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First gas forge build and NARB


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Hello experts, as the title states.... I'm looking to start my first gas forge and use a NARB. I have a couple options for the forge body and am leaning toward one, but don't want to have "that forge" in the corner collecting dust and taking up space. I like to make knives, want to do damascus, and have a bit of a thing for cleavers at the moment. I'm leaning toward the overpack drum in the pic with a flat floor and floor mount NARB, it's a little bigger than a standard 20 lb propane tank. My thoughts are to build "plug" ends to help keep the openings small when I'm not needing space for cleavers since they're big and awkward. I also have a few different refractory options that differ from the standard go to, but they cost me nothing so obviously I'd like to make use of them rather than buy if possible.

Thanks in advance for helping me not repeat mistakes already made. 

Josh

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Welcome aboard, glad to have you. Do you have a preferred handle or nick we can address you by? Writing out your log in is pretty cumbersome so we'll have to make one up for you. Do you trust US that much? REALLY?:rolleyes:

Certainly NOT the Kastolite 20 li. It's max working temp is printed on the sack and 1,440 F. won't survive the first firing. Kastolite 30 li is pretty much the consensus go to castable refractory currently. 

You want to build the ONE forge to last so you won't have dust collectors. Where have we heard that before? I still have my first successful propane forge and it's WAY oversized burner collecting dust. 

I highly recommend you build smaller than you think you want, I know a number of bladesmiths who have forges under 350 cu/in. The local club had a forge / burner build clinic and the chambers are IIRC, 4.5"x 9" x 9" and are run on a single 1/2" T burner.  Guys are making swords, knives and axes in them. 

A small forge has several advantages: they're easier and cheaper to build, they don't burn as much fuel, They're a good way to learn how burners and gassers work. There is to it more than just turning them on. AND maybe best of all, they don't take up as much room nor collect as much dust WHEN you build a replacement. You WILL build probably several more forges before you find what works best for you.

From my personal bag of mistakes do NOT weld your NARB to the forge. If you can remove it you can use it in version 2. ;)

Frosty The Lucky.

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Frosty we can go with WTF, Josh, dummy .... lol 

I'm pretty easy going so whatever works. There are two bags of Kastolite one is 20(I know... way too low) and a bag of 26LI as well. I was leaning toward the sparcast28 since it has the highest temp rating, but I don't know if it's insulating or if it's essentially casting a hard fire brick heat sink (shooting myself in the foot) then there's the mysterious vesuvius lol.

As for size..... I was originally going to use that refrigerant tank, but after lining I don't think a damascus stack would fit let alone my current weird obsession for cleavers. This is where I thought of flat floor and plugs that would make that overpack's interior smaller and still allow bigger openings when wanted. I do however trust the opinions of several of you quite a bit. (I've been lurking and there's a wealth of knowledge I'd like to sponge up)

I'm up for creative suggestions to make it as small as possible and still have the ability to a BIG cleaver. (Don't ask.... I don't know what the obsession is about)

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Might ask Stormcrow about what he uses when forging the carcass spliters---two handed cleavers!

https://www.iforgeiron.com/topic/66365-giant-carcass-splitters-of-doom/

I'd agree start small and work your way up; you will be wanting powered equipment to do larger pattern welding blades anyway, (Powerhammer, hydraulic press, rolling mill, trained strikers....)

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I had to look up Sparcast 28. No Joshing I did! :P Looks good, it's a high alumina and has a max sustained temp of 2,800f. Kastolite 30 li has a max working/ sustained temp of 3,000f. 

The hard refractory is just a high temp durable layer to protect the insulating outer layers. I was recommending 1/2" but more and more guys are applying it 3/8" thick with good results. Their forges are lasting. Being an insulating refractory is a plus but hardly necessary so don't get stuck looking for it.

How large you build is up to you, it's your shop. I've been building the darned things and burning them up for maybe 30 years and still build them larger than I should. My latest, the 2 NARB forge would've worked better if it were maybe 4-5" shorter. 

There are two basic approaches to a double liner. You can put the ceramic blanket in a layer at a time, rigidizing as you go and trowel the hard castable in later. Or, alternatively, you can make a mold and cast the hard inner liner, once cured wrap it in ceramic blanket sprayed with rigidizer and sliip it into the shell. A final coating of kiln wash, Plistex or Matrikote provide the final layer of armor as the flame contact face.  Plistex is the current favorite with this gang and one of it's attributes besides firing like ceramic is it's low thermal conductivity which means it absorbs energy from the flame but passes it on to the cast refractory layer more slowly than it absorbs it. Energy always takes the path of least resistance so it's radiated back into the forge chamber at a greater rate than it is conducted into the forge liner. 

