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Archive for May 2nd, 2011

What Would Barbie Pack …

Nerf pistol on build plate

Nerf pistol on build plate

… if Barbie would pack heat?

It’s actually a snub-nosed version of that, cut down by 15 mm to fit the TOM’s vertical space; the nozzle homed 3 mm above the last of the 345 layers.

I wanted to discover three things:

  • Are there any axis skips in a 4 hour print?
  • Can ABS film + aluminum plate anchor a tall object?
  • Can I use up all the pink filament?

Answers: no, just fine, not quite.

I did not re-check the platform alignment after installing the new Y axis motor and fiddling a bit with the Y axis rods. Quite to my dismay, the platform was about 0.5 mm too high (crunch!), so I gave the Z axis leadscrew a mighty twist and salvaged the first layer during the Outline extrusion. Despite that, the first layer seemed to be flat within the usual 0.2 mm (eyeballometrically measuring the first infill, as the Outline was trashed) and adhesion was fine.

The grip delaminated a bit and the butt pulled the film up, which isn’t entirely unexpected for huge objects.

Nerf pistol grip - lifting and delamination

Nerf pistol grip - lifting and delamination

Nerf pistol - grip detail

Nerf pistol - grip detail

A better view of the grip showing the cracks:

I enclosed the build chamber before starting this print, but the temperature still isn’t all that high in the Basement Laboratory and the plastic was barely warm when I took it out. I’m not convinced any reasonable chamber temperature will solve the problem; it may work out better to assemble large objects from thinner parts.

This was the first full-up test of the X Rod Follower and the new Y axis stepper motor. Prior to printing this thing, I did a quick torture test (about which, more later) and dialed the motor currents back:

  • X REF = 0.63 V → 315 mA
  • Y REF = 1.76 V → 880 mA (in a 2 Ω winding)
  • Z REF = 0.54 V → 270 mA
  • A REF = 0.99 V → 450 mA (in a 2 Ω winding)

After four hours the Y, Z, and A steppers were barely warm to the touch and a thermocouple stuck into one of the X stepper’s bolt holes reported it was 38 °C, just above barely warm. I’m adducing evidence that the MBI steppers aren’t appropriate for the TOM’s requirements and that the default current settings are much too high.

Now, for some Nerf darts…

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