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Earlier this year whilst working on designs for a 1/24th Westland Wasp, my hand was forced into learning how to cast aluminium (using vacuum processes) on a small scale, on account of the part(s) concerned needing to be much stronger than white metal was capable of providing. On the principle that the problems specific to modellers rarely feature in Youtube tutorials for such processes, it may be useful for others how this process can be adapted to our hobby on a cheap, reliable, but most importantly, safe, basis as home. In relation to scale and detail, the species of metal-casting videos in closest proximity to our craft tend to be those made by jewellery designers and from which you can form the misleading impression that you need to drop €2-3K on kilns, furnaces and the like to even get started. Those guys are working with precious metal on a market-volume routine basis so necessarily need consistent, professional gear to run their practice on a daily basis, unlike those of us needing only small volume or occasional metal parts. Before proceeding any further I cannot stress the safety factor enough - foundry work (even at this small scale) involves materials and equipment working in excess of 700°C, so as a minimum you require: A well-ventilated outbuilding or outdoor area (with a concrete or stone floor), with the casting area itself well away from any flammable materials. Safety equipment: protective footwear, along with a thick industrial apron and foundry-type gloves like these: Protective goggles are also advised. If you have neighbours right next door as well, in terms of noise pollution/public nuisance, be aware that the furnace emits quite a roar at operating temperature, as well as fumes when the wax resin is being burned out. Metalworking gear sold online with the word 'jewellery' appended is as a rule wildly expensive for the home user, however, much of what you need can either be made or adapted cheaply yourself with only basic DIY-level skills. For clarity, the following is split into three sections regarding tools, materials, and then the sequence of events involved in producing the parts. Tools 1. Casting flask & base. These flasks are just a stainless steel cylinder and go for silly money online. I bought a cheap length of 3" wide stainless steel exhaust (for a Mini) from a local car-parts seller for the price of a single flask and cut it down to produce as many flasks as I need: The rubber base you see it sitting on is one of these, again, an inexpensive item. 2. Foundry tools. The melting crucible is a 1kg carbon graphite job. You can pick these up cheaply enough online from the likes of Amazon however many of them come without a pouring lip which I found made pouring the metal awkward so you can see at the 3 o'clock position on it tbar I ground out my own lip (easy enough using the Dremel). Both the black crucible tongs and flask tongs (yes this latter are really just a big BBQ pair) can also be sourced cheaply online. Ensure your tongs match the size of both your flask and crucible though - in my case the black tongs work fine with the crucible but don't open wide enough to lift the flask in and out of the furnace, hence the second pair. A large screwdriver is useful for digging the part out of the mould after casting, whilst the tool on the far right is simply an old BBQ spatula folder over in the vice to produce a handy item for scraping slag off the top of the liquid metal whilst it's in the furnace. 4. Furnace. You'll find plenty of rather costly gas propane furnaces online for blacksmithing, jewellery etc., and an equal number of cheap knockoffs. I sought advice about the cheaper alternatives from a sculptor friend with experience working a range of metals: his verdict was that they were too cheaply built to last, plus also noted that on H&S grounds you still had to spend time making them safe to use in terms of treating the thermal blankets from spewing off fibres. As I had already had one of these roofing torches from previous building works, the heat source for the furnace was already taken care of. If you need to source a burner yourself, there's a lot of simple cheap furnace torches of the venturi type available online, or even build your own. Whichever route you follow, you're working with gas and high temperatures, so be careful. There'd been an empty Calor gas cylinder knocking around in the garden ever since we moved in about two decades ago; I'd never thrown it out thinking 'it'll come in handy one day' and sure enough, this turned out to be its hour of glory, being transformed into a furnace using Brian Oltrogge's impeccablly concise beer keg method: Not needing such a large furnace as Brian did, I cut the middle 25% out of my cylinder's original height, whilst the handles were simply recyled from an old airbrush compressor: Not needing such a heavy amount of heat as a larger furnace to get up to operating temp. (typically 732°C for flask burnout / approx 700°C for melting the aluminium in the crucible.