Why cast in Sugru?
This guide will show you how to make a cheap and simple mould out of a silicone compound called Sugru. From this heat-resistant mould one can create a Pewter casting, for jewellery and such. Although a professional casting will deliver a more robust and larger mould, it is fair to say for small, detailed 1-offs, I found using Sugru to be a simple and cost-effective method. Indeed, the moulds I've made here have been re-used 3-4 times with pretty good results. (The moulds can also make wax candles too, for a geeky AFOL Birthday Party!)
About the materials.
Pewter is a silver-like alloy, which melts at 170-230C, and can be cast in a variety of things from RTV Silicone to MDF. Sugru is an variety RTV Silicone, but with one key difference - it a paste (like plasticine) and does not need to be poured, (e.g.) allowing you to make as localised 'skin' of casting compound around the object, rather than having to pour a large mould.
I also realised after doing this project, that nepheron has also done a great Instructable - this time casting in Solder rather than Pewter... The amount of creative work on Instructable never ceases to amaze me - so please check it out too! :)
Note: Just to be open about this, I work for Sugru as Head of R&D, though the views and ideas expressed here are my own.
Summary of the process
- Sugru will first be used to make 2 halves of a mould. This will cast a wax 'copy' of your object. (Note - you can just stop here with a wax mould of a Lego figure - you could even make it into a candle as I did!)
- Sugru is used again, this time to encase the wax copy in a shell for casting at high temperature.
- The cast is cut open and Pewter casting is then removed, and polished.
It could just be a fun gift, necklace or specialised component for a project...
Disclaimers & safety
- As with many projects on Instructables, these ideas are not 'industry approved', so you do this at your own risk. Please ensure no children or pets are nearby while casting. Wax and Pewter can 'spit' and splash, so always wear protective gloves, eye goggles, and ideally an apron/overcoat. Always work in a well ventilated area as fumes might be created which are harmful. If in doubt, ask a professional
I hope you enjoy this and other projects! Please vote if you enjoyed it, and do post a picture if you have a go!
TL;DR — How to cast your own Lego Minifigs in Wax (also for candles!) and Pewter (metal), using Sugru.
Oh, and if you liked it, please vote - I'm mean, how often can you enter a Wax, Metal and Fandom Contest - all at once...What are the chances?? It's like some sort of Instructables Trifecta!
Step 1: Equipment
Stuff you probably need to buy:
- Sugru - I suggest an 8pk. I've used colours to make it obvious which half is which, but I'd suggest a black and white 8pk is probably best. It takes 2pk for each 'half' of the Wax Mould and 2pk for the full Pewter Mould, so you'd have 2 left over for other projects!
- Lego Minifigure - any will do, but perhaps not your Dad's collectible 80's Space Man.
- Metal Casting Ladle - cheap is fine. (Or a large spoon will do - but wear gloves!)
- Pewter - each lego figure probably requires around 30g (inc. excess).
- A selection of Needle Files, 'Wet&Dry' Paper and Wire Wool - for finishing the cast.
- Rotary Drill (Proxxon shown) - optional, can use a small hack-saw also. With various cleaning/polishing heads, often included with Drill.
- Gas Blow-Torch - (technically Pewter will melt in your oven, but this is far from sensible!).
- Optional (not shown) - 5ml or 10ml Syringe for injecting wax into mould.
Stuff you probably have to hand:
- Old Metal Measuring Pan - with a handle. To melt wax in.
- Scalpel / Craft Knife - Any sharp blade will do, but a #12 Curved Blade is rather good for mould-making/releasing.
- Cup of Water (with a few drops of washing up liquid in it) - helps the Sugru not stick to the Lego figure.
- Wax Candles - Tea-Lights will do, or any old candle stumps work fine. (Add colour with crayons if you like!)
- Rubber Bands - help bind your wax mould halves together.
- Blu-tak, or Plastacine - useful for fixing the mould to the table to avoid tipping over.
- Coffee Stirrers - optional. Useful for pushing Sugru in small places.
- Old Toothbrush - scrubbing.
Safety is #1 priority: Wear Gloves & Googles!
