Shower thought 3D printed rocket cores for rocket mass heaters

I was just taking a shower and had this thought "could you use a big 3D printer to make a rocket core for a rocket mass heater?" I have watched all of the Better Wood Heat: DIY Rocket Mass Heaters 8-movie Set and listened to a few of Paul Wheaton's pod casts on rocket mass heaters. And have done a little reading on The Rocket Mass Heater Builder's Guide.

Have you seen Better Wood Heat the 8-movie set? No. Well follow this link to watch it on permies https://permies.com/wiki/63837f426/Wood-Heat-DIY-Rocket-Mass
Internet slow? Check out the dvd set here https://permies.com/wiki/69260f426/Wood-Heat-DIY-Rocket-Mass

Here is how I think it could work. A 3d rocket core printer using fused deposition modeling would build up the core. I think lasagna but the material is high temperature ceramic being built up one layer at a time. This would also mean that different sizes could be printed a the same time.  And how could this be better than using a mold to cast the core?  One printer with the right size printing bed could make many in a run. Also being a computer program human errors could be prevented and have repeatability . The down to casting is scalability if you need to change a casting mold than you need to build a new one. On a 3d printer you can use a computer to change an aspect of the print. If it does not work well you can change it back.

Is this shower thought a good one or do I need to get the water out of my ears?

Is someone working on this and do they have pictures?

What are your thoughts?

I cant think of a suitable material to use?

I have seen other folk using printers to make inner and outer molds from foam.

Perhaps a water jet cutter could cut refractory cement but that would be a large expense.
There may be a solid ceramic product that I dont know about but again that would be massively expensive!
Ceramic fibre board might work but ‘A’ it would cause massive and dangerous dust and blunt cutters. ‘B’ it wont stand up to the riggers of a fire box.
Perhaps Vermiculite board but apparently diffacult to get in the States and again would blunt cutters in a second.

It's an intriguing idea, that's for sure. What about using a geopolymer as the casting material? Otherwise I'd lean to 3D printing a positive model and using that to make a run of negative molds. Sort of like the lost wax method.

I wonder whether a variant of a ceramic powder coat as used on metal castings might work?

The high temperature coating product can withstand temperatures in excess of 1200 degrees and some coatings can withstand temperatures higher that 1600 degrees.

from procoatmetals.com

The cure times for metal can range depending on how long it takes the oven to get to temp and the size of the oven. Typically degrees ranging from 250(low cure) to 400 are required for the powder to heat up enough to bond.

from mauipowderworks

I'm imagining a version of selective laser fusion (explanation here). You have a layer of powder, cure it in a pattern with a lazer, spread another layer of powder and repeat. As far as I can tell people only do it with metals and polymers as yet, but I can't see why it wouldn't work with these powder coatings.


Most of the time for curing powder coated parts is getting the metal castings up to temperature. The trick will be making sure the different layers are cured together properly.

It's a long shot but it might just work....

There is a thread on Donkey pro boards about 3d printing but based on molds and casting.
https://permies.com/t/155825/printed-Peter-Van-Den-Berg#1220996

Fox James wrote:I cant think of a suitable material to use?

Nancy Reading wrote:I wonder whether a variant of a ceramic powder coat as used on metal castings might work?
Most of the time for curing powder coated parts is getting the metal castings up to temperature. The trick will be making sure the different layers are cured together properly.
It's a long shot but it might just work....

What about using a clay slurry that is pumped under a little pressure. Then build the core using the coils of clay and baking the print in an oven. One material does come to mind fire clay powder.

Is there a .stl file of a rocket core for a RMH? Or any other file type that can be used in Ultimaker Cura 5.1.0? I do have a 3d printer and it would be fun to print one out.

If a suitable fire clay powder is available, then a variant of selective laser fusing, using a powder bath of clay powder and just using water, or possibly a light binder (I'm thinking PVA, but maybe there is a better one) to print in layers (Rather than a laser) would make a clay model that could be fired, once dry.

This sounds like a good approach, Nancy. I wonder if methyl cellulose would make a decent binder? Nontoxic and water soluble, basically the good old wallpaper paste ingredient.

Nancy Reading wrote:If a suitable fire clay powder is available, then a variant of selective laser fusing, using a powder bath of clay powder and just using water, or possibly a light binder (I'm thinking PVA, but maybe there is a better one) to print in layers (Rather than a laser) would make a clay model that could be fired, once dry.

I idea I had today  use a caulking gun thing. So have a handle with a nozzle that clay slurry comes out of then onto the bed. I also thought about building a mass with a caulking gun like thing. In theory one person would run the "gun" another moving the hose to help the builder. One running a feeder and a few more to trade out jobs.