Replacing MPCNC belts with chain

I have built a 37" by 37" MPCNC router and have finally gotten all the code and wiring bugs worked out! I ran many pen tests to break the machine in with no issues and finally set to cutting some birch plywood. Nothing to fancy. Some circles and some squares. I am using a 1/4" end mill and have it set to cut through the wood in 1/10" passes. The Rouger is the Porter-Cable 450 1.25 HP Compact Router. The circles seem fine, but the squares came out skewed. The error is in the direction of travel of the router bit so I am guessing that the bits spin in the wood is pulling the belts on the Y axis. Does this seem plausible? I am going to work on belt tension tomorrow, but I was wondering what issues in changing the belts out for chain would be. Has it been done and is there more to editing the firmware then changing the diameter of the pulleys. Thoughts?

Thanks for your input.


The firmware needs to know steps/mm. It doesn’t break it down by pulley size, etc. So you start with the number of steps per revolution, microstepping resolution teeth on the pulley and teeth per mm. There are calculators online to make it easy.

What kind of chain are you talking about? The belts are pretty good, even on much larger builds. They don’t flex much and they have very little backlash.

Are you sure your machine is square and that the gantry is square when you start the motors? With 37" build, you should be able to get it very close with just a tape measure. 1-2mm over 1000mm is pretty good.

I would post a pic of your belts, including the zip ties in the troubleshooting forum before changing out the belts. They do a very good job, imo.

Interesting thoughts, but I’d bet your problems lay elsewhere. My recent cuts have been square across diagonals within a few thou, making more aggressive cuts in aluminum than what you posted in wood there (with finishing passes dialed in). That’s with the standard 6mm belts and screw tensioner.