Gas Forge Design

[Bladebaka]

Hello all,

I've been wanting to get into blacksmithing since Man At Arms made Leona's Zenith Blade in 2013. (I took a detour into metal casting first, then I got into welding...) 

I'm currently halfway through my Welding Engineering degree and have a work-study at my tech schools' machining and welding lab, and that comes with access to all the great toys there (5-axis CNC mills, CNC plasma table, like 80 welding rigs, etc)

Anyhow. I'm trying to finalize my forge plan, but everyone and their anvil have different opinions on everything from size to whether or not Kaowool is better than firebricks, so suggestions and such would be much appreciated.

 I'd like to use a single burner (probably Frosty's Tee) and I'm thinking internal dimensions of 4"W 3"H 10"L would be more than enough for my first forge. I'm currently leaning towards the Kaowool (1", 24" x 12") with a halfsize firebrick from Tractor Supply as a platform for the work to sit on while its heating.  I'm not sure whether or not there needs to be a vent in the design as half of the ones I've seen have vents, but the other half don't. I'm planning on having a "porch" on the front to set a firebrick as a door and have a place to maneuver the metal going in and coming out:

Haven't decided on the rear yet, but I have an extra couple inches lengthwise to play with. I feel like the 4x3x10 chamber is sufficiently large for a starting forge, and should also help keep the propane costs down for me as well as ensure one burner can heat it thoroughly.

My plan at the moment is to construct the shell out of either 11 gauge or 1/8 steel, cut either using the CNC plasma table or a metal shear. I could even fabricate a door, which could be better than a brick.

Questions:

Burner placement? Is top center going to ensure proper heat and air circulation? Should I put it on a side?

What should I do about the rear face? Leave it open? seal it entirely? drill a couple flow holes?

Brick vs. fab door?

Thoughts and criticisms welcome.

 

--CK

[ThomasPowers]

All naturally aspirated forges must have someway for exhaust to escape, generally it's through the same opening that you put the work in. Just a given---unless you can pour a gallon of beer in a pint glass at one time and not have any overflow!

As for the back end.  Take a 3' length of steel and place it in your forge so the middle section gets hot.  Rather hard to do so without some sort of a pass through in the back of the forge!  (The back door on my forge only gets opened a couple of times a year---but when it's needed it's *NEEDED*!

Top Mount Burner: I don't like top mount burners; other people do, watch out for chimney effects when you shut it down and beware of re-running exhaust through the burner too.

[Latticino]

Fabricated steel doors will get hot, warp and scale away in time. If you do use one design for that.  Personally my favorite doors have a high temperature castable hot face that is held in place by a thick steel frame with some kind of operating system to be able to be opened with a foot pedal, or one hand at worst. Of course I still haven't made one for my current forge...

Make sure you leave space under your half fire brick for insulation. 

I prefer 2"of blanket for better insulation. 

[Bladebaka]

Thomas, with the Tee burner design, would the chimney effect still happen?

Latticino, I'd planned for the 1" blanket to go all the way around with the half brick sitting on top. With a forge this small, is the 2" necessary?

[ThomasPowers]

Does it have a tube going straight up that then connects to the "outside"?  Why wouldn't it act as a chimney?  The "Tee"?---If you search on images of chimney pots you can find a number of them with quite a similar T termination which doesn't seem to affect their being part of a chimney.

Hot air rises!

 

[Bladebaka]

Oh, I thought you were talking about carbon monoxide. I'm not really sure what effect the Stack Effect will have on a forge burner. I suppose a horizontal burner wouldn't be too hard.

[Frosty]

Welcome aboard, glad to have you.

I've been accused of being too blunt recently and maybe it's true. But you're making a pretty typical mistake most folk make breaking into a new field make. You're trying to design a specialized piece of equipment you don't understand or know how to use. I apologize if that's too direct but that's the beginning of the list of things wrong with your design and I don't want to be taken for ripping into you for listing them.

Instead I'd like to recommend you do some reading in the gas forge section of Iforge and the more current forge thread "Forges 101". There is so much contradictory how to pages, podcasts, blogs, videos, etc. online it's impossible to no be confused until you have a basic grounding in the subject and getting a handle on the jargon allows asking good questions and understanding the answers without having to explain every term. 

Frosty The Lucky.

[Mikey98118]

Please listen to Frosty. You don't even know what the questions are yet.

