I printed Peter Van Den Berg's optimized J-tube

I printed Peter's 3d Model of his optimized cast rocket core.

I'm a visual thinker so I had to see it in person, even if at 25% size.

Way Cool Solomon!!!  Can you print it full size?

Hmmmm.  Could you print a mold for a castable core? Even if it had to be multiple prints and fitted together.  That would solve a BUNCH of issues.

I could print out forms for a castable core, but my present printer can only print 250x250x300mm. So I would have to split it up in a bunch of pieces which is a little beyond my skills at this point.

But if I get a much larger printer, perhaps a belt printer or one with a 1 meter square print bed, I could pull it off.

It would be much easier to ship plastic pieces and bags of mortar than a delicate already cast core.

It would be easier if you had a big printer, but if you could find someone to help split the files (that only has to be done once) then anyone could print them locally.

Way beyond my abilities, but you have me thinking in a whole new direction!

Looks cool, I can see the potential for casting intricate shapes but one would need a high frequency vibrating table to produce a good end product.
Are Dragon rocket stoves still being made?

I do functional mechanical 3d modelling on a daily basis. If someone could send me the original model or drawing, I would be happy to split it up into pieces that could be printed on the typical 200x200x200 printer. Purple Moosage for email addy!

Oooh, pretty. That's a good teaching tool as well.

I did this the old-fashioned way: I made a reverse mold from wood and then poured castable refractory. I did top and bottom halves instead of L-R so that joining them wouldn't be critical. The RMH is a 4" system in my glasshouse and it performs well, but I will need to demolish and rebuild the core sometime soon (hopefully before cold weather returns) because it has cracked and spalled pretty badly with use. I have gotten three seasons out of it and lots of education, so it's been a good first step.

Here is what I learned:

* I really should have set up a vibrating table for the casting process. I suspect a large part of the deterioration of the refractory material is down to the voids and inconsistencies in the cast body.

* The next iteration, if it's a J-tube, will have some extra depth to allow ash buildup without throttling airflow. Several times I've gotten reverse draft because too much fuel lodged as coals in the burn tunnel.

* Those intricate castings are weak at corners and transitions. If I do another cast core, I will make slab forms instead of the hollow molded halves. Sort of like firebrick splits, but with the detail of Peter's design fully incorporated. Fit of the pieces will be done with simple rabbets or grooves to allow for differential expansion and contraction, as I think this has been the number one driver of cracks in my core. I want the parts to shift within limits and not stress the weak spots.

Or, I might go for the gusto and build a batch box. Traipsing out to the glasshouse every 30 minutes on cold winter nights does get old.

I have been thinking of how one could do this using super wool inserts....    


What if instead of squares we made it circular so super wool could be put inside....

I was thinking taking aluminum sheeting and make the form to hold the superwool in place we could print this form and have the high heat protection with the wool in place.......   or...   how about chicken wire with spikes  that pierce the superwool to hold it in place....


I was thinking if we had superwool thread  one could sew the chamber together. to a chicken wire exterior frame...

Scots John wrote:Looks cool, I can see the potential for casting intricate shapes but one would need a high frequency vibrating table to produce a good end product.
Are Dragon rocket stoves still being made?

Somewhere on Peter's site (or somewhere) is instructions on how to make a vibrating table. They are indispensable for casting cores.

Dragon stoves are still being made, but for the $1100 price tag, I can think of a lot of ways around buying one. That's just me though, I rarely buy something I can build. I can justify a lot of development costs and tooling to figure it out for myself for that price.

R Scott wrote:It would be much easier to ship plastic pieces and bags of mortar than a delicate already cast core.

It would be easier if you had a big printer, but if you could find someone to help split the files (that only has to be done once) then anyone could print them locally.

Way beyond my abilities, but you have me thinking in a whole new direction!

I'm trying to see what's possible in a more technically advanced direction. RMHs have been around and popularized for over a decade now, and there are new things that can be applied, like 3d printing.

So many people have printers now, with the right models, anyone could put together a core mold in no time, even if you had to make it out of a bunch of smaller pieces.

And that goes for batch boxes too.

Peter has worked out a lot of this stuff in Sketchup, so the models already exist. It's simple to convert them to be printed like I did here. But the real fun would be to create negatives to make molds with.

Joshua Rimmer wrote:I do functional mechanical 3d modelling on a daily basis. If someone could send me the original model or drawing, I would be happy to split it up into pieces that could be printed on the typical 200x200x200 printer. Purple Moosage for email addy!

Sent you a moosage.

In the spirit of the makerverse, it would be so awesome if we could work out an open sourced project with this. The models are out there, I got this one from Peter and the batch box models are on his website.  It's the splitting of the models and making negatives that I need to learn how to do.

Because this seems to me to be the road to printing out our own rocket cores (sort of). Being able to quickly modify molds and cast new cores, this can only lead to newer and quicker innovation in the RMH world.

Solomon Parker wrote:

Scots John wrote:Looks cool, I can see the potential for casting intricate shapes but one would need a high frequency vibrating table to produce a good end product.
Are Dragon rocket stoves still being made?

