Category Archives: 3D Printing
3D Print Finishing
I was looking at trying my hand at doing some detailed finishing of a 3D print. Since most 3D printers lay material down in small layers (.3 mm) the print has a layered and striped look. With ABS prints you can soften the layering the effect with acetone. The acetone will dissolve the plastic a little bit before evaporating, thus smooth over the layers. Too much acetone will leave the part a bit droopy looking. But with PLA that process is not as easy. And larger prints come out looking better with PLA (more uniform, less shrinking, less warping). Also a friend of mine was looking to try to apply a mirror/chrome finish to a 3D print and I knew exactly the model I wanted to try some finishing techniques on.
Enter the Trimaxion Drone Ship from the 1986 ‘Flight of the Navigator’
Here is the trailer for those who don’t know.
In the movie the ship was mainly CGI. But that shouldn’t stop me.
I found a model of it here.
http://www.thingiverse.com/thing:357472
I would describe the shape as a silvery stretched out acorn squash. I liked the shape because it was simple, symmetric, smooth for the final product, and clearly defined lines. I knew there was going to be a lot of sanding and I didn’t want to worry about sanding small holes or something.
The print came out in two parts. And even through I printed it out in PLA there is still a little warping. So the first step was to sand down the two meeting faces to make them flat as possible and then glue them together. After I glued them together I applied some automotive body filler (Bondo) to fill in the crack. After the bondo set I sanded with 100-200 grit sandpaper. The first pass is below.
After that I did some wet sanding with 400-500 grit sand paper.
Next step was to apply some primer.
After that the process is wet sand-prime, wet sand-prime…
In the pictures below you can start to see the lines disappear. But still more wet sanding and priming.
And below I’m starting to get to what I want.
And finally I did one last wet sand with 1000 grit sand paper. I painted it with a three coat system from spaz stix. You start off with a back coat, in this case black, then apply the chrome paint, and finally a clear top coat.
Here is final product.
Lessons or what I would have done differently.
- Start with a slightly larger model. This wasn’t too bad, but a little bigger would have sanding the lines a little easier.
- More coats of bondo or other filler. I only used one coat of the two part bondo. They also have a one part that is meant for smaller details. I would have used the two part mix for the gap between the two sections. Sand that, then applied the one part over the entire thing. I think I spent too much time trying to fill in with primer.
- Use more filler primer. There is a type of primer that leaves thicker coats of primer. Again, save time on paint-wet sand cycles.
- More gentle with the final paint coat. I was using spray cans and that can be a little difficult to regulate the amount of paint that gets applied. Spaz Stix has jars you can get that you can use an air brush to apply the paint.
- Take more time between coats of paint. When I was finishing with the top coat a small pool of paint formed on an edge. That pool dissolved everything down to the primer. Also I marred the surface a little when I was moving the model to paint the underside.
Overall it was a simple project. I got to learn some of the basics and will inform me on my next project.
Thing-o-matic Printer
Way back in 2011 I joined the 3D printing craze and got a Makerbot Thing-o-matic kit. I put it together over the course of a few weeks.
Here is a picture of my Makerbot Thing-o-matic #6001
Appearently they started at number 3000. So at least 3000 were sold. Notice the spool holder I printed and the brown little trinkets surrounding the machine. It was a wonderful little machine.
Here is a sample of some of the things I made on my Thing-o-matic.
A weird twisted not:
Heart Gear:
Two litter water bottle rocket adapter to easily launch it with an air compressor:
Hemostat:
Planetary Gear Model:
I still have the husk of the machine. But once MakerBot moved on to selling the Replicator I knew it would be harder to get replacement parts. So eventually I got print size envy and cannibalized the moving parts and electronics and created a larger machine.
Wood Gears
I have always wanted to work with gears. A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part to transmit torque, in most cases with teeth on the one gear being of identical shape, and often also with that shape on the other gear. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source.
When I first got my 3D printer I made a 3D printed grandfather clock.
