hotplot Posted November 26, 2020 Share Posted November 26, 2020 I recently built my first "proper" forge and thought I'd show you all what I'd done. The design is definitely not new, but I haven't seen many other people using it - which is a shame, because it works quite well. Hopefully this post inspires some other people to try it out I shamelessly copied the idea from Eric Fleming's web page The basic idea is that I have a refractory table top, with a ribbon burner sticking upwards, and can sit any size or shape shell over the burner as required by the project I'm working on. Here's a picture: This design has some nice practical advantages: No danger from chimney effect (in fact, the chimney effect acts to keep the burner cool in this design since the burner is below the forge) It's fully self-contained and portable, which makes it very quick to set up and shut down It's trivial to change the forge size when necessary - just sit a different shell on top. It has much less thermal mass to heat than a brick pile forge, and is much more reconfigurable than a propane bottle forge The burner is a ribbon burner inspired by the great posts on this forum from Frosty and others. It uses a custom 3D printed inspirator which I'll put some pictures of below. I did not expect to be able to use the plastic inspirator for anything beyond prototyping, since PETG starts to lose strength at around 80ºC and the forge is operating at >1100ºC. In practice the burner stays cool during operation and the plastic inspirator has been working without issue for a few months now. The inspirator was designed using information from the paper Design of Atmospheric Gas Burners, which was linked in another 3D printed inspirator thread somewhere on this forum. It seems to be pretty efficient at inducing air. As you can see in the photo, I have to choke it off to almost nothing to get a slightly reducing flame. The gas nozzle uses a 1.0 mm 3D printer nozzle (which is substantially smaller than a 0.9 mm MIG tip... Go figure) and at 40 kPa (about 4.3 PSI) the forge sits comfortably at 1150ºC (2100ºF). I've pushed it over 1200ºC but haven't needed to keep it that hot for any extended period yet. Running cost is NZ$2.30/hr, or about US$1.60/hr at todays exchange rate. Honestly, I'm pretty stoked with how well it works. It's cheap to run, and it gets *hot*. Of course, I made plenty of mistakes during this project and most of them were immediately obvious in hindsight. The two main ones are: The tabletop should really be thicker, and have more insulation. It currently has 25 mm of kaowool under 25 mm of refractory, but when the refractory eventually fails and needs to be replaced I'll put some taller sides on and 50-75 mm of insulation under the refractory. When I cast the tabletop, I calculated that I would need 22 kg of refractory based on the numbers in the datasheet and the volume of the tabletop. It turns out I actually needed closer to 26-27 kg - which was a bit awkward, since I only had the one 25 kg bag... It isn't a big deal, but it means the surface of the table isn't as gorgeous and smooth as it could be. And a few other improvements I just haven't got around to doing yet: Making the forge shell thicker and more robust. Since the shell in the photos in the one I'll probably use almost all the time, I'll make a more robust version with thicker kaowool inside a stainless shell and a decent refractory lining. Making insulated doors, rather than the heavy heat-sinking bricks I currently use Lining the floor and shell with an IR re-radiator Building an even better ribbon burner Adding a frame to secure the LPG bottle so that it doesn't fall off when I take the forge off-roading Maybe... Doing some actual blacksmithing....???? I can post more photos or info if there's anything else you want to see. Ah, that's unfortunate. And I can't edit the post to remove the link text? I'll attach them here instead. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted November 26, 2020 Share Posted November 26, 2020 The burner is interesting, but a table top forge, with various top shells and a bottom mounted up facing burner was built and featured in Gas Forges for Forges, Furnaces, and Kilns sixteen years ago; that one could mount various sized Mikey burners below the table top. But the use of a ribbon burner is novel. There are no new ideas anymore; just new takes on old ideas, which is fine by me Quote Link to comment Share on other sites More sharing options...
