Mikey98118

The short answer is no. Furthermore, most people who build a gas forge, find out that large or small "it isn't the right size," shape, or whatever. No it isn't actually wrong; they just want a second forge that's different So, it would only be smart to jump all over that offer, before the people at Mister Volcano come to their senses.

Drilling and Threading Stainless-steel The softer stainless alloys (300 series) tend to gum up tool edges, which then rapidly become dull. Three-hundred series stainless-steel also tends to compress during drilling and threading, when using dull tools, compacting its surface; this is a form of work hardening. That compacted surface becomes denser, and begins to act like a bearing surface; dull cutting edges then ride on it (instead of penetrating): causing rapid heating of the cutting tool, which is why only sharp drill bits should be used on stainless-steel. Stainless-steel work hardens rapidly if a dull tool is used, if too little feed pressure is applied, or if drilling fluid isn’t employed; tapping oil is perfect for this, and can be purchased in amounts smaller than a pint). But, even cooking oil is better than nothing. It can take mere seconds to overheat a dull drill bit in stainless, and dry drilling will dull cutting edges rapidly, ending up with melting temperatures on a drill bit’s leading edges; this is followed by transference of some of the bit’s high-speed steel material to the part’s surface. Thereafter, no further drilling is possible, although the resulting mess can be reamed out with diamond coated, or tungsten carbide burrs, applied with diligence. When breaking through the far side of a hole, the leading edges of a drill bit can bind in the part’s thinning material, as it deforms; small drill bits snap off at this point. To avoid breakage, ease up on feed pressure when you feel the bit breaking through the far side of the material; this is true for any malleable metal--not just #300 series S.S. Pure copper can snap small drill bits at any point during drilling, if more than minimal pressure is used; not just when breaking through the far side of the material. It is generally a good idea to employ the drill bit recommended for different metals. The drill bit sizes listed in tap and drill bit charts are normally meant for use on soft metals like brass; they produce a 75% thread engagement. Only 50% thread engagement is recommended for steel alloys. However, the relatively few threads produced in most tubing and pipe are under more than moderate stress at times; this makes the additional pressure on your tap, which comes along with an additional 25% thread engagement, a recommended risk, when mounting set screws in burner mixing tubes. But, when threading through thick and/or doubled stainless parts, used in a burner’s flame retention nozzle, the recommended 50% thread engagement is necessary. “High-speed steel” drill bits are the cheapest grade of tool steel; if you are careful, you might get as many as four holes in thin stainless tubing before they need resharpening. “Cobalt” bits are made from high-speed steel, with cobalt added, for further hardening and heat resistance. When you can find cobalt bits with 118° points (standard angle for drilling ferrous metals) in the size you need, they are well worth their higher prices, in hardware stores; they are usually only available in fractional sizes. Cobalt drill bits can be purchased through Amazon.com for the same price as mere high-speed steel bits will cost at a hardware store. Look up any drill bit chart to understand the differences between fractional (fractions of an inch), wire sizes (adhering to wire gauge numbers), letter, and metric drill bit sizes; all of them are a few thousandths of an inch different, than the closest size in one of the other classifications. The harder the alloy the more brittle it is; therefore, treat cobalt drill bits more gently than plain high-speed steel bits, and tungsten carbide bits more gently still; use light feed pressure on cobalt and carbide drill bits; do not forget the cutting oil, and they will serve you well. 135° split point cobalt drill bits also work well for drilling stainless steel; these bits come in a greater variety of sizes than 118-degree chisel point bits: including number and letter drill sizes. Because they are made for drilling hardened and stainless steels, hard bronze alloys, and titanium (all tough jobs), cobalt bits have thicker webs, leaving smaller clearances than standard bits; which means you will have to work diligently at chip removal. One of the advantages of split point bits is that they do not tend to “walk” (move around on the part surface before penetration) like chisel points do. Try to buy American made M42 (8% cobalt) bits; most of the imported cobalt bits are only M35 (5% cobalt). If you look cobalt drill bits up on eBay (the drop shippers paradise), make sure the bits you choose really are cobalt. Amazon may be a safer market for these bits. Note: Sets of tungsten carbide (and of tungsten steel) micro drill bits embedded in 1/8” mild steel shanks are available online for low prices. Tungsten steel will hold its temper up to 932 °F, and tungsten carbide is immune to tempering, but is quite brittle. Common high-speed steel bits lose their temper above 400 °F. Threading in stainless steel: The greater thread engagement (75%) needed on thin tubing walls, is one of the reasons you only want to use taper (AKA starting) taps; not plug or bottoming taps. The other good reason is that, unless you are going to start the tap in a drill press, (with the part trapped in a drill press vise, after drilling each hole, without moving the part), it is not likely that the tap will be started at true right angles. Starting taps will self-correct to that position if your aim is “in the ball park.” Plug taps will not. The way to tell the difference in taps is amounts of chamfer in taps are: Bottoming taps (1 to 1.5 chamfered threads); Plug taps (3 to 5 threads); and Taper (8 to10 threads). Lazy sales clerks and ignorant drop shippers are likely to offer plug taps in place of taper taps, so count those chamfers before buying. Another difference in tap designations are “straight” hand taps, and “spiral” CNC machine taps. Spiral taps have deeper groves for faster clearance of chips, and are therefore weaker than straight taps; take extra care with small spiral taps; there are other types of thread taps, but these are the most likely types to be offered on line. Start threading with your tap as close to right angles as possible, and only turn the tap until you can feel resistance suddenly increase (the “quarter- turn and reverse tool to break burr” rule of thumb is not adequate for stainless or high carbon steels); instead, you must back the tap off as soon as you feel a sudden increase in resistance to movement. It does not matter how little progress you make before breaking the burr away from the thread end, and starting another twist; have the patience to follow this advice. You are going to be using small (and therefore easily broken) taps on these burners. Be liberal with your tapping oil, and back the tap out completely (in order to clean out collected metal chips) every full turn; dealing with a broken tap is even less fun than removing high speed steel layers left from partially melted drill bits. Should you break a tap off in the hole, gently rap back and forth on the protruding point within the tube (with a rod), to loosen the embedded point; then, try to back it out of the hole with pliers. Otherwise, you must drill that piece of high-speed steel out with a diamond coated or tungsten carbide rotary burr. Once the partially threaded hole is cleared, try to continue threading it with a new tap; most likely this will work out well enough to accept a screw, but if there isn’t enough thread left to properly engage the screw, you must start over by drilling and tapping for a larger screw. There are three kinds of taps: "Bottom," "plug," and "tapered” (AKA “starting”) It should be obvious that stubbornly insisting on a tapered tap (even if you have to special order it), will return big dividends once you start threading in S.S. Learn the difference between starting and plug taps, to defend yourself against ignorant or lazy sales clerks. It is better to pay a premium price and/or special order a taper tap, than to try forcing a plug tap to work in stainless-steel. Any malleable metal will form a raised area on both the near and far surfaces of the part, during tapping; #300 series stainless steel more so than other ferrous alloys. The inside face of threaded holes in the burner’s flame retention nozzle and other close-fitting parts must be sanded flat in order to keep proper fit. After sanding, the tap must be run through the threads again to “chase” them (to help clean out debris and get rid of burrs and/or deformed thread ends). Chasing and sanding the inner face of tubes must be repeated back and forth, until all screws turn smoothly, and the part slides smoothly over other tubing.

