Internet of Things in Smart Homes: For Smaller Carbon Footprint
Finishing 3D Printed Parts in 1 Simple Step

While building Rumy (A portable sensor/controller for smart thermostats), we wanted to have a display prototype. The stringy surfaces of 3d printed parts leave something to desire. But using some simple techniques, a nice and final-product-quality finish was achieved.

We used a pretty old rusty Flashforge creator (1st gen) 3d printer that we bought off craigslist, second hand. The print quality was not the best that was possible. However, using good techniques we could get a shiny finished look. It took us two hours to finish both the parts of Rumy. Total cost was about $25 to buy the sand paper (Lowes) and the polishing compound (Walmart). But we had plenty left when we were done. We didn't need to use any acetone or coating like XTC-3D, mainly because we didn't have any small angles or creases which were not sandable. This made the process lot cleaner and safer, let alone, cheaper.

Sand paper for 3d print finishing
Original CAD Model and 3d printed part. We have used a blue filament here to demonstrate the method. Our actual product was finished with black ABS (image below).

Start with a good print

To have a better finish it is absolutely necessary to start with a good quality print. One should follow good printing techniques in general. Few extra things to consider:

Sanding

Five to six gradually increasing grades of sand paper is recommended (we used papers with grit 100, 240, 400, 600, 1500 and 2000 bought from Lowe's paint section). We started with the 100 grit and sanded it to the point where we couldn't see any odd lines/scratches. Larger grits take longer time. Sanding with 100 grit is the most important part to remove any odd bumps or deep scratches. We washed it occasionally to verify. Its very important to verify at every stage (under good light) or else, once moved up to higher grit papers, the scratches neglected will become prominent and you may have to start over.

Sand paper for 3d print finishing
All the odd bumps and scratches must be removed at every step.

Initially the surface looked ashed. However once we started using paper with grit 600 and higher, the surface started to be cleaner and smooth. It was somewhat shiny with the 1500 grade sand paper. If done right, there will be no stringy texture (striations) on the surface at this point. Check out the gradual increase of shine below.

Original
Original print.

Sanded with grit 100 paper
grit 100

Sanded with grit 240 paper
grit 240

Sanded with grit 400 paper
grit 400

Sanded with grit 600 paper
grit 600

Sanded with grit 1500 paper
grit 1500

Sanded with grit 2000 paper
grit 2000

Painting (optional)

We tried to avoid painting and luckily had filament that matched to our final desired color. However, painting can be done easily with the spray can (Use good painting practice with proper ventilation.) We recommend sanding with at least grit 240 before you spray paint. After drying properly, carry on sanding with higher grit papers to get the smooth surface. Good priming and painting techniques can be found here and also easily with a quick google search.

Polish (optional)

To get stunning result, polishing is recommended. Plastic finish compound was bought from walmart (~$6). It gives a shine that is comparable to regular injection molded plastic. This can be important for product photography. We had a Dremel handy so we used that to polish, but hand polish will also work.

finished Rumy
A sanded and polished Rumy. This was done with a black ABS. No painting was required.


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2015-12-26
Arif Iftakher and Thomas Stilwell