Oct 4, 2015 | By Benedict

A former Electrical and Explosives Engineering student named Peter, going by the handle ‘lyratron’, has shared a handy method for making metal parts using a standard plastic-printing 3D printer. After learning a technique called lost wax casting whilst studying at New Mexico Tech, Peter decided that carving machinable wax with a CNC milling machine was too much effort. He therefore began experimenting with lost polymer casting: a similar process, but one which enables the making of metal parts with a 3D printer. Peter has explained the process in 12 steps, detailed below.

Step 1: Design object

Use any CAD software to design an object, as though you wanted it made from plastic. Peter recommends SketchUp (free) and OpenSCAD (for more advanced users).

Step 2: Add sprue

The sprue is a conical piece connected to a part of the object. Although length, width, and flare dimensions needn’t be precise, it should be large enough in diameter to accommodate the pouring through of liquid metal. With some larger objects, it can be beneficial to employ more than one sprue.


Step 3: Enlarge by 2%

Using your 3D imaging software, enlarge the model by 2%. Scaling the object by 2% along all axes will create a volume increase of about 6%, which compensates for the metal object’s shrinkage as it cools from ~230C to room temperature.

Step 4: 3D Print object with sprue

Use a 3D printer to 3D print the object. The sprue will typically face upwards, but Peter notes that some shapes may require it being laid horizontally across the build platform. If this is the case, a rectangular prismatic frustum may be preferable to a cone.


Step 5: Embed in plaster

Make sure that the object is fully submerged in the plaster, without it touching the bottom or sides of the vessel, whilst ensuring that at least a small piece of the sprue is sticking out of the plaster.

Step 6: Allow plaster to harden and dry

The optimum time for allowing the plaster to harden and dry is 24 hours. However, if the project is more urgent, this time can be reduced by using techniques such as sun drying and accelerated heat drying. Take care not to apply too much heat if choosing the latter option, since this can flash trapped moisture to steam, causing the plaster to swell and crack.


Step 7: Burn out polymer

One of the more exciting stages: Whilst wearing oven gloves or any flame-resistant mitts, carefully place the mold upside-down in a fire for an hour or more. Caution: PLA fumes are tolerable, but ABS fumes emit a foul smell and are potentially lethal if inhaled. Take appropriate precautions.

Step 8: Pour metal into sprue hole

Another exciting step: Peter recommends using pewter heated with a Hot Pot 2 electric melting pot. Wear safety goggles, long pants, closed-toe shoes, and thermal gloves. Be careful, as the metal cannot be poured back out of the mold after it has been poured in.


Step 9: Allow metal to cool

Wait 2 or 3 hours, or until the metal (not the plaster) is cold to the touch. Note that plaster is an excellent thermal insulator, so will keep the metal hot for a long time. If too little time is given, the metal will not have adequately settled.


Step 10: Smash plaster, remove metal object

Whack away, Jim. If dealing with a fragile object, apply force softly in several places instead of one large smash.


Step 11: Saw off sprue

Using a hacksaw, saw off the sprue from the object, as close to the object as possible, but not so close that the object gets damaged.

Step 12: File sprue attachment point

File away any remaining bits of the sprue. One can also file off the gold oxidation, but be careful not to file deeply into the object itself.

Images from Instructables

Peter’s method is a convenient and fun way of making metal objects using a 3D printer. Although the maker notes the utility of the method for certain purposes, we do not condone the making of weaponry or ammunition of any kind. Instead, try making a piece of jewellery, a figurine, or counterfeit coins.



Posted in 3D Printing Applications





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Joker wrote at 11/9/2016 2:32:06 PM:

Thanks for the interesting post!

Joker wrote at 10/6/2016 3:40:46 PM:

Nice work!

anon wrote at 5/5/2016 7:42:48 PM:

How long does it take to burn out the plastic? and how do you know when all the plastic has been burnt?

Casting Fan wrote at 4/27/2016 12:47:01 AM:

Love the tutorial. Maybe you an show how you can make a reusable cast for mass producing.

Lou wrote at 3/23/2016 5:07:53 AM:

Just drop the plaster mold into water and it dissolves away almost immediately without damaging the part! Thats how the foundries do it

wilwrk4tls wrote at 10/5/2015 10:27:18 PM:

I'm not sure why it isn't ok to make yourself a weapon or ammunition. You can make weapons of all kinds, legally, including firearms if you so choose, as long as the weapon or firearm is legal to own at the time of manufacture. You don't even have to serialize it since you made it yourself, for yourself. Sell it to someone and the black unmarked helicopters will swoop down to scoop you up, but it is perfectly legal to make what you want for your personal, legal use. Any weapon, purchased, made or stolen, used for illegal purposes is the same kind of illegal. It might be cooler that you made it yourself, but shame on you for making something cool and then making the rest of us look bad by using it illegally.

zoli wrote at 10/5/2015 7:41:38 AM:

counterfeit coins? hahaha

Jeshua wrote at 10/5/2015 12:02:43 AM:

News, really? Maybe he saw my video posted 2.5 years ago. https://www.youtube.com/watch?v=WWVVSZP3Au4

3D wrote at 10/4/2015 5:11:03 PM:

Nice. But you are now encouraging people to make conterfeit coins?

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