New Gas Forge - Build out of an old air compressor

[Jaret]

I thought I would post the progress of my forge. It will take awhile as I am building it in phases that I can afford.

I bought an old air compressor yesterday at the scrap yard for $20. In the past 24 hours I have stripped it down and figured out what I want to do.

I do have a question about the propane burners.

See attached pics. The last pic is kind of what I had in mind.

Tank dimensions after doctoring would be about 18" long by 12" in diameter.

2 - 1" propane burners, which can be swapped out to 3/4" burners if needed. Those are the exsisting hole and a new hole i will drill in and weld 2 1" eyelets.

Only the front door will open. I will cut out where the "X" is the reattach the cut off part as the door.

1.5" of kaowool to surround the inside. Will cut a small hatch on the other side to slide steel through if needed.

I want to forge weld. What do ya think? Will this work? Overkill?

Ideas, thoughts, criticism?

Thanks

J.

[Frosty]

Is 12" x 18" the finished inside dimensions? If so properly tuned 1" burners should hit welding heat.

Why only 1.5" of Kaowool? Where are you going to find .5" or 1.5" Kaowool? Why not 2", it'll reduce the volume of your forge some sure but it will push the burner to volume ration over into the sure thing it'll weld range.

Frosty

[WillyP]

Hi, just reading your post here, I thought of a suggestion.



Please realize that I am by NO means an expert, I'm very new at Blackmithing, (like I've been at it 'maybe' 8 weeks). I've just been reading up as much as I can, asking questions where I can, and trying to build what I can!

Here's my $.02 worth.

Why not just cut round holes in each end about 7 or 8 inches in diameter. You can keep the circles that come from that and line them with your Kaowool and use them as "caps" for the ends.


I did this to an old propane cylinder that I used for a forge body. I welded some round rod to the caps as hooks and hangers (on the forge body) out of the same rod, lined the plugs with kaowool by using a couple 2" dia X 1/4" slugs that I got from work. A bolt goes through the slug, the kaowool and outside of the end cap. I realize that eventually I am going to have to replace that 2" slug because they take A LOT of heat, and eventually it will deteriorate. I left lots of extra koawool on the back cap so it seals very well, and the front one I made to sort of fit inside the hole; it does not have to seal tight but it can; which is handy for keeping the heat inside after the burner is off; it's sort of perfect (or as perfect as my limited experience has seen) when you're annealing a piece that you've case hardened.

[Frosty]

Welcome aboard Willy, glad to have you.

A lot of guys do just what you did, some don't. That's the best thing about building your own, you can build what you want. Then after a while you can build something else you want and finally after a few tries get one you actually like. Seriously, every time you build a piece of equipment, tool, etc. and start using it you realize there was something else you wanted on it, something you never use or want somewhere else, etc. etc. It's never ending.

This is my most recent propane forge, less than a year old and I have a change list nearly as long as the original plans. (Plans . . . RIGHT! )

If you'll click "User CP" and edit your profile to show your location it can make a big difference. IFI is represented by members from more than 50 countries and a lot of info is location specific. If local folk know you're around they can invite you to get togethers, tip you to tool deals and offer hands on help.

Frosty

[John B]

Hi WillyP Why do you anneal after you Case Harden? Doesn't that nullify the hardening effect?

[Frosty]

naw, it doesn't make a difference either way. Case hardening is only a surface treatment and usually used on mild or low C steel so annealing doesn't do anything. There isn't any depth to a case hardening to speak of, certainly not enough to benefit from heat treatment.

There are however times you case harden high C steels, usually for abrasion resistance, in those cases further heat treatment may be called for.

Frosty

[bigjohn]

Hey Frosty, what's with all that green stuff on the forge it looks suspiciously similar to paint. I'm pretty sure there is a rule somewhere that has outlawed paint in blacksmith's shops. All tooling and materials should be a uniform rust color. Nice looking setup even with the paint.

[Jaret]

Welcome aboard Willy, glad to have you.

