3D Printing Rotocasting Machine?

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Sandy H.

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I was curious if there would be any real interest in seeing a rotocasting machine prototype I built with the intention of casting nosecones based on 3D printed masters that were used to produce silicone molds. The method of rotocasting (or slush casting) is well known and how to make a silicone mold from the master (3D printed or otherwise) is covered in detail on lots of YouTube videos.

This project was to try to automate the task so that after making the molds, I could quickly and with little human intervention produce nosecones that were hollow plastic in a volume that would support a small rocket business. After exploring it and with the micro margins and people seemingly being fine with flying filament printed nosecones, I decided to bail out on the project.

The videos I made were to share with my dad who was going through a lot of health issues, so the videos aren't tutorials or anything like that, but were supplements to conversations we had on the phone so he could see the progress on the project. If there is interest in seeing more detail, I can try to edit it in such a way that it is at least way shorter and shows the major functions of the machine.

The features were:

1: A somewhat unique method for rotating the mold in the rotocaster. All that I have seen published rotated constantly in 2 directions, using belts or similar mechanisms. My version rotated in 2 axes, but instead of doing full rotations, it would stop on one axis and reverse (i.e. +/-180 deg, instead of constantly rotating 0-360-720-1080 etc). This was done to make electrical wiring more logical. At the end of the day, I suspected that gravity didn't care if something was going +/-180 deg vs constantly rotating through 360 deg. From my testing, I believe this assumption was proven.
2: It was programmable for rotations, not relying on mechanical/belt drive ratios. I did this using 2 stepper motors controlled by an Arduino. So, if you wanted to rotate axis #1 at one rate and axis #2 at a different rate, it was just a program parameter, not a physical belt change.
3: Less interesting was using a carrier tube that you could put multiple molds in and quickly switch them in and out of the machine. Not a bad idea and the method of the carrier worked well, but I never actually got farther than initial testing, as I figured I'd be working for less than minimum wage running nosecones.

Attached is a picture. As I said, if there is interest, I can spend some time editing old video footage together.

I'm getting ready to part it out and use the components on another project, so after that's done, no more video will be available.

Let me know your thoughts.

Sandy.
 

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Sandy H.

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I got one of these when it was a kickstarter years ago. There's a short video there.
Neat video and it explains the process well. When looking at the machine (this build or many others) you note the pulley on the second axis being driven by the primary axis, meaning the ratio of axis 1 rotation vs axis 2 rotation is fixed (or changed by changing pulleys). I'm curious if the version you bought had multiple pulleys to change ratio or if the ratio that the machine came with worked for all of your projects?

When I built a similar version, I found that I got better results switching pulley ratios depending on the shape of the part being produced (i.e. long/thin was different than short/fat) by a good amount. I still have my version built to that concept and once dialed in it worked great, but my build wasn't as clean as theirs. It used furring strips and trimmed 2x4's vs lasercut parts. The quick-grips they used were replaced by straps on my first attempt, but still, very similar execution as they are derived from lots of previous designs.

The iteration I did in the first post is different in many ways, but the interest so far has been 2 people in 3 days, so not much, I'd say.

Sandy.
 

vcp

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I think the ratio is fixed at 3:1, the pulleys aren't changeable. The only time I was ready to use it, the belt had rotted. I've since gotten a new belt, but haven't seemed to ever get the belt and machine in the same place. That new belt is probably rotted by now.
 
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