Fitting new belt to X axis

Hi anyone got a guide to fitting new or even a measurement for the X axis belt? Googled like crazy but no luck. I got it by the roll at 2m (marked for k40 size 5mm) and need to know what length to cut it and allow a bit for the drill holes. My old one is a bit fire melted so not a good starting point.

If you bought GT2 belt you have the wrong one for your K40 it uses MXL 2.03mm pitch belt. sells the correct belt for replacement.

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Best I can find is 36". Before cutting, I would recommend loosening out the belt tensioning screws on the right side and thread the belt around the pulleys. Pull the ends of the belt tight past each other and that should get you close to where you will need to cut with some overlap.

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In case you need to know, here are the x-axis tensioning screws.


(Image from an older post by @Alex_Krause.)

Alex also did a brief Youtube overview of removing the x-axis laser head and belt.


The stuff I bought comes on a roll and matches the height (5mm) and step of the old burned one, should be fine.

Yes I managed to take the old belt off using the videos and get the proper replacement, then was amazed that nowhere has a guide to fitting a replacement. I suppose I will be winging it as usual and trying to get kinda near when the things really need to be quite accurate as there is little scope in the tensioning screws for more than a couple of “teeth” wrong.

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I’m… impressed that you can tell the difference at sight between 2mm and 2.03mm pitch. That’s better than I can do. :relaxed:

2.03mm is 0.08 inch, and this is intentional so that the K40 has 1000 steps/inch.

Also, the GT2 and MXL tooth profiles are different. You’re pretty certain you’ve got the right thing, so maybe this advice is for the next person who reads this, but… MXL is a trapezoidal tooth profile, whereas the extremely common GT2 2mm pitch belt used very commonly in 3D printing (where metric is the norm) is “modified curvilinear” profile. The teeth are different shape, and if you have the wrong tooth form for the pulley you will experience either backlash, wear, or both.

I have both GT and MXL belt for different applications, and the difference between the profiles having experienced it is obvious to me, but if you haven’t seen both of them together it might not be as instantly obvious.

FYI, and hope that helps.


I put them side by side and counted over 20 steps with them still in perfect sync so it is similar enough I think. For what I cut exact measurement is not important just relative and consistent. It says MXL5 on the packet so fingers crossed.

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MXL is what you want, that’s 0.08" pitch. :tada: