8-Inch Portable Modular Rocket Engine with Forge, Crucible, and Kiln Attachments

SO pysched on this one!

The 8-inch core is complete!  The crew is working on the modules today.

Pics from yesterday, courtesy of Richard Quintano.  Thanks, Richard, keep 'em coming!

The rocket crew hacked a hole straight up through the bottom and top of an old, repurposed electric kiln and fired it up, testing both the rocket kiln AND some Wheaton Labs site-harvested clay - they shot well past 2,000.  I'll grab some pictures of the unloading tomorrow . . .

I'm very interested to see how well the kiln lining holds up.
I'm also hoping they make provisions for loading and draining the crucible while its in operation.

That stove looks like a beast. And it is obviously built to last. Good job to the rocket team.

Pretty cool!  Got to help build the rocket engine and riser that fired up this kiln!  Also got to make pottery that was then fired in the kiln!  Others in the group went to go harvest the clay on site and then processed it so that we could make the pottery.  Thanks to Lisa for making the clay and pottery happen. Thanks to Uncle Mud for making the rocket happen.

After the first rocket kiln was built and fired, Paul proposed that a better hotter more amazing kiln with better kilny glory could be made if the configuration was changed so that the kiln sat above the riser and stratified the gasses around the pottery stuff inside.  So Mud worked some design magic and the crew welded up this prototype in a day and guess what!!  Paul was right!  This prototype certainly needs some finishing, but it worked really well, achieving 2300+ deg F i believe.  

Fascinating! I'd wondered if a rocket heater could be used for a kiln for a while. Looks like I'll have to try it here when I have time to experiment. Thanks for the info!

This is very, very, cool! You all are awesome! I want to try and build one as I have two old electric kilns that I've saved from going to the landfill. Are there more pics of the kiln on top of the riser and the construction process from the beginning? Any additional info would be greatly appreciated!

That's awesome!!!

Very cool!!  

Will there be plans or a tutorial available at some point for those of us that can't get to Montana?

Lordy! I’m sorry to be missing this.  I thought the kiln was just going to take the place of the riser, and just could not figure out how the turbulence and super heat was going to be created…

Now I get it.

Well done!

Will there be photos of the forge, too?

Rob Viglas wrote:This is very, very, cool! You all are awesome! I want to try and build one as I have two old electric kilns that I've saved from going to the landfill. Are there more pics of the kiln on top of the riser and the construction process from the beginning? Any additional info would be greatly appreciated!

I dont have much more that's useful, but others may post.  Maybe WL will put together a video.  Stay tuned and hope hope hope.

::sniff sniff:: Is this a new kick-starter I smell perhaps?   RMH noob/dingleberry here:  is there any chance the modularity/inter-change-able-ness of components could also include a canning pot insert (Lorena cookstove-ish)?  

 How long a burn did it take to fire the pottery?
Are the pieces usable as is or do they need a second firing, with glaze perhaps?

Since the kiln is set so high on top of the riser now , building a raised work platform next to it could be use
I think all of the attachments might benefit from being set after the riser instead of before.

I can grasp the kiln-forge- canning pot gets more heat if it is “after” or above the riser, but I am not understanding what creates the turbulence (that I always thought was integral) if the rising gasses don’t hit the top of the barrel, and the rapid cooling (from exposure to cool barrel sides) draws more air in, fanning the flames and sustaining the controlled continuous explosion.  Can anyone help me out?

That is an interesting project but there seems to be a lot of exposed  ceramic fibre, are you concerned  about any heath issues as breathing in super heated ceramic fibers is said to be very dangerous?

Some more kiln progress!  Details to come!





We also ran the modded electric kiln on a 6-inch rocket engine, and reached hi-fire.



Proud unveiling of folks' site-harvested clay creations.











The proof is in the coning.

The proof is in the coning.


