Non-Symmetrical Errors

I am noticing what appears to be errors that are not mirrored about the central axis of the machine in some of my cuts.

To flush it out, I cut a 4 foot long 1 inch tall blank which was centered on the machine horizontally, it was probably about 8-10 inches above the center line vertically.

The result was that the right hand side was about .15 inches thinner in height than the left hand side. The difference in height seems to be close to a straight line from one side to the other.

Any ideas what might cause this?

No idea, but some questions - Are both the horizontals skewed with respect to the top edge of the workarea sheet or is just one of them skewed? If they are different, is the difference in the right-to-left cut direction, or left-to-right? is one end correctly cut 1” tall, the other off, or are both ends wrong?
Looking for some asymmetry in the machine here that might give a clue.

Any ideas what might cause this?

As a matter of looking at the code, it makes all it’s calculations on the left
side and then just switches the chain lengths for the right side, so errors that
are not symmetric from one side to the other indicate some sort of mechanical
problem, not software problem.

Are you sure you start off with the chain lengths the same?

They are both skewed by about the same amount. The top cut on the left side is 1/16 higher than the right and the bottom cut is 1/16 lower than the right.

I figured as much.

I certainly thought so, but I guess that is worth recalibrating the chain lengths.

You might want to mark the chain link at the top of each sprocket when the calibration finishes. I used a white paint marker, nail polish would work too. This way you can quickly check to see if the changes are “right“ in the future.

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someone should add this suggestion to the assembly wiki (I don’t have time right
now, I’ll try to do it later if someone else doesn’t do it first)

I don’t even see a reference to calibration in the assembly wiki. I think we need a step 8.

@krkeegan, I see you’ve written a PR#374 in GroundControl to simulate a slipped chain - was this the cause of the distortion you wrote about? If not have you narrowed it down?

Based on what the distortion showed, I don’t think so. I need to center the sled, mark the chains and then rerun the chain calibration, but I bet I will see that it has not changed.

I am confident I am seeing some dimensional distortion, inches are smaller in certain areas of the workspace. But I need to spend a little more time characterizing it. I think I can borrow a laser grid projector which might allow me to do the simulation presentation in real life.

I redid the chain calibration tonight. It turned out exactly the same.

I think the next thing I am going to do is confirm that this is happening buy cutting a 1 inch square block in multiple locations on the work piece and then comparing their dimensions.