.

Wondered if anybody has run across this issue with the Z losing where it is.

Lately I've been finding on long cut jobs, that my Z will be up to .125 lower by the end of the run. I cut a lot of MDF, and I'm using a .375 spiral upcut bit. My pass per depth is .3, and going about 2 in/sec.

I see it because the .3 depth is how deep I'm cutting rabbets/dados in my parts. At the beginning of the run, I'm at .3 deep, by the end, I'm at .4 or almost .425 deep.

I thought it might be my router or collets, but I have changed all of those out recently, and I still have the problem. I also tried marking the shaft to see if the bit was getting pulled out, but it is staying put.

I'm wondering if my spur gears/rack-n-pinion is getting worn out. I've replaced the spur gears on my other axis'. Or could it be the internal gears in the motor head?

Would love to hear any thoughts.

Thanks,
Matt

[srwtlc]

Not sure, but what about positional loss of steps due to a bad driver or weak motor. An upcut bit will always pull down on the router. What happens if you travel slower with lighter cuts? Try a test run with a downcut bit and see if it pushes it up.

The usual of checking the machine for worn and looseness anywhere and pinions.

Scott