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This instructable will guide you through drawing a part in Autodesk 123D, having it 3D printed, making a mold of the part, and casting the part in polyurethane rubber.  I will gloss over some of the mold-making and casting since there are already so many good youtube videos on the subject.

The MuscleTreads™ water bottle massagers are polyurethane rubber rings made from Smooth On's Vytaflex® 60.  They are designed to fit over a 1-liter SIGG bottle (or any bottle ~3.2" in diameter) to turn your water bottle into a back massager (used on the floor or against a wall or chair).

The MuscleTreadsTM water bottle massagers are patent pending.  You are welcome to make these for non-commercial use.

(This instructable has been updated to include instructions for how to make a one-part, open mold for this project.  See Step 13.)

Step 1: Start Drawing the Part in Autodesk 123D

Download and install Autodesk 123D from http://www.123dapp.com/123D

Open a new project/file, set the units to inches (labeled "in Eng"), and scale to 0.1in.  

Select the front view from the view cube, start a new sketch (the pencil icon in the toolbar), and select the XZ plane.  

Select the circle tool and draw a circle with center at the origin (0",0") and radius 2.5"

Draw another circle with center at the origin again and radius 1.425" (a shortcut for this is to right click and select "repeat" -- this will put you in the circle tool again).
Does the acrylic gesso bridge the pores? I have tried epoxy, but the plastics in the original repelled the material and it beaded up. Have to try the gesso, thanks for the tip. I have also experienced chemical inhibition when casting printed parts in silicon, have you? No fun to see your expensive stuff turn to unuseable goo, and your master as well. Nice job here.
The Krylon Crystal Clear does also seem to work for making the 3D print non-porous for molding purposes.
Two coats seemed to do the trick (after one coat, I could still blow air through the pores). The folks at Reynolds also said Krylon Krystal Clear would do the trick. I think the platinum cured silicones like MoldStar react to less stuff than the tin cured silicones. I haven't done any casting in silicone (yet) so can't be of any help there.
This is really interesting. I'll have to look at this in more detail, it should be useful for making all sorts of other molds and forms. Do let us know how you get on with a single piece mold though, I can't quite see how that would work.
The trick is locating the sprue in a clever location. So imaging the donut lying on its side. Now locate the upper edge of the inner diameter. Imagine building a clay wall a half inch tall and a quarter inch wide along the top inner edge of the donut. Now turn it over so that the donut is resting on the clay wall/ring. If you pour the mold in this orientation (and with something flexible like the MoldStar® 15 or 16), you can just "pop" the cast out of the sprue once it's set. Does that make sense?
If I understand that correctly you are suggesting an &quot;Open Face Mold&quot; with the open face being one entire sidewall of the tyre? Using the springy nature of the mold and the tyre to get out from the overhang.<br><br>Was the original 3D printed wheel damaged in the casting process? Why do you need to get a new one to test this method?
I've added a Step 13 to document some of my adventures making the one-part, open mold, which works fairly well. I think the mold life will be a bit shorter given the stress the mold takes for demolding. It turns out that the ABS print floats in the mold material... so the ceramic glazed prints were much easier to deal with!
Yes, an open face mold with the open face being the the inner quarter or third of the flat part of the tire. MoldStar 15/16 is very flexible!<br><br>The original was not damaged in making this mold, though I almost destroyed it trying to make a plaster mold... luckily I was able to free it (eventually) without any damage!<br><br>The reason for the waiting is that I have prints coming in smaller sizes for the most common bottle sizes (also they'll come pre-sealed in ceramic glaze!)
Very nice! This is a great idea. :D
Thanks! :)

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