*) I also replaced the original nozzle of my propane torch with a smaller bore version and made sure that the diameter of the tuyere opening matched it during construction so that it would fit comfortably into the opening like so: For the refractory lining of both furnace body and lid I followed Lionel Oliver II's homebrew mixture to the letter and it works superbly, as long as your initial warming and firing process to cure it follows Brian Oltrogge's curing steps of air, heat lamp, then steadily increased the burner temp over several hours, which he outlines in his tutorial videos. Vacuum chamber/table Unluckily my defunct airbrush compressor was a diaphragm rather than piston version, otherwise I would have had a go at converting it to a vacuum pump along the lines used by Tariq Curtis. That said, Vevor sell a decent, inexpensive pump/chamber combination that provided plenty of scope for modification along the lines required here. It didn't have to be pretty, just work consistently, and was modified thus: The chamber comes from the manufacturer with the connection and gauge mounted onto the lid, so as I needed to be able to swap the lid out for a casting table (which I made from that circular steel plate you can see hiding behind the pump), the side of the chamber was drilled out and the connection repositioned to there, with the original hole in the lid being sealed by that highly professional and sophisticated method of sticking a 50p piece over it using JB Weld: That then gave me the means to both de-gas the liquid investment inside the chamber when casting the 3d printed pattern, and then by swapping the lids over, use it outside as a vacuum casting table. By no means is that combination an original idea on my part (it's a well known and widely used process with some beautifully-engineered equipment produced by others) but has the virtue of being quick and cheap to produce in this instance. If buying a similar pump/chamber, go for a pump with the higher flow rate as you will need that extra speed at the metal pouring stage. Casting 1. The 3D print and investment mould. The initial casting step proved the most expensive part of the process as, in experimenting with both resin and homemade casting mixtures, you pretty soon find out that there is a reason that specialist materials exist. You gets what you pay for! After satisfying myself that tens of thousands of people around the world weren't lying about the fact that standard resin doesn't cook off when subjected to extreme heat but just turns to ash: - I realized that it was necessary to buy one of those printing resins especially formulated for metal casting. After going square-eyed from reading brand-comparisons (as well as bug-eyed at some of the prices!), I settled on Siraya's well-known 'Tech Cast Purple' as a compromise between quality and cost. It's been around a while, is well spoken of, and gave excellent print results first time out: Did I say compromise? Actually there's no compromise here in quality terms, the surface finish being on par with anything I've got from Elegoo's standard grey: the only issue I found in regular use was the occasional apparition: This particular blend of resin does require a more elaborate cleaning and curing cycle post-print, however if you're prepared to pay a bit more then I undertand the newer Blue version simplifies this step. Prior to obtaining the vacuum gear and a custom investment powder I explored some of the cheaper options for investment casting first, having several goes at using a 50/50 mix of Plaster of Paris and silica sand and just the effects of gravity to get the metal into the mould. Many people have routinely gotten great results from such inexpensive materials but for producing larger chunkier parts than what I required here, so it was no surprise when I was unable to get the proccess to produce more than a 70% complete print on such small parts. Remarkable however that it yielded that much! A brief reading up on the chemical composition of investment materials rapidly convinced me that for 3d printed materials at this scale, the use of a professionally-produced powder was necessary. Digging around online I was able to find a supplier in Spain who was able to ship a box of Ransom & Randolph's 'Plasticast' blend, specifically formulated for using with 3d printed materials, at a reasonable rate: It has a lovely creamy texture and performs consistently well, plus you get to sing Mud Mud, Glorious Mud whilst degassing it: When it comes to the actual mixing and casting process, George on Makerspace gives a far better demonstration of this visually than I can ever hope to achieve in written for. Essentially follow everything he does here and you will get good results. Hat tip to you George. One crucial difference is that he uses a kiln to fire his flask whereas as I use the gas furnace: This obviously lacks the precision of a digitally-controlled thermal environment so aside from a handheld thermal temperature gun (which will only give you an approximate understanding of the internal temperature due to confusing reads off the hot gases emerging at the top) you have to work old-school and judge the required temperature by the colour of the steel flask. This is not as hard as it sounds once you get your eye in. One issue I balked at when humming and aahing about buying an expensive investment powder initially was the multi-hour temperature-control cycle the manufacturers recommend for baking your