Ultra Quick Resin Cast Parts




Introduction: Ultra Quick Resin Cast Parts

About: Untidy, disorganised and a bit silly. I am a photographer, artist, body artist, sculptor, prosthetic maker, model engineer, and general idiot who likes making stuff and messing about. I give hands on worksho...

If, like me, you tend to ignore the instructions given with most materials and try a few 'mad' ideas instead, here's an ultra quick resin casting method using the 'wrong' materials.

For high quality, long lasting moulds, most cold casting methods use an RTV rubber of some kind. These are excellent, and I do use them, but they are expensive and pretty slow to cure. Usually 4 to 24 hours. The polyurethane resin favoured by most small parts casters, such as Easy-Flo or one of the other 50% / 50% mixes are easy to use but need to be ordered in and again can be expensive.

I wanted detailed results VERY quickly so I chose to use Alginate as my mould making material instead. The resin is car repair resin, which I can pick up 5 minutes down the road.

Step 1: Materials

The materials needed are:

A pattern with very little undercut
Alginate powder
Car repair resin
Some plastic cups
Stirring sticks (the ones from the coffee shop are best and free)

The problem with Alginate as a casting mould material is that it is not very strong, it cant handle big undercuts and it's considered to be a 'one shot' mould. Dentists use it to cast your teeth. The advantages of alginate are, that it takes very fine details, it very safe to use, and most of all it cures in 90 seconds flat. Also it is MUCH cheaper than RTV

You may have to think out of the box a little when making your patterns. I wanted to cast a set of small tank wheels. I had to fill some of the undercuts with plasticine, then grind them back with a Dremel after casting. I also built the main pattern  so that there were no undercuts at all.

Step 2: Setting Up the Fence

To fence my wheels I used a cut off plastic cup.

The pattern is mounted using a bit of plasticine, with the main 'face' of the pattern uppermost.

Step 3: Pour the Alginate

Mix the alginate 1 part powder to one part water by volume and give it a good stir with a stick.

once it is unifirm, carefully pour the alginate into the bottom of the cup. Ensure that the pattern is completely covered to a depth of not less than 25mm or 1 inch.

Using this method should ensure that the bubbles rise to the surface and don't cock up the pattern mould.

Step 4: Wait 90 Seconds

After a minute and a half the alginate will have cured into a strange wet rubbery substance.

Turn the cup over and press out the mould. CAREFULLY (I use tweezers) draw the pattern out of the mould. The mould shape should mean that it is self supporting.

Step 5: Pour the Resin

The car repair resin comes in two parts. The resin and a hardener. The mix is very forgiving, as long as you don't go mad either way (too little or too much hardener) you are pretty much guaranteed a quick cure. 12 minutes to de-mould is the time I generally get.

Be sure to mix the resin until it is a uniform colour before pouring. I mix it in a plastic cup using another coffee stick.

Step 6: Demould

Using tweezers carefully remove the cast. If your mould has very little undercut you shouldn't damage the alginate too much.

The heat of the curing resin tends to 'leach' a little water from the alginate into the mould. This is as bad as getting bubbles in the rubber. Just blow the mould out with a little air (I use an air can for this).

Step 7: Repeat

Using this method I managed to get 10 good casts before the alginate began to fail.

Step 8: Cleaning Up

The parts need to be worked with the Dremel to complete them. Here are a few I have started on.

The entire process including casting 10 wheels took 2 hours.

Step 9: The Finished Article

Here are some finished wheels on a scratchbuilt M39



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    57 Discussions

    Fiberglass resin, i was thinking Bondo when you were talking about car resin

    Cool tank! Try to avoid jargon (or at least explain it) I didn't know what "undercuts" or a "Fence" were.

    i use the same resin. i wanted to cast a knife out of it so could you please tell me how strong it is and how chip proof. also do you have and advice on casting?
    Please respond

    5 replies

    It would be far too brittle for a thin section knife blade unless you added fibre matt to it. Easier to make the two side seperately and then glue them together.

    i was thinking of a knife about 3/4th of a centimeter for purely decorative purposes. i still want it to be strong so please tell me.

    yep, I would certainly cast it in two halves reinforced with fibre matt then glue the two halves together.

    Hello again!
    I decided to finally cast some resin, and tried to make ezio's pauldron buckle. It is a simple belt buckle size. It came out ok, but the resin had a lot of pin holes on the side which was in contact with the alginate. Perhaps due to the water, so do you know how i can seal the alginate before casting polyester resin?

    I'd recommend for safety purposes, using a cup NOT made from plastic, due to the exothermic reaction of the resin and hardener.

    A vacuum box will lower the air pressure that will allow the bubbles to escape leaving a much better copy.