I agree that most first forges are built too large. I also suspect that your evaluation of your forge is right on the money. This is the first gas forge I have heard of, to run quite well in both fan-blown and naturally aspirated modes. The photos show a yellow-white interior, which is always a very good sign. Because builders have a strong tendency to get a delirious with joy when their first forge works properly, a cautious reader learns to want particulars. Loads of first time builders have will have something more to hang their hopes on, should they choose to imitate yours

What you shared about the Mister Volcano burner did for your forge was helpful, but we can't get into your head. You need to give us a verbal tour of what you particularly like about this forge...what it does well for you

You are quite right; I didn't even think of that

Cutting with a rotary tool: If you stop the disc during a plunge cut (with a circular or a chop saw) before the cut is finished, it will usually cause kickback. The opposite is true when surface cutting on sheet metal products, like pipe and tubing, with a rotary tool and cutoff disc. Attempting to remove a moving rotary tool from the kerf will usually cause kickback. Those OEMs (like Dremel Tools) who bother with a thorough list of safety tips in their instruction manuals, all advise the operator to run a cutoff disc back and forth on the part surface, gradually deepening a groove at the cut line, until the disc begins to break through that groove, which is then called a “kerf.” Unlike chop sawing, or plunge cutting through thick parts, the operator is supposed to bring the disc to a halt before exiting the kerf; it is different to other cutting processes, because your disc isn’t deeply buried in the part. There is very little material for the disc to “walk up,” creating an opportunity for kickback, as the disc stops. Also, the numerous tiny grit edges don’t have anything like the tendency to grab unto stock that the teeth of circular blades do. Most kickback from resin bonded cutting discs come from the sides of their discs binding against the kerf. So, surface cutting creates a unique situation, where stopping the disc before removing it from a groove or kerf is safer than removing the disc, while it is still in motion. Die grinders are treated the same as rotary tools for surface cutting (my own description of this technique). You will notice that friction makes the disc want to move in one direction; take note of it, and make sure that the disc is traveling in the opposite direction, when breaking through the kerf. Otherwise, the disc will tend to bump against the end of the kerf, creating kickback. Maximum safe RPMs of cutoff discs vary by manufacturer and thickness; if a marketer doesn’t list the maximum RPM for a cutoff disc, the rule of thumb is not to use larger than 1-1/4” diameter generic disks at 32,000 RPM, or 20,000 RPM for 1-1/2” generic disks. Brand name cutoff discs (ex. Dremel), and discs used in electric die grinders (1/4” and 3/8” arbor holes) are typically much higher quality, and are designed to run at higher RPMs than generic rotary tool discs. A 25,000 RPM rating is typical of 3” die grinder discs, and 30,000 RPM for 2” die grinder discs. But it is wise to bring the rotation up slowly to those speeds in unrated discs. Better to be safe than sorry. To avoid surface cutting problems: (1) When starting a cut, be sure the accessory is already turning; do not start, or restart a cut, with the tool still. (2) Gently lower the disc unto the part surface, with the tool held firmly, and lightly run the disc back and forth on the part surface, next to the cut line, to establish a groove. Deepen the groove by continuing to run the disc lightly back and forth, until it starts to break through the material’s far side; when the groove starts breaking through the material’s far side, it is called a kerf; cutting through the kerf is far more likely to create kickback, then deepening the groove. Don’t press the disc against the part. Just let the disc do the work. (3) Always delay cutting into the kerf until you have no other choice. (4) Start and stop the cut short of the end of the marked line, and finish the cut later, with a small diameter disc, for greater control, as these two areas are the most likely to create kickback. (5) Allow the disc to come to a complete stop before removing it from a cut, to avoid jamming the disc, and creating kickback. (6) A common cause of kickback is a disc that is moving even a little out of parallel to the kerf; the problem is multiplied when the disc is deeply inserted into the kerf. It is safer to only try cutting through the material, after the disk begins