hotplot Posted November 26, 2020 Author Share Posted November 26, 2020 Yeah, it certainly isn't a new idea. It's just an interesting alternative to building a more or less fixed-size forge in an old propane tank, which currently seems to be the standard approach for new blacksmiths who want a gas forge. There's nothing wrong with a propane tank forge, it just doesn't suit my needs very well and I didn't want to commit to a single forge size when I want to be able to try all sorts of different projects! It was nice to see the occasional alternative design like Eric Fleming's when I was searching for ideas, and I'm hoping this post can serve a similar purpose for others who want something other than the standard fixed-size or brick pile forge. Quote Link to comment Share on other sites More sharing options...
tinkertim Posted November 26, 2020 Share Posted November 26, 2020 Interesting 3D printed inspirator. How well did the pipe thread at the end of the mixing tube work out? I thought 3D print threads are always a weak spot unless they are enormous threads. Also gut-feel is that the choke should be fitted the opposite way round, to guide the flow of air into the neck of the inspirator, rather than acting as an edge that might cause turbulence behind the jet. I guess a problem could be that you might not be able to slide the choke all the way shut, without it coming off the jet pipe, as the design currently stands. Nice idea though. I'm planning on printing an inspirator for a hand-held 1/2" burner for occasional DIY use, where I cannot justify my 3/4" heat monster. Good luck with the tinkering. Tink! Quote Link to comment Share on other sites More sharing options...
Frosty Posted November 26, 2020 Share Posted November 26, 2020 Nice write up Hotplot. This set up is something I've wanted to do for some time though not necessarily an updraft burner. One of the guys in our club has an updraft ribbon burner and it works nicely at all temp ranges. I can't go with your gut feeling Tink. I don't think the conical profile of the choke plate has much significance, it'd be nice to try a few different ones and see though. Regardless I believe the combustion air entering on the perimeter without being "guided" towards the jet is beneficial in two ways. First the longer it takes the air to reach the gas jet itself the lower the pressure becomes and better the induction / inspiration. Secondly the farther the air travels the stronger the vortex, which increases mixing distance/time and lowers pressure further. The mixing tube looks long to me but it's tapered full length so is probably a beneficial feature. One thing I'd love to see in this type forge would be a ribbon burner that can be aligned at different angles from the vertical up. In one of my brick pile configurations I laid the ribbon on it's side on the forge floor so the flame was parallel with and about 1" above the floor. I only used it that way for a couple hours at a demo so it may have been as bad an alignment as I think it should've been. However it performed darned well I just haven't gotten around to playing with it further. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
hotplot Posted November 27, 2020 Author Share Posted November 27, 2020 On 11/27/2020 at 2:44 AM, tinkertim said: How well did the pipe thread at the end of the mixing tube work out? I thought 3D print threads are always a weak spot unless they are enormous threads. Seems to be holding up fine. The first version was printed in PLA and that was definitely weaker - I could hear little creaking/cracking sounds whenever I threaded the inspirator into the plenum, and eventually the last turn of the threaded section sheared off. The current version is printed in PETG and hasn't shown any sign of failing. I printed using three perimeters which means the section is solid right through for most of the inspirators length. For a handheld version I would be more concerned about the two legs holding the jet in place. They won't break off, but they flex easily (thanks again to the PETG) and you would need more reinforcement to keep the jet aligned correctly with the centre of the throat. Using three legs rather than two would definitely help on that front, but I think flex would still be an issue. How hot do you think a hand-held burner would get? The ribbon burner has the advantage that not much heat is actually conducted back up towards the plenum, but I suspect a steel burner would get a lot hotter. Of course you could always cast the inspirator in bronze or maybe aluminium, but that's a lot more work than just 3D printing it... 21 hours ago, Frosty said: The mixing tube looks long to me but it's tapered full length so is probably a beneficial feature. Yeah, I would like it to be shorter. I did try a shorter version, but the flame became unstable once the burner was up to temperature. It looked a bit like the air flow in the plenum was turbulent and causing the flames to leap around chaotically. I'd like to experiment more with this though. Not sure why the burner temperature should have significantly affected airflow from the inspirator into the plenum so I have almost certainly misunderstood what was actually happening. I don't think forge back pressure would have changed. Sam Quote Link to comment Share on other sites More sharing options...
