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Archive for August 21st, 2011

Thing-O-Matic: Wiper Rebuild Doodles

Unlike most folks, it seems, I’m a big fan of automatic wiping at the start of each print. It’s particularly important with the Z-min platform height switch, because a little ABS snot on the end of the nozzle changes the initial layer thickness in a bad way: additional height at the switch reduces the first layer thickness.

The problem is that the default wiper position at the right front corner of the platform requires a cutout in the build plates and the wiper gets in the way of the first several layers of very large objects.

I’m thinking of moving the wiper to the center rear of the platform, sticking out beyond the plates. There’s a convenient hole in the HBP platform for a mounting bracket, it won’t hit either of the Z axis rods at either end of the X axis travel, and maybe it’ll be low enough to stay out of the way.

In the nature of a prototype, I smoothed a layer of Permatex copper-loaded silicone gasket compound into the corner of an old dental floss container to get a more-or-less right-angled shape:

Silicone-copper wiper - curing

Silicone-copper wiper - curing

That’s much thicker than the usual gasket that you’re supposed to make from this stuff, so I let it cure for a few days before popping it out, then another few days to get into that big lump in the corner. As expected, it doesn’t stick to polyethylene at all.

After trimming, it looks more like a wiper blade, albeit with Orc Engineering artistic sensibilities:

Trimmed wiper

Trimmed wiper

It’s fairly soft stuff, which is what you want in a gasket, so it’ll require support on the bottom and back. Right now, I’m not sure which is which, which is why I troweled the stuff into the mold with one thick side and one thin side.

A simple bent-metal bracket should do the trick, with a screw in a hole punched through the wiper blade mounting the whole affair to the HBP plywood. Of course, it’d be even better with a printed bracket.

The silicone’s temperature rating goes up to 700 C for intermittent use, which sounds about right for this application.

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