breaking through the part’s far surface. (7) The only relief from torsion kickbacks is provided by Dremel’s EZ-lock mandrel and special cutoff discs; this nearly eliminates torsional forces, making an end-run around that problem. Save the last 1” of their diameters for surface cutting in problem areas, like inside corners. (8) Another cause of kickback is the disc bumping into the end of the lengthening kerf. Try to only move the disc counter to the direction that friction inclines it to “walk” along the part, once you start cutting into the kerf; this will help you to avoid bumping the disc against the end of the kerf; always ease into the cut, to avoid kickbacks. Aside from cutting through the kerf from the right direction, practical relief from bumping kickbacks is provided by smaller diameter cutoff discs. (9) When you can, try to cut beside of the cut line, and then grind back to it afterward; this allows you to concentrate on two separate tasks, instead of looking after two cutting factors at one time. After you finish all cuts and remove unwanted material, then start grinding back to the scribe or ink lines with a small stone wheel, or diamond disc. Do not use cutoff discs for grinding; it dangerously weakens them. Note: The cheap variety of imported diamond incrusted rotary discs are too thin to keep the diamonds on their rims from rapidly being lost; they are useless for steel cutting. However, this doesn’t hold true for the diamonds on their two faces, making them a good choice for precision grinding work. EZ lock mandrel and cutoff disks are one of safest ways for a beginner to surface cut with a rotary tool; they are more expensive than generic cutoff discs, which run in standard mandrels, but considerably easier for a newbie to deal with, when doing the work needed to build a couple of burners. By the time you use up the disks in one their mandrel and disk kits, you should be well enough acquainted with surface cutting to take advantage of the more economic offers for regular discs and mandrels. You will still find yourself reverting to the EZ lock system for tricky cutting jobs. The special discs that come with this system are 1-1/2” diameters. It is wise to save the last 1” of each disc, rather than wearing them down completely. The small used discs are very handy for making interior cuts in small parts. Begin by inserting the EZ lock mandrel all the way into the collet nut on the tool’s spindle, and then tighten the nut. To mount a disk, push the plastic part of the head down against its spring, dropping a disk past the mandrel’s bow tie shaped end piece, and then turn it ninety degrees, to lock it in place. You can buy the discs and mandrel in kit form online, and from most large hardware stores. The spring and locking mechanism are what makes this system unique. It eliminates the usual locking screw, so that grinding and sanding wheels can be used nearly parallel to part surfaces, without interference from a protruding screw head. The disc is positively locked, because there is no screw to loosen from vibration, allowing the disc to spin on the mandrel. But most important of all, the spring allows your tool to move out of alignment with the kerf, without creating kickbacks, by nearly eliminating torsional forces. Disc mandrels: You don’t want to employ just any disc mandrel for steel cutting. The standard jeweler’s mandrel, which only has a 1/16” standard machine-screw head, was designed for making very short cuts in silver and gold ring bands; not for making extended cuts in steel. There are special mandrels with 1/16” crews that have oversize screw heads, threading into oversize mandrel faces, and similar mandrels for 1/8” and 1/4” arbor holes; these far outperform the minimal screw head variety; you can find them offered through eBay, Amazon.com, and through most jeweler’s supply houses; input “SEINC 1/8” rotary tool mandrel” to find them quickly. Preamer 1/8” mandrels are excellent for spinning 1-1/4” diameter fiberglass reinforced aluminum oxide cutoff discs, which are handy for cutting on burner parts. Note: Poorly finished mandrels, provided along with some cutting discs, can cause cutoff discs and grinding wheels to wobble. This is a common problem that is seldom correctly diagnosed. Customers incorrectly blame the discs. What is actually happening is that the mandrel’s face is out of true right angles to the shank’s axial center. Or, or the washers provided with cheap mandrels aren’t perfectly flat. Circular motion on fine sandpaper can flatten washer surfaces, and the mandrel can be spun in your rotary tool, while its forward face is quickly trued up with a diamond coated cutoff disc, or diamond coated flat file.

