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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).

Step 2: Extrude and Fillet

Select the area between the two circles (left click anywhere along the donut).  A widget will pop up.  Select the widget with the box with a blue top and arrow pointing up (this will bring up the extrude option).  Select extrude, type in 0.75in, select the 3rd icon in the toolbar that comes up and select "symmetric"; then, right click and select OK.

Change views using the view cube in the upper right corner.  As you bring your mouse over the cube, a "home" icon will appear.  Choose the home icon and you should see your boxy torus.  

Hold the shift key and select the two outer edges of the donut.  Then select "fillet" and type in 0.75in and press return.

Now, hold the shift key and select the inner edges; select "fillet" and type in 0.1in and press return.

You should now have a round donut-like part.

Step 3: Draw Spheres to (later) Pattern Around Donut

Select the "right" view from the view cube, start a new sketch, and select the YZ plane.

Next, choose "sphere" from the primitives menu (next to the pencil in the toolbar).  Choose -0.5", 2.2" as the center and 0.15" as the radius.  

Now select the sphere you just drew and select "mirror" from the patterning icon in the toolbar  (four squares, one blue).  Then select the 2nd widget to choose the mirror plane.  Expand the view of the origin on the upper left browser tree and select the XZ plane.  Right click and select OK.  You should now have two sphere (see accompanying screenshots).

Start a new sketch and select the YZ plane again.  Choose "sphere" from the primitives menu.  Draw a sphere at 0.0", 2.4" with radius 0.20"

You should now have three spheres on the donut.

Step 4: Pattern Spheres Around Center

Choose the home view.

Select one of the two smaller side spheres.  Choose "circular pattern" from the patterning menu.  Click on the 2nd item on the popup toolbar "select pattern center."  Click on the inner cylinder.  Type 24 into the box that pops up.  Right click and select OK.

Repeat with other small sphere (the one you mirrored).  You will now have two rows of 24 spheres each.

Now, select the larger sphere.  Choose "circular pattern" from the patterning menu.  Click on the 2nd item on the popup toolbar "select pattern center."  Click on the inner cylinder.  Type 48 into the box that pops up.  Right click and select OK.

Now select the front view from the view cube, hold the shift key down, and select the spheres that are in line with the smaller spheres (24 of them).  Right click and select delete.  Select home from the view cube.  The center row of larger spheres should now be staggered from the smaller spheres.

Step 5: Combine Components Into One Part

Select the main component by selecting "solid" from the component tree on the left.  Right click and choose "combine."  Then hold the shift key down while you select component 1 and component 2 from the component tree.  Right click and select OK.

Save your work by clicking on the disk icon in the upper left.

Step 6: Save Your Part As an STL File

Now, let's save your file as an STL file that can be 3D printed.  Go to the "3D" icon in the upper left and choose "Save As."  Then choose the STL filetype among the options in the dropdown menu.  Click save.  

Congratulations!  You now have a file you can send to a 3D printer.

Here is a link to the finished file in the Autodesk 123D Gallery.

Step 7: 3D Print Your Part

You have a few options here.  I had mine printed in ABS at the local hackerspace (http://artisansasylum.com/).  It's the first image below.  Here is a list of hackerspaces around the world.

For this instructable, I will be using the 3D ABS print.  

You can also have it printed in ceramic and glazed at Shapeways.  When you upload your STL file, choose "millimeters" as the units because this is the way Autodesk 123D exports.  Note that the ceramic glaze adds some thickness, so based on my last experience with printing something this shape, I'd make the inner *diameter* about 4mm/0.15" larger than you want the final inner diameter.  No guarantees here -- this is based on one data point -- I printed a 3" diameter and it came back with a 2.85" diameter.  Shapways has instructions for designing for ceramic printing.  

Step 8: Seal the Part With Gesso

Though solid and fairly sturdy, the 3D printed ABS is porous, so you have to seal it before making a mold.  I sealed mine with two coast of acrylic gesso applied with a paintbrush.

Step 9: Gather Materials for Moldmaking and Casting

What you will need:
  • non-sulphur clay 
  • hex cap nuts
  • glue gun
  • masking tape
  • xacto knife
  • foam core board
  • Smooth On MoldStar® 15 (you'll need 2 2lb starter kits), MoldStar® 16 or 30 will also work fine
  • something rigid to support your mold (I used 2 6" pieces of 2x6s) -- you probably don't need this if you're using the MoldStar® 30.
  • Vytaflex® 60 (or 50 or 40, depending on the hardness you want) -- might as well get this while your getting the MoldStar
  • if you want a color, some So Strong® tint (I used black)
  • Mann's Ease Release 200
  • a scale (ideal, but not strictly necessary)
  • straws or dowels (for the pour hole and air vent)
  • disposable containers for mixing -- something that will hold 32oz for the mold and 16oz for the casting
  • disposable stirrers (I use tongue depressors)
  • latex or nitrile gloves
To make the mold, you will need to construct a mold box that's about 7"x7".  You can use foam core, plywood, 2x4s, basically anything that you can assemble and hot glue into an watertight 2.5"x7"x7" container.  I used a re-usable acrylic mold box that I purchased online.  There are tutorials on how to make your own re-usable, adjustable mold boxes.

Step 10: Make the First Half of the Two-part Mold

First, assemble your mold box.  If you're using foam core, cut four 3"x7" strips and hot glue them together on a square of foam core (at least 7"x7").  I found that with the acrylic mold box, hot glue is very difficult to remove when you're done, so I've started sealing the seams with clay.  You want to make sure it is completely water tight.  The mold box should allow for 1/2" of clearance on any side of your part.