The re-radiated IR from the liner to the work is what makes a regenerative forge work so you WANT the hard shell thin so it gets hotter and re-radiates more energy. A thick hard refractory has a faster recovery time as it's a larger thermal battery so if you're moving a lot of steel through the forge a thicker heavier liner is more practical. 

For low numbers and a more relaxed rate a forge that heats up quickly and economically but heats the work more slowly is a good thing.  

Does that make sense? 

Frosty The Lucky.

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Frosty that absolutely makes sense!

I'm crunching numbers (and I'll admit I'm not great at it) that overpack has a diameter of 14" and is 15" deep before subtracting the insulation and refractory (I'm using 5") (two layers of 1" plus 1/2"  on all surfaces) which leaves a diameter of 9" and depth of 10"  ..... I'm calculating 282.6 c.i. without subtracting a floor/ burner (I'm thinking the bottom 1/4-1/3) or "plug ends" (that will fit inside (making it shorter yet when in place)

Am I doing the math wrong? I'm trying to make this thing small with the abilities to fit odd shapes and be able to open the ends for pass through and heat treatment. 

Sorry if I'm beating a dead horse here I just thought I had gone over and over the numbers and had a solid plan other than the obviously unknown materials factor. 

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If you're describing a 9" x 10" cylinder your calcs are way off. If it's a vault shape mailbox, etc. I just like the term vault but no matter. If it has a flat floor then you left it's dimensions out, so your calcs can't be checked. 

For a plain cylinder as you describe, I get 636 cu/in. You'll need a 1" T to make welding heat in volume. You'll need about 2x the outlets in the burner block but that's a semi educated guess. I suggest you make wooden test blocks to determine the necessary number of outlets.

Frosty The Lucky.

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I still have and use the first gas forge that I built and it is extremely efficient. The only thing that I modified on it was the burner. A good burner will make or break a forge. I would not use any hard firebrick or any firebrick at all even on the bottom of the forge as firebricks are huge heatsinks and soft firebricks are a waste of money as they are too fragile and will crumble on you. I'd just stick with whatever castable you can get locally. You can buy the Kastolite 30 and other castable furnance cements online but they cost an arm and a leg to buy online because sellers need to make a profit and shipping charges for cement are high. Lastly, if you compare the properties of the different castable cements they only differ in terms of what they contain by a tiny amount in most cases and most are designed to handle way tougher conditions than a forge will ever have to put up with.

So if I were you, I'd buy everything local if you can. I'd also invest into either buying a really good burner or better yet, building a good burner. It will take a few attempts to build a really good burner but it will pay off in the short run and the long run since your forge will run hotter while using less gas. 

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Nah, it happens to all of us. I don't have as much trouble with circles since I stopped using "pi r square".

".7854 d squared" matches to at least 6-7 decimal places and I rarely work closer than that. It saves a couple steps so it saves me chances to screw up.

If you were to fill the bottom half of that cylinder with additional layers of rigidized ceramic blanket until it was about 350 cu/in or less, you'd have your full 9" width and length. Less plugs of course. 

You might want to look into what Mike says about thermal baffles rather than actual doors.  Might have to search that out. Use your favorite search engine and add Iforgeiron to the terms. The search engine on the IFI provided by the site OS is stinky, sucky B A D. 

Frosty The Lucky.

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Alright frosty .... now you got the gears in my head turning.  I was going to be a little below the halfway point with my "flat floor/ floor mounted burner" idea... if I changed the burner to a side or the top I could get away with smaller yet.  Is there an optimal position for a ribbon to be mounted in a "D"? My original floor mounted logic was to help the flame swirl. 

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Never having made a vault shaped forge with any kind of burner I can't say. Discussions indicate aiming the burner flame to impinge the floor at an angle to impart a strong swirl. Another popular alignment is across the top again imparting a strong swirl. I think the updraft alignment would be worth trying. Smart Alec remark deleted.:ph34r:

Frosty The Lucky.

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I have been using a D shaped forge with a floor mounted NARB for the past couple years.

As with most things, there are benefits and drawbacks. 