Good one, Frosty; nice word picture

Exhaust size and shape One thing backyard casters and blacksmiths both worry over is how large to make the exhaust openings on their equipment. Too small and you have high back pressure killing burner performance; too large and you can't retain enough heat to do your work. Of course, the closer to the "right" opening size your equipment is the stronger the forge or furnace can be built. Just don't confuse the right size for a “perfect” size. As long as burner output can by varied (turn-down range), there can't be any such thing as a perfect opening size. The right size is what is needed to accommodate the burner's highest output (the highest you are willing to take it to). Variable is the optimal opening size; all other dimensions can be outright wrong, but are seldom just right, with a burner flame that can be varied. This is one of the many reasons for controlling exhaust flow with an external baffle wall beyond a larger than needed ringed exhaust opening; thus, allowing the least heat loss through radiation, while maintaining optimal atmospheric pressure in the forge. Why include a ring around the exhaust opening? To divert hot exhaust gasses away from the shell, where it can super-heat its metal. If you decide on a movable brick baffle wall in front of the forge, keep the bricks at a small distance from the exhaust opening, to allow hot gases to move up and out, between the opening and brick, while bouncing most radiated heat off of a re-emissive (heat reflective) coating on the bricks, and back into your forge. Keep the stock entrance only as large as is needed to move parts through. This arrangement helps to slow the flow of expended gas in the forge interior, as it heads toward the exhaust opening; and then speeds the gas up through the opening; another desirable trade off. So, you are gaining hang time for the heated gas in the forge, and recuperative savings from bounce-back of radiant energy; a win-win situation. A baffle wall also minimizes infrared and white light from impacting your eyes and skin, improving your health and comfort. Doors Maximum part clearance can be provided with a hinged and latched forge door (stainless-steel toggle latches are your best choice); it should contain built-in interchangeable baffle plates (high alumina kiln shelves are perfect for this). A door makes building the refractory structures inside of equipment much easier, and permits larger parts to be heated than would pass through a narrowed exhaust opening. Best of all, it allows closely contoured movable internal baffles to be employed, which would not pass through a narrowed exhaust opening; this promotes the use of single burners for small pieces, saving money in tunnel, oval, and “D” forges, which are run by two or more burners; on these forge shapes, the door is a big step up from an exterior brick baffle wall; it should include a parts entrance that can be varied in size; for instance, with several round (or hexagonal) kiln shelves with different openings cut into them (for passing stock through); these can be exchanged, and held within a pocket structure on the door. These improvements don’t all need to be seen to at once, so long as a hinged and latched door is included in the forge shell. Some people prefer a vertical or horizontal sliding door, instead of hinges. High alumina kiln shelves are seven times more insulating than hard fire brick; they are very tough at incandescent temperatures, which is an important consideration for something you will end up shoving parts back and forth through. Exchangeable kiln shelves, with different part openings drilled and cut into them is fine, but building an elaborate system of moving kiln shelf parts to ape the ability of bricks to infinitely vary their openings comes under the heading of "gilding the Lilly." The additional energy savings it provides probably is not worth the effort. Make up new openings in door mounted shelves sparingly. Diamond coated and carbide coated rotary burrs (and diamond or carbide coated hole saws) are the preferred way to drill holes in kiln shelves. Friction cutoff blades and diamond coated blades are the best ways to cut out straight lines between those holes. A hinged and latched door, can also work on a box forge. Yet, movable bricks, trapped in an angle iron frame will work out better than the hinged door. Furthermore, the angle frame works best, by sliding up and down; counter balanced by a weighted wire, and running through pulleys, or simply sliding sideways. You want to coat the hot-face side of either kind of door with one of the re-emission coatings. You can use a formula of 95% zirconia silicate powder (crushed zircon) and 5% Veegum (or 5% bentonite as an alternate); this mixture makes a tough heat reflection coating for wear surfaces. The ingredients should be available in ceramic supply stores. Zirconium silicate can also be mixed with fumed silica to make a tuff and heat reflective coating on hard refractories (but not on ceramic fiber products). There are other choices, Like Plistix 900F, but none of them are easily purchased in other countries. Zirconium silicate and bentonite clay should be readily available in pottery supply stores, all over the globe. Note: fumed silica in water is also known as colloidal silica. Silica (silicon oxide) is the main ingredient in common glass. However, glass has a much lower melting temperature than silica, because lime and potash are mixed into it, for the express purpose of lowering melting temperatures (the lime), and promoting the process of melting (the potash). Fumed silica melts initially, because the powder’s particles are so small that it has a tremendous amount of surface area, to promote the melting process. After the initial firing, this silica becomes glass like, and remelting it would take far higher temperatures. This is why fumed silica easily melts (once) on the surface of ceramic fibers, to make rigidizer on fiber insulation. And why it also works as one of the binders in some high alumina refractories. Casting furnace lids All these advantages can also be applied in casting furnace mode, if a round kiln shelf is placed in a hoop, which can be swung into position above the furnace and swung out of the way during crucible removal. A mall center hole in the shelf allows observation and metal to be added to the melt; it also provides a rest for preheating metal to make sure it is thoroughly dry before placement in the crucible. But the hot exhaust gasses will heat re-emission coatings into incandescence, causing energy to be radiated back into the furnace.

