Strange path after multiple passes?

What causes errors like this:

Google Photos

IT will go over 3 or 4 passes then suddenly the tool seems to veer off in an odd direction. This has happened in the first two jobs I attempted to cut. It has happened on both straight and curved cuts.

What do the control motors sound like when this happens? Anything different?

Does the motion of the machine become very jerky at this point?

Its hard to say what the motors are doing because the event is unexpected and since the tool head is removing more than a small layer of material my attention is drawn to the router not the motors. I can say the right chain seems to be bouncing around more. After the error occurs, it will happen again (or in a very similar fashion) on the next pass too.

The first time I saw this behavior was on my first job for the sled and the error happened in the lower right hand corner at around 5’oclock where the right side brick would mount. The next job I did, was doing larger parts and this cut was a 16"x12" profile cut and it again happened in the lower right around 5’oclock

The errors only seem to happen during profile cuts (not pocket cuts). The tool has always been moving in the counterclockwise direction and so far both errors happen in the lower right of the job.

See example two:

Hmm not sure what is going on.

We are working on an some sort of memory or buffer issue where the machine become very jerky after running for a while. You may want to try rerunning the same gcode again (you don’t need to put the router in the sled) and see if it seems like the same problems crop up around the same time. If they do, then this is likely the same issue. You can see the discussion here:

The title may be a bit misleading.

If that isn’t your issue, I don’t have any idea.

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Thanks for the response. I will give it a try with the router removed tomorrow and see if I have the same behavior.

What causes errors like this:

If you are saying that it cut the stright portion without a problem and then cut
the humps, that is a great indication that the sled is not sliding, it’s
catching on something of sticking so that as the chain continues to pull, it
first tilts the sled, then the sled comes free and it falls back in place fairly
quickly, and then the problem repeats.

I was thinking this could be the case but in both instances the first few passes go fine so I would not think the sled was catching on something on the surface of the workpiece. In both examples the sled is moving along an existing gap and none of the edges of the sled are encountering an edge or anything that it should get caught on. Perhaps its a defect in the plywood like a gap or concentration of glue?

The ‘lead in’ to the error looks really smooth. I had cement in a Chinese ply, but that just ruined the bit. The vacuum being dragged by the hose?

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Perhaps its a defect in the plywood like a gap or concentration of glue?

it’s possible, if the bit was a bit dull, that could make it harder to cut
through a defect and slow it down.

David Lang

I have experienced that a few times, @Gero is correct. It is the vacuum line, or the power cord, or a friction of the sled. Mine was vacuum line getting caught on the bottom of the frame as the hose is ribbed, and it doesn’t take much to pull it out of the track.

I did not have a vacuum attached at the time of any of my errors.