X Axis missing steps - Problem Solved!

[Tim Summerer]

Hey Everyone,

I thought I'd share a problem solved story

Recently one of our PRT Standard Shopbots has been getting off in the X axis. The problem has been inconsistent, unrepeatable, and very frustrating. A file would finish and upon measuring the parts, they might be .25-.75 inches off. I began to go through all the troubleshooting steps - bit's sharp, router's good, file's good, computer's good (lots of possibilities for problems here, but our's is top notch), electrical is good, grounded like a rock, carriage moves smoothly, rails are square, etc, etc. Finally, I saw an old post that said to check your pinion (or spur) gear. Now I had looked at mine plenty of times while inspecting the carriage - it seemed to fit well and roll smoothly. However, we have two PRT machines and I had the sense to compare the gears between both tables. Simply from a visual comparision I could tell that my problematic machine's gears were worn out. I called ShopBot and ordered some new gears and the difference is HUGE.

As you can see from these pictures, the old gear (on the left)(cleaned up for photos) is very worn out. The teeth are thin and pointy, the ends are sharp, and the diameter is slightly less. The new gear fits much better within the rack and I have safely increased my Jog speed with no issues.

I wanted to share this for the benefit of other users who, like myself, have older machines. This was a difficult thing to catch because the gear *looked* like it fit correctly, and it *seemed* to roll ok, and part sizes were ok. If I had not had another machine to compare to, I think I would still be pulling my hair out.

Hopefully these pictures will help give people an idea of the difference between a new and a worn gear.

[Robert Bays]

Tim,

Thank you for the post! I know now if my machine ever starts doing this the first place to check..

Good stuff,

[TMC-GSO]

I have a PRS standard as well and I am having the same issues. The X-axis will periodically jump itself. The inconsistancy of the problem makes it worse cause if I have shopbot tech support come out it might not happen. I have checked the gears and they look fine. I am at a loss cause the communication should be good, both motors work together.

Any ideas for me to troubleshoot before I have to have shopbot come out blind?

Thanks