A lot of guys do just what you did, some don't. That's the best thing about building your own, you can build what you want. Then after a while you can build something else you want and finally after a few tries get one you actually like. Seriously, every time you build a piece of equipment, tool, etc. and start using it you realize there was something else you wanted on it, something you never use or want somewhere else, etc. etc. It's never ending.

This is my most recent propane forge, less than a year old and I have a change list nearly as long as the original plans. (Plans . . . RIGHT! )

If you'll click "User CP" and edit your profile to show your location it can make a big difference. IFI is represented by members from more than 50 countries and a lot of info is location specific. If local folk know you're around they can invite you to get togethers, tip you to tool deals and offer hands on help.

Frosty

Using 2 inch Kaowool with bricks on the inside would give me a working area of about 6" x 12". Is there an ideal spacing for the burners? What I am spacing mine at is about 5.5 inches. Should they be closer or will that work. I can always add more kaowool and brick to make the inside tighter.

Thanks

J.

[WillyP]

John B -

In regard to my coment and your question.

I'm just new at Blacksmithing. All the metal working experience I have comes from working in a Metal Stamping Facility for about 19 yrs. I am laid off now so I am taking the oppritunity to learn in a new area (Blacksmithing). In the factory, I Started off just a labourer, worked up to "Senior Press Opperator" and then moved into set-up, and then what they called QDC (Quick Die Change in case you're not familiar). Anyways, I've worked along side the Tool & Die Makers for 4 or 5 yrs, not along side like an apprentice, but being at the top end of the Press Shop, when there was trouble and the Tool Room had to be involdved, so did I. A good friend of mine is one of those Tool Makers and I've learned some things from him etc. etc.

Now the reason I said what I said is simply because when we had to make a jig or fixture at work - or if something broke and had to be either repaired or remade (and hardened) it was generally made from tool steel. I've just always learned that once you've heat treated a part, you need to draw it back slightly to be sure that it does not shatter.

I'm just learning more - or more details now.

Kind of a lot of words to just say, "Ah, I really did not know, but thanks for pointing that out!"


Jaret-

I also use 2" kaowool with 3 half fire bricks on the floor of the forge (with kaowool underneath too).

I measured my forge (now that it's cool) - My propane cylinder forge has a 6" opening (at each end - although I keep the back closed whenever possible) with an internal usable diameter of about 7" - 71/2" - The length is about 12" - and I can easy heat a length of 10" using one 1-1/4" burner using an .035" nozzle. I built my burner after the Mini-Mongo style.

I still have to learn more about my flame though. I think I'm usually using an oxidizing flame. (That's too lean right? I'll need to lessen the airflow a little?)

If I can figure out how to post a few pictures like you guys did I'll do it.

Any help or suggestions can't hurt.

Thanks

Willy

[WillyP]

Ok now that I went to the FAQ I can post a couple pics of my forge.

I included one with the burner going - before I put the doors on :)

[Fe-Wood]

Hi Guys-
I'll throw in my .02 cents;)
Air tank forge, nice way to retire an air tank:)
May I suggest when cutting the ends off, cut 3 strips of the round about 1" to 1 1/2" wide to use as a way to put the domed ends back on with a slip joint. To do that, slit the rings you have cut off, slip it over the "body" of the forge and weld the domed end to the ring. Be careful not to weld the ring to the forge body:o You can cut "fillers" for the slits from the 3rd piece so you don't have to round anything. I hope this makes sence... Makes it really easy to reline the forge and modify the ends if you want to.

WillyP-
Try using a .045 mig tip for your 1.25" burner. Sounds like you may not be getting enough fuel. Also, you might try using a piece of 1/8" X 1" to line the opening. Cleans up the edge and helps keep more heat in the forge.


Heres a picture of my forge, note the ring on either end and if you look closely at the opening you'll see the "trim" around it. I left about 3/4" outside the forge opening and just spot welded it so it can be easily replaced.

