I appear to be having multiple issues with the x-carve, but want to tackle them one at a time.
My x axis belt keeps slipping. I adjust and tighten and it just slip through before I can get a sample cut done.
I have two thoughts on how to address this.
small zip ties at the belt bracket. I’m thinking two at each end should hold.
drill two small hole in the maker rails to hold a small bracket in place over the belt bracket.
Any other ideas would be welcome.
I use a piece of shrink tube on each end of the belts and I have never had a slip.
You can see the shrink tubing on the second picture in this post, it is red.
How sensitive is the belt to heat? I like the idea, but worry I might damage the belts.
I used a heat gun to tighten them up, no issues.
They just might tighten up on their own today, 100 degrees here in Georgia 
Once I got them where they needed to be I put a staple thru both sections. No problems after that. Just used an office stapler.
I use a single small zip tie on each side and it works well.
I used the shrink tube method and a lp torch (VERY CAREFULLY!) only enough to shrink the tube, not enough to warm the belt. Never had a belt slip from day one.
I am skeptical of the staple suggestion due to the peircing action of the staple. unless i am envisioning this incorrectly…
The method I used that has never slipped at all was to use a drop of cynoacrolyte (super glue) on the fold-over, then put a piece of shrink tubing over that. I’ve never had the slightest bit of belt slip, it’s still holding tight as can be a year and a bit later.
I tried melting a section of belt cuttoff, it takes the heat very well, you would have to get really carried away with a heat gun to affect it. Nice thing with shrink tubing is you can slip the tubing off to make adjustments and put it back on, holds great.
Had to go back and look. The suggestion for zip ties & heat shrink is under a tips and tricks video.
IMHO though, this is good enough, and has caused me enough headaches, it should be in the main instructions.
Thanks for the point out…
Make sure you’re putting the belts through the clips properly, and as multiple people have suggested… shrink tubing works perfectly fine on my machine.
I just used a piece of electrical tape around the belts. In reality all you will really need is a little external force to hold the two belts together in the vertical direction. (Shrink tubing works too). The horizontal forces tugging on the belt are held together with a mechanical hold facilitated by the teeth in the belt.
