Optimal forge design/pattern from air compressor tank?

[JG Custom Metal Works]

All my supplies and parts are in. I thought I was ready to get after it tonight, but said to myself, “maybe I should check online and see how other makers are cutting their compressor tanks up.” Of course now I’m doubting my design. I had planned on just cutting the whole front part of the tank off, making a 5”-6” hole in the front, and reattach it to the forge body with the use of a hinge on the side. I’m reading a few places that that might not be the best way to go about it. What do you guys think?

Oh and I was just planning on doing a simple 3”-4” rear port on the back. I still think that will be okay, but am open to suggestions.

A little more info on what I’ll be using. The air compressor tank I have is 10” diameter and is about 18” long. I have 1” Kaowool and was planning to put two layers on the inside and slather it with Satanite. I might layer the floor with some flux proofing. It will be a blown forge. I’m using a blown burner kit from High Temperature Tools.

Where would be the best location to but the burner?

What would be the best way to make the front of the forge with what I have? Also, any other recommendations would be greatly appreciated.

 

[Stacy E. Apelt - Bladesmith]

16" length is good.
Hinged from design is also OK.
Your ports sound fine. Use firebricks to make them smaller if needed. Welding a 3-4" shelf outside the ports makes placing firebricks and resting tongs easier, BTW.

10-12" diameter ( which is it?) with two layers of 1" wool and a good layer of satanite will give you a chamber of 5" to 7". That is a pretty large chamber. Fine if doing larger work and damascus, but big for a general blade forge. You might consider putting in another layer of wool. Take 8 feet of wool and roll it up. Slip inside the and unroll until snug to the inside. Put the end "bump" at the bottom ( where you will build up the floor with bubble alumina or such). If that is too small a chamber, take it out and trim off 1 foot and try again. Once you get the final length, trim the roll to the chamber length. Use the extra from cutting to 16"for doing the ends.

A trick for getting the wool to stay in place is to put a piece of 1/4" mesh hardware cloth over it. This makes the wool more rigid and allows better strength and bonding to the refractory coating. Don't worry about it being galvanized, it will be encapsulated by the satanite. On the door ends, you can tack weld it to the shell to hold it securely in place before putting on the satanite.

 

[JG Custom Metal Works]

Thanks a TON for the info Stacey. I just emailed you lol.

The forge body is 18” long and 10” diameter. So that would leave me an inside diameter a little smaller than 6” after all the satanite and bubble Alumina floor is on. That’s with two 1” layers of Kaowool that is. Do you think that would be too big? I’m kind of wanting this forge to be a little larger if possible. I have been using an Atlas Mini Forge for years and have kind of been a little constrained with it. 4” is still decent sized though I guess. I will probably do Damascus at some point though. Would you suggest that I go with a third layer, or do you think a 5.5”-6” inside diameter is too big?

The only thing I forgot to ask was about burner placement. Where would you place it?

Lastly, do you think 18” is too long for just the one forced air burner? I’m hoping not as I’d like to keep it the full length if possible. Hopefully that burner will be enough. What do you think? I DID get the 60psi regulator.

Oh and you can disregard the email btw.

Here are some pics of when I’m working with.

 

[weo]

Another suggestion for the kaowool is to (and I'm going to paraphrase Dave Lisch here. Check out http://www.blacksmither.com/ep-113-david-lisch-pilot-forged-fire-story/ he describes how he makes his forges starting at about 27:30 into the interview) first mix up some of your cement as a soupy consistency, soak the kaowool in this mixture before putting it into the forge. Then mix up the rest of the cement into a oatmeal consistency and coat the kaowool to finish the forge.

 

[weo]

do you think 18” is too long for just the one forced air burner?

That should be fine.

 

[weo]

Where would be the best location to but the burner

the ones we use at the NWBA mentoring center (that Dave built) all have the burner in the middle of the forge.

 

[Ken H>]

I'll let Stacy confirm this, but on burner placement the hole should be cut about 1/3 of way back from front (maybe a tad more) at about the 9 o'clock position. The burner should be angled toward rear so the flame would hit around 2/3 of way toward rear at around the 3 o'clock position. This allows the whole forge to heat without having hot spots on the working piece.

Stacy - have I got the above correct?

I built my forge couple yr ago and messed up by putting the burner at mid point and at the 10 o'clock position and pointing direct toward the 5 o'clock position so it hits almost at bottom of forge. I have to be really careful and keep piece at full left side as best as possible to help prevent hotspot. It works, but requires care when forging - especially with San Mai and Damascus.

 

[Stacy E. Apelt - Bladesmith]

I sent JG an email, but though the rest may want the info:

That tank will make a great forge. The burner you have will be fine.

The chamber will be about 15" long and 5" diameter once you install the two layers of wool on the shell and ends... and apply the satanite. I highly recommend putting a floor of bubble alumina or Cast-o-lite in it. If you don't have these I'd be glad to send you a flat rate box full of cast-o-lite 30.

The place for the burner is 20% to 30% back from the front of the chamber ( about 3" back), at a tangent to the top of the chamber walls ( to make the flames swirl around the forge walls), and at a rearward angle of 15° to 20°.

