Sunday, December 9, 2018

A New Self-Locking Belt Clamp Design

Here's a quick, simple one, in case you're tired of my long-winded posts.

I am rebuilding the Y axis in SoM for belt drive (long-winded blog post will appear soon) after finally giving up on getting rid of the resonance in the ball screw drive.  To that end I needed to make a belt clamp that will mount on the carriage plate (SoM is a bed-flinger).

I decided to try a printed belt clamp because they seem to work well in SoM's X axis and in all three of UMMD's axes.

The drive pulley on the motor and the end pulley, on an aluminum mount I pulled from a piece of surplus junk, are at different heights (about 1 mm).  The belt has to be parallel to the guide rail on the side of the loop that attaches to the carriage plate.  I could either figure out a way to put the pulleys at the same height, or I could adjust the belt clamp design to hold the belt at one level above the carriage plate on the motor side and at a slightly higher level on the end-pulley side.  That was the easier way to go.

I played with a couple single piece designs, but in the end I decided to make two different but almost identical parts and screw them down on the carriage plate.

Here's what I came up with:
The printable belt clamps, one holds the belt 1mm higher than the other.  The belt enters the slot on the other side, folds over the steel pin, then goes back into the slot.  The slot is just high enough to fit the belt with the teeth interlocked, so the belt can't come loose.

A sectional view of one of the clamps.  Each clamp is held down with a single flat head screw.

The belt folds over in the slot and its teeth interlock.  I used a 3mm diameter steel pin (left over from the sand table project) to stop the belt from pulling back through the slot, though I suspect it would be OK to make the whole thing printed plastic.  Even if the pin broke off the plastic, it won't fit through the slot so it would still do its job.

Y axis belt clamps in place.  There's plenty of clearance for the belt above the clamps.

I pulled the upper part of the belt away to make the clamps more visible.
This design depends on the strength of the plastic on either side of the belt - if the slot is too tight the belt might produce enough force to split the plastic layers.  We'll see how long it lasts.  SoM's printed X axis belt clamp has been working fine for about 5 years...

Fusion360 design file is here.

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