Friday, December 31, 2010

Willow Gets Some Dental Work

I started noticing that my round holes were not quite round, so I checked my belts and determined that the X belt was a little looser than I would like.  I tightened it and started printing again only to discover a horrible noise and  the x motor binding and skipping.  It happened at a few points across the bed but ran fine between them.  I looked around for the problem, what did I mess up by tightening the belt?

Broken Tooth

It turns out all I did was make an existing problem worse.  The x-axis pulley had lost a tooth.  For the looks of the hole where it use to be it had been gone for awhile. (Also note the wear on the teeth from the belt...)

Broken Tooth

Which explains some other strange x-axis noise I could not place.  Lesson learned "Listen to your bot!" if there is a strange noise look around more and look under things.

The easiest way to fix this, and keep my nice pulley, was to remove the pulley, flip it over, and put it back on.  Easier said than done...

Once I started looking at it closer I realized why the tooth broke.

Hollow tooth


Four of the teeth are completely hollow.  I am not sure what infill settings we used when printing the gears.  But the 4 that are are 45° from the infill direction have none in them.
I then became concerned about my other pulleys.  I checked and they all have the hollow teeth but Z and Y both have all of them still.  But I will have to keep an eye on them.

How to reinforce the pulley so that it won't break again?
It turns out the holes were big enough that some of my waste PLA (0.5mm) would slip down into them.
0.5mm waste PLA (for filling the void)


So I cut 4 pieces, mixed up some epoxy and glued them in.
Pulley with voids filled


Here you can see the reinforcement PLA inside the teeth.
Pulley with voids filled

I then pressed the pulley back on with a bar clamp.
Pressing pulley onto motor

Fixed motor


I then reinstalled it on Willow and re-tightened the belt.
Fixed motor


Back in business and printing again.  The x-axis is quieter now, which brings my back to "Listen to your bot!" if there is a strange noise look around and look under things.

A final thing to note is even professionally printed pulleys will eventually wear out.

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