- Goggles are essential: Wax can 'spit' if over-heated or if it has any water in it. Pewter can of course give very serious burns. Although I have used Nitrile Gloves, I suggest using more heavy duty gloves if are new to casting with Wax or Pewter - although they have low melting points, they still can give a serious burn.
(Though if goggles are too dull - check out these ones I made with 360degree lights!)
- The the unlikely even that you do start a fire, don't pour water on metal or wax as it will spit. Use either a fire blanket or sand. Do this at your own risk and get adult supervision if working with gas/flames.
Step 2: Making the 2-Part Wax Mould
FIRST HALF (orange)
- Take 2x 5g Packs of Sugru and knead into a rectangular blog.
- Stick to a piece of paper of card (it will help later).
- Dunk your Lego Figure into water (with some soap in it).
- Press into Sugru. Do this in a confident firm motion.
- Some Sugru will squish out away from the figurine - press it back in.
- Grab the Lego figure by the head and wiggle him free.
(If it looks a bit rough, add more water and press in / remove again quickly).
(If you really mess up, you can re-knead the Sugru and start again. You probably get 2-3 goes).
LEAVE FOR 24 HOURS (or overnight).
SECOND HALF (yellow)
- Prepare your other 2 packs for the second half.
- Insert your Lego figure in the DRY Sugru half.
- Wet the Lego figure and the mould (the orange one).
- Quickly mould the yellow half over the figure and the first half mould.
- Press on a second piece of card/paper on.
- The Sugru will stick to the Paper more than the Lego/Mould - so pull the second (yellow) half away carefully.
(The Paper helps to keep the shape from distorting too much with all the manipulation).
- If the mould needs a second 'press' - add more water and press again to get a good finish.
LEAVE FOR 24 HOURS (or overnight).
You can now peel off the paper and you are left with the 2 halves of the mould.
HOW TO COVERT TO A CANDLE
- If you'd like to make this into a Lego figure candle, simply lay a wick in the centre of the mould and pour/syringe the wax into the mould.
Step 3: Cast Wax Mould
This is the preparation for what is called a 'lost wax' technique. For more tips on this, check out this...here.
- Prepare your equipment to have everything to hand.
- Bind the two halves of your mould together with an elastic band.
- Trim off the 'base' of the mould to ensure it sits upright.
- Start melting your wax in the metal pan/cup.
- If you have a Syringe, draw some of the wax up into the syringe and inject it into the mould, taking care that the wax might spurt-out when it fills up - hence why this step is optional - so if you feel more comfortable pouring it in works just fine, but you need to make a wider hole in the top of the mould.
TIP - firmly tap on the table, as if you are knocking on a door, to dislodge any air bubbles.
- Once you've filled the mould, remember to squirt out the last of the wax into the cup, to stop it blocking up.
- Remove elastic bands. Carefully pull the two halves apart - taking particular care on the hands.
- Don't worry if you make a mistake - just reheat the wax and try again.
- Use a knife to trim away the excess. Note - you can quickly put the blade in the flame to allow you to not only cut quickly - but also 'stick' any broken bits back again - like the tiny hands!
- Admire your Lego replicas! Get ready for the metal cast.
Why not just cast the pewter in these two half moulds?
From what I understand of moulding (which is limited, so comments are welcome), having this intermediate step, rather than casting straight with metal has a few advantages:
- the 2 half moulds allows you to correct and modify any defective areas, until you cast the perfect wax mould.
- when the wax hits the mould, it might find a small hole, but as it is a lower temperature than the pewter will cool and quickly set in it and 'plug' the gap, allowing the cast to fill properly - where as the pewter will just keep leaking all over the place! (I did try this and don't recommend it!)
- consider the wax as your 'prototype' - make all the mistakes with this, as it's better to have a mistake with wax than metal, both in terms of safety, but also time and cost.
- as you will see in the next step, having a fully 'encased' mould for pewter is much more reliable. If I had simply made an encased lego mould - it would have stuck to the lego figure, where as with two halves I could also define the division of the mould halves.