Benefits:

Can quickly remove the shell while leaving the burner in place.  This is great for repairs or in theory for placing a differently shaped shell over the flat floor.

Reduces the amount of fittings/hoses sticking out and around the forge.  On mine the T and mixing tube runs under the forge so not very much sticks out.

With the burner mounted on one side of the flat floor naturally aimed at the curvature of the shell above, I get good swirl in the forge.

Drawbacks:

The burner takes up part of the floor space - more than you'd think it would.  You need to leave a little space so the flames aren't impinging directly on the wall as they exit the burner block. In mine this amounts to nearly one third of the floor being off limits for stock placement.

My burner is recessed a bit from the level of the floor, so it's possible for debris to fall on the burner head or potentially fall through the ports into the plenum.  This has only been a minor issue for me a couple times.  The flames will tend to push small/light pieces away, and the "poof" when you shut the burner down tends to blow things out of the way.  I created a little bit of a bump/dam on the floor next to where the burner is mounted to make it less likely for me to push debris on top of the burner head.

Overall I have mixed feelings about this way of mounting the burner.  Although one of the reasons I built my forge this way was to be able to quickly change out shells for other shapes if needed, I have yet to ever do it.  The thing I notice the most is the reduced floor space.  It's not an issue at all when dealing with straight, or nearly straight, stock.  However it can be a challenge to keep the stock out of direct flame contact when dealing with odd-shaped objects.  When it comes time to build the next one I'm not sure if I'll stick with this configuration or not.

 

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  • 2 weeks later...

Ok frosty I've been crunching numbers and have decided I'm going to back burner the bigger forge (for now) and build a significantly smaller one for knives, mokume, and try my hand at some pattern welding. I'm thinking 150-160 ci with a 1/2" T .... but I'd still like to do a NARB. So I am curious if you're aware of anyone that's done a 1/2" NARB (so I can copy what works) and then my other question is regarding tuning.... I understand these need to be tuned prior to fitting the ribbon and that they need to be tuned in a forge, but I'm looking for a workaround to somehow tune without the actual forge being built as I'm thinking NARB and that will obviously be a bigger cut out in my lining. 

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I have a "no weld" version that I posted here partway down the page:

 

I've since switched to a different setup using a piece of insulting fire brick for the burner head, but I'm not comfortable enough with that one just yet to recommend it to others.

My personal experience on the tuning of the NARBs is that they do not respond much to changes in the length of the mig tips compared to the single port burners.  However, if you do get a standard T burner tuned properly it should function well when you attach it to the plenum of a NARB with the appropriate size and number of outlets.

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I'd have to ask around out club to see if one of them has made a 1/2" inducer driven NARB. I  know there's been talk on IFI but I don't know if anybody here has either. I haven't so you'll need to experiment to find out orifice number, best effective arrangement, length, etc.

Please post your results here so everybody can benefit. We LOVE new mistakes. :) I'm serious about posting things the don't work so other folk who have that idea can try for a new mistake. Remember to use something disposable for test blocks, they're too much work and expense to cast test blocks from refractory. I used wood, the 10-15 seconds of reasonably clean flame was enough to evaluate the flame and tune.

Yes, I've swapped numerous T inducers on my 2 NARBs and being connected to the NARB the inducers are less sensitive to being tuned optimally. Good and close is good enough. In or out of a forge seems to be fine.

Frosty The Lucky.

 

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Buzzkill I recall you mentioned it in another post I had commented on... you're running 1/8" holes on your drilled IFB correct? Have you come up with a solid number of said holes? Tried that bad boy in a forge? Somehow I missed that thread you linked and now will have to go over it with a fine tooth comb. You and Frosty seem to agree that the T being "dialed in" isn't super important on the NARB so I'm thinking slap a bell on the end get it as close as I can in the vice and get to trying NARB head ideas. 

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You might want to put a little more effort into it than that. Remember what Buzz said about trimming the mig tip didn't seem to make a lot of difference? That means if your NARB is out of tune the usual method of tuning doesn't have a lot of effect. That is my interpretation of what he said based on discovering that effect on my own developing the NARBs. The burner NEEDS TO BE running close to neutral BEFORE you connect it to the NARB.

I said, "good and close" is good enough. Meaning you don't have to try for as close to a neutral burn as you can get, like a single nozzle burner.

Less sensitive does NOT mean insensitive. Just throwing some parts together is a poor approach to making good tools and equipment unless it's an urgent situation.

Frosty The Lucky.

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