Belt Lifted Z-Axis for a 3D Printer

Since I changed the belt clamps, my steel core belts were too short to put back on the machine so I installed some Gates LL2MR09 glass core belts. 

I originally chose steel core belts for the hoped-for minimal stretch, though there wasn't much information about them available.  I measured the displacement of the bed surface with 4 kg piled on it,  It worked out to 42 um per kg of print load, equivalent to a maximum of 1.2 um in any single layer of a print that covers the entire bed.  

Yesterday I checked the glass core belt stretch.  It was about 3.4 x greater than the steel core belt- about 150 um/kg equivalent to a maximum of 4 um in any single layer of a print that completely covers the bed.  Probably still not an issue for most prints.

More:  https://drmrehorst.blogspot.com/2018/12/comparing-steel-core-and-glass-core.html

New clamps and glass core belts installed and working fine.  

The Z axis was recently behaving strangely.  I noticed the belts were flopping around so I retensioned them.  In a couple days, they were flopping again.  I took them off the machine to see what was going on and instead of finding that the steel cores had broken, I found this:

The polyurethane belt had slid/stretched over the steel core (of course it did!) inside the belt clamp.

I have redesigned the belt clamps so the ends of the belt will fold over and the teeth will interlock.  That should prevent this sort of problem from reoccurring.

I have used this folded self-locking type of clamp for years in the XY stage and in SoM, my other printer.