More Lessons Hot off the Press

It's been about two weeks now since I started printing the Chevy Camaro V8 LS3 engine on Thingiverse designed by Eric Harrell and I've learned a couple more things that I wanted to capture for future reference.

This is a picture of the first cylinder head being printed, we're about 60% of the way through the print at this point.

The policy "if it looks clean, it runs good" is usually a reliable philosophy in engineering. Clean parts usually run well, there are no contaminants or abrasives gumming up the works. But when I looked at the glass plate on my 3D printer and decided it was so gross I had to clean it, the decision turned out to be a mistake.

Let me take a step back. Typically I spray the glass plate that is the base for printing with hair spray. The hair spray coats the plate and, as the plate heats up, the hair spray becomes sticky and the PLA filament from the nozzle wants to stick onto the bed. This is desirable because if your part is not fixed in place while you are printing, the layers will not line up with each other. I've been disappointed many times when I came back to a print 2 hours later and found that the part had shifted away from where it started and now my printer was trying to print onto a part that wasn't there anymore.

So last weekend I looked at my glass plate covered in layers of hair spray and strands of plastic filament and decided to clean it. Then I put the plate back on the printer and sprayed it once with hair spray before starting the next print. That didn't work; I think the multiple layers of hair spray were critical to holding parts in place. So now I'm not going to wash my glass plate for a long time.

A close-up shot of the cylinder head in progress.

Unfortunately, once I applied a couple more coats of hair spray, the parts were fixed so solidly to the glass plate that I couldn't remove them with my bare hands. (I don't use tools because I don't want to damage the glass.) So I took the glass plate off the printer and ran it under cold water - usually the thermal shock is enough to loosen the plastic parts and with a little manipulation they came free.

After that incident I tried printing some parts with a raft. In 3D printing, a raft refers to sacrificial layers of plastic that are printed below the desired part. The pattern that forms the raft is usually looser than the pattern for the actual part (i.e. each thread of filament is spaced far away from the next one). It turns out that there is not enough material on a single layer of a raft to stick to the glass plate, and my parts started slipping around again. I've decided from that experiment not to use rafts going forwards. I'd rather have to put my glass plate in the freezer to get a part off.