Somewhere on Peter's site (or somewhere) is instructions on how to make a vibrating table. They are indispensable for casting cores.

Dragon stoves are still being made, but for the $1100 price tag, I can think of a lot of ways around buying one. That's just me though, I rarely buy something I can build. I can justify a lot of development costs and tooling to figure it out for myself for that price.

Hmm that is quite expensive, especially as the average rocket stove builder seems to be on a tight budget!
I am only guessing but, perhaps there would of been around $1500 2000 investment for a proper vibrating table, $5000 for the mold construction and $100 of refactory for each unit?
I don’t have much experience with casting ‘refractory’ cement but I work as a formwork engineer on large building sites and I did train with the use of vibrating tables, (35 years ago) I think the version of table you mentioned is based around an offset shaft electric motor that tend to shake rather than vibrate the cement, they would probably work ok but would not settle a dry mix very well.
Great work in any case....

Scots John wrote:I am only guessing but, perhaps there would of been around $1500 2000 investment for a proper vibrating table, $5000 for the mold construction and $100 of refactory for each unit?

What? No!

If you want to just go buy everything, sure. But nobody was talking about that.

IIRC, one can build a vibrating table suitable for casting cores for less than $20.

The molds we are talking about PRINTING would cost $20-$30 in PLA filament, plus a few bucks for wood backing boards, and whatever for the refractory.

If we can't do this for HALF of the cost of a Dragon Heater core, then we're doing something wrong. Plus we'd get to keep the tools and forms. Or perhaps if the forms didn't survive, we could just print new ones.

AH! I found a video on making a vibrating table.  Just a motor, a tire, a piece of plywood, some bolts, and a dimmer switch.

I think you miss read my reply to your answer... I was suggesting the the presently available Dragon core was expensive and I was also suggesting some figures that they might of experienced while manufacturing the product!
I would of through their  mold is a multi use structural construction and would of cost quite a lot of money?
Yes those type of vibrators do not work particularly well  with dry mixes and as far as I know, refectory is mixed very dry?
I did not say it would not work as I don’t actually know that but casting course dry mixes and expecting good results with fine detail would normally require a high frequency vibrating table?
I was not implying anything negative about your model!

Scots John wrote:I did not say it would not work as I don’t actually know that but casting course dry mixes and expecting good results with fine detail would normally require a high frequency vibrating table?

The vibrating table is in the video I just posted. I believe this is the sort of thing that Peter uses.

I have no interest in the dragon heater. I'm figuring out how to do this for people who want to make their own stuff. Money ruins everything.

I made a styrofoam cavity model to cast my 8" refractory J-tube core, with top and bottom sections instead of left-right to minimize differential expansion and stresses between areas. It has served well for four and a half heating seasons so far. Both sections have cracked in several places, but are still locked in place and not in danger of failing. Notably, the burn tunnel roof with trip wire molded in is still unbroken and almost perfect. I do see a difference between the bottom which I cast first with cement that had started to set and was honeycombed in spite of vibrating, and the top which cast perfectly. The top is largely still smooth from the plastic bag mold release material, while the bottom (patched solidly where honeycombed) has spalled to a rough surface in a number of places.

https://permies.com/t/60784/a/45819/IMG_0860-w600.jpg

styrofoam core mold on form box

That looks great. We're figuring out that exact sort of thing only 3d printed.

One of the good things about Peter's designs is that they're already in sections. Smaller sections means fewer problems with cement batching. And parts can be replaced if they fail. The J tube core is two pieces, the best extent batch box is three pieces.

Another thing we can do is create true circular and exponentially curved edges, rather than squares and octagons.

If designed with proper draft and good mold release surfaces, a core mold can release easily and be perfectly reusable. With my experience of the behavior of my core, I might do another with different section divisions, like floor, complete sidewalls left and right, and burn tunnel roof. Or maybe just bottom and top as the original but feed sidewalls full height and burn tunnel roof and riser base as one part, since those don't seem to have any cracking issues. Running the feed tube sidewalls all the way up would leave fewer narrow sections of casting. My core mold is good for many more uses, but I think I will be making batch boxes for future projects unless I get a job for a simple installation.

I believe this would be the next step for making a mold.....

I don't think that's quite the next step. What I'm suggesting is not people building their own printers or CNC machines, I'm just talking about printing molds on standard off the shelf printers that are already all over the market.

This is certainly an option, especially if someone is using EPS or XPS foam. But I think building a CNC machine is going to be a bit daunting for most people interested in casting their own core.

Solomon Parker wrote:I don't think that's quite the next step. What I'm suggesting is not people building their own printers or CNC machines, I'm just talking about printing molds on standard off the shelf printers that are already all over the market.

This is certainly an option, especially if someone is using EPS or XPS foam. But I think building a CNC machine is going to be a bit daunting for most people interested in casting their own core.

All options are on the table,  if it works use it.

Yes, not everyone has these machines or the desire to build them.

Very cool!  3d printing is *very* cool technology.

It's awesome to see the "guts" of this thing like this.

Very educational!