X Axis Travel Accuracy

Sometimes i'm very pragmatic...
And change scale..

Thanks Mike,

I’ll give it a go and see how she goes. Effectively I’ll be calibrating the axis. Must have been a fluke the Y axis came out right. The gantry axis was the one I expected to cause pain but it was the easiest...

Cheers,
Jason.

If you calc 5*32+31/32 / 6*32 you get 0.9947916666666
precision of rack pinion combo..... Not bad
Mike

You may want to check your Y axis closer. If X axis is twice as long then if the mech's are exactly the same the error would be half of 3/16 on the Y.
What I am saying is if the X is like 8 foot and the Y is 4 foot a 3/16 error on X would equate to a .09 error on Y. That's hard to pickup with a tape.

Hi Bevins,

Both the X and Y are the same length. The working area is 4' x 4'.

I have to say that the Rack and Pinion system that CNC Routerparts make is very good. This is just the standard version too.

I guess I'm probably under the misconception that once you enter the parameters in stepconfig wizard that all should be good. It now seems that it will get you in the ball park and then the user needs to fine tune things.

Cheers,
Jason.

If the round gear is undersized on the pitch diameter I think it could cause this. 8m trying to visualize it in my head.

Get 2 dowel pins and measure your two gears 180 deg apart and see if they are the same

Was my first thinking too. But as there are theeth i suspect the rack...
Just scale it

Ok a bit of an update.

Last week I tried scaling both the X and Y axis to improve accuracy. Unfortunately this had a negative effect on circular cuts so I reverted back to the old settings.

This week I had another look at things with the scaling. This time I used the calibration utility within LinuxCNC to tweak the settings along with a dial indicator. I was only moving the machine 0.1” and taking readings. Unfortunately (again) I found the setting changes to be misleading. My immediate thought was slop in the system. With the dial indicator resting against the gantry I was able to move the indicator +/- 0.0075 on the right side of the gantry and +/- 0.003” on the right side.

Interesting... Upon further checking I’ve found that the pinion gears are actually worn. I also found that belt tension had an impact on slop too but I believe the root cause is pinion wear.

I bought these rack and pinion drives from CNC Router parts. Interestingly they now offer spare pinions for their system specifically for people using their machines in a production environment. The plot thickens... Just lately I’ve noticed the circularity of holes has degraded hence chasing down this issue in more detail.

Anyway, I’ve ordered some more parts and will update this thread with the results. Hopefully this will be of help to others out there.

Cheers,
Jason.

Does your setup allow you to adjust the pinion depth?

You could probably tighten it up a little. But too tight will accelerate wear also.

Hi Leon,

The Rack and Pinion system does use a preload spring to pull the pinion against the rack.

I'll pull one of the pinions off the machine today and post some pictures of the wear. I guess it's better to wear the pinion than the rack.

Cheers,
Jason.