cutting your forge's cubic area in half will more than cut your fuel bills in half. During the time that you are only running one burner out of the two, that fuel bill will be quartered. Finally excess flame heats up your shop; that can be a pain even in December; in July this could lead to foul language and a poor attitude

You have time and work invested in your way too large cylinder. Rather than scrapping your planes, consider building a "D" forge, instead of a tunnel forge; that puts it interior down to easily handled by one 3/4" burner (workable), or two 1/2" burners (a much better choice). Yes, scrapping planes is a great waste; so are scrapping plans

With a multi-flame nozzle, I would bump the burner size to 3/8" because it has a larger turn-down range to play with. Also, It is actually easier to get the 3/8" size right than the 1/4" size. This is because the smaller the burner the smaller any deviation from perfect construction that remains in the ballpark. Furthermore, linear burners are less finicky to tune in these small sizes. Just a couple of things to think about...

That is way more flame than such a small space can handle. One-gallon containers are equivalent to coffee-can forges; those can use burners as small as 1/4". A 3/8" burner needs to be turn down quite a bit to run well in them. The problem is back-pressure. However, multi-flame burner nozzles, a couple of which have been shown on this group, can be sized down as far as you like. Consider a pipe reducer with a stainless steel face plate, with small holes drilled in it. There is always a way to play

You are in a good position to compare a good fan-blown, and a good naturally aspirated burner in the same forge. Tell us what you like, or find limiting about one type versus the other, since yours is likely to be a reasonably unbiased opinion. Or does it turn out that you like both equally, but prefer on over the other for particular tasks?

Frosty is right about your burner, Lee. Once or twice a year on IFI, someone shows us something neat about burner design, or forge design; but seldom game changing. The pattern of your burner's flames dove-tails nicely into short WIDE-WIDE-LOW box forges; this could be a game changer for many smiths

Your burner continues to provide good lessons. The second one is a reminder that the flame doesn't always need to complete combustion in a single flame envelope, to do quite well in heating up a forge. If I hadn't seen it with my own eyes, I wouldn't have believed it to be possible. Once again, circumstances alters cases. Thank you for refining what I think I know about burner and forge design

