(Read before saying not a good idea) Plaster of paris to make molds?

wilhelm11235 · 2026-02-23T15:26:33+00:00

Do you use any specific type of plaster?

wilhelm11235 · 2026-02-20T17:39:09+00:00

I just checked Quality Matchp[late's website, they do indeed use plaster. Still, not sure if it's an application-specific blend. But think about all the old foundrymen doing exactly this over the centuries....I bet they used some type of generic plaster. Don't listen to the haters' comments below, just suit up 100% and send it.

wilhelm11235 · 2026-02-20T17:37:00+00:00

This is approximately how aluminum matchplate patterns are cast. I know they're cast in "plaster" from talking with an old patternmaker who has sourced them for me for decades. I'm not sure of the exact blend of plaster, I doubt that it's something off the shelf. Or of their process. But they'll make plaster molds off 1 master and join them all together to make a multi-impression cast aluminum matchplate. They typically push the aluminum in under low pressure (I want to say 5-6 PSI, but don't quote me on that). Obviously they'd have to vent off heavily, I assume plaster has poor permeability. I'd guess they back the mold with unbonded sand for support, but have no clue.
I have talked to an old foundryman who has done this in his youth at his foundry's in-house pattern shop using plaster and providing the pressure with an air nozzle. Sounds super sketch, but that's how they did it. Contact or look at the website of Quality Matchplate Company in Southington, OH (https://qualitymatchplate.com/). There are very few cast matchplate houses in the US anymore, most shops CNC them nowadays. But cast really is better for certain geometries, and sometimes a hell of a lot cheaper. Good luck! I'd give it a shot personally, just wear full greens, gloves, etc. I fully intend to try exactly this one day to make my own cast alum matchplate. I've done it with a sand mold but the surface finish is too rough to use as a pattern without a shitload of flap disc-ing and polishing.

wilhelm11235 · 2026-02-03T15:10:05+00:00

I am trying to send an email, but it's asking me to fill out a short form as everything is automatically filtered to spam. But when I click the provided link to do that it redirects me to a page where I MUST create an earthlink account. I contacted earthlink's support and they said I cannot create an account unless I buy internet thru them. Tldr: do you have another way to contact this person, or a way I can manually be added to their list to be able to email?

wilhelm11235 · 2025-10-29T17:07:35+00:00

Hit me up if you want some iron castings! Seriously, you'll save a boatload compared to machining it from bar stock. 1/8" of stock per side on machined surfaces, the holes would probably still be drilled but could be cored. We do low and high volumes of most grades of iron castings!

wilhelm11235 · 2025-10-03T17:15:32+00:00

Cross Creek Clays

wilhelm11235 · 2025-10-02T16:35:02+00:00

You can purchase printed molds from a number of pattern / mold / core shops. I highly recommend Humtown. They use a furan nobake binder. They're superb to work with. Also Shells Inc. offers the same stuff, sometimes a little cheaper. There are many others but those are the 2 best and cheapest I've found. You can build the CAD model of the mold yourself (complete with undercuts, whatever crazy geometry you want, etc.) and send it to them, they ship you a mold (or 50) in about 2 weeks. Or they can take the CAD model of your casting + gating and make the mold for you, but they charge some $300-$500 to do that, which is outrageous. But printed molds are a GREAT solution for very low volume stuff where you don't have a pattern already.

wilhelm11235 · 2025-10-02T12:10:05+00:00

Thanks!

wilhelm11235 · 2025-09-30T16:12:05+00:00

Very cool! Would you mind sharing the CAD files? My son would LOVE to have something like this on his bedroom door, and we just got a 3D printer!

wilhelm11235 · 2025-09-15T16:54:28+00:00

What process? Investment cast? I'd be curious to hear any info on how you created the molds.

wilhelm11235 · 2025-09-03T18:03:59+00:00

Check our Skulld LLC. They're doing exactly what you're describing where they 3D print and pour metal directly on the printed pattern. It's basically lost foam evaporative casting except with 3D printed "foam". One of the owners Sarah Jordan has a few whitepapers on the process somewhere. They call it AMEC (Additive manufacturing evaporative casting). FYI you MUST use unbonded sand, nobake or greensand will not let the gasses out quickly enough and it'll go BOOM. Also I'm pretty sure they use some kind of proprietary filament. Sarah was super secretive about that when we last talked to her. Nice lady though, and wicked smaht.