Yes!  The ceramic cones indicated the heat work (ware/interior mass heating) done by the heat in the riser atmosphere.  All our firing attempts were a little uneven top to bottom.  Both repurposed kiln firings were hotter on the bottom our 2-hour low-fire one (on the 8" rocket engine) came out with cone 1 bottom cone 04 top---translation: 2077 bottom and 1945 top , and our high fire (with kiln high atop a 6" rocket engine) came out with cone 7 on top 2259F and cone 9 on bottom 2296F in just over 5 hours.  So the heat stayed toward the bottom in both.  We tried to allow the heat enough space to move up through the kiln-- probably different shelf arrangement is needed for a more even firing.  Paul's kiln was hotter on top with both firings, getting to cone 1-2 on top (call it 2088F approx) and almost cone 04 on the bottom 1945F also in a little over 5 hours. Interestingly, both top and bottom pyrometer probes read almost even on Paul's design, but the heat work was much greater on the top.  Probably all these kiln types would be improved by different kiln furniture stacking arrangements. Speed is NOT necessarily desired by potters as both clay and glaze development can get better with a little more time, but the concept of firing clay, glaze, glass, and probably forging, etc is proven with the low resource, low pollution rocket engine technology.

Personally I think Mud's design drawings at the top of this thread with the kiln/forge on the lower part will work well as research continues.  That 8" engine is killer at delivering plenty of heat in a very short time, though the 6" did the job great also.  Having an easy coal cleanout was SUPER helpful, and gave the handy byproduct of biochar (needs inoculation before use)  It is also well working at these temps not to have to work right over or near any chimneys, -- those things give off lots of heat.  

While these kiln experiments were VERY successful in my view, potters and probably permies with a pottery project they care about will require a way to fire more evenly.  I look forward to seeing how this might be achieved using a rocket engine + kiln in the future.

Michael Gaglio wrote:
I dont have much more that's useful, but others may post.  Maybe WL will put together a video.  Stay tuned and hope hope hope.

Thanks, Michael!

This is a fascinating project and I want to follow it as it matures.  One question - I have a good sized deposit of a very fine grained, clean clay that comes out with a bail looking like commercial slip.  It fires at a lower temperature than this is reaching.  How would one be able to control the burn to modify temps for various materials as some will turn into a useless puddle (although probably purer) if subjected to full heat?  I would think that calibration of a unit by using cones internally and then getting the temperature of an outside surface to create a table might be possible.  Any other thoughts on how to keep an eye on the internal temps?

Richard Henry wrote:This is a fascinating project and I want to follow it as it matures.  One question - I have a good sized deposit of a very fine grained, clean clay that comes out with a bail looking like commercial slip.  It fires at a lower temperature than this is reaching.  How would one be able to control the burn to modify temps for various materials as some will turn into a useless puddle (although probably purer) if subjected to full heat?  I would think that calibration of a unit by using cones internally and then getting the temperature of an outside surface to create a table might be possible.  Any other thoughts on how to keep an eye on the internal temps?

You can just put your clay into a rocket kiln, choose cones that match the ideal temp for your clay, place them inside the kiln next to your clay, and stop the firing at the temp correct for your clay. This is what we did.  To find out the correct temp for Wheaton lab clay, we did make test bars that we overfired some of them just to make sure. We got lava at higher temps.  So the cones and clay are both inside and one has to peek through spy holes in the kiln to see if cones are bending.  

These tempatures are amazing.
I'm excited by the hope that a rocket kiln could produce fire brick.
The work of Jon and Flip Anderson focused on this kind of bootstrapping, as they used un fired earthen rocket stoves to fire other earthen rocket stoves, achieving a better product for the next iteration.


Lisa, is making firebricks in these kilns a realistic prospect or wishful thinking on my part?

Fox James wrote:That is an interesting project but there seems to be a lot of exposed  ceramic fibre, are you concerned  about any heath issues as breathing in super heated ceramic fibers is said to be very dangerous?

The fiber you see is almost certainly biologically inert.
It is pretty standard at this point, other ceramic fiber insulations are cheaper but explicitly dangerous.

There are some who have said that  biological safe ceramic fibers are rendered dangerous by direct exposure to the heat and gasses inside a rocket stove or heater.
That conclusion doesn't seem to be widely accepted.
If it is true many of the most common builds might be spewing dangerous fibers.
That would be a real blow to progress in rocket combustion devices.
Like emissions,  this is something that should be tested to know for sure.

William Bronson wrote:These tempatures are amazing.
I'm excited by the hope that a rocket kiln could produce fire brick.
The work of Jon and Flip Anderson focused on this kind of bootstrapping, as they used un fired earthen rocket stoves to fire other earthen rocket stoves, achieving a better product for the next iteration.


Lisa, is making firebricks in these kilns a realistic prospect or wishful thinking on my part?