Using Air/fuel torch-heads There are a large variety of air/fuel torches, new or old, that can be re-tasked into equipment burners. Recently, I have been seeing MAP gas hand torches marketed online (AKA dual-fuel torch-heads) that are rated to burn propylene as well as propane); some of them feature a stainless steel flame tube (AKA flame retention nozzle), which makes them fit for use as equipment burners; with the addition of a doubling tube to prevent their flame tubes from being rapidly oxidized away in the super-heated equipment atmosphere. Some air/fuel torches now come with a short fuel hose, instead of just being mounted on a 16 oz. canister (none-refillable gas cylinder). Separating the torch from its fuel cylinder allows it to be easily positioned at any angle, while the cylinder, which must remain upright, can do so unhindered; but its main value when mounted on a forge or casting furnace is that the fuel cylinder can then be kept a few feet away from the hot equipment. The latest versions of air/fuel torches also feature two needle valves. One valve is part of the cylinder fitting, while the other valve is mounted on the torch head. You may wonder why two valves? The answer may be safety. With a separate valve at the fuel cylinder, the hose and torch can be exhausted of positive pressure after shutdown, while a second valve on the torch can then be closed, preventing ambient air from mingling with fuel gas in the hose. Without positive pressure, even a needle valve is unlikely to leak, while pure fuel in the gas hose is no more flammable than pure air is. We might think that simply detaching the assembly from the fuel cylinder will do the same job, but the reason that 1 lb. fuel cylinders are not supposed to be refilled is that, once opened, their valves are no longer reliable; they can leak. The whole point of discussing air/fuel torches is that they can be used, with some modification, as a practical substitute for 1/4" burners, which can be built, but would cost more than these torches, to do the same job; that job would be running two-brick and coffee-can forges; at less than $30 they can be a bargain. Note: there are fuel hoses of different lengths available, which have various fittings on their ends; some of them have female fittings on one end to connect with a fuel/air torch and a male fitting, with a needle valve included, on the other end to attach to a fuel canister; these allow you to use the torch-head of your choice to do the same jobs cylinder mount torch-heads. “Flame tubes” are one of the various names manufacturers hang on the combination mixing tube and tip that their air/fuel torches use as flame retention nozzles. I have seen double, and even triple flame tubes on air/fuel torches; so long as their flame tubes are stainless steel, they should work okay inside miniature forges and casting furnaces, for a short while. But, even when their flame tubes are made from stainless steel, things "are no slam dunk." My torch has a single stainless steel flame tube, which has an internal fin for helping to mix the fuel air mixture; that appears to also be stainless steel, but it might have been made of brass in a cheaper torch; this would have made it undesirable as an equipment burner. A double or triple flame tube isn't going to be easy to mount in a burner portal opening. More than one flame tube is going to be hard or even impossible to slip a doubling tube onto. My burner's flame tube wall is only about .030" thick. When mounted in a forge or casting furnace, the superheated portion of stainless steel tubing will rapidly oxidize away. Without a thick walled doubling tube, that torch wouldn't last very long. Also a doubling tube allows us to use thumbscrews in the burner portal’s tube to securely hold the torch in place. What it boils down to is that just because we can get away with a thing (for a while), doesn't necessarily mean we should try to. Note: the self-igniting option on air/fuel torches does not usually work for long; its piezo eclectic crystal is durable, but the spark wire portion of the unit can fail in short order. What happens is that for a split-second during ignition there is some blast force generated on the wire’s end; this gradually moves the wire enough to prevent the spark from jumping the gap between wire and the torch body (which provides its ground). You can push the wire back into position two or three times, and then it breaks off. So why is such a poor idea featured on so many torches? To raise their price tags. The STK-9 air/fuel torch: I choose this air/fuel torch, not because it will make the cheapest or hottest burner to build, but because it is a reliable model, and allows the easiest miniature burner to construct. Aside from fitting a thicker doubling tube over its flame tube, all other parts are purchased with the torch. Building miniature burners from scratch are only fun for diehard enthusiasts. Furthermore, once you get down to a 1/4” homemade burner size, reasonably priced propane torches can match their output for little more money that you would spend on building materials to construct the burner from scratch. So, for use as air/fuel hand torches, building such burners are largely a waste of time. Until recently, canister-mount air/fuel torches didn’t get mini forges and casting furnaces hot enough to be a practical choice; the problem was that their brass flame tubes had to remain outside the equipment’s burner portal, to keep from being melted; this led to excessive secondary air being inducted into the equipment by the burner’s flame; interfering with proper heating. Stainless steel tubes have been appearing on some air/fuel torches in recent years, so that they would able to also burn propylene fuel safely (since the Canadian plant was switched over to it in 2008, all so called MAPP fuel has consisted of propylene). A stainless steel tube also allows, “dual fuel” torches to heat miniature forges and casting furnaces (coffee-can size and smaller) efficiently, through mounting in a burner portal exactly like commercial and homemade propane burners; this also holds true for “two brick” miniature forges. The TurboTorch STK-9 dual fuel torch, has a goose-necked stainless steel tube (AKA swivel stem) that is bent at a seventy degree angle; this flame tube, can be rotated through three-hundred-sixty degrees, and then locked in place; this allows the torch to be aimed upward through a forge’s burner port, while its fuel canister remains upright, or remain upright while the burner’s flame tube is aimed horizontally through the side of a casting furnace. The STK9 torch produces 1,800 Btu on propylene