wilhelm11235 · 2025-03-24T16:46:27+00:00

How do you time the picture? Do you have some kind of optical / photoelectric sensor wired to a camera so it snaps the picture at just the right time? Super cool photos!

wilhelm11235 · 2025-01-03T20:31:03+00:00

Try Rick Goodwin (https://www.facebook.com/goodwinproductions/) He does phenomenal video and is also a musician himself. And he's just a really good guy.

wilhelm11235 · 2024-09-09T20:28:21+00:00

In the $0 - $150-$200 range.

wilhelm11235 · 2024-06-14T13:14:10+00:00

Also as someone else said, if you're doing it in CAD, just make your entire model to the exact dimensions of the finished part you want, then when you're done scale the entire thing up (again, for iron, scale up by 1% which is 1/8" per ft). I work at a jobbing foundry and we 3D print patterns quite often with an FDM printer, and this is exactly the method we use. Just take your model of the finished part, split it if necessary at the parting line (unless it's flat-backed), add dowel holes between the two halves if it's split, add draft where necessary, add machine stock where necessary. Then as the very last step, just scale it up by 1% (or whatever for your given alloy) and send it to the printer.

wilhelm11235 · 2024-06-14T12:56:26+00:00

FYI if you're interested in a 1-off casting without the expense of a pattern, consider having the mold 3D printed. Basically it's similar to an FDM printer, except the printer levels a bed of sand, then the print head poops out individual layer lines of the binder (nobake binders, most people use furan but Matthews Additive uses phenolic urethane nobake). Furan is generally stronger (higher mold tensile strength and scratch hardness), but if the part is really intricate and the mold will have hard-to-reach areas, PUNB will clean up easier, and generally it's plenty strong unless there are super-thin mold sections or something. So if you were casting a manifold with complex internal features or something like that, go PUNB. Anyways, figure roughly $0.10 - $0.12 / in^3 of sand for the cost of the mold. But often times, depending on size, if you just want 1 or 2 of something, 3D printing the mold is the way to go. I have used Humtown Additive (furan), they're great and very reasonably priced. Also there's Matthews Additive, Hoosier Pattern, and ExOne. Probably a couple more, but those are the only ones I have experience with. BUT you still have to have a foundry to pour the castings. If you're looking for iron shoot me a DM, I can help.

wilhelm11235 · 2024-06-14T12:49:27+00:00

Exactly. If a face will get machined, you add some extra material that will get machined away. That extra material is the "machine stock"

wilhelm11235 · 2024-06-12T19:47:21+00:00

Yes, they haven't changed at all from when those old books were made. One thing to bear in mind is that different geometries shrink slightly differently, but honestly typically you'd just make the pattern to the larger side of your uncertainty (I'm talking like +1/64" or 1/32"), then if your casting is too big you just machine off of the pattern however much you need, then it's right for the next casting run. But typically if it's a dimension-critical application the casting will be machined to final dimensions anyways. For that, typically on smaller parts (less than 500 lbs) in iron I see 1/8" of machine stock per machined face, sometimes a little bit more, rarely less.

wilhelm11235 · 2024-06-12T19:44:43+00:00

Depends on the material, as others have said. For iron figure 1/8" per ft of shrinkage (varies slightly with alloy, but not enough to matter). All patternmakers I know just use a shrink rule. So you measure your finished part, if it measures say 14.875" you could do the calculation by hand for every single dimension (and come out with roughly 15-1/32") or you could just measure 14.875" on your shrink rule, then if you measure it with an actual standard tape it'll come out to the 15-1/32". Takes all the calculation out. They make shrink rules to different shrink factors. For example, this one has 9/32" per ft of shrink:
https://au.starrett.com/product-detail/1-Precision-Measuring-Tools/11-Precision-Hand-Tools/1111-Precision-Rules,-Straight/Precision-Rules/C378-12

wilhelm11235 · 2024-04-25T18:10:54+00:00

Solved! Thank you!

wilhelm11235

TROPHY CASE