Yes no reason why not.  You might have to fire pretty slowly in the beginning, think about not having water boil at 212F inside your firing brick.  That said, a quick search brought up all sorts of DIY firebrick recipes. Bricks are sort of thick, so long drying +slow firing is key. Long ago when I volunteered at the San Antonio missions as potter in residence, I was able to access some antiquities unearthed around there, including a spanish mission brick.  It was thinner than usual bricks, probably because of drying time and the vagaries of firing lots of bricks right there on site.  Have you seen how they stack up house bricks for firing in Mexico?  They are all criss crossed with tunnels of air between for airflow.  Try something like that maybe.

William Bronson wrote:

Fox James wrote:That is an interesting project but there seems to be a lot of exposed  ceramic fibre, are you concerned  about any heath issues as breathing in super heated ceramic fibers is said to be very dangerous?

The fiber you see is almost certainly biologically inert.
It is pretty standard at this point, other ceramic fiber insulations are cheaper but explicitly dangerous.

There are some who have said that  biological safe ceramic fibers are rendered dangerous by direct exposure to the heat and gasses inside a rocket stove or heater.
That conclusion doesn't seem to be widely accepted.
If it is true many of the most common builds might be spewing dangerous fibers.
That would be a real blow to progress in rocket combustion devices.
Like emissions,  this is something that should be tested to know for sure.

Ceramic blanket (the older Kaowool) was considered dangerous when it was handled/moved because the fibrous dust could get in the lungs and cause long term probs.  I just re-read the MSDS for superwool that WL is using, and it encouraged not getting on skin or in lungs ("wear appropriate safety equipment"), but states that rats exposed to it for years never developed health problems.  I think in general best to avoid touching it which breaks its fibers.  Heat applied to it is no issue, I still cling to my old habit--best not to touch it and crinkle it, etc.  I am glad to know there is safer ceramic blanket.

Thekla McDaniels wrote:I can grasp the kiln-forge- canning pot gets more heat if it is “after” or above the riser, but I am not understanding what creates the turbulence (that I always thought was integral) if the rising gasses don’t hit the top of the barrel, and the rapid cooling (from exposure to cool barrel sides) draws more air in, fanning the flames and sustaining the controlled continuous explosion.  Can anyone help me out?

Combustion should  be completed before the gasses exit the riser.
Usually it is recommended that whatever you want to heat sit right at that point, in order to avoid sapping
J tubes are built with square corners in order to create turbulence.
Many also include a projection inside the burn tunnel that does the same.

Lisa Orr wrote:

William Bronson wrote:

Fox James wrote:That is an interesting project but there seems to be a lot of exposed  ceramic fibre, are you concerned  about any heath issues as breathing in super heated ceramic fibers is said to be very dangerous?

The fiber you see is almost certainly biologically inert.
It is pretty standard at this point, other ceramic fiber insulations are cheaper but explicitly dangerous.

There are some who have said that  biological safe ceramic fibers are rendered dangerous by direct exposure to the heat and gasses inside a rocket stove or heater.
That conclusion doesn't seem to be widely accepted.
If it is true many of the most common builds might be spewing dangerous fibers.
That would be a real blow to progress in rocket combustion devices.
Like emissions,  this is something that should be tested to know for sure.

Ceramic blanket (the older Kaowool) was considered dangerous when it was handled/moved because the fibrous dust could get in the lungs and cause long term probs.  I just re-read the MSDS for superwool that WL is using, and it encouraged not getting on skin or in lungs ("wear appropriate safety equipment"), but states that rats exposed to it for years never developed health problems.  I think in general best to avoid touching it which breaks its fibers.  Heat applied to it is no issue, I still cling to my old habit--best not to touch it and crinkle it, etc.  I am glad to know there is safer ceramic blanket.

Well there seems to be scientific evidence that suggest otherwise, I have been working with ceramic fibre for many years as I build wood fired ovens for a living.
I have always been reasonably   careful but it appears that when the fibers are exposed to temperatures above a certain level, the structure changes making them potentially very dangerous and that is an issue with rocket stoves far more than pizza ovens.

You can find discussions with linked evidence  on Donkey pro board forum as well as other forums.

Some of the more recent ceramic fibre products  are said to be ‘body soluble’ meaning any  fibers that enter the body can dissolve but it appears than when super heated the fibers take on a different chemistry and can sit in the lungs or other organs for years waiting to cause issues in later life!
To be clear I have no idea if any of that is really true but…. I would advise folk to read the evidence if they are at all concerned.
Personally I will continue to use ceramic fibre where the product is completely enclosed in lower temp zones, but not where it is exposed to direct flame path.

