Chain keeps jumping off of the left motor sprocket

First of all, let me introduce myself as a new M2 owner. I have my mini-frame built as a 4’ x 4’ workspace and have my M2 calibrated to 1mm accuracy.

Upon placing a 2" thick slab of maple on my workspace, and starting to run some gcode I generated with Aspire, the left chain seems to be jumping off of the motor sprocket sending the sled crashing down into the wall adjacent to where my frame is setup.

I have noticed that it is possible to lower the ring that the chains attach to, and was wondering if this is supposed to be adjusted based on the height of your workpiece or not? if that is the solution to my problem I will be very satisfied. If it is not, I am rather concerned as this has happened 3 times in a row now and its quite startling each time it happens.

Thanks in advance for any advice or support anyone is able to offer.

Your chains need to be parallel to the workpiece. If they are at an angle your chains will jump.

Do this by adjusting the motors in or out.

The ring should be positioned at the sleds center of gravity. The sled hangs level when suspended away from the workpiece.

You may be able to adjust the ring enough, but it may cause some lifting if your center of gravity is too far off.

that makes sense I was only able to screw down the top side of the workpiece so its not at a 15 degree angle exactly

a small difference ftom 15 degrees isn’t going to matter, but what matters is
the angle of the chains as they get to the spockets. Roller chain is designed to
tolorate a little bit of misalignment (think bicycle chains with multiple rear
sprockes), but it’s only something ike 3 degrees of misalignment. If your chains
are at too much of an angle, they will climb off of the sprocket.

So look at your machine from the side and look at the angle of the chains as
they hit the spockets.

your workpiece being a 1/2" further out at the bottom than the top isn’t going
to cause a problem, but it’s common for peope to build the maslow with the top
beam a couple inches further out than it really should be.

David Lang

Here is a guide that I cut out to prevent the chain angle from getting to great to cause it to jump off (only works if the workpiece is out further than the motors). Hot glued some plastic from a milk carton so the chain rubs on it instead of the wood. The guide pressing down on the chain may cause some inaccurate cuts, possibly. Check out my adjustable top beam idea I just posted if you are going to cut a wide range of thicknesses.

First fix any issues with the motor angle to the work piece as @dlang described

You can also 3d pring chain alignment parts to keep the chains on the motor sprockets. I printed a set, but never put them on. Seen here:

Petg. They were printed as part of a push to dial in that filament and I’m pretty happy with the print quality from this printer.

One part goes behind the sprocket with the thicker part over the top and they bolt together. Because my frame folds up and out of the way I often reset the chains and opted not to use these, so they have never been used.

They were on thingiverse. Not sure if they were moved over to printables so you could print a set if that is an option for you. I’d be willing to part with them… Let me know if that is of interest.

The problem I am having I believe is due to the fact that at some point the ring ripped off of the sled. and now some screws aren’t holding it properly and it is peeling off of the sled.

I purchased my kit used, it had not actually been used, but the sled was already assembled. Is it my understanding that the ring did not have pre-drilled holes for the ring to screw into and I can just remove it and re-position it to the proper center of gravity and re-screw it into the sled? as I also noticed when I was reducing the distance the ring was from the sled that when it got closer to the sled it was not properly distanced andd would start bending due to the ring being screwed in too closer together on one side.

Just make sure the ring centers around the router center so when the sled spins on the ring the bit doesn’t wander. You can always cut a new sled base and make new holes. One trick my grandfather showed me with door hinges with stripped holes was to pack the hole with steel wool and then rescrew it and it will hold. Perhaps not a long term fix for cnc, but it might get you going.

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Can you just rotate the bracket so the “foot” faces inwards instead of out.

drill the hole larger and glue a dowel in it, once the glue dries, it will hold
a screw long-term

David Lang


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Depending on the size of the hole, you can glue in toothpicks as well. I’ve done that on a few home repair projects where screw holes were stripped out.