Introduction: Make a Rotational Casting Machine for Under $150

About: Just a SF local tinkerer, entrepreneur, and artist.
In this Instructable I will be showing you how to make a rotational casting machine using ordinary items. What you decide to do with the machine after you are done is completely up to you. I will not be held responsible for any inadvertent pregnancies, rodent infestations, snow storms, or sightings of James Dean.

I can tell you that my plan is to use the machine to create hollow casts using urethane molds.

I tried to make the directions as obvious as possible, but clearly my day job is not as an assembly instruction director, so please email me ( if you have any questions that arise during this Instructable. I heavily stress relying on the schematic as your guide.

Step 1: The Supplies & Schematic

The totally cost of supplies will be $150 give or take. The most expensive parts are the chain rings ($20 a piece) and the gear chain (about $20).

The schematic I created for the roto cast shows you where things are going to go, but doesn't get into the details. Most importantly, it shows you where the secure and loose joints are going to be.

Here is what you will need.

Strong power drill
Full set of high quality drill bits
Pliers or Leatherman
Glue gun (w/glue)
Metal/Plastic epoxy (2,500 pounds per square inch strength)
Staple gun
Bicycle gear cutter tool
Hack Saw
Wood Saw

2x 20 inch 2x4
1x 25 inch - 2x4
4x 5 inch - 2x4
2x 18 inch - 1x1
2x 16 inch - 1x1
2x 14 inch- 1x1
2x 12 inch- 1x1

Threaded Rod:
2x 4.0 inch - 5/16 inch rod
1x 4.5 inch - 5/16 inch rod
1x 8.5 inch - 5/16 inch rod
1x 3.5 inch - 5/16 inch rod
3x 4.0 inch - 3/8 inch rod
1x 6.0 inch- 3/8 inch rod
1x 12 inch - 3/8 inch rod
1x 3.0 inch - 3/8 inch rod

10x 5/16 inch stop nut
13x 5/16 inch nut
5x 3/8 inch stop nut
5x 3/8 inch nut
Box of 4 inch wood screws
8x 3/8 inch washers (probably will have extra)
8x 5/16 inch washers (probably will have extra)
4x 3.5 inch 22 teeth bicycle chain rings with 4 pre-existing mounting holes, NOT 5
2x 1/8 inch t pipe connector - to support the rotation axle
2x 1/8 inch elbow pipe connectors - to use for the crank
12x L flat brackets used to strengthen joints for frames
3x 3.0 inch flat metal plate with 4 holes in it - this comes in packages of 4, and would normally be used to secure to pieces of wood together. These plates should be able to bolt into the chain ring holes. You will have to drill a whole in the center of the plate though, as there is no existing one there.
14x14 inch piece of mesh

Step 2: Assembling Frames and the Base

This is probably the easiest step in the process. Your job is to make two square frames using the 1x1 inch wood. One frame needs to be 14x14 inches, and the other needs to be 18x18 inches.

As I assembled my frames, I used the glue gun to make the bond that much stronger at the joints. I then used the L brackets to secure the corners to really make the frame strong. I used 8 brackets - front and back -for the bigger frame, and only 4 for the smaller frame, as the smaller frame will eventually have mesh stapled to it, which will strengthen it just as good.

For this step you will also need to construct the base of the roto cast machine. You will need to grab the 30 inch 2x4 piece, and slap the two 20 inch 2x4 pieces on either side of it at a 90 degree angle. I used the glue gun to help secure the connection. You will then also need to attach the 5 inch pieces of 2x4s to every end of the 25 inch plank at a 90 degree angle in order to allow the machine to stand upright without tipping over.

Step 3: Inserting the First Gear

This is the first rewarding step to building your roto cast machine. The first steps are to drill holes in preparation for the threaded rods. You will need to drill a series of 4 holes on the 18x18 inch 1x1 frame, and 2 holes in the 16x16 inch frame. All the holes for the 18x18 frame should be drilled in the exact centers of each side. The holes for the 14x14 frame should be drilled in the center of the top and bottom sides.

Once you have the holes drilled, you can then put the threaded rod to use. We will be putting a rod through the top (the 3.5 inch 5/16 rod) and bottom (the 4.5 inch 5/16 rod) of both frames. (refer to schematic) The rods will need to be fastened incredibly well to certain parts of the frames to allow for secure rotation. Additionally, other parts will remain loose. For the loose parts, it is still necessary to put a washer and nut on either side of the hole to ensure that the motion of the machine is not thrown terribly off swagger. I used a stop nut on the ends of the rods, and regular nuts on the inside of the rods.