Lisa Orr wrote:

William Bronson wrote:These tempatures are amazing.
I'm excited by the hope that a rocket kiln could produce fire brick.
The work of Jon and Flip Anderson focused on this kind of bootstrapping, as they used un fired earthen rocket stoves to fire other earthen rocket stoves, achieving a better product for the next iteration.


Lisa, is making firebricks in these kilns a realistic prospect or wishful thinking on my part?

Yes no reason why not.  You might have to fire pretty slowly in the beginning, think about not having water boil at 212F inside your firing brick.  That said, a quick search brought up all sorts of DIY firebrick recipes. Bricks are sort of thick, so long drying +slow firing is key. Long ago when I volunteered at the San Antonio missions as potter in residence, I was able to access some antiquities unearthed around there, including a spanish mission brick.  It was thinner than usual bricks, probably because of drying time and the vagaries of firing lots of bricks right there on site.  Have you seen how they stack up house bricks for firing in Mexico?  They are all criss crossed with tunnels of air between for airflow.  Try something like that maybe.

This process might improve using something I found in fire testing of non-metallic concrete beams vs steel reinforced beams and steel beams.  The non-metallic reinforced concrete did not spall (lose small chunks from the surface) as much as the steel reinforced concrete.  The investigator opined that the non-metallic fibers, being plastic might have melted on the surface and left inadvertent relief passages for steam.  That might provide a way to improve efficiency of build.  Add small particles of waste plastic (or better yet, reinforcing materials) to the fire brick to be fired.  Letting the steam escape during firing run up would protect from product failures and reduce potential explosions due to pressure build up.  In fact, use of moderate chopped straw might provide a similar efficacy.  As the outer straw carbonizes, it would allow steam relief but would have increased mechanical strength of the brick at least until post-firing.  BTW, both test types of concrete beams exceeded steel beams for fire resistance before failure to support.

I am giddy with excitement. Like over the moon. I have been researching for awhile to try an find an alternative to a gas kiln and this is the first realistic possibility. I figured there had to be a way to fire a kiln with a rocket engine. I would happily buy plans for this! And the bonus of a forge and crucible? This is my dream thread.

Lisa Orr and I are meeting in Ohio the first week of February 2023 to build our demo rocket kiln for the Nceca Ceramics Conference rocket kiln firing demo at Queen City Clay in Cincinnati Ohio in March 2023.  Anyone want to come play?

Chris McClellan wrote:Lisa Orr and I are meeting in Ohio the first week of February 2023 to build our demo rocket kiln for the Nceca Ceramics Conference rocket kiln firing demo at Queen City Clay in Cincinnati Ohio in March 2023.  Anyone want to come play?

I do I do!  

Chris McClellan wrote:Lisa Orr and I are meeting in Ohio the first week of February 2023 to build our demo rocket kiln for the Nceca Ceramics Conference rocket kiln firing demo at Queen City Clay in Cincinnati Ohio in March 2023.  Anyone want to come play?

Thanks for the invite. See you (and Lisa)  there!

Chris McClellan wrote:Lisa Orr and I are meeting in Ohio the first week of February 2023 to build our demo rocket kiln for the Nceca Ceramics Conference rocket kiln firing demo at Queen City Clay in Cincinnati Ohio in March 2023.  Anyone want to come play?

Aw, man. If it were at Lisa's place I'd be there!!
Maybe another time...

Chris McClellan wrote:Lisa Orr and I are meeting in Ohio the first week of February 2023 to build our demo rocket kiln for the Nceca Ceramics Conference rocket kiln firing demo at Queen City Clay in Cincinnati Ohio in March 2023.  Anyone want to come play?

I would absolutely come if I lived closer. What an awesome addition to NCECA. I can't wait to see the results!

Here's a new podcast that paul just released where he talks about the Permaculture Technology Jamboree and lots of other stuff: https://permies.com/wiki/215113/Podcast-Office-Cleanup-Updates-Part

Hi thank you for sharing all this information! Very interested in trying to build a j-tube rocket kiln. We are in baby stages and have a few questions regarding the dimensions. Please see drawing. Based on the videos the inside dimension of the tube is 8” but does the length of the “flu” between the firebox and the kiln / chimney matter?  Thank you!