One reason for my chain jumping

This is why you must watch the beast when it is moving. After the incident below, that chain started skipping, much more than before. I noticed the chain itself had a pronounced twist to it and that was one cause of the chain jumping.


My right chain has a slight twist to it near the end that mounts to the sled. It twists one way and then twists back. Early on, my chain got caught in the sprocket during calibration (twice) because (first time) I wasn’t paying attention and then (second time) because I couldn’t get from my laptop to the right sprocket quickly enough to make sure it didn’t wrap (there’s now a delay in GC to give people time). My right chain certainly has a propensity to get caught more than the left during calibration. It might be that the twist was introduced due to the early on chain wrapping.

I thought about replacing the chain, but fortunately, the twist is near where the sled mounts and never reaches the sprocket during regular operation. It might if I cut in the top right corner, but I stay away from the extremes generally.


I am going to lube the chain with some goop used for bikes. I caught it trying to wrap again and the chain on the take-up side was trying to wrap underneath the sled side. I was able to grab the chain and jerk it to prevent it from wrapping. It seemed to have stuck to the drive sprocket, so a little lubrication might stop it from grabbing.

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There could be a couple of issues that could cause that. In the picture the motor bracket looks a little skewed so there could be an alignment problem. The initial frame is a little flimsy and could also add to the alignment problem.

Looks to me that your chain guide is too low down on the timber plate. If the sled was to wobble on the workpiece (Rotation about the x or y axis - Sled does not remain flat to the workpiece) I could see the chain easily slip off with the chain guide providing little protection given the angle from the image.

Kind Regards Stuart

And the slack portion of the chain is supposed to go on the other side of the guide… Might have jumped because of the wrapping, though.

I found my chain was trying to catch as well.

When I cut out my frame pieces, I was left with two pieces of 2X4 about 6" long.

I attached those at 90 degrees onto the bottom frame pieces (where the brass hook and pulley are) so they stuck out like feet on each side. I then moved the bottom brass hook out (and in front) of the work piece so it was directly in line with the sprocket above it. Ended up being 4 3/8" in front of the face of the rear frame arm.

The sprocket chain travels smoother now.


Could you share some pictures?

As you can see, I am cutting without issue. Aligning the chain inline with the socket seems to have helped.


That is excellent advice! I’m planning to do a total frame redesign pretty soon and this seems like a great feature to include. How did you join the 2x4s and would you recommend doing it that way? Is there a way we could use a CNC cut piece of plywood there that would be easier?

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I joined the 2X4’s using the supplied long black screws (2 per side). As the stress is really minimal, I’m sure adding it to the 3/4" plywood SVG’s would be no problem.

As this is just my temp frame, I will probably incorporate into my final frame was well.

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Oh, and Bar…I suggest replacing the bottom brass hook with one of the small black screws as well (as I did). The brass hook works it’s way loose pretty fast.


Already included in the next batch :grinning: I couldn’t agree more.

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I’m getting close to calib/test cut time! Just mounted both motors and now looking at the non-working end of the chain. Whilst trying to fathom out the attachment it occurred to me that the chain jumping issues I’d read about a few days back could well be caused by the elastic end of the chain arrangement being out of plane with the rest of the working end of the chain. Combined with any flexing in the frame and mountings could exacerbate the problem. Then, whilst looking for where to post this I find that you’ve all already sorted this little concern ;¬) Wow, problems don’t last long around here do they?!
I like the idea of some Maslow-cut ply hangers to go on the frame for the bottom of the elastics, someting that can be easily demounted so that I don’t keep catching my shins on it!