Make the burner port tube go through the shell and come out even with the wool. Gut/grind it in the needed curvature so it is even. When applying the satanite, flare the refractory from the end of the port. The outside of the port tube usually sticks out about 3" past the shell, and has three clamp/alignment bolts (1/4-20).

Hinging the front works fine. When closing it up, mortar it up good with satanite and close/latch the front. Reach through the front port and smooth the excess around the joint. Clean off the outside nd let it all dry.

The front and read port are best as a "D" shape with the flat side down. The bottoms of the "D's" should be level with each other and at the height of the chamber floor once the bubble alumina or cast-o-lite 30 is poured.

A front and read shelf that sticks out 3-4" and level with the port is a good idea. You can place firebricks on them to make the ports different size as needed.

A really good option is to weld two pieces of 1/2" black iron pipe on the sides.
The pipes should be about 2" longer than the forge body ( not counting the shelves). They should be placed down the sides so the top of the pipe is just shy of even with the shelves, ant the end sticking out about 1" past the forge body.
A good way to position the pipes perfectly is to clamp a piece of 1/8" bar under the front and rear shelf, and clamp the pipes to the 1/8" bars. Weld the pipes to the sides of the forge.
Remove the 1/8" temporary bars, slide two 24" long 1/2" steel rods in the pipes, and clamp a 1/4" thick by 1" wide steel bar to the rods, butting it up to the shelf at the front port Weld this bar to the slide rods. This slide will allow you to pull it out and rest long bars of steel, tongs, or handles when doing damascus. When pushed in it makes the shelf an inch larger. If your shelf is thicker than 1/8", use an appropriately thick bar across the rods to make it even with the front shelf.

Once the forge has been lined and dried a five days to a week, fire it slowly. Start with a small flame and run it for just a minute or so. Let it sit for an hour. Repeat with a 3 minute fire on low flame, rest an hour, repeat with a 5 minute fire on low. Let rest overnight. Fire on low for 10 minutes and then turn it up a little at a time until it has run for 30 minutes at full blast. Shut down and let cool overnight. Use satanite to patch up any cracks or chips in the refractory if needed. Once the satanite is cured, you can pour in the Cast-o-lite/bubble alumina floor so ir comes up even to the port. Let it sit for a couple days and cure it with several low firings.

 

[JG Custom Metal Works]

Thanks a ton for the info guys. Especially you Stacy. You’re the man!

In regards to the front of the forge, what do you guys think about having a hinged door? I’m thinking it would be easier to do the main part of the forge, but more of a PITA in general as there’d be more moving parts. I have everything assembled and this is one of the last things I’m trying to decide on.

The other thing I’m trying to decide is where to put the burner. Stacy had mentioned putting it where the existing hole is, but I think it might be too high up. Where do you guys think would be the best place to put the burner?

Lastly, in regards to hooking up the blower. Would it be okay to hook it up directly to the gate valve? I thought about using some JB weld or similar epoxy to attach a piece of threaded 2” pipe to the blower, and then screwing it into the gate valve. Unfortunately the blower isn’t threaded. It does have a little half inch lip though. 2” threaded pipe fits snuggly inside of it, so that was my first idea. What do you guys think?

 

[Stacy E. Apelt - Bladesmith]

"Too High UP" ?? - If the chamber is a circle and the burner enters at a tangent, no place is really higher than another. Most forges have the burner at the top portion.

Yes, attach the blower by whatever method works. Make an adaptor plate that it bolts to or epoxy on a pipe nipple. In many cases, a pipe flange can be drilled and bolted to the blower flange/lip. Using one in PVC will be simpler and cheaper. Seal it with caulk or RTV when bolting it on.

 

[JG Custom Metal Works]

Thanks Stacey.

In regards to the hinged front door. Is that more trouble than it’s worth? Any advice on doing that? I wonder how much material I should have on the door? What I mean is, how far back should I cut? I’m thinking it might be easier to mount a hinge if there was a little bit of material without a curve on it(like the front has). I mean it will still have a curve, in that it’s round, but it will be only on one dimension. Not bowl shaped like the front.

Or should I just forgo the front door all together? I have a couple 12”x12” pieces of insboard to use on the front and back. I guess the main benefit of having a door, would be for easier access to the guts if it needs repaired or replaced. It will also make it easier to install at first. But it might be kind of a pain in the neck to insulate the door...

 

[Stacy E. Apelt - Bladesmith]

Hinging the front is fine. It makes lining things much easier. Cut it about 1.5" back. You can build up insulation and satanite in the door, or just fit insboard in it. Once everything with the chamber is done, mortar up the end of the chamber liner and around the door edges and shut it for good ( until it needs to be opened for relining someday).

That said, Just making the chamber a cylinder and having no ends is a very good option. Stack firebricks or use 1" insboard to make ends any size desired for varying projects. This allows you to change the openings as needed. When doing HT or welding you can close off the back completely, open the front wide open for forging hawks and axes, etc. You will notice more and more smiths doing their forges like this. It also makes lining the forge and repairing the liner super simple.