How To Sand Cast 3D Printed Objects

      As anyone with access to a 3D printer knows, it's relatively easy to print off custom designs from the printer in a few minutes or hours. However, many people come up short in how to translate these fragile plastic pieces into actual working parts on a budget. This instructable is courtesy of our friend, Evan Daniel, who teaches metal pouring at Techshop RD. All credit for an awesome Saturday goes to him. We took the pictures and generally got in the way. If you are interested in following more of his work, simply click his link to view the latest Instructable he's put together. To make a 3D metal piece from plastic, you will need a few simple tools:

1) Plastic part or model master
2) Sand
3) Molding Box
4) Raw aluminum or other metal
5) Kiln or furnace to heat the metal  (We used Techshop RD's)
6) Cold water to cool off the metal afterwards
7) Baking oven (you can use your oven at home or any oven that heats up to an even 400 degrees)
8) Tongs
9) Protective metal gear: gloves, helment, and apron

        Now, you're ready to make a real cast from plastic in a few short hours without breaking the bank. We cover simple medallions, complex 3D prints like this owl, and compound machine parts. Hopefully this will allow you to do 3D casts of anything you can dream up at home or your local hackerspace/techshop.

Step 1: 3D Print Your Plastic Model

         This first part is pretty simple. Plastibot, Instructables, Techshop, Shapeways, and a number of other services in our area offer competitive rates for 3D printing. If you want ideas or are looking for something fun, I encourage you to check out Thingiverse. We used Plastibot to do ours as we find they have the most detail for the price when doing 3D prints, better than even MakerBot. Plus, they use PLA which bakes out more evenly.
          Again, for your print use PLA, not ABS, as you want something that melts cleanly and is non-toxic. If you have any specific questions, Luis Freeman (owner of Plastibots) who runs our local 3D printer meet-up group every two weeks here is very knowledgeable. These are a few pictures from our March Workshop Event on How-To-Make-3D-Printers from scratch. Lots of fun all around.
         So print in hand, what do you do next?

Comments

[professorred]

I would think that an IR thermometer would be a great addition to your toolbox at this point. Suggestions?

[Li Sashay]

An IR thermometer is overkill for this. All you need is a metal stick to swirl around in the molten steel and check that it's melted like making candy consistency($1-2 at any Lowes or Scrap Yard). We've had the same stick for daily pours for almost 3 years running now. You can see it in a couple of pictures.

[professorred]

I just meant to make sure that it is cool enough to handle at the end as an extra safety precaution for those that would want such a thing. Just as a suggestion reinforcing the whole "hot aluminum looks just like cool aluminum".

I agree that for melting, surface temperatures of the molten metal are useless.

[jmichelin]

Hey guys love this, im trying to cast some arrowheads this method, but i cant get a 3d print of what i wants, can you guys help me??

[Li Sashay]

Shoot me an e-mail at: [e-mail] with specifics. I bill hourly for spec design work, we can discuss details to see if I'm in your price range or not for the job.

[geoffd123]

I have not tried this with PLA masters, but with wooden masters you can lightly coat them with a thin film of PVC/PLA glue which smooths out the gaps and lines. This should work on a 3D printed master.

[Li Sashay]

Interesting, I normally just sand them down, but will have to try this. The model here has not been sanded as wanted to be as realistic as possible to the quality you can get starting out on a budget.

[chuckyd]

An important notice to users new to aluminum casting is that hot aluminum looks just like cold aluminum. It does not change color like many other metals.

[bewise54]

Excellent instructable! I have one comment to add though: While it very likely doesn't matter for a visual/artistic application, quenching non-ferrous metals (i.e. Aluminum, as used here) makes them softer than simply allowing them to cool naturally, which could be beneficial if you have sanding or further machining to do, but could cause problems if the cast parts need to withstand some stress. This is the opposite of what occurs in most steels/cast irons, because the martensitic reaction, as it is called, has different results in non-ferrous metals. Then again, by the time the casting is free of the mold it has probably already cooled enough to avoid softening, but for those high test applications even a little extra strength can help. Hope that helps!

[Outthnk]

Nice work. For the pitting in aluminum you might try cedar chips in in the smelted metal. A tip I learned from an old geezer who really knew his metals.

[Tomdf]

Very well done instructions and great pics! Do you add anything special to the sand to get it to keep its shape, or does just getting it wet do the trick?

[grunthos]

It is definitely not just sand and water. The water-based sand for casting is known as "green sand", and typically consists of a sharp sand, bentonite clay, and water. Green sand is a major staple of the casting industry.

[Li Sashay]

Hey Tomdf, just getting it wet does the trick for us. However, casting sand comes in two types water based and oil based so you should look at the directions on the back of your bag to see what you have. Oil sand generally is ground finer and has more detail to it as a result, but more expensive and requires more maintenance. Not as easy for the beginner. You can compare and contrast the detail on the two here: http://www.foundry.ray-vin.com/k-bond/k-bond.htm

[tmasse]

Very nice.
I notice that even the detail of the printing layer line (scale) do show on the finish product.
So I guess it's a good idea to send the printed model before sand casting.
Tony

[Li Sashay]

Mmmm, actually I find the metal is easier to work with as it does not break as easily as plastic. The metal will clean up nicely after you cut off the sprue and polish it. What you are seeing here is a raw form pulled directly from mold before cleaning. See this other instructable on bronze casting if you want an idea of what it will look like after cleaning: http://www.instructables.com/id/Bronze-casting-your-3-D-print/step19/Final-Product/. If fine detail is important to you, you should see about using oil based sand instead of water. It can generally pull the details off a quarter and is used in jewelry work. You can buy a pretty big bag for $25 off ebay.

[Li Sashay]

However, if you want to sand beforehand, it is a perfectly respectable way to go. Just realize you will have to do it twice.

[rimar2000]

Very good work!