Buzzkill

That's a difficult question to answer. That design would have limited appeal for me. The fabrication looks fine, but the dimensions and material thickness are not right for my needs. Without calculating anything I'm guessing it weighs 50 pounds or more. In my opinion even 1/8" thick shell material is overkill. The outside width is about 7.5 inches, (7" interior width) so if we add the typical 2+ inches of insulating blanket and refractory material, we're down to about 3 inches of width in the chamber. If the perimeter is a square then the height is likewise 3 inches or less after adding insulation and refractory. The length is excessive for anything but very specific work, such as decorative twists on long (and straight) stock. When using a hand hammer it is typically difficult to work more than about 6 inches of stock before it needs to go back into the fire. Heating more than that can be wasteful at the least, and repeated re-heating to forge temperatures can actually have a negative impact on steel - especially high carbon steels. There are more burner ports than I would use as well, although the unneeded ones could be ignored when lining and just covered. So, as far as value goes, that depends on the end user. For me it would have little value, but if you could find someone who needs to heat long straight stock it may be worth a bit.

IIRC it was about 240 cu. in. That was 3 forge bodies ago though.

I'm waiting for updates with interest. Vinegar works, but I'd prefer this solution (both meanings) if it is suitable for the task.

Just FYI, if you use DuckDuckGo's browser, they have their own video player. It gets rid of all of the ads on YouTube, and also removes the comments and suggested videos. However, there are some videos it will not play due to some form of copyright issues. Without ad blockers/removers YT is unusable for me. If they ever get to the point where I can't block most of the ads that will be the point I cease using the platform. This formula does look promising. It goes on my list of things to try when I get a chance.

If safety is your main concern I recommend taking a look at oscillating tools. I have a Bosch with variable speed. It certainly works better for some things than others, but since the cutting edge is essentially vibrating rather than spinning there is no real danger of something like the catastrophic failure of a cutting disk or anything getting wrapped up on a spinning shaft. Of course it does require that whatever you are cutting has enough mass or is held stable enough so it doesn't allow the vibrations to be absorbed.

Low pressure is not his issue. If it was a low pressure issue he'd be getting burn back in the mixing tube or similar results. This sounds like blowing the flame off the end of the burner. If it were me I'd be looking at axial alignment of the mig tip and the mixing tube. Just for troubleshooting purposes I'd also cover one of the inlets on the T and then partially cover the other with my hand while trying to light it. If the flame stays on the end of the burner with most of the intake air blocked off, but blows off the end of the burner when you remove your hand then at least you know for sure it's not a low pressure issue. From experience I can say that without a flame retention feature on the end of the mixing tube some T burners are difficult to keep lit until the forge starts glowing. While I don't necessarily recommend a 3/4" to 1 1/4" reducer fitting as a permanent flame retention feature, it can be useful in troubleshooting. Check the easy things first.

Yes, that will be fine as long as it isn't directly exposed to flames - which it shouldn't be. Once it's coated/covered with refractory it should be fine for everything through forge welding temperatures.

I built it. However, I didn't like the noise of the blower (I had a bouncy house blower) and being tied to power, so I didn't use it for long. I went back to a standard T burner until you introduced the NARB to the forum. I've tinkered with a number of variations of NARBs since then, but I don't foresee ever going back to a blown burner or a single port burner. I was trying to figure out how many years ago it was that I used a blown burner based on that progression. It had to be at least 7 years ago now, and I can't tell you the exact dimensions of the design. If I still have notes from that project I'm not sure where I put them. I did (and do) a lot of tinkering with burners, but I have a tendency to toss records of the things I didn't feel turned out well. If I don't do that then I have piles of papers with "bad" designs and over time I forget which ones are worthwhile.

Fair enough. I have limited experience with blown burners, but I don't recall having difficulty getting fairly even flames using a rear mounted inlet and a diffuser. However, I never tried a side mounted inlet on a blown burner, so I can't personally compare the two designs.

The temperature at which you should forge is dependent on the specific alloy you are working with to some extent. For instance, it would be a bad idea to forge O1 at a yellow heat. Generally speaking though, orange heat is enough for a lot of simple steels. When you get into the yellow territory you are at, or at least rapidly approaching, welding heat. Also generally speaking, high carbon steels do not move as well under the hammer as mild steels. Some alloys have a very narrow forging temperature range and seem to resist deformation by hammering to a significant degree.

Frosty, it appears as though he's planning to use a blower on his burner, and unless I'm mistaken you were giving advice based on your experience with a naturally aspirated ribbon burner. I'd hate to confuse the guy.