Good luck and keep us posted:)

[Fe-Wood]

Suppose I ought to post the picture I am referancing

[Frosty]

Using 2 inch Kaowool with bricks on the inside would give me a working area of about 6" x 12". Is there an ideal spacing for the burners? What I am spacing mine at is about 5.5 inches. Should they be closer or will that work. I can always add more kaowool and brick to make the inside tighter.

Thanks

J.

Yes, 5.5" on 3/4" burners is just about right. Your forge's volume says one 3/4" burner will do the trick but it's long and narrow so two is better for even heat. You can always turn them down.

Frosty

[lanchie76]

thats a nice looking car behind it what type is she

[Frosty]

Willy. Don't sweat it, everybody had to learn the terminology so we'd all know what we're saying. . . Well . . . Okay. So there's a better chance we'll know what we're saying.

A 0.035 tip is WAY small for a 1.25 burner. I haven't run any numbers but 0.045" is what I run in my 1" burners so I'd start at 0.055" and see how it works.

Frosty

[lanchie76]

sorry if im changing the subject a bit

is there any differences on box or cylinder shaped gas forges or is it just what people have to work with?

thanks

[WillyP]

A 0.035 tip is WAY small for a 1.25 burner. I haven't run any numbers but 0.045" is what I run in my 1" burners so I'd start at 0.055" and see how it works.

Frosty

Thanks Frosty, I actually started with an .045" tip, and I had a different stle of flare - I was having some difficulty with the flame being stable, so I asked some questions and was advised to change down to a smaller tip ( I was told that an .025" may even work better ) - And at the same time, to change from an external flare to adding a piece just inside the burner tip.

Well I did both. It worked. I was HAPPY! :D:D Just cause it worked! Anyways, I ended up trying both an .025" and the .035" and since the .035" worked as well as it did I stopped. I'll try the .045" today.

Lesson learned: Only make one change at a time or you'll never know which change was the one that made the best difference.... I wish i had a nickel for every time I've had to relearn that one!


Question 1: When I change tips, how - or - must I change fuel pressure accordingly?

I've been running the .035" at roughly 12-15lbs propane.

Question 2: Is Question 1 dependant upon my air choke? i.e. Can I run "any size" tip at "any pressure" simply by tuning it via the air choke?

[Frosty]

Change only one thing at a time is a hard one to remember, I spend too much time relearning it myself.

How much gas can be delivered through a specific size orifice depends on pressure, the more pressure the more flow.

So yes, as you increase the diameter of the jet the pressure needs to decrease. With the smaller orifice the propane is moving fast and even though it's delivering enough for a neutral burn it isn't in the tube long enough to mix properly. Or in some cases and I suspect yours is one 0.025" is just plain too small to deliver enouge prop. without pushing it to 30psi or something way too high.

A choke is a good way to fine tune a burner but if it's too far from right it won't make enough difference.

As a rule of thumb the length of the tube needs to be about 9 x the diameter of the throat. For a 1 1/4" dia burner the tube should be 11 1/4" long to induce air and mix it with the propane properly. Your air intake area needs to be 2x the bore area or more.

Frosty

[Fe-Wood]

The car in the picture is a 1967 Volvo P1800, Good runner:D

Persoanaly, I like a round forge interior because the reflected heat is aimed to the middle of the forge.

WillyP- Try the .055 too, I would have suggested it but didn't know if it was available.

Thanks for the info Frosty:)

As far as pressure and choke, thats the T & E area. Something to consider while experimenting: If the fuel volocity is to high, it won't totaly mix with air in the ventury (not good). I run my forge between 4 & 12 PSI. 8 PSI seems to be the best though. My burners are to small for the area inside my forge however so I can't forge weld yet...New burners are on the bench, under construction...

Something else to consider, Possition the burners in a location to cause the fire to swerle around inside the forge. I've not tried this but it has been suggested by a few folks and may have some merrit- Frosty, any thoughts?

[Frosty]

Inducing vortices in the forge chamber or not depends on the taste and needs of the smith.

I like having a hot spot most of the time so didn't set the burners at an angle in my latest forge.

If you want even heat throughout the forge then mounting them tangential is the way to go.

Frosty