Sunday, 16 October 2011

The First Part to Break on my Reprap Mendel

When I started a print today I was confused to see the first layer of plastic getting squashed down very flat, so that it was noticeably thinner at one end in the Y-axis. When I stopped this and checked what was happening with the extruder movement, it seemed as though the bed had lifted up at one end, which was confusing since there was no way for the sprung bolts supporting the bed to have unfastened with nylock nuts on them.
However, upon investigating a strange rattling noise that I was hearing on the opposite side of the printer, I found this:

It seems the torsion exerted on that square projected section holding the bolt that supports the bed was too much for the plastic, after the fatigue left by printing a few kilograms of plastic over 6 months, especially with the heavy 5x230x230mm aluminium plate being supported by the corner bolts.
It's an uncommon failure mode - many FFF 3D-printed things can break if they are subject to a stress that tends to peel layers apart. Normally they should be fine with a reasonable stress acting in the X-Y plane that the object was printed, but here the sharp corner at the bottom of the bolt support has probably caused the stress to concentrate there.

It looks like I'll have to glue the part back together and print a new one, since funnily enough with all the parts I've been printing for the Prusa Mendel, I haven't made spares for such structural parts on my own printer, not knowing that this part would break so soon, having forgotten any worries I had about the part when first assembling the Y-axis.

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