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3D printing is great, but what if you need your object in a material that can't be printed (yet)? Rubber, translucent plastic, concrete, or chocolate could all be used inside of a mold. This project will focus on making two-part molds that can be used over and over to produce multiple copies of an object. I will also explain how to use the molds to produce rubber copies of the original 3D printed objects. You could use these steps to cast just about anything, though.

If you're in the New York City area, I highly recommend going to The Compleate Sculptor for supplies and technical advice. They helped me a lot.

These instructions will work for a 3D printed object of any type. The figures used/pictured here were printed on a ZCorp powder-based printer. These steps will also work for plastic-based printer.


General Materials:
Popsicle sticks
plastic mixing containers (1 quart)
1 inch chip brush
wide rubber bands
rubber gloves
apron
long bolt of any size with matching nut
small piece of wood (approx 1 x 5 inches)
foam core board
utility knife
small digital scale
mixing sticks (usually found at paint stores)
toothpicks
hand-held drill
sandpaper (400, 600, 800, 1000, 2000, 4000, 8000, 12000 grit) - yes, you need all of them

Casting/Molding Materials
Plasteline sculpting clay
Mold Silicone (if you're new to this, start with Smooth-On Mold Star 15 SLOW which has a 4 hr. cure time. When/if you're more comfortable, try Mold Star 16 FAST which has a 30 minute cure time)
Mold Release (I used Mann 200)
Casting Silicone (in my case, Sorta-Clear 40)
Pigment (I chose Silc Pic Pigment, black)

Optional Materials
60 mL syringes with catheter tip (optional).

Step 1: Sand Your 3D Printed Objects.

In mold making, what you see is what you get. If your 3D printed object is shiny before you mold it, it will come out shiny. If it has little bumps, they will not magically disappear in the molding process. If there is a texture, it will come through. Before you begin the process, make sure you know exactly what you're going for in terms of the final surface. 

In most cases, you're going to want to accurately reproduce your shape while minimizing any surface anomalies. For that reason, you're going to have to do some sanding. But don't worry - you only have to do this to the original and it will pay off in the end.

1.) Sand the object you'd like to duplicate until it is as smooth as possible. Start with a rough grit paper to insure that you are getting past any bumps in the surface, then work your way up incrementally by 200 until you reach 1000 at which point you can proceed by steps of 2000. Wet sanding is recommended.

Why do I have to use so many grades of sandpaper?
To get a super smooth surface, you need to use a very very high grade sandpaper. If you jump too many grades as you work your way up, you risk leaving textural differences in your surface. In other words, if you scrub your object with some 400 and then skip to 1200, there is no way you will file down every little groove you just blasted into it with the 400. By working your way up gradually, you are actually saving yourself time because it's easier to correctly sand a 400 grit surface with 800 paper than it is with super fine 1200+ sandpaper.

In this case, I want extremely smooth rubber objects, so the more sanding the better.

2.) If the object is dull and you would like a shiny final object, finish with shellac and resand with higher grit paper to make sure all surfaces are smooth and shiny. In my case, I just used an off-the-shelf spray shellac. I applied a light coating, sanded the surface with the top two levels of sandpaper, and repeated the process one more time. 

* PHOTO EXPLANATION *
1 - Objects fresh out of the printer. These were printed with black powder. If you're printing with powder, make sure you've infused them as recommended by your printer's manufacturer. 
2 - Midway through the sanding process, the objects loose some of their color. That's normal.
3 - Objects have been painted black with spray paint because I wanted them to be shown along with the final rubber versions. This added some extra sanding. Then they were shellacked as described above.
I'm in the process of trying to make a parametric mold on Rep 2. <br> <br>http://www.thingiverse.com/thing:53298 <br> <br>Finding out that you need a well-behaved printer that performs well on finest settings to get mold half to meet. which is why I'm reading this great tutorial :)
The object I'd like to make a mold is a bit irregular. It's something like a rectangle with a hollow spot in the edge of it that runs fairly deep. On the front, one side is partially open....making it somewhat easier. <br> <br>Anyway, enough of my rambling. Do you have any advice for making molds that have some hollowed out sections?
this makes me wonder... does everybody has 3d printers now? O___o
A really nicely thought out and well documented instructable, I particularly like the drill vibrator trick.
Hi all, according to Mold Star Tech Spec. sheet, the max temperature for this mold is 450 degrees: http://www.smooth-on.com/tb/files/MOLD_STAR_15_16_30_TB.pdf
Thanks for the link, I might have a go with pewter the melting point is (338&ndash;446 &deg;F.
I know pewter CAN be cast with this kind of material, but it's not the way I'd recommend doing it usually. Plaster of Paris works (as long as it's REALLY dry) for low temperature alloys like Pewter and it's probably cheaper, though the steps for producing a good mould are more or less the same whatever you use.
great instructable thank you <br>have you tried printing a mould rather than the object? <br>Is plasticine the same as Plastalina ? <br>
That's a great idea! I haven't tried printing a mold yet but I think it's a great suggestion and I will certainly test it out! And sorry for the plasticine typo. What page was that on? I'll fix it.
Hi again, its the title in step 2 and in the instructions 1-4 as &quot;Plasteline&quot; and Plastalina left me a little confused?? <br>I should of realised it was a typo, I just thought it was some product I had never heard of. <br>Do you know how much heat you can put into silicon before it burns, or goes bad? <br>just thinking silver, or pewter products.
Metals other than Tenn require too much heat. Ok, maybe beryllium... Silver and Pewter are out. Been there, done that. I've tried this many times as a professional, sorry. Correct me, please!
The disadvantage being you cannot improve the finish before casting. Your mould will determine that... just saying.
one of us needs to find out if it's possible to print green sand... pouring an iron graphic that somebody printed the negative of would be awesome!
Hi waldosan <br>if you printed of the pattern (which is the hard part) the process of making the mould in green sand only takes a couple of minutes, and you get to keep the patten a the end. A pattern Looks a bit like the finished product but it split in two with dowels to locate the parts. <br>have a look at <br>http://modelenginenews.org/techniques/pattern_making.html
Very useful info, thanks!
Ever try: http://composimold.com/ <br> <br>Great stuff! Reusuable, and microwaveable! <br> <br>Great Instructable, thanks for the information!

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