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New NARB forge advice


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Hey everyone! I am new to forging. I just started with knife making. I hand made my heat treat oven and my 2x72 belt grinder. I'm pretty handy and enjoy the challenge of making it myself. I am wanting to build a forge and have some questions. First, the forge will be used primarily for knife making and small blacksmith projects around the house(making closet hooks..etc...the wife has a list) I would like to have the ability to move up into damascus at some point. I have been debating a 5 gal airtank design vs an 11 gal air tank design. the 11 gal air tank has  outside dimensions of  29-3/4 in. x 21 in. x 13-1/2 in. My thoughts would be 3 layers of 1in kaowool, 1/4-1/2in of refractory, IR coat, hard brick floor. I would put doors at both ends with a slot opening in front door. I want to build a NARB for it which brings me to the question of how big a NARB do I need? I am estimating the chamber to be 622 cubic inches before adding fire brick floor if I use the 11 gal air tank. It would be about 5in high by 22 in long. Thank for any and all advice!

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Can you tell us why you need such a large forge?  I've been using one about 9" wide and 14" long for over 20 years now.  Unneeded length is just paying for extra propane you don't need to.

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Definitely don't "need" a large forge. I would just like to build something that will be able to grow with my knowledge and experience. I have been looking at 5 gal air tank plans too,gives about 4inch by 12 inch chamber.  I am just worried that I have read a lot of the 5 gal builders talking about needing to build something bigger.  I can shorten the 11 gal air tank by just chopping some off too. 

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Remember that the liner of your forge will have to be replaced many times before the forge is "worn out".  So you are going to spend all the extra fuel cost and then rebuild your forge before needing the extra space?

BTW: How do you get 4" by 12" from 29-3/4 in. x 21 in. x 13-1/2 in? Tanks are generally cylindrical so a diameter by length is generally used.  (Now they can be heavy walled, my current forge was made from a large welding Oxy tank with (3/8"?) wall thickness.

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I have the end caps from an even thicker walled tank, and then there are ridiculous tubes out there...Time to redo the liner on my propane forge, that is a titanium hammer head we are working on...

End caps:  

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   bigbell3.jpg.3b22dbe881a02e500b13cb140b95bfb2.jpg

 ridiculous: 

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Charles has a good idea there!

 

 

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I have a heat treat oven that can take an 18 in blade so I don't need separate forge for that.

 

Thomas, Thanks for those pictures! The 4x12 would have been for a 5 gal air tank after lining and placing hard fire brick floor, The dimensions are for the 11 gal air tank would give me a 7in by 22in chamber after lining and hard fire brick floor. I could shorten than down by cutting some of the air tank off though

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OK that's great!  The issue is the steel you cannot actively forge in a heat is being degraded: grain growth, decarburization, scale losses.  So in general your forge should only heat what you can work.  Starting out its a fairly short length; as skills and stamina increase it gets longer; but you really need powered equipment to work long pieces.

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That makes alot of sense. Thanks. Do you have a general recommendation for chamber length starting out? I am planning a press in the future for damascus, after I learn a bit more general forging skills

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So cut the smaller tank in half, making a 7” by 10.5”. Flip it cut end down and put the burner in the end, cut a pair of hatches. Repeat and trade the second to a buddy... 

7” is more than enugh, moving back and forth you can heat almost a foot to critical. 4-6” of hot steel is plenty for most forging

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If you will be doing balusters a long narrow forge is helpful. If you will be doing 4" billets then a short fatter forge is better with lots of insulation and flux resistant inner coating. If you will be working spirals then a clamshell forge will be best. If you want to...  This is basically an "I'm going to buy a vehicle; tell me what I should buy?" question. Without knowing if I need it to haul 15 people, or 15 tons of gravel, or commute 150 miles a day, or cross open water or reach the international space station; it's hard to make a useful suggestion.

If you need to work long pieces be sure it has a closable pass through in the far end.

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LOL, I totally get it. I am mostly going to be working knives and hopefully damascus. My wife has some ideas about closet hooks/smaller house things. I have a homemade trailer mounted smoker made from a 250 gal propane tank and was hopeing to make some bbq tools for it. Thats is about it and the direction I am thinking if that makes sense.

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A number f bladesmiths in our club are using one of these to forge in. They heat treat in purpose built units or subcontract heat treatment. It's a no weld clamped brick pile using Morgan ceramics K-26 insulating fire bricks (IFBs). It's powered by a 1/2" T burner. The club held a two day burner / forge build workshop and I believe about 24 of these were built. If a person needed a longer forge often enough another one of these could be easily be attached to one end to double the length. 

Ah HAH! I was typing when you replied. These little forges routinely weld damascus and make axes along with various serious sized knives. The chamber is 9" long. count the bricks if you're interested in dimensions.

The outside dimensions of a propane forge don't mean anything other than space to put it. The numbers that count in conversation, especially when you have questions is the volume. This determines the number or size burners though shape can effect the number as well. Long and narrow won't develop an even temperature with a single burner. Ribbon burners are actually more suited for heat treat or other projects requiring even temps.

Frosty The Lucky.

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Any advice or knowledge on refractory coatings? I see Hellcoat 3000 on xxxxxx, I hear about Kast-o-lite, Mizzou...... Started the build today with a 20lb propane tank. Thanks for all the help so far!7F71D7D3-B6C0-4BA5-89E4-D043F4485479_1_105_c.thumb.jpeg.e5059dfa258b1e476cfa13bb5a346aff.jpeg

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Wanted to share the progress so far. Forge cart is all welded up with casters. Forge is pretty much welded up. burner body and mold are made for NARB. Just waiting on castable for ribbon burner, rigidizer, refractory and ITC 100. I plan on lining each half with kaowool and refractory, then closing and sealing split with refractory then coating closed forge with itc 100.

 

 

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