Lots of chain slack

Help! I ran through the calibration process so many times this weekend I’ve lost count. I’ve got everything measured as close as I can, and the chain calibration procedure is spot on (yet somehow is only 2mm accuracy??). The issue I am having is the lower corners have extreme chain slack, which makes calibrating by measuring from the lower corners virtually impossible.

I finally tried cutting a part on the RH side of the frame and as it got toward the lower rh corner, but still a significant distance away, the cut got really, really bad. The RH chain was taut, but the chain coming from the left would develop a ton of slack in it at a few points and cause massive errors.

Afterward I moved my sled to the RH middle of the board and just pressing down with my hand with a few lbs of pressure would cause a significant movement of the bit because of the slack. Is my sled too light? Chain too heavy?

This is a picture of some slack while cutting:

Here is the piece I was cutting, notice how the bottom right is a shitshow. The rectangle with part of the corner chunked out is where I tested by adding pressure, which made it cut the correct line.

This is what the part is supposed to look like:

This problem also appears with holes… the friction of the sled will mean it sticks and stops instead of following the hole accurately, so small holes are really oddly shaped (these are supposed to be 0.292", cut with a .125" bit). Even in the upper center, my holes are not very circular.

how heavy is your sled? (27 lbs?) is your vacuum sucking the sled down, is the board rough? This issue you describe is best resolved with a 12’ beam. You space the beam up so the motors are 30" from the work space and you need longer chains.

I think it should be a bit better than that. Try spraying some silicone on the sled base, or wax it. Be sure there is no excessive splintering above the cuts, perhaps due to slow router speed or cuts that are too deep for one pass. Yes, the lower corners are sketchy due to the shallow angle of the outside chain, but, if the sled moves freely, it can work… that dust collection hose cannot exert any lateral force in the corners. I switched to a 12’ beam, which solved the corner problems.

In the meantime, I suggest, especially for parts like you are cutting, set the machine to cut one at a time in the center of the board, and just slide the board between each cut. Don’t go crazy with machine mods until you can successfully get accurate and precise cuts in the center area. There is a lot of good cutting that can be done from the center, with good results up to 6’ wide.

Hope this helps!

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The vacuum may be sucking the sled down on that cut. I wasn’t using it during calibration and this issue still existed though.

I will check the sled weight and report back.

Can I use an automotive wax on the bottom of the sled (because I have some laying around) or do I need a wood wax?


The sled weighs 23.8lbs with everything attached, picking it up from the center of the board.

The board is smooth.