This time we recreated the gorgeous gCreate Official Rocket Ship in our various metal filaments to take a look at polishing as a post-processing method.
You can find the Rocket Ship on Thingiverse: http://www.thingiverse.com/thing:427789
The top was printed in copperFill on the Makerbot Replicator 2. Printing two side-by-side not only allowed for plenty time per layer, it also gave us a backup because the point is pretty fragile. The flame is made from brassFill and the smoke is glowFill printed on the STACKER 3D printer. It not only prints really smooth but the glow-in-the-dark effect also gives it a little extra at night!
Printing for about a full day on the Delta Tower was the biggest eye-catcher. We used a 0,8mm nozzle to create the bronzeFill body of the rocket. With 3 perimeters, 0,12mm layerheight and 15% infill this piece weighs around 1,2kg. This adds to the feel of the model and creates a sturdy model ready for post-processing.
REINFORCING THE MODEL
With a pretty heavy model and a rather small connection area to the smoke, we decided to add a little internal strength to the model to make sure it survives. A M8 threaded rod was inserted into the drilled out bottom of the body and glued in place used an expanding Polyurethane adhesive. The flame was re-drawn in CAD to allow for the rod to go straight through and the top of the smoke was drilled out to receive the other end of the M8 rod. From the same hole in the smoke we filled it with plaster to weigh it down and make sure it stands strong.
After printing all rocket parts were sanded smooth by hand starting with 280 grit, a sanding sponge and a set of small files. First working on the small edges and inset details allows you to give these spots the proper attention. You will inevitably also hit the bigger surfaces so by leaving those for later, you can make sure they look good and smooth without having to do them twice.
As always when working on these types of materials, be careful not to generate too much heat in the model. With a glass transition temperature of around 55°c it’s quite easy to permanently deform your model if you work it too hard. So only work a specific area for a few seconds at a time and let the sandpaper do it’s work. Sanding underwater will help to prevent heat building up and dust from forming but if you work patiently you will be fine.
The goal is to smooth out the model as much as possible and to create a flat surface on the metal particles. With a smooth surface there are no spots where dirt and shadows can form on the model, thus giving you the most shine. That’s why after the initial sanding we continued with a finer 600 grit sandpaper to create an even smoother surface for some of the areas we’d want to really stand out like the big dome on the body and the copper nose.
With a smooth model ready to go it’s time for the final touch: polishing. We used a DYI method of polishing, with a small polishing wheel mounted on an old drill. The polishing wheel is something that you can simply pick up at your local hardware store and usually it contains a polishing stick as well. For the polishing compound however we used a more professional stick, going straight to the super-finish high gloss material from Menzerna. But most polishing compounds for softer metals should work fine. The easiest way to set this up is to mount the drill in a vice and just leave it running while you move the print over the wheel. Pro tip: use an old drill as these sideways forces are probably not what it was originally designed for.
Polish with care and plenty of patience. Just as with the sanding heat can quickly build up while polishing and it would be a shame to waste all that work! Take your time and vary between several spots to allow the material to cool down in between passes. We noticed the best results by pressing the print into the wheel with quite a bit of force for just a few seconds while moving up and down in big strokes.
LOOKING A BIT CLOSER
Let’s take a closer look what happens when the material is polished. The material contains tiny particles of the metal powder in the form of spheres. The goal during post-processing is to create a flat surface on these balls to increase the reflective surface. The smoother the model has been sanded beforehand, the more metal particles you will hit when polishing. Take a look at the picture below, taken by a 200x microscope. The left image shows older polished bronzeFill (with some patina in between) while the right is unpolished bronzeFill. We had to turn down the lighting on the polished shot to properly show the flat surfaces.
THE FINAL RESULT
We are really happy with the way the rocket came out of the post-processing, especially because we only used basic equipment that you can easily use at home. The darker tones may look like a special patina finish, but they are just the residue from the polishing. The shiny parts like the copperFill nose and the dome have had a cleaning with Brasso to eliminate this residue and really unleash the shine. All-in-all this was a great learning experience and it goes to show that post-processing your 3D printed pieces into a beautiful piece is not rocket science.