    2 replies

    True, but then if you're going to those lengths you might as well use RTV and have done with it. Also it increases the time (and expense) of creating the mould. I use one for my RTV moulds, but this is designed to be quick and dirty.

    It's terribly easy to put your mold flask onto a smallish board (say 12" square scrap of plywood, cutting board, etc.) and set something like an electric toothbrush, razor, or dremel tool against the board so that the whole thing vibrates. If you chuck a 10d nail into your dremel with a wee bit of a wiggle in it, it'll set the whole thing to vibrating violently enough to shake the bubbles out. Don't go putting a 90 degree bend in the nail or anything, and make sure it's chucked tight, and wear safety goggles - also use a low speed on the drill/dremel if you go that route.

    either way, about 10 seconds is enough to get the bubbles up and off the bottom surface of the cup and pattern.

    A nice instructable - thanks. 
    I have a question, what would be the best material for both strength and flexibility?
    I am tryiing to 'cast' some tiny gears - around 12m diameter and 2mm thick. I do not have the equipment to cut metal ones and wonder if casting them would be a practical method?

    6 replies

    It would depend entirely on the stresses placed on the gears, the proposed size of the teeth, and the speed they need to run at.
    I would suspect that resin based gears of this size would be liable to stripping teeth if placed under any sort of load. They would also wear far too quickly.

    I would be looking to use ABS or one of the hard nylons (Delrin), but these would need to be machined rather than cast.

    Maybe somone else has used cast resin gears. Of course you could always try some backyard metal casting and use aluminium, but they would probably need machining too.

    does anybody know how to coat plaster paris molds so as to make them non pourous so that resin can be cast into them?also i read somewhere long ago that adding alum and or borax to plaster paris makes it as hard as marble and outdoor statues used to be made from this mixture in victorian times . does anyone know anything about this?if so please advise.

    Thanks - I would prefer ABS to aluminium or metal but will still need to machine it.
    I will keep digging.  

    If you know the diameters, but don't have a specific number of teeth in mind there are number of cheap alternatives.
    Most model shops, especially RC ones, stock ABS gears in little sets. The ones I bought for a worm gear project were £1.76 GBP for three gears and a worm gear.

    I get most of my Delrin nylon gears from old printers, the last HL4 I stripped offered up a dozen gears of various sizes, two silver steel rods 300mm long and 2 aluminium rods of the same length (and an LED laser to boot).

    The ABS and Nylon can be machined successfully with a Dremel and some patience and imagination. That's how I finish my cast wheels too.

    You might try ThermoSteel (available at any auto parts store) -- it's an epoxy resin with steel powder used for high-temp (up to 2400°F) metal repair. Comes in a cup the size of a film canister, about US$8-9. You just stir it up into a thin paste and apply. It should cast pretty well, and I think it's fairly strong. I've used it for repairs but not casting. (I do know a lot about casting metal though - see my Instructable on making your own metal lathe....)

    Another option might be FastSteel (any home store near the epoxy) - a stick of epoxy putty and steel powder filler that you knead together (it's about the consistency of a TootsieRoll). It doesn't shrink, and can be sanded, painted, machined, etc. Website says it's good for rebuilding small engine parts, making handles, etc. It's not what I'd call "castable" -- it's not a liquid -- but you could make a plaster mold and press it in. Color is grey but it's paintable with a metallic paint, obviously, and should be strong enough.

    Similarly, you might try JBWeld (any hardware store) - one of my favorite "miracle products" (like WD40 and duct tape). It's (again) a 2-part epoxy that you can repair a tractor engine block with (no kidding, says so on the package). I've never cast anything with it, but I've made parts with it and it's STRONG. Again, it's machinable, sandable, drillable, paintable, etc.

    eHow has several articles on using 95/5 solid lead-free solder (basically casting pewter - any hardware store), and carving a mold from cuttlefish bone (any pet store sells 'em for birds to nibble) -- you could use plaster (any Michael's crafts store). You can melt it on the stove (be careful!) or a camp stove, BBQ, or with a propane torch (any hardware store). You can also cast pewter or any of the "white metal" alloys in RTV rubber molds made from actual parts.

    Finally, there're a bunch of low-temperature metal alloys that might be exactly what you want (they're just not all as cheap or easily available). Search Wikipedia for Wood's Metal, Rose's Metal, and Field's Metal. You can buy low-temp melting casting alloy from McMaster.com (they're amazing, and fast!), search for Bismuth. You can melt some of these alloys in boiling water, and you get over a pound for US$35-40. (Note - they contain lead - toxic. Some have cadmium - highly toxic. Standard disclaimer: you may die, you've been warned, I'm not responsible.)

    (Also search McMaster for "castable" and look at all the options for both casting and mold materials.)