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New Propane Forge Idea


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So I'm almost done with the build and I'm approaching the point that I'm going to have to cut the holes for the burners. 

My question now is: should the burners be evenly distributed in the forge, or should they be a little closer to the edges?

I.E. The forge is 15 in in length. Should I space them at 5 in and 10 in, or spread them out a little bit more?

In the picture, I marked the center line in blue and evenly spaced with red circles.






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Most gas forges have a closed back, or at most, contains only a very small opening in the back, to push long parts through.

So the rear burner (in either kind of design) can be placed much closer to the back wall, and still its gas will be bounced forward to exit the larger exhaust opening.

Therefore, the forward burner is best place closer to the middle of the forge, to increase "hang time"; this leaves more of its energy in the forge, and moves the burner's air opening(s) farther away from the spent gases.

Your present forge design seems more than a little high. One more piece of sheet across its front opening, and about one fourth of the height, would allow you to fill up a lot of that excess space with cheap Perlite, creating an insulating bed beneath more expensive insulation; turning a problem into an asset.

The changed interior shape would then gain a lot by moving those burners from the forge top to high on one side wall, or the other.

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So this is where it is now.

I've finished welding the body and frame.

The rear is built identically to the front.

Once I add the refractory, I calculate the interior dimensions to be about 4.25"w x 15"d x 5.25"h, or 335 cubic inches.

If I add a 3" plate to the top of the entrance, it will leave me a 3.5" opening.

Should I add a 4" plate to the back for a 2.5" opening?




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On 11/27/2020 at 1:19 AM, Frosty said:

I've had guys come by for instruction who couldn't calculate the volume of a cube in sq/in.

How do you calculate volume of a cube in square inches?  Wouldn't square inches be area and cubic inches be volume?  I figure you either know something I don't (entirely possible/likely) or it was a typo.  Just trying to clear it up for those who come after.

On 11/27/2020 at 2:10 AM, Valeas said:

Yes, the planned internal dimensions would be 4.5"w, 15"d, 5"h.

If you plan to do long twists or something similar, you may need to be able to heat 15 inches of steel at the same time.  Otherwise it's pretty much a waste of space and fuel.   Assuming you will be using a hand hammer, you will be hard pressed to work more than about 6 inches of hot steel before it cools to the point where it needs to be reheated.  We typically put pass through openings on the rear of the forge so we can work with longer stock, but only heat the portion we will be working on.

Most of us have built at least one forge that was way larger than needed.   I had to change my mindset from "it's better to have it and not need it...."  to "how small can I build this and still do what I want to do?"  The larger the forge, the greater the initial costs, but what really matters is that over time the fuel costs add up. 

For sake of reference, the forge I use has a chamber only about 9 inches deep.  On the few occasions where the forge chamber size is limiting for me, it's nearly always the height or width of the forge chamber that is the issue, since I can pass longer stock out the back end. I use a ribbon burner powered by a single (modified) 1/2 inch Frosty T burner and I am able to reach forge welding temperatures.  Just some food for thought before you get too far along.

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That comment was from about a week ago. 

The forge is already built now.

(See latest pics in my last comments)

I'm adding plates across the top of the opening, front and back, to close the opening off a bit, and Frosty has recommended using two 1/2" burners, which I'm working on building right now.

The only thing I'm waiting on now is to decide the burner placement. 

If I REALLY HAD TO, I could cut out lateral sections from each side to shorten it down.


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At this point I think you're in the "try it and see how you like it" stage.  It may be exactly what you wanted.  If you find you're going through fuel faster than you hoped you could try inserting some shaped IFB's (with a pass through of course) or add bricks to raise the floor to decrease the overall volume and maybe run one burner.  If you get the openings mostly blocked off it shouldn't be too bad on the fuel, but you could probably do nearly all the same things with a smaller volume forge.   Let us know how it turns out.

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22 hours ago, Buzzkill said:

How do you calculate volume of a cube in square inches?  Wouldn't square inches be area and cubic inches be volume?  I figure you either know something I don't (entirely possible/likely) or it was a typo.  Just trying to clear it up for those who come after.

Yeah, typo. It was supposed to read can't figure the area of a square in sq/". I rarely fault anyone for not obeying natural laws. Good catch Buzz, folks are confused enough without getting the explanations wrong. <sigh>


Frosty The Lucky.

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