Step 4: Prepare Your 'Lost Wax' Mould for Pewter Casting
These steps show you to 'encase' our was figure with Sugru, which will provide a mould of your wax model - capable of withstanding the heat of molten pewter. This mould will only be cut in half when the pewter has been poured - not before!
- Prepare 2x 5g packs of Sugru. Knead together.
- Add small pieces to the fine-detail areas first.
- Shoulders and arms next.
TIP: Hold the figure in the middle, to avoid crushing the hands.
- I suggest shaping a chunk of Sugru between your fingers to be about 2-3mm thick, and press it on, to give an even 'skin' of Sugru.
- Build up around the head - take care pressing around the neck.
Leave the top of the head un-covered.
- Make a small 'funnel' as shown.
- Add this to the head - ensuring the wax 'top' is visible - so the wax can flow in.
(In case you were wondering, this funnel is useful, as you need the 'head of pressure' to force the metal into small places, and also as the metal cools, it 'sucks' more metal into the mould, so this 'reservoir' is essential).
Use up any excess Sugru on the rest of the body, especially the base - for stability, as shown.
LEAVE FOR 24 HOURS TO DRY/CURE.
- Next place the mould(s) into a container - upside-down. Again the funnel is useful here.
- Place in an oven around 70-80C for about 15-30mins to melt the wax out of the mould.
- You will see the wax is 'lost' from the mould - hence the name.
- While still hot - give the moulds a vigorous shake to get any remaining wax out. Leave to cool.
Step 5: Casting in Pewter
- Take your mould, ensuring that it is stable.
- Add a little blue-tak to the base to stabilise it if needed. Ready your Gaz, Lighter, Pewter and Melting Vessel.
- *Wearing Goggles, Gloves and Apron* - start melting the Pewter. Do this in a well ventilated place.
- If you see impurities starting to gather on the surface, gently scrape these to one side using a paper-clip.
- The Pewter should look bright and shiny - and not smoking hot.
- Pour with care, in a steady flow. Pour expecting it to overflow, don't 'pour too little, as this will creative a visible 'weld line' between the different pourings.
- Stop once the funnel is nicely full.
As with the wax mould - give the table a 'knock' to displace any air.
- The mould will be hot for around 10mins (for this size). Take care.
- Cut your mould down the sides with a knife - don't cut too hard, as else you'll have to polish out the scratch marks later!
- Carefully pull and cut until the two halves come away easily. You have your rough-cast Lego figure!
TIP - Don't cut through the base if you can avoid it, as it will help with the following...
Although the first moulds from this method are best, I did find that I could get 2-3 extra mould form this, before the copy was getting a bit messy. To do this, I held the two halves together with elastic bands again - but I left the base joined together, which aligned the halves more easily.
Step 6: Cleaning Your Pewter Cast
There are numerous ways one could clean a Pewter mould, but I found that scrubbing the small amounts of residual Sugru with a brush was a good start. I then cut off the 'funnel' with a rotary tool - take care, it does get got if you cut for a long time. Make sure to cut with some 'excess' - as you don;t want to lose that famous 'bump' on the lego figure's head! I then filed and polished the figure with a variety of tools - most of which come with the rotary tool.
With regards to finish, I left this 'rough' - i.e. all the major blemishes were taken care of in about 20-30mins. If one wanted to get it to a 'mirror polish' this would take a lot longer. It's your call, depending on how much time you want to spend on it, but this certainly get your started on mould making, so I hope you found it useful.
Step 7: From Wax to Metal
I hope you've enjoyed this Instructable. Do post images if you make anything using this technique(s) - be it in Metal or in Wax only - as you can see, the next section takes advantage of the moulds to make fun candles!
Step 8: Bonus Project: Mould a Wax Candle
Supposing you love the wax moulds so much, you want to make candles, all you do is lay a 'wick' in the middle of the mould and repeat the process. Take care to carefully pour the wax around the wick or syringe to one side of it. You now have the coolest candles out there!
Step 9: It Was Late...and It Amused Me...
A quick animation I made in about 15mins. Like the 'dystopian casting scene' earlier...I'm not sure why I thought of this. Don't read into it too much, ok...
Please post any images of what you create using these technique - or if you have any better ideas!
Thanks for watching and voting if you liked it.