After you have the rods secured, you will then need to attach the gear. To do this you will need to clamp the flat metal piece across the gear, and mount it on the gear using the two of the mounting holes. From there, you will then need to drill a 5/16 inch hole in the very center of the metal plate for the rod to go through. After that is completed, secure it to the rod with a regular nut on the inside, and a stop nut on the outside. Then place epoxy over the nuts, to ensure the gear can not become loose.

Step 4: The Undercarriage

This is where things are going to get a little harder. You will now need to create the connection between the gear that rotates the inner frame, and the gears that cause it to spin from the rotation from the bigger frame.

You will need to grab the 8.5 inch 5/16 rod, the two 4.0 inch 3/8 rod, and the two 1/8 inch T connectors. First, drill out the threads inside of the T pipe connector. This is done so that the 5/16 threaded rod does not grab while it is rotating inside of them. Next, I recommend securing the supports to hold the axle. Drill two holes on the bottom right of the big frame and fasten the 3/8 inch rods to them with the T mount at the bottom of each rod. Make sure the 3/8 rods are really secured to the frame by using nuts on either side of the frame. Once again, I used a stop nut on the outside and a regular nut on the inside.

From there, put the 8.5 inch 5/16 rod through the supports. Once this is done, attach the gears at either end. Use two nuts for each gear to support it to the rod. Afterwards, hot glue them into place.

Next, I used epoxy to glue spare nuts in front of and behind the T connector. These nuts were glued on top of the 5/16 rod, and was done so to prevent the axle from moving back and forth too much.

Now, it is time to test out how well the gears line up. The axle (the 8.5 inch 5/16 rod) should rotate the gears affixed at each end of it. The gear closest to the center of the big frame, should have its teeth line up with the gear that is attached (via the 4.5 inch 5/16 rod) to the small frame. The two gears should form a right angle. If everything goes right, the axle should rotate and in turn spin the gear, which turns the small frame. You might have to do some small adjustments here to make stuff work.

Step 5: The Final Gear and Mounting Frames to the Base

Hopefully your mechanism is functioning, and it is time to mount it to the base. Before you do this, you will need to drill a 3/8 inch hole 15 inches from the bottom of the base (see schematic), and into the side of each 20 inch 2x4. These holes should be at the exact height!

On the side where the crank is going to be, you will need to also drill two 5/16 inch holes to secure the final gear in place (see schematic). You can drill the holes in the right place by placing the final gear on the outside of the 2x4 where the 3/8 inch hole was drilled, and mark the wood where the mounting holes are on the gear. Try to center the 3/8 inch hole in the exact center of the gear while doing this.

Next, take the 6 inch 3/8 rod and secure it on the left side of the base. Once again, try using a combination of stop nuts, regular nuts, and washers.

Now, secure the right side of the frames to the base. Slip the 12 inch 3/8 rod through the hole on the outside of the 2x4 and into the 3/8 inch hole of the big rod, however, you will need the rod to go through the gear, as it will be impossible to mount it in the right place if you do not. After you have secured the 3/8 rod, you will need to mount the gear. Take the two 4 inch 5/16 rods and slip them through the holes you drilled. Then loosely mount them using two regular nuts.

Step 6: The Chain Installation and Crank Creation

Take the long length of chain you have and drape it over the loosely mounted gear on the top of the machine. Hopefully the gear should nicely line up with the bottom gear attached to the axel. If not, make the adjustment necessary. Now, use the chain cutter to cut the chain to the right length, and then link the chain together.

Now, take the remaining 3 inch and 4 inch 3/8 rods and make the crank using the 1/8 inch elbows. Once you have made those connections, use the epoxy to ensure the connections at the elbows are really strong.

Once the epoxy sets, you should be able to crank the roto cast machine no problem! I covered the handle in duct tape so that the threaded rod would not scrape my hand too much.

Finally, staple the mesh onto the small frame.

Enjoy! Decorate if you would like. I thought about spray painting mine.

Step 7: Put the Machine to Use

Now it's time to start making stuff.

I used a urethane mold of a rhino head that I created to make a hollow rhino head using polyester resin.

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