[WayneCoeArtistBlacksmith]

Check out the Build a Gas Forge attachment for how I like to build a good, tuff, efficient, long lasting forge.

You can use a Frosty T burner on it very well.

Let me know how I can help you..

 

Wayne

[Frosty]

Please pick a set of plans, the ones on Wayne's site are all good solid designs, efficient and tough. Pick ONE set of plans and follow just those plans. Mixing and matching is a B-A-D idea when you're just getting started.

Those of us who experiment with forges have sometimes decades of experience AND lots of failed experiments. I have one very bad design broken up into pieces in the shop now and my most recent new forge is going to be retired and replaced as soon as I finish with another project It "works" but not satisfactorily. What's the problem with it? It's too BIG.

Ayup, Been making these things for more than 25 years and still make them too large. 

I'm going to tell you something I rarely tell ANYBODY, probably the most basic technique of the blacksmith's craft. It's not a secret but we don't talk about it directly very often. The technique is mastery of "Failure Analysis." For example Try something. Observe the results. Decide what's not QUITE RIGHT. Do it again slightly differently. Observe the results. Repeat till it's good enough.

Oh SHOOT! I let the other basic fact of the blacksmith's craft slip. Perfection isn't in human's reach, we have to settle for good enough. We can make things better but not perfect. Human perfection isn't in our cards.

A little knowledge and a LOT of practice is how you earn the craft. Stick with us buddy it's worth the effort.

Frosty The Lucky.

[ThomasPowers]

Blacksmithing is an iterative process

[Bladebaka]

@Frosty This is why I posted here! I've been reading a lot of the Forges 101 thread, but grammar and a lack of illustrations makes it difficult for me to follow. Most of the "tutorials" I've seen use cut up gas cylinders, and after working as a gas refill clerk for a time, (and watching footage of welders repairing gas cylinders) that seems like the the most dangerous thing after getting an up close and personal tour of Chernobyl.

As for perfection, I'm a welder-in-training! I screw up all the xxxx time, and I've received harsher brusqueness from much worse instructors. I came here to ask for help because I don't know what I'm doing, was getting conflicting ideas from all over, and decided to ask someone smarter about it all.

Looking through the YouTubes again, I've discovered this video by Joe the Builder, showcasing his forge build. I think it's too large for me by far (and has one too many burners), but it seems well within my abilities to fabricate.

Because I have access to all the neat toys in my engineering lab (as well as an awesome professor/boss who likes me) I figured I'd fab up the shell and such because it would be cheaper for me (squared designs are more visually appealing to me as well as having easy-to-work-on flat surfaces). I'm well aware that cheaper is not always better, and if I need to put off my intro to blacksmithing for a few months to save up money a bit longer, I'll bite the bullet and do so.

I'm still working through the Forges 101 thread and the PDF on Waynes' site, but it's slow going with run-on sentences and low amount of visual aids. Thanks for the advice and smack down!

 

--CK

Edited July 3, 2017 by Mod34
Edited for language

[Frosty]

Did I really come across as a smack down? That's not how it was intended.

Here's a smack down though. WATCH YOUR LANGUAGE!  You'll get a couple free passes with Admin editing but if you keep it up they'll put you on the "Moderated" list and nothing ticks off the guys keeping this site operating this smoothly like having to read somebody's posts and editing them for language. See? I give smack downs in bolded caps.  

Joe the Builder is a great example of good video production and poor forge design. If you've looked at the illustrated T burner design I posted you can see how senselessly complicated he made connecting the propane to the jet. 

I'm not going to list the mistakes in that forge. Making the shell is okay though he cuts the sheet the hard way. I have an old sacrificial skill saw I put an abrasive metal cutting blade in. I would've made those cuts faster than I could measure and mark them. Do you have a square shear and box and pan brake at the metal lab? Remember when you make the shell you have to leave room for a liner 2 1/2" thick. 2" of Kaowool and 1/2" hard refractory flame face. Overall the shell's ID will be 5" greater than the chamber size.

Don't use a propane cylinder it you're not comfortable cutting on one. Use a helium or freon cylinder, party stores and HVAC service companies have to throw them away, they're not refillable. 

Build a rectangular shell if you wish my forges are usually rectangular. The only draw back is getting the Kaowool to stay on the roof without sagging when hot. I run screws in through the top of the shell part way through the Kaowool.