flask. No way would this be practicable or affordable on a gas furnace. I was heartened though to read in Tim McCreight's Practical Casting (a superb handbook to have) that there was a 'quick and dirty' 3hr bake you could use instead (essentially the same routine followed by George in his video). Certainly this has worked fine in my case, despite the difference in equipment. As to the actual metal pour, this is the setup I use out back, with plenty of leg room between furnace and vacuum table in order to avoid tripping over anything: The black cylinder is an old airbrush tank cut down and insulated (so that I can stick the baked flask under to keep hot whilst melting the metal down) whilst that silicone gasket on top of the vacuum table is just a cheap piece of catering sheet cut out with a hole in the middle for the flask to sit over. A fresh pour: Surprisingly the vacuum setup exerts a stronger pull with hot rather than cold items, I've no idea why. You want to avoid the flask shedding too much heat whilst out in the open on top of the table as the chamber evacuates and you fetch the crucible of metal over, so I bung a couple of large rocks into the chamber to drastically reduce the volume of air the pump needs to remove. The subsequent cooling and cleanup cycle again follow what you see George doing in his video, whilst the net result of the above has remained pretty consistent from cast to cast. Here are copies of the parts in question - the forks which hold the main rotor blades on the Wasp - neither resin, plastic, or white metal capable providing the required tensile strength to hold the blades without making these fork elements grossly oversized: These are all still in their raw state out of the mould so the next task of course is to begin cutting them off the sprue and give them a sand and polish - hopefully I can start that over the next few evenings. Is this work going to make any jewellery designers feel threatened? Hardly. But it is capable of reproducing features down to about 0.15mm in size on parts that need to be stronger than more commonplace modelling processes can provide. And that's all that was needed in this instance. I'll post up a photo of the forks in the finished condition in a few days. Kind regards, Tony *This Vietnamese foundry produces the best guide I found anywhere online about the temperature ranges for pouring aluminium, in terms of balancing strength with surface detail.

There is very useful information on-line about converting 2-1/2 gallon paint pressure pots on-line. One you-tube video shows this in great detail, while a .PDF shows combining pressure and vacuum into one pot, requiring two gauges and a vacuum pump. I like to find the cheapest, simplest way to do the job, so without further ado, here is my poor(er) man's option. I began with scrounging up an old mechanic's or HVAC hand pressure gauge set. Since most of the modern world has gone to expensive, fancy machines to cature freon, these gauge sets are readily available. They are distinguished by having a low-side gauge, which reads both vacuum and pressure (up to 12o PSI), and a high-side gauge, which reads pressure only, usually up to 300PSI. They may be configured for either R-12 freon, R-134a freon, or whatever is current in the HVAC field. Doesn't matter which you use, as all you will need are the low-side gauge, the hose, and the appropriate fitting for the vacuum pump end of the hose. I had an old set laying about that was already broken. The high-side gauge had been broken off, but the rest was intact. After removing the hose, and the low-side gauge, it looked like this: The low-side gauge looks like the next photo where the "P" and "V" refer to the pressure and vacuum reading parts, respectively. The next thing required is a vacuum pump. Usually, the recommendation is either a purpose-designed pump or a recycled refrigerator pump. Since I also had a cheapie (read about $29.00) automotive venturi-type pump, I used that. The photo below shows mine, where the hose from an air compressor comes in (about 100 PSI needed), and shows the odd-ball adapter I added, so I could use the pump with either R-12 or the later R-134a type car setups. If you use one of these, it doesn't matter, as long as you can adapt your hose from the pressure pot to the pump. The fellow on-line that offers the PDF file gutted his pump, and just hooked up the guts. That was a little to exposed to damage for me, plus I already had the hose and fittings, so I went that route. I suggest you due a search on-line and then go your own way. The next photo shows my hook-up to the pressure-pot's lid: The next photo shows some of the mods to the pressure pots, that are pretty much the same for everybody, given I only use one gauge. Of note are the 1/4 turn air shut-off valves, red for the vacuum side and yellow for the air pressure side. These coors are not significant, and only ended up because I got the valves at two different places, and one had a female end where the other had a male end, and they ended up in these positions solely because of the brass fitting I had laying around. I did have to buy a couple, and they are available at automotive stores or big-box or hardware stores. Also shown below is the T-handle for the pressure regulator. The