Working with Shapeways’ “Frosted Detail” Plastic

(c) 2016 P. Matthews
for use with Frosted Detail models from Matthews Model Marine, a shop at Shapeways

The “Frosted Detail” plastics from Shapeways are not the same as the molded styrene in your typical plastic model kit. In fact, the Shapeways material is harder to work with, and requires some special handling. But this is the price we pay for custom parts that can’t be found anywhere else.

First: How is my part made?

Two things make this type of 3D printing possible:
1. A liquid “photopolymer” acrylic resin that can be hardened with ultraviolet (UV) light;
2. A device- a print head- which can deliver drops of the resin to particular places on the print platform.

So basically, the process is like an inkjet printer head, sweeping back and forth, spritzing out droplets of resin which are then flashed with UV light to harden them in place. Do this in layers… layer after layer… and you build up a three dimensional part. Easy!

But there is an additional trick required:
If a new layer’s edges overhang the layer below it, the droplets will fall out of place, just as surely as what happens to Wile E. Coyote after going off a cliff. So some support is required. The printer does this by printing out droplets of a waxy material wherever an overhang is planned, providing a soft platform for the next layer of resin.

OK, what do I have to do special?

1. Be careful with your parts. Very careful.
The parts are very brittle, nothing like the rather flexible styrene in model kits.
– Snipping a part off a sprue, when it’s retained in multiple places, can shatter it. I use a very fine tooth saw while carefully supporting the part.
Hint: Look for “EXCEL” #13 saw blades, which are super fine, and can be mounted in an Xacto handle.
– Drilling a hole can split the part open, or shatter chunks off.
– Even normal handling can break smaller parts.
– Test fit parts, but never force them… file as needed to get a happy fit.

2. Wash your parts.
The support wax has been *mostly* washed off. Get the rest of it with warm water and detergent, or Simple Green or similar; scrub gently with a toothbrush. An ultrasonic jewelry cleaner can be helpful when doing lots of parts.

3. Post-cure your plastic.
This should be taken care of by Shapeways, but it isn’t. The flash of UV light that cures each layer doesn’t get 100% of the resin. And traces of uncured resin in the plastic matrix will lead to problems with paint. The cure? Post cure with a good dose of UV light… a few hours in the sun, or under a UV-A lamp, should do the job.
Note: NOT a heat lamp, not a flood lamp, but a UV lamp, preferably in the “UV-A” band. You can find UV-A 15W flourescent bulbs for a few bucks, they fit in the small under-cabinet fixtures.
The real test is whether enamel primer cures on the part. If it doesn’t, wash with paint or lacquer thinner, and post-cure some more.

4. Scrape and sand your parts.
After washing and drying, you will see “frosted” surfaces wherever the support wax contacted the plastic, while areas that were on top in the print process may be almost optically smooth. The frost and other print line artifacts can be scraped and sanded off. Instead of just cleaning mold marks and seams, as with a commercial plastic kit, you’ll need to clean the entire surface on about half the part. Please enjoy this time spent bonding with your new model!

5. Glue with epoxy or CA (cyanoacrylate). You may need to use CA “kicker” to get the CA to set.
Note: This is an acrylic plastic, and solvent glues for styrene models won’t work. Possibly solvent glues meant for Plexiglas would work– I haven’t tried them. Also note that solvent cements work best when the joint can be held under pressure while setting.

6. If you post-cured the parts, you’ll be able to paint with your choice of paints. I recommend enamel primer in all cases.

(c) 2016 P. Matthews
for use with Frosted Detail models from Matthews Model Marine, a shop at Shapeways

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