As a side note, when I say "Kaowool" I'm NOT suggesting you use Kaowool it's just easier for me to write on autopilot. Any comparable ceramic wool refractory blanket is just fine. You can look up the specs online once you know what's available. What I get for free is 1" 8lb., rated for 2300f and occasionally they have some rated to 2,600f. in the scrap bin.

How many and what size burners you use depends on the interior volume and shape of your forge. One well tuned 3/4" NA (Naturally Aspirated) burner is good to bring about 300-350 cu/in roughly mono dimensional chamber to welding temperature.

 Mono dimensional means all 3 dimensions are the same, a cube or sphere. Long and narrow needs more but smaller burners to make an even temperature. 

It doesn't need to be perfectly mono dimensional a 6" x 6" x 10" rectangle will heat pretty evenly, more so if you orient the burners at an angle to induce a vortex. Make the chamber 6" x 6" x 12" and you're pushing the upper limits of the expected temperature range but it's not going to heat evenly. So this would call for more burners of equivalent output as one 3/4" burner.

In the instructions I lay outputs out. One 1/2" burner has an output 1/2 that of one 3/4" burner. If you install two 1/2" Ts in a long forge the heat will even out. 

A good trick for down the road would be to make the shell so you can take it apart to a degree. Removable top maybe or bottom. Leaving 3 sides connected helps keep it's shape when you're working on it.

Frosty The Lucky.

[ThomasPowers]

Tis a sad thing indeed that some of the best made youtube videos have the most bogus information in them.  I guess the folks that make them are experts in video production and idjits in forge building/knife smithing or general blacksmithing.  And they get talked up by people who don't know any better!

I have a set of videos on power hammer techniques that are almost painful to watch but the guy demonstrating *is*  a world renowned expert in using powerhammers and I learn more and more every time I watch them.

[Bladebaka]

Sorry about the language! The smackdown comment was in jest; I have a fairly thick skin nowadays, so lay it down as you see fit.

As for tools, we have a manual brake, a metalworker (punch, shear, notcher, and angle cutter AIO but only on metal less than 1" thick) a large metal shear (IIRC it has a 10ft blade, with adjustable rake and depth aperture, good for paper to 1/2" plate), a miter bandsaw, a damaged bandsaw (some of these welders can't or won't read labels and instructions T_T) a portaban, disc grinders, wheel grinders, 7" and 4" hand grinders... And that's just the welding fab area. On the machining side, there's tons of manual and CNC lathes, several types of drill presses, a heat treating oven, some CNC mills... There's even an ASO.

how does the ceramic board stuff hold up? I'm guessing since you didn't suggest it, that the rockwool is better or cheaper, or both? As for disassembly, that's a good idea, should be a breeze to add some bolt points to the shell; my only concern there is the rockwool not holding its' shape properly.

I'm assuming your 6x6x10 is just an example; that sounds pretty big! I don't intend to be messing around with anything that needs space that big for quite some time. I do see your point with two burners providing a more even heat; I'd imagine that the burner angles would be opposites, slightly towards (but not directly) opposite corners?

An evenly-sized shell of 10x10x10 with a rear door would be a 5x5x10 interior. Two 1/2" burners with a 20* angle on each, one facing towards front left, the other towards rear right.

. . . In my head this is starting to look a lot like Sams' forge design, haha.

Still reading through the Forges 101. Vertical and Clamshell sound like more trouble than they're worth.

 

--CK

[Bladebaka]

I'm wondering if the HVAC department here at my school has scrap ceramic blanket pieces. I'll have to check on Wednesday when everyone comes back.

[Frosty]

Would those be Clifton's videos Thomas? I've watched some that were as poor production standards as I've ever seen and great info but I don't recall who's. 

CK: Yeah, I used the 6x6x10 as a 360 cu/in even numbered example.

Okay, gloves off then, don't make me get out the cyber soap. 

If the instructor lets you build your own projects you've got it made. Come up with the internal dimensions you'd like, figure the allowances for the liners and ask the instructor about efficient cut and bend patterns.

I've considered using insulating ceramic board but I can't buy less than a full sheet. You bet, talk to the guys in building maintenance about blanket rems. Heck, they may even use ceramic board refractory, that'd be sweet.

Yeah, read what I said about Sam's idea, it won't work for you either. Not even the Senate or Congress can disobey the laws of physics. No matter what legislation they pass.

Vertical and clamshell are worth the trouble IF you need that particular function.

Frosty The Lucky.