pot supports 60 PSI. I set the regulator shown here at 50 (AFTER setting the pressure relief valve, shown later to 55 PSI). Below is another view of the pressure pot lid: All joints are sealed with three wraps of teflon tape. The "T" fitting under the regulator was actually supplied on the pot as a piece of cast pot metal or some-such, and it gave me fits trying to get it to stop leaking. I finally replaced it with a brass fitting. A WORD OF CAUTION HERE!: Before doing ANY mods to your pressure pot (should you try one!), Follow the instructions, put it together and then pressure test it up to 60 PSI and see whether it will hold the pressure for an hour or so. Get yourself a real bottle of leak detector fluid from your plumbing supply stockist. Do not rely on the dish soap and water mix, as it is NOT sensitive enough. The right stuff will show you tiny leaks, by exhibiting dozens of really tiny bubbles, a half-hour after you apply it, if any leaks exist. Regular soap mix will fool you into thinking you are leak-proof, even if you aren't. You may feel free to ask how I know this... In any event, if you cannot seal the factory-provided parts prior to your modifying the pot, take it back, and exchange it for another! I got my pot off E-bay for $33.00 plus shipping, when the pot usually goes for around $100.00 new from Harbor Freight, so I figured that there would be some problems. I had to replace some fittings, chase the threads in the lid itself, and replace the original lid gasket, so I ended up being in it for around $80.00 all up. If you sign up on the Harbor Freight website, they will eventually send you a coupon worth $20.00 off a $100.00 purchase. Since they also sell the quarter-turn valves cheaply, pop for a couple and -- Bob is somehow related again. The fellow who has the you-tube video suggests cutting a wooden disc out of 3/4" ply to make up for the fact that the bottom of the pressure pot is NOT flat. Below, is my quickie answer, a piece of 3/4" lumber cut to length. I will probably do a proper circle covered with some resin-shedding product eventually. I also added a plastic 4 or 5 quart plastic ice-cream container to catch resin burps, etc. Below is a look at the whole shebang, put together. BTW, tighten the lid clamps as tight as you possibly can! Below is a picture of the compressor I use to drive this pot. It is kept in my garage, and normally used for putting air into tires or driving nails or other housely things. It replaced a larger, old one I had for driving air tools and such years back, that finally gave up the ghost. Also, please be aware that your airbrush compressor will not drive this rig, unless it's pretty awesome. I set the regulator on the output end of this compressor to 60 PSI, when used for casting. I usually use this rig as follows: I make the mold masters in one of the time-honored traditional ways, the I mix the RTV rubber in a larger cup than needed. I put the rather violently-stirred mix into the pot, shut off the pressure intake side, and then plug the compressor onto the venturi vacuum pump. I can pull between 24-26 inches of mercury with this setup (anything over 20 is fine). When the vac hits 20+, I shut off the vac side also and turn off the venturi pump. I give it 2-3 minutes under vacuum, then pull the relief plug to release the vacuum (semi-slowly). When the gauge reads zero, I open the pot and pour the degassed mixed silicone into the molds. I then put the molds into the pots. Unless they are somewhat large, I do not use vacuum at this stage, but if the molds are larger or have adequate pour stubs to contain the resin, I might use vac before pressure (perhaps 2 minutes). For the rockets and gun barrels, I used none -- just pressure. If I have used pressure, I simply shut off the vacuum side while holding the vacuum, re-attach the air hose to the pressure side of the pot, and start up the pressure -- again, without releasing the vacuum, if used. I then wait until the pressure pot hits 50 PSI, and then walk away for the needed time for the resin to cure, Then, I'll return, shut off the pressure side, and pull the relief valve to De-pressurize the pot and remove the castings. The air compressor will turn on and run if needed due to tiny air loss, to maintain the needed pressure. The last photo shows some of other folk's resin masters that I test the rig with. There are 1/72 rockets and machine gun barrels, and a Hasegawa B-26C turret sprue. The 20mm tailgun turret in the center is my master. I have cast resin in various ways for many years, and this is the first time I have ever gotten perfect casts, all the time. Any minor problems I have had are all resulting from improper mold design. One last thing I neglected to mention. I so far have used OOMOO 30 silicone and Micro Mark's CR-900 resin, mostly because of longer pot times (15-30 minutes). This gives me time to do all the de-gassing, but are not suitable for production work. The CR-900 however, has one very useful feature -- that tiny molding, like the rockets and gun barrels become very hard and strong AFTER SEVERAL DAYS. This stuff is great for super thin castings, but you could probably do better for thicker stuff. Thanks for tuning in. Comments, suggestions or outright attacks always welcome. Ed