The clock worked ok. I printed the parts on a machine that was a little small for the design. The machine would work for a short time but I was able to see how the parts work. But I still wanted to design and build a machine of my own.
Several people on Thingiverse, a website dedicated to the sharing of user-created digital design files, have various models and scripts that create gears and gear based machines. I feel as I explore more mechanical design ideas, I will need to explore basic simple machines like gears to fill in gaps between motors and the work I am trying to drive.
On Thingiverse the user Leemon Baird shared his script to generate Public Domain Involute Parameterized Gears. This script simplifies lots of the details. For example, according to wikipedia, details like the angular velocity ratio between two gears of a gearset must remain constant throughout the mesh. That sounds difficult and would overwhelm someone new to making gears. Leemon made a function that takes 9 parameters but you only need to enter 4. These variables are: the circumference of the pitch circle divided by the number of teeth (millimeters per tooth), total number of teeth around the entire perimeter, thickness of gear in mm, and diameter of the hole in the center in mm. With this basic script to went to task laser cutting gears out of thin plywood panel. I had to goal but to see how many I could put on a board and see hard/easy to drive the gears.
As you can see from the picture above I made a lot of gears. They were a little rough to drive all of them at the same time. I was having alignment problems as well. As I was moving the gears some wouldn’t engage. I placed an acrylic guide over the main drive gear, the one with the handle, to try to resolve the alignment issue. And the gears where attached by 3mm bolts. So the entire surface of the gear was rubbing against the attached panel.
After the laser cut gear experiment I had a few lessons for my next attempt. First, I need the cut the gears out of thicker material. The laser cutter is nice because I just load in the parametric design into the computer and cut, but the laser can only go through thin material. Second, I need to keep the gear floating above whatever it is attached to so I don’t get that surface drag. And third, I need the gear to use bearings and bushing to reduce friction on the fastening bolt.
CNC Panel Router
So to cut out gears out of thicker material I need to learn a new tool. And that tool is the stinger CNC router.
A CNC router is basically what it sounds like. The machine has a router mounted on an arm that moves in the X,Y and Z axis and the arm is controlled by a computer. You can load a computer design file into the computer, the computer will determine the tool head path based on the design file and the type of bit on the router. This machine can use the same files I generated for the laser cutter, but can cut through up to 3 inches of wood. There is a little more setup involved that the laser cutter. The laser beam is a simple point and doesn’t change, it simply follows the line. The CNC router is a bit that can be one-eighth to three-quarters of an inch thick. So when you define the tool path you need to specify whether you follow the inside or the outside of the line.
The CNC router also allows other options that a laser cutter doesn’t. First, you can specify the depth that you can cut down. You can cut all the way through or just a shallow cut. Second, there are different drilling profiles. You can drill hole, a pocket where all material is cleared away, cut on the inside or outside of a profile, engrave a shape into a surface, or cut a relief on a surface.
For the gear I needed three things, the ability to a gear profile out of a piece of three-quarters inch plywood, drill a hole through for a bolt and bushing, and a pocket for a regular skate bearing. I was able to take the files from my lasercut gears and use them to generate some vector files for routing. I can select each line in the vector file and create a different cut style. For example I can select the teeth profile and tell the software to route all the way through the plywood from the outside of the line. The inner two circles have a different cut path. The center most circle will cut all the way through from the inside of the circle. And the outer circle will cut a pocket half way through the plywood. Below are some pictures showing the a vector art being loaded into the tool path generation program.
I configured the tool path generation to use two different bits. The Teeth profile and center circles can be cut with a single end-mill bit. This bit will leave straight edges. The lettering will be engraved with a 90 degree V-bit. After generating the tool path and then saved out the commands into two files. I am now able to load the tool path data into the CNC router driver software.
Once to plywood is loaded onto the machine and the bit head is aligned and configured I can let the machine cut out the parts.
Once I can take off the gears I just need to place in the bearing, screw on the bolt, and attach a magnet to the bolt so the gears can attach and slide on a metal surface.
And here is the final product.