fuel; enough to silver braze 1-3/4” copper pipe (Up to 1” pipe on propane), or run a coffee-can forge or furnace on propane. Note: TurboTorch STK-11 is the next step up in heating ability, but at its price you would be as well off to build a 3/8” burner from scratch. Maintenance: While it has a solid reputation, its regulator tends to lose the ability to completely shut off gas flow, over a two or three year period of frequent use as a hand torch; this is only to be expected, since regulators are designed to control gas flow; not to stop it. Ball valves work best as open/close controls. The torch has a three year warrantee available. A few plumbers, who reposition the flame tube frequently, have also noticed a leak develop around the tightening screw for the gas tube. A little gas rated medium strength (removable) Threadlocker can solve that problem; keep it away from the last two threads at the nut’s forward end. When mounted in heating equipment, this part should never develop a leak. Propane, is not anywhere near as clean as the triple refined butane fuel used in modern blue flame torches and lighters, but the tiny gas orifice typically used on both propane and butane fuel/air torches are pretty much alike. It should not come as a surprise that you will need to clean out the gas jet when using propane fuel. The stem that the fuel runs from the canister through can be unscrewed, soaked in solvent, and then blown out with a canister of compressed air from an office supply store. This torch also has an easily cleaned gas jet orifice screwed into its flame tube, instead of in a hard to clean fill stem (as is common on cheaper air/fuel torches). The protective sleeve (AKA doubler): The end of the thin wall stainless steel that is used for a flame tube will oxidize away, when the torch is used in a forge or casting furnace. Although its crimped end is designed to retain the flame out in open air, it isn’t necessary when the torch is mounted in an equipment portal at an angle, so that the flame can swirl through the equipment’s interior; in that position the flame will be retained without need for the crimp to aid flame retention. Therefore, it is prudent to use cheap digital calipers to find the flame tip’s outside diameter, and buy a stainless steel tube to slide over the flame tip, to strengthen and thicken it; doing this at the beginning will also simplify mounting the burner in the equipment’s steel burner portal, without danger of the clamping screws denting the thin walled flame tube. You can buy stainless steel tube cut to size from Onlinemetals.com and from other online retailers, and have the part shipped for very little added expense. The flame tube on my STK-9 torch ended up measuring out at 0.505” diameter near its threaded brass air to fuel mixing chamber, and only 0.499” to 0.500” diameter along most of its length. A 5-1/2” long piece of welded #316 stainless steel tube (0.620” outside diameter, and 0.495” inside diameter) costs $5.70 and shipping, cut to length (part # 4236 at Onlinemetals.com). Welded tubing has an internal ridge. Cutting a slit through the ridged area will eliminate it and allow the tube to spring open a few thousandths of an inch along most of its length. Leaving the last inch of the tube uncut, and using a grind stone accessory (spun in a rotary tool) to flatten the remaining internal ridge, and then to enlarge the end of the tube just enough for a snug sliding fit, allows it to pushed over the flame tube, also protecting it from being dented by thightening screws during mounting. The doubler tube is 1/2” longer than the flame tube, protecting its end, and greatly slowing high temperature oxidation damage. Use a small angle to ensure scribing a straight line on the outside surface parallel to tube’s internal weld bead. Fuel: Available fuel for air/fuel torches include propane, propylene, LPG (which are commercial mixtures containing propane and butane), and pure butane. Both butane and LPG mixtures are available in refillable cylinders in some areas of the USA and in other countries, but their nonrefillable canisters are not the same design as the non-refillable canisters (AKA throwaway cylinders) of propane and propylene, which mount unto different torch-heads. Always read and understand the manufacturer’s instructions before attempting to use an air/fuel torch. Caution: Non-refillable (AKA throwaway) 16 oz. propane and propylene canisters can be refilled from larger refillable fuel cylinders, through use of special connector fittings, but it is illegal to do so, because the valves on those 16 oz. cannisters tend to leak after refilling. For a few more dollars than the refill fittings cost, you can buy an adapter hose, and run your torch from one of the larger refillable fuel cylinders, saving fuel costs legally; but that cylinder must then stay outdoors. NFPA (National Fire Prevention Association) safety guidelines state that LPG (liquified petroleum gas) cylinders larger than one pound (16 oz.) are not to be used or stored within habitations; you can assume that will include garages or other structures people frequent. The cylinders are to be stored and used outdoors, out of direct sunlight, on a concrete surface above ground level, in an erect position, and twenty feet from any ignition source, including electrical outlets. Most municipalities closely follow NFPA recommendations in their safety codes. This means that in case of a fire or explosion, breaking NFPA guidelines will almost certainly void your insurance policy, and leave you wide open to devastating lawsuits: LPG products include methane, propane, butane, propylene, and combinations thereof. The STK-9’s flame tubes can be positioned to allow a 16 oz. fuel canister to rest below most of a mini-forge or casting furnace’s body, but it is safer to move the fuel cylinder a few feet away from your heating equipment. It is a lot handier to move a hand torch independent of its fuel cylinder, and so short extension hoses are marketed for use with air/fuel torches; these have a female connector for a torch-head at one end, and a male connector for a throwaway fuel canister at their other end. Note that not all these products are built with reliable quality; don’t look for the cheapest products, and take the time to read what other purchasers have to say about them before purchase Throwaway cylinders get expensive; especially for propylene fuel, so now much longer extension hoses with canister connectors for the torch end and POL connectors for refillable fuel cylinders at their other end, are available online from Amazon’s propane section, and from other retailers.