I have a few thoughts, but most are my opinion. That seems like a lot of burner for a small forge. Most people want to make a forge that is too large. Your design is not. You say you want to make knives, but forging a large kukri style knife needs a different forge size/shape than a puukko. Personally I prefer the "D" shape forge so I have a flat floor where the forge interior is at its widest. Mine is nearly 9" across at that point and is right for me. You may not need as much space. If you are using a quality high alumina refractory it does not need to be that thick. I think of the refractory as armor to protect the insulation from damage. The thicker the refractory, the more heat is absorbed. That translates into more time required to bring the forge up to temperature. For everything but the floor I'd probably stay in the 6 to 8 mm range. As far as casting a recessed area on the floor for a brick or kiln shelf, for me this is determined by whether you intend to forge weld. If you plan to make pattern welded billets and use flux then I do recommend casting in such a way that you can use a replaceable floor slab. Over time flux tends to make a mess of your floor and it's nice to be able to replace that portion without having to refurbish the entire forge. Keep in mind that the forge interior will deteriorate with use. The combination of thermal shock, mechanical damage, and some chemical attack from burning fuel/gas and flux takes a toll. Nothing I've seen is impervious to those conditions. You will get cracks in the refractory. Coatings such as Plistex, Matrikote, or ITC will flake off or be rubbed off and have to be patched or replaced periodically. Since you are planning to use forced air on your burner it doesn't require a high level of precision. I didn't see any glaring problems with the design. Feeding it with a 1.5" pipe shouldn't be a problem. However, you do want an elbow and/or a change in pipe diameter between the point where the fuel is introduced into the air flow and the burner. This is to aid in mixing the air and the fuel gas. Propane and air don't naturally mix well, so creating turbulence before the fuel/air mixture reaches the burner is a good thing. For a blown burner the fuel pressure is not nearly as important as volume. If your regulator allows enough throughput it doesn't matter that much if it's at a low pressure. However, you shouldn't use a highly restrictive orifice (like a MIG tip) to inject the fuel into the air stream if you have low pressure. The only real value (in my opinion) of knowing the pressure is to note at what pressure the forge maintains the heat you desire. That is still variable depending on what you do with the air. You need to be able to control the flow of air and fuel independently in order to achieve the desired atmosphere (oxidizing, neutral, or reducing) over a range of temperatures. While it's a good idea to have a specific plan with precise dimensions for assessing the quantity of materials needed, when it comes to functionality that level of precision is not needed, nor is it likely to be attained. Generally speaking it looks like you are on the right path. Without knowing the largest knife you plan to forge and it's shape I can't say whether your design is appropriate. If you plan to do any forge welding you may also find your designed chamber a little restrictive for placing a stack in when starting a billet. Hope that helps.

It looks to me like your first pictures show a contrast of dull grey and a shiny silver color in the layers. That's probably the best you are going to do. If there is any variation in topography you may be able to restore that condition with some high grit sandpaper (around 3000 grit or so) on a flat surface and a lot of patience combined with elbow grease. That would shine up the high spots and leave the low spots as dull grey. The only other thing I can think of that *might* work is using electro-chemical etching to darken the whole thing (if that will even work on stainless) and then sanding off the high spots. Again, that requires at least a little change in topography between the two types of steel to be effective.

I haven't had very good luck getting pictures with accurate colors, but I'll give it another shot soon when I get a chance to fire up the forge again.

Well, so far my latest block doesn't burn back at all even after being at welding temperature and dropping back to under 1 psi. It doesn't even pop when I turn off the gas. However it has about 180 ports that are 1/8" diameter, and the ports are nearly 3 inches long. It's a big heavy burner block and if I didn't have a 3d printer I wouldn't have even wanted to attempt the mold. I think the distance between the outer burner head surface and the plenum is playing a significant role here. I have less than 100 hours on the burner head at this point so I don't know how it will hold up long term. Some of my previous attempts started out very promising, but showed degradation in the performance over time.

Oh yeah! The mohawk works well.

We're still learning and innovating: https://www.popularmechanics.com/science/a60964033/new-alloy-defying-the-limits-of-metal/

I believe most modern RR track is 1084 equivalent or possibly even higher in carbon content. It's not heat treated like cutting tools, but it does work harden at the surface. If you have the desire and means, you can make good tooling or blades from it.

Nice. I've heard that a strong magnetic field can affect a welding arc. Did you notice anything different while welding on the chuck?

Is there some particular feature of Hoffman's blown burner that interests you? I've built and used a blown burner, but I'm not familiar with any design specifically attributed to Mr. Hoffman. In general, forced air burners are rather simple to build and operate. Also, since you can manually control the air and fuel independently there isn't the level of precision required for proper functioning that is needed for naturally aspirated burners.

