Wood CNC Y-axis repeatability


#1

Since getting the wood CNC set up I’ve attempted to use it a couple times, and have been disappointed with the repeatability of the Y axis. I investigated with the help of @Gear105 and we found that it seems to lose steps, but not due to mechanical slippage as far as we could tell. I think it’s an issue with the electronics. The two Y motors are wired in parallel to a single driver, so perhaps it is not delivering enough current at times, either due to configuration or capability.

Today I made a test case G Code and made a video…

The test case goes back and forth between Y=100mm and Y=200mm, and dwells for a second so we can read the gauge. Here is the file (YTEST.TAP)

G4 P3
G0Y200
G0Y100
G4 P1
G0Y200
G0Y100
G4 P1
G0Y200
G0Y100
G4 P1
G0Y200
G0Y100
G4 P1
G0Y200
G0Y100
G4 P1
G0Y200
G0Y100
G4 P1
G0Y200
G0Y100
G4 P1
G0Y200
G0Y100
G4 P1
G0Y200
G0Y100

I’d love to get this fixed. This is a great tool but without better repeatability it is only useful for surfacing.


#2

Can you change the acceleration/deceleration parameters to lower values and see if that helps? Also add an equal dwell on the opposite end of the travel from the gauge so that you are doing a truely equal movement in each direction, it might be trying to change direction while still physically decelerating.

What is the driver set to deliver for amps and what are the motors pulling?


#3

To test if its the drivers we can rewire the X driver as a Y split the motors and test its repeatability. Otherwise it could be a current setting on the driver, or maybe problems with the driver itself.

I’ll be there later today and might try to do this.

Thanks,
Luke


#4

I already tried adjusting the parameters and it made no change.

@Lukeo
Wiring two motors to one driver is not recommended. You are loosing a lot of power because the set draw will be split between the motors. I think there also some other strange downhill effects of doing this as well, in that when you are energizing two different coils on different motors along with the effect of micro stepping between coils, things get… muddled. I recommend splitting the step dir before the drivers.


#5

Are the cables shielded?


#6

Swapping the drivers is a good place to start. If swapping the drivers ‘fixes’ the problem then it’s likely an adjustment on the Y driver board.

Of course also clean the X and Y axis slides to make sure there are no sticky spots, check for warps etc. Try running the text in sections of say 1/4 the distance and see if there is a sticky spot that you can’t see visually.

Reduce the speed and see if that helps, if it does then likely you have a current problem, weak motors or as was pointed out it may be the motors just don’t like to play in parallel together.