Help with replacing timing belt

My Y axis timing belt snapped a little while ago. I’m getting a replacement tomorrow. The one that snapped was a closed loop belt. I bought an open 5m length belt from Amazon on Carbide3D’s recommendation. Any advice I can get would be appreciated. I know that the Y belt is 994 teeth. Will cut the appropriate length and will use the pressure plate underneath the milling bed to join the loop.

There are four slotted screws that hold the motor in place:

And two screws that help you tension the belt:

Any tips you might have for me?. How can I calculate the right tension for the belt?. Is it that critical?

Thanks in advance for any help.

Tension is important — suggest matching the tension for the other belt.

Once things are installed please see: to calibrate.

@WillAdams Thanks for the info. It says:

“For accurate cuts, it is necessary to calibrate the number of steps in Grbl to match the physical dimensions of the belts as tensioned on your machine. Doing so will require precision measurement tools such as a dial indicator or pair of good quality calipers”

I’m interpreting the instructions as follows:

-Install and tension belt by feel matching it to the same approximate tension as the x axis.
-Mill 3 circles and measure with calipers the distances
-adjust my Nomad’s calibration using the belt stretch calibration procedure in the link

My question really had to do how much tension to apply to the belt after I install it. I’m guessing that as long as it is nicely taught, it will be ok given that I have to recalibrate my machine.

That should be the case — I missed out on the Classic, so no direct experience (I did ask the team about it and waiting on a response) — rather than 3 circles, I’d suggest the traditional diamond-circle-square:

(after calibrating for runout)

Thank you for all the help. I got my new timing belt yesterday. Replaced it and recalibrated my Nomad for belt stretch and ran a quick box to test. All ran beautifully and good accuracy.

This box is parametrically driven. All I have to do is give the dimensions of my available stock and I get the biggest box that fits in it.


That is pretty cool. Is the program commercially available, or freeware, etc? Post a link if you can. Thx!!

The software is Fusion 360 and you can get a free copy if you like. A little bit of a learning curve but plenty of videos online. There are many parametric modelers out there but Fusion incorporates CAD and CAM in one package.

Cool, I didn’t know f360 had that feature…thx for sharing!