If you're trying to get into this hobby addiction inexpensively here are a couple topics you should check out: https://www.iforgeiron.com/topic/44842-just-a-box-of-dirt-or-a-simple-side-blast-forge/#comment-463468 https://www.iforgeiron.com/topic/52308-a-collection-of-improvised-anvils/#comment-556220

Is this mystery steel or do you know the designation of the alloy? The reason I ask is some alloys are notoriously difficult to weld to themselves. It is possible to get a good weld even in a slightly oxidizing atmosphere if you are using flux. The main purpose of flux is to keep oxygen from reacting with the the surface of the hot steel. So, if you have a clean surface (that means absolutely no contaminants or forge/mill scale) and you apply the flux as soon as it will stick to the steel, that should keep the surface from oxidizing and provide a good welding surface. Is there a group or a person around you with a little experience that can help you with this? It's one of those things that seems complicated, but once you can judge when you've reached the right temperature and can see and hear when the weld is set it seems far less complicated. Even after you set the weld, the pieces can separate easiest at the weld seam if stressed. It takes a few additional welding heats and hammering to get it to the point where it is one solid piece without a weak spot. Goods is correct that if you want a seamless transition you do need to scarf the end of the piece so you can work it into the parent stock without a sharp transition that creates a weak spot. However, if you're just trying to practice and understand forge welding you may not want to go that far yet. What you are attempting is good practice for making fire pokers, btw. Keep in mind that even with pristine new steel if it cracks, additional stress on the steel will make that crack run longer and deeper. Likewise, you can have a partially welded piece that when stressed will start to separate at the seam, and additional stress will cause cracking down that seam. A complete failure to weld will usually result in full separation along the weld seam. It's not uncommon to get a partial weld when starting. I still get them occasionally. One more thing: You want to hammer in such a way that you don't trap flux between the layers. So, you want to start at one end and strike along the center line as you work towards the other end of your weld. For wider pieces you'd then work the sides in subsequent heats. Think of it kind of like toothpaste that you're trying to squeeze out from between the layers when you hammer.

I would not recommend starting with round stock to practice forge welding. In my opinion high carbon steel flat rectangles that are 1 to 2 inches wide and 3 to 5 inches long are some of the easiest welds to achieve. If the mating surfaces are freshly ground shiny and the edges are all lined up so there is no overhang you should get good results. Thin layers cool rapidly, so I'd suggest at least 1/4" thick layers to start with. If I were to try the stock you are showing I'd probably square a section, let it cool, grind it clean on the intended weld surfaces, and cut most of the way through so I could fold it back on itself as prep work for welding. I assume you were originally striking with the pieces on top of each other rather than next to each other as you show in that picture. I don't think temperature is a problem for you. When I zoomed in it appeared to may as though you may have actually overheated the steel in a couple places, but I'm not 100% sure. It could be oxidized flux. The reason for "soak time" is to ensure that the steel is heated uniformly through the entire piece. The outer surfaces will reach incandescence first, but the center of a piece of stock may still be at a black heat. It is possible to heat a piece so rapidly that you burn the outer surface before it's thoroughly heated. If the center is cooler then you will be losing heat both inside and outside the stock you're trying to weld. You only have a few good seconds to set the weld after you remove your stock from the forge, so you don't want to lose any heat unnecessarily. Your hammer does not need to be particularly big for this. Your blows should effectively be "dead blows." You don't really want any rebound. If you hit in such a way that there is significant rebound, that can cause the layers to separate. So, relatively light blows at first to set the weld, then back in for more heat. Until pieces are successfully welded you will usually see a dark line between the layers as they cool, and often one of the layers will darken faster than the other as they cool. Once you have a successful weld there will be no noticeable line where one layer cools faster than the other. They will have become one piece.

We have the one you pictured above. It specifies a 2 minute "on" and 5 minute "off" duty cycle. I grabbed a 1/2" diameter bolt and put the head in a vice. Surprisingly to me, after about 90 seconds I'd say the threaded portion I was affecting was hot enough to forge, but just barely. The glowing portion was a little over an inch long. The heat resistant material on the coils was smoking a little at that point too. So, I guess I'd say I have to revise my earlier statement just a little. You could potentially do a little bit of short-term forging with one of these within certain parameters. However, I still don't think it would be a suitable option for sustained work on even a hobby level.

What he said. I do have a vacuum system and use the aforementioned Cactus Juice to stabilize some of my knife scales. I've also used stains to get the color I want and then followed up with Tru Oil or something similar and have been pleased with the results. Stuff that is made for the beautification of wood gun stocks tends to also make wood knife scales really pop. Just follow the recommendations for the product as if you were treating a gun stock and it should turn out well. But yes, using a test coupon for just about anything you haven't tried before is a good idea.