Intro: Rotational Casting Machine
Here are some basic instructions needed to build a rotational casting machine. Below is a list of the tools and supplies I used for the project. You don't necessarily need all the tools, but I found them to be incredibly useful. If you build this let me know what you did with the belts and how it worked. Best of luck!
1. Chop Saw
2. Drill press
3. 1 1/8” bit
4. Power drill
a. Phillips driver
b. Small drill bit – size of screw shafts
c. Big drill big – slightly bigger than the head of the screws
5. Table saw (for trimming down the sides of the 2X4s to make them square)
6. Ruler up to 38”
7. 3D printer
a. filament – 1.75mm PLA
8. Sandpaper – 120 grit
d. M30 – 1” and coinciding nuts for the corner pullieys
10. 2mm/6mm steel core belt – 5 meters (a little extra is nice to have on hand)
11. 2 part plastic epoxy
12. Barings – 4 for the corner pulleys
13. ¾” PVC pipe about 3’
14. Wood glue
Step 1: Print Parts With 3D Printer
The first step in this whole process is to print out the pieces you need. Use 3 shells and at least a 50% infill for strength. It doesn’t matter what color you print in, but pick one you like. You can find a listing of the parts and stl files here: https://www.thingiverse.com/thing:2723443
a. Rotational pulley – print 2
b. Stationary pulley – print 2
c. Corner pulley – print 4
d. Short end-cap – print 2
e. End-cap – Print 2
f. Washers – print at least 8, but you may need more
g. Bushing – print 4
Step 2: Wood!
The second step is to cut all of the wood to the lengths that you need. I used 2x4s that I cut down slightly to square off the edges. Remember to measure twice and cut once. I made this mistake and had to recut some pieces wasting wood.
a. 25.5” – cut 4 (inner axis)
b. 30.5” – cut 4 (outer axis)
c. 31.75” – cut 2 (frame bottom left/right)
d. 14.25 – cut 4 (frame bottom left/right)
e. 24” – cut 2 (frame upright)
f. 38” – cut 2 (frame front/back support)
g. 35” – cut 1 (frame center)
h. Bracers that are 20.25” on the long side with a 45* angle – cut 4
Step 3: Lets Make Holes
Using the drill press and the 1 1/8” bit drill holes at the mid points of the six pieces of wood that will be spinning. 2 of the inner axis pieces and all four of the outer axis pieces.
Step 4: Cut You PVC
Cut the PVC pipe so that you have four lengths that are about 6.5” each. You will have some pipe left over, which is ok.
Step 5: Alignment Check
Lay out the inner axis so that you can see how the pieces are going to fit together. You want it to be wider than it is tall.
Step 6: Pilot Holes, Sink Holes, and Screws
Using the small drill bit (the one that is the same size as the shaft of your screws) drill pilot holes where you are going to place your screws at the corners.
a. Make sure your box is perfectly square before you drill the pilot holes all the way down. This will make sure that your pilot holes are exactly where they need to be.
Using the larger drill bit (the one that is slightly larger than the head of your screws) drill your counter-sink holes down about 1/4” using the pilot holes as placement locators.
Repeat this process with the outer axis, making sure that it is the same layout as the inner axis.
Using your 2” screws (16) screw both your inner and outer axis boxes together.
At this point you can set your inner and outer axis's aside so you can work on your frame.
Step 7: The Frame
My recommendation is that before you do any drilling or screwing you set up your frame so you have a general idea of exactly how it goes together. It's like a weird puzzle, but you'll figure it out. This also allows you to see if any adjustments need to be made to any of the lengths of wood.
Step 8: More Holes
You'll want to drill two more spin holes, using the 1 1/8" drill bit, in the side supports of the frame. I did it so that the top of the hole was 2" down from the top of the side supports.
Step 9: Wood Glue Is Useful
Using the 31.75" and the 14.25" left/right boards set them up and apply glue to the contact points.
Step 10: More Pilot Holes, Sink Holes, and Screws
Drill 2-3 pilot holes in the boards at the points where they will attach to each other, keeping in mind where you need to place your side supports.
Then drill your sink holes where the pilot holes are about 1/4" down. Just like before.
Step 11: Clamping and Screwing
Clamp your frame together and make sure it is squared. Then you can use your 2" screws to attach your pieces together. Use a little extra wood glue if needed to make sure that you have a nice solid frame.
Step 12: Wait
Let the glue set and dry for 24 hours before continuing.
Step 13: Putting It Together
Using the 3D printed parts you should be able to piece the machine together. You'll need the 1" screws to attach the printed parts to the wood pieces.
This is the point that you'll want to use the M3 screws and nuts to put the bearings in the corner pulleys.
Step 14: Belts
The belts are the tricky part. I am still working on perfecting it. In the minimal instructions given on the original thingiverse post it mentioned using staples to put the belt together. this didn't really work. The belt was either too slack, or the staples didn't hold. I am still working out the kinks in the belt issue.
I did solve some of the slippage issues by using epoxy to glue a length of belt to each of the rotational pulleys. This made it so that they had teeth for the belt to hold onto.
If the belt it too loose there will be lots of slippage and your machine won't do what you need it to. The best bet to get a nice tight belt is to wait to put the second corner pulley on each diagonally opposite corner. That way you can use the pulley to increase the tension to what you need it to be.
Make sure the teeth of the belts face in so that they connect to the teeth on the pulleys you added.
Step 15: What Crank?
Due to how construction works there was no way to attach a crank to spin the machine, even though in the original thingiverse post says there should be one.
It's not a problem though. It really is easy enough to just manually move the outer axis. If everything went together right it should automatically cause the inner axis to rotate at the same time.