“D” forges: Are usually less portable than tunnel or oval forges; they should be mounted on a table, unless they are constructed with very rigid bottoms. Both tunnel and oval forges do a better job of shedding excessive heat from their shells. There is no denying that the “D” on its side shape is a much easier and cheaper forge to build than an oval; its floor is completely flat, making it natural to employ Thermal Ceramic’s (a Morgan company) K26 tough and highly insulating firebrick as their floors, and ceramic board and/or Perlite under the brick as secondary insulation. The vault (top section of the shell) can be shaped by bending sheet metal over a propane cylinder, or cutting a pail in half. Rigidized ceramic wool will stay in place under the vaulted (arched) portion of its shell. Miniature “D” forges are often built from old mail boxes.

I gave up on herding cats and other fruitless pursuits.

You don't need to look to the far east for that. Cheap imitations made by second raters are as American as apple pie.

The point of gas forges is to conserve heat. Even a second rate propane forge can enable you to heat steel better than the largest rose-bud on an oxyacetylene torch, for a small fraction of the running costs. However, a properly designed forge can run rings around that second rate tool. If you want to design a first rate forge, you need to know what goes where, and why. So, lets discuss the WHY of insulation and finish coats inside your forge. Obviously, the layers of insulation are there to slow heat loss through conduction, but why should that be so very important? No, it isn't about some desperate attempt to conserve all the energy possible. If your forge was just a steel pipe, devoid of a scrap of insulation, the bulk of heat loss would still be straight out of the exhaust opening; not that steel wall. The main point of insulating the forge's interior surfaces is to deliberately build the level of incandescence on those surfaces. As a forge's internal surface temperature rises, so does the percentage of energy transferred to your work pieces by radiant energy. Past 2000 F the majority of energy transferred by radiant energy is greater than that transferred directly from the gas flame; and that process only becomes stronger as the color scale goes up. This brings us to finish coatings. Slowing heat loss by conduction is accomplished in two ways; insulation, and heat reflection. We call it heat reflection, rather than radiant reflection, because what is actually going on is re-emission of radiant energy from incandescent surfaces. All the heat that is being emitted and re-emitted from surfaces isn't available to be lost through conduction, making the insulation work harder to do its job. High alumina refractory will re-emmit around 70 percent of heat, if the surface particals are small enough; the rougher the surface the more that figure gets slashed. Zirconium oxide will re-emmit over 90 percent of heat enery, if the particles that make up it surface are small enough. So, how small is that? Small enough to remain in in solution with water; colloidal is how small. So, by starting with zirconium flour, and dissolving some in water, the amount that stays in solution will tell you what percentage is colloidal; that should be nearly all of it. Apply the same test to any refractory oxide you are considering; like, for instance Zircopax

That does seem to be the new small U.S. business model, doesn't it! I suppose it beats drop shipping factory rejects from China, for a living

No; the tea shops have their own commercial vision for success, and their game-plans are different, from one another; it isn't that they are a good alternative. It's more like "any port in a storm" time. If I think much more about this subject, I'm likely to get depressed. "The times, they are a changing."

You may find this strange, but the proliferation of drive-up kiosks and the pandemic mess didn't do regular coffee shops any favors. Normally, I just go to a restaurant to have a coffee sit down. In Seattle these days, it would probably be easier to find the coffee shop experience in a tea shop; weird huh?

What I don't see is an external supporting shell. Are you planning on adding external mechanical support with heavy layers of Perlite that is bonded together with water glass? That would also act as secondary insulation. "water glass, also called sodium silicate or soluble glass, a compound containing sodium oxide (Na2O) and silica (silicon dioxide, SiO2) that forms a glassy solid with the very useful property of being soluble in water. Water glass is sold as solid lumps or powders or as a clear, syrupy liquid." Copied from the Net

Well, we could start calling the top part its "vault"; I like that term better than "top."