Acetal Hypothesis…Confirmed!

As you might have read in a recent post, I had a gut feeling that the reason Acetal filament fails so catastrophically compared to Nylon might be a function of the thermal conductivity of the print bed. The standard aluminum bed of the printrbot simple, while great for a heated setup, works as a heatsink for materials. Acetal/POM, which has a low thermal conductivity easily shifts its heat over to the printbed, and cools down too quickly.

However, that’s just a guess. The only way to confirm this would be a trial with a less thermally conductive bed. Thanks to the wonderful folks over at the Metrix Create:Space over on Capitol Hill (in Seattle), I was able to get some acrylic sheet and composite board cut to replicate the bed of my simple[1].

After attaching the bed to the simple, I ran some trials with PLA to get everything calibrated in and setup.

Then I began running the Acetal.

I think the white acrylic is pretty slick looking.

Results were interesting. The material initially printed and laid down well, and was actually beginning to look quite great. As is the case with POM/Acetal, the filament was extruded as a clear plastic, and stayed clear for some-time. It began to cool down, and return to its natural white color.

Unfortunately, the print began to curl at its edges, and at about the 7th layer, it curled up enough to catch the print head and get pulled off the bed.

The “finished” piece is below:

So yes, there was a failure, but there was also forward progress. This is the farthest I’ve gotten in a POM Print, and it confirms that one of the limiting factors in getting accurate prints with this material is its ability to control the rate at which this material cools.

Next steps, are to begin sourcing parts and materials for a heated bed, and put together a heated bed setup. Also, to get a large rubbermaid container to place the printer in during prints, to try and limit the amount of formaldehyde produced from printing this material at high temperatures.

[1] eps file for printbed 

[2] Printed at 245C for First Layer, 235C for Subsequent Layers. Print layer height of .4 MM


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