When we last heard from our fearless Engineer he had printed and glued together 16 different pieces of a Storm Trooper helmet. Now is the time to fully finish the helmet and make it look like the real thing. There are many ways to finish a 3D printed part. The process I will go through is a similar to the process you would use for prepping and painting your car.
The first part of the process is sanding the part. The way this helmet was sectioned it was just straight cuts and all the parts were butted together. There was no location geometry. Typically when you are sectioning a large part you would use location features like finger joints, dove tail joints and tongue and groove. This kind of sectioning can all be done in the Stratasys Insight software. Insight also has some easy to use auto-alignment features you can add when you are processing your parts. One of the coolest features is the section with profile feature. You select where the section line of your part will be by clicking on the screen or typing in the location dimension. The software will then create a diamond pattern through your part. The cool thing about this is you can control the amperage of the pattern and it aligns the two pieces in the X, Y and Z. For this helmet thought I would just make some finger joints to locate the pieces together. I started sanding with some 120 grit sand paper where most of the large stepping occurred and where some of the pieces didn’t align perfectly.
After sanding, I started with 3M Bondo Glazing & Spot Putty. I like working with this when prepping a model because it dries quick and its smooth when it comes out of the tube. Once it’s dry, it also sands nice and smooth. You have to be careful not to use too much because you will be sanding for days if you do. I usually spread it around like peanut butter with my figure pushing it into all the layering. When printing with the Fused Deposition Modeling (FDM) 3D printers, and your model has large rounded surfaces, this is when you start to see the layering or large stepping in you parts. If you plan to paint your model, these layer lines will show through the paint. This is why we use the spot putty. This is not needed for all models; this is just something you would do if your model or prototype needs to look like the real thing.
I kept adding the spot putty and sanding back and forth until I had the smooth surface finish I needed for painting.
At this point I use a high fill primer. I like to use the Bondo version, but every spray paint company has a version of high fill primer. This type of primer fills in any small voids or cracks in the surface. You have to be careful with this type of primer because if you spray it too far away from the part it can cause a rough surface. This primer is really thick so it can dry too much in the air before it lands on your part if you are holding the can too far away.
Other than that minor note, the primer works great for filling in uneaven surfaces. This primer also requires sanding. I also go back and forth sanding and spraying with this until I have the surface as smooth as I can get it.
At this point you should spray your part with what is called a primer sealer. This is a thin primer that creates a really nice smooth surface for painting. This is optional; I did not do it for this particular project because I was in a time crunch trying to get this helmet finished for the Design2Part Tradeshow we do every year in October. (The timing also worked really well because the helmet would be ready for Halloween!)
Unfortunately, I did not get a picture of the helmet when it was primed; above is a picture of the first coat of paint after the primer. The paint I use for the base white was Rustomleum ultra cover. This goes on very well and is formulated for plastic. The rest of the detail is hand painted arcylic, paint marker and blue duct tape. I am very happy with the way this helmet came out. I just have to straighten out some of the details of the part. Like vent holes for breathing and ear holes for hearing. It was fun to wear this to a Halloween party, but I could barely hear anyone, no one could hear me and I couldn’t eat or drink. Womp, womp.
Some of the new features I will be adding shortly are a speaker in the mouth area and lenses with LEDs behind them. Thats all for now. Thanks for reading and if you have any questions please post them in the comments below.