tinkertim Posted November 28, 2020 Share Posted November 28, 2020 For a hand-held 1/2" burner, I was thinking of printing a design based on some of Another Frankenburner's (AFB's) spiral-vaned designs. With the 3 vanes it will be more rigid, and I can build a small handle into it. As with his designs, I will just print the spiral inducer part initially in PLA, I'll try and get some stainless tubing for the mixing tube, as it conducts heat less that the maleable iron pipe, so for occasional use I might not need to cast the inducer in Aluminium. As for the flare, for occasional use I would probably get away with a stepped stainless sleeve, but if it wasn't up to the heat, then as AFB has done, I might cast a refactory flare. It is all for Tinkering sake, and just a bit of fun. I could buy a basic LPG burner head from a plumbing suppliers for less time and money, but then it wouldn't be tinkering. Tink! Quote Link to comment Share on other sites More sharing options...
ede Posted December 27, 2020 Share Posted December 27, 2020 Where did the photos go? Quote Link to comment Share on other sites More sharing options...
MT Hammer Posted December 30, 2020 Share Posted December 30, 2020 Ya, I was going to ask the same question — I doubted I was the only one who couldn’t see any images. I see the placeholders, and filenames only. I’m using an iPad. Is that an issue, or is it a server problem with IFI? Quote Link to comment Share on other sites More sharing options...
Irondragon Forge ClayWorks Posted December 30, 2020 Share Posted December 30, 2020 No not the ipad, I think the OP must have removed them from where they were saved. Quote Link to comment Share on other sites More sharing options...
hotplot Posted December 30, 2020 Author Share Posted December 30, 2020 Yeah they seem to have vanished. I uploaded them to the forum so they should have been stored on the IFI forum server. I'll add them again when I'm back home. Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted December 30, 2020 Share Posted December 30, 2020 When you get around to uploading them, load them in this thread and I will move them to the intro post to keep things easy to follow Quote Link to comment Share on other sites More sharing options...
hotplot Posted January 23, 2021 Author Share Posted January 23, 2021 Well it took a bit longer than expected, but I'm finally back with the photos... Here's another photo showing the burner mounted in the table top Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted January 23, 2021 Share Posted January 23, 2021 It looks very hot. Would you like to go into your choice of ceramic shell for your first foge top? Forge Quote Link to comment Share on other sites More sharing options...
hotplot Posted January 23, 2021 Author Share Posted January 23, 2021 Hi Mikey It probably isn't as hot as the camera makes it look. I think it was about 1175 C / 2150 F in that photo. I usually keep it around 850-900 C for forging. The shell is just a simple kaowool shell with a thin refractory liner. This time I rigidised the kaowool before applying refractory, but I probably won't do that again. The refractory doesn't seem to soak into and bond with the kaowool as effectively once it has been rigidised. I'll make another at some point. Fortunately with this design there is relatively little effort required to make each shell Sam Quote Link to comment Share on other sites More sharing options...
tinkertim Posted January 23, 2021 Share Posted January 23, 2021 Hi Hotplot, Did you remember to "butter" (that is dampen down with a spray of water) the rigidised blanket before you applied the refractory? If not, then the dry blanket will suck out too much moisture from the refractory, and prevent it from binding properly to the blanket. Tink! Quote Link to comment Share on other sites More sharing options...
hotplot Posted January 24, 2021 Author Share Posted January 24, 2021 Hi Tim I did butter it with water, and I've had good results doing that in the past. In this case the kaowool seemed to be slightly hydrophobic after rigidising, and that probably stopped the refractory from soaking into the surface enough to bond. I used water and West Systems 406 Colloidal Silica as the rigidiser. Sam Quote Link to comment Share on other sites More sharing options...
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