Next, you want to fill the mold box with clay up to the "halfway" mark on your part (the parting line).  This class will represent one part (the 2nd part you will make) of your two part mold.  I used clay that came in 1/2" thick rectangles, so it was easy to cut and make that the first layer which will just be a 7" square.  Then, I made a tube of clay to wrap around the bottom.  You want to fill the box up to the midline of your part.  Then you press the hex cap nuts to make the registration marks where the two parts will fit together.  Place the straws as shown (fill with clay first to make this easier) and this will be the pour hole for casting material and air vent for the displaced air.

Put on your gloves and spray (outdoors or in well-ventilated area) with the Ease Release 200.

Now, mix 14-oz each of parts A and B of your MoldStar® silicone molding material and pour into the center of your mold.  It should come close to the top of your mold box.  Make sure there is no leakage.  If there is, try sealing with clay.

Let the mold cure for four hours.

Step 11: Remove Clay and Make 2nd Part of Mold

Now remove the mold box from the base and turn it upside down. Carefully remove the clay without damaging the part or mold.  

Remove the hex cap nuts (leave the straws in place).

Put your gloves on.  Spray with Ease Release 200.

Mix another 28 oz of MoldStar (14oz each of parts A and B).

Pour, allow to cure four hours.

Step 12: Free Your Original Part and Start Casting!

Take your mold out of the mold box and separate the two parts.  Remove the straws and your original part.  Clean off any clay you see (rubbing alcohol and a cotton swab work well). 

Put on your gloves.  Spray the area where your part will be with Ease Release 200.  Put the two mold halves together and sandwich them between the two blocks of wood (or other rigid material).  Secure with masking tape.  The first few times you try this, your mold may leak, so consider making a little more of the vytaflex mixture to compensate (the amounts below work well if you have no leakage).  

Note: I am going to describe the lazy person's minimal environmental impact way to do this.  Smooth On recommends using separate containers for parts A and B, new stirring sticks for every operation, and two containers for the part A/B mixture.... I will use one container and one mixing stick... see the Smooth On YouTube videos for the officially-sanctioned ways to do this.

Get out your scale, Vytaflex, and 16oz container (I use old containers from the grocery store -- deli containers, yogurt containers, etc.).   
  1. Zero the scale with the container on
  2. Shake/stir your parts A and B in their containers (if you're using the gallons, do use separate mixing implements here!)
  3. pour 5.50oz of part B into your container on the scale
  4. add 5-10 drops of So Strong (you'll have to experiment to get your desired darkness)
  5. stir until well mixed
  6. zero the scale
  7. pour in 5.50oz of part A
  8. mix well, scraping the stick and sides of container often (at least one full minute)
Pour the vytaflex into the pour hole, start a few inches above and pour slowly, increasing the height and pour speed with your comfort level -- it will take 2-3 minutes to pour, so get into a comfortable position -- I usually use one arm with its elbow on the table as a brace for the pouring hand.  The stream is very easy to disrupt... breathing and speaking will affect it.  Tap the mold to free air bubbles.  When you are done, the pour hole will be full and you will see some material coming up the air vent.

Allow to set overnight and demold!  Trim with xacto knife.  You're done! :)

ps. In theory you can use Kick It to accelerate the vytaflex curing.  In practice, I found the mixture thickens too quickly and I cannot finish the pour in time.  If you do this, make sure to enlarge the pour hole.  The folks at Reynolds in Boston gave me a idea for doing a one-part mold which will solve the leakage problem and seam issue (the current seam is not in an ideal place).  The new mold design may also allow for faster pouring.  I'll post a link to the new mold once I get my new models from Shapeways and make the new mold!

Step 13: Bonus Step: Make a One-part, Open Mold

The folks over at Reynolds Advanced Materials gave me an idea for how to make a one-part mold to avoid the current two-part mold's seam flashing issues.  The idea is to make a sprue along one side of the torus and take advantage of the flexibility/deformability of the mold material (10 - 16 shore) to pop the cast out.

My first attempt was with the 3D printed ABS model that was used for the two-part mold... when I poured the mold material (MoldStar 16 -- a fast-setting silicone), the model quickly floated to the top of the material.  I ended up turning the model upside-down (it was initially sprue-side down) so that the sprue side was up and held the model submerged until the viscosity of the mold material was sufficient to keep it from floating back up to the top.  This mold (not shown) worked fairly well, except for one other pitfall -- I had used a mold box that was too soft, a popcorn container, so the bottom bulged during mold setting.  When I set this mold down to pour, the inner diameter ended up poking out and being higher than the rest of the cast.  

My second attempt (shown) here in the blue MoldStar 15 and plastic container was more successful.  First, I used the ceramic glazed 3D print from Shapeways which is denser than the mold material so did not float.  The steps are fairly straightforward:
  1. Seal the model with gesso if it is not completely sealed (for some reason, the inner surface could not be glazed... when I got my last print in white, they had no problem glazing the inside as well)
  2. Make a clay wall representing the sprue (I used a new block of clay, metal ruler, and xacto knife)
  3. Invert the model and sprue into the mold container/box (if you're using a lighter print, you may want to hot glue the clay to the model and mold container)
  4. Spray with Ease Release 200
  5. Mix and pour your mold material  (for this set up, you'll want about 34 oz)
  6. Demold the model, spray some Ease Release 200, and start casting!
The second to last photo is an attempt with a very interesting reusable mold material called ComposiMold.  The material turns into a liquid at 130 degrees fahrenheit.  I did not have quite enough mold material (32 oz wasn't enough), so I had a very thin bottom with a lot of bubbles.  I carved away some of the thicker parts of the mold and remelted it in the microwave.  Then I pour the melted mold material in the thin areas to fill them in... only to melt and collapse the entire mold!  Oops.  I've ordered more material so that I can try 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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