# Casting in plaster?



## Jwest7788 (Sep 12, 2017)

Hey Guys,

What material would you reccomend for mold making for casting aluminum?

I bought a 3D printer, and am hoping to print the positives (is that right?) for mold making. --> Will be encasing the 3d print in plaster(, or whatever you reccomend) then baking the plastic (PLA) out, leaving a mold behind.

Just have to source something I can use to make the mold, ideally inexpensive, ideally at a home depot or similar.

Going to start with something coffee can sized as a proof of concept and learning experience.

Will take pics as I go.


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## Tom O (Sep 12, 2017)

I have never done the 3d casting but they recomend heating it while heating the furnace to make sure there is no mosture.


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## Jwest7788 (Sep 12, 2017)

Hey @RaySWT 
You have any thoughts on this one?

JW


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## Dabbler (Sep 12, 2017)

For investment casting they use a 'slip' made out of watered clay to cast the positive.  The positive is melted out before casting in a low heat furnace to set the slip before casting.  There are differences in using plastic and wax, so there may be complications (??)


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## Bofobo (Sep 13, 2017)

I've never used the plaster method but from what I can see online the details look crisp but like sand it's one time use. Unless your neighbours like burning plastic smell or you need only the one cast with no way to achieve the detail you would require from the cast it may be worth your while to acquire "green sand". I've tried lost foam in play sand (rough) and made "green sand" from the same play sand mixed with bentonite clay (better lines but still rough) in a more traditional approach as well.  Love the idea of using printed parts as mould makers but less so of the volatile toxic fire ball associated with the "lost ;wax/foam/plastic" methods. One thing I will tell you from my experience is that you really want a lot of venting holes especially when using the burn it all methods simply for safety sake.


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## Tom O (Sep 13, 2017)

I use golden sand from Burnco it's a fine sand (cheap) used in mortar mix it almost feels like velvet in the hand and it packs well with bentonite added I've put vent holes in mine but I don't think it was needed.


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## Alexander (Sep 13, 2017)

What 3d printer did you buy?


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## Jwest7788 (Sep 14, 2017)

I bought a Monoprice select plus (wanhao i3 plus rebrand)

Thanks for the insight guys. It's super helpful. 

I'm interested to see how bad the smoke and fire is with the PLA plastic, which is know is an organic plastic. 


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## Dabbler (Sep 14, 2017)

You can contain the bulk of the offensive smoke by using a water filter to take out the majority of particulates.


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## Johnwa (Sep 14, 2017)

from what I have read, Plaster of Paris works.  Final burnout has to be in a kiln to remove all the moisture and then poured while still hot (500-1000F).  IIRC the mold is pretty fragile and needed an outer coating of a sand and P of P mixture.

First burnout can be done in a regular oven as you just want the pla to liquefy and drip out.

A fellow at protospace did some lost wax casting, he was using a special plaster that he ordered from Ontario.  It was likely better than just P of P.

For green sand I bought some 120 grit silica sand from Target Products.  It's fine enough that I sometimes get finger prints on my castings.

Here's a link to an instructable
https://www.instructables.com/id/How-to-make-a-mold-for-lost-wax-casting/


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## kevin.decelles (Sep 15, 2017)

I'm on the same journey.  I bought p of p from Home Depot and intend to mix that with 50% sand (advice from forums etc). 

For melting this out I'll use my electric homemade furnace as I can regulate the heat

For curiosity sake I tried just embedding my pla part in my oil bonded sand and did a pour of aluminum .  Short answer :   It didn't work and the smell made me gag

I have a vintage lathe circa 1905 and the thread dial is missing .  My goal is to print the gear and cast in metal




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## kevin.decelles (Sep 15, 2017)

Back to your question, I think that if the pla is melted out slowly there should be no fire and limited smoke

When I did my test and poured directly the smoke and smell were bad and the gas from the pla caused the aluminum to bubble like mad (pretty crazy) which was not smart on my part and quite dangerous


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## Johnwa (Sep 15, 2017)

kevin.decelles said:


> I have a vintage lathe circa 1905 and the thread dial is missing .  My goal is to print the gear and cast in metal


A bit off topic but here's some pics of an on again off again project.  It's a threading dial for a 9" southbend.  I have a metal one but found this 3d model on the internet so did it  just for fun.


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## Bofobo (Sep 15, 2017)

The fire bricks I picked up earlier this year have worked out great as a quick to make mould, it's a pain to carve accurately by hand but has been working great after 10 castings, I had nothing to burn out (foam/wax/pla) but without a vent a bubble can still form and ruin the cast. At work when making rubber moulds for O&G the vent hole was small but crucial as they use an injection moulding process and air needs to escape the mould quickly. here is how I've been pouring and the result. Note the "biscuit" in the lower one, the result of an under cut in the fork breaking out after the first cast


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## Jwest7788 (Sep 20, 2017)

Found a great solution for anyone on the 3d printing journey. 3d printable wax:
Also machinable wax... But why not just machine metal then? lol.

http://www.machinablewax.com/product.php?product=52





--> This can also be printed hollow, which is awesome.


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## Johnwa (Sep 20, 2017)

Good find Josh.  Machinable wax is easy to machine or even work with hand tools but 3d printing it opens up a lot of possibilities.


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## kevin.decelles (Sep 21, 2017)

I'll have to check that out and see if my printer will print that materiL


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## Alexander (Sep 28, 2017)

What printer do you have kevin?


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## Tom O (Sep 28, 2017)

Mine is a Replicator 2 I may have to give this a go, even if it does'nt work the wax could be used in pattern making radiusing the joints.


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## kevin.decelles (Oct 11, 2017)

Geertech i3 prob acrylic build it yourself

I also have one of the tiko printers that came off kick starter but that project failed

The geeetech is a prusa clone, but has been good.  $250 cdn delivered to calgary, can't complain


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