Mikey98118

Gas Assemblies for Free-flow Burners It has been well established that the gas tube, and whatever MIG contact tip, or 3D printer nozzle is used as a gas orifice, should be centered with, and aimed parallel to the axis of a linear burner’s conical air entrance; and that this funnel shape must be centered on, and kept parallel to the mixing tube’s axis, by whatever means is convenient. But how you choose to mount the gas tube, is your first and best chance, to create an intense burner flame; do not waste it! Why such emphases on a “minor” detail? Your burner has an energy budget; it is limited to the air induction that the fuel gas jet creates via Bernoulli’s Principle; this is a naturally aspirated burner's engine. The least obstruction to incoming air, will subtract the least energy from your gas jet’s small output; this is an important factor to consider. As with the whirlpool in your bathtub drain, nearly all air is going to be induced near the conical opening’s periphery. No significant air will move down the center of the entrance. So what? So, this tells you just where obstruction impedes air most—and where it does not. The smaller your burner’s air intake diameter the more this factor matters. Finally, it takes energy to get incoming air moving, or to change that air’s direction, to create swirl. Any blade structure at the air funnel’s opening, starts incoming air moving laterally, instead that starting within the funnel, where it costs more energy. Mounting a gas assembly has two aspects; what is easiest and what works best. There will be no "perfect” method of balancing these factors, because aside from tooling and skill levels, we all have task preferences; mine is for maximum control of the parts being assembled, having found that the best results for the least work is attained, if Murphy’s law never gets the chance to muck anything up. Gas assemblies for free-flow burners are best mounted by suspending them in mounting plates made from fender washers, of up to 2” diameter; keeping your labor at a minimum, by requiring only part of the work needed, to create a mounting plate from scratch. For larger openings than 2” you must lay out the plate with dividers, on sheet metal. So, why start with sheet metal, or a fender washer to make a mounting plate? Why not braze, or weld the separate parts together instead? When you begin with a flat surface; all you need do, is avoid bending it, to assure that the gas assembly mounted to it will remain in line with the axis of the conical shaped air opening Fender washers come in various thicknesses, over which you have little control; because they all have 2” or smaller diameters, that is okay. But the larger mounting plates that you make from sheet metal need a minimum thickness, to ensure that they stay flat during construction, and installation. A 0.079” thickness in stainless-steel sheet is strong enough to remain straight, while being screwed or silver brazed to a funnel’s flange, but not so thick that it is difficult to drill holes and cut air openings in. How thick aluminum sheet should be is more dependent on what alloy is used, rather than funnel diameter. Choose 1/8” thick 6061 (AKA T651) aluminum plate; it is the most rigid aluminum alloy available, but is no more work to drill, thread, or cut, than a soft aluminum alloy. Use dividers, and a prick punch, to lay out a disc of the same size as the outside diameter of the funnel’s flange, or ink a line on the sheet metal, using the flange as a model, and use a cheap plastic center finder to mark a place to drill a center hole in it. Note: Small metric (ex. M2) cap screws and matching nuts are the inexpensive and simple way to screw mounting plates to smaller funnel flanges; they allow you to drill matching holes through both parts and use nuts to hold them together, while avoiding the use of tiny taps (which are inclined to break off in the hole). You can find them in kits for under ten dollars online. Drill an oversize hole through both parts (use 1/8” M35 high speed steel drill bits for M2 size screws). If the flange has room enough, using 10-32 cap screws will save on tool costs. Drill a hole in the middle of the disc for a Rivnut (a threaded rivet nut); this holds an externally threaded gas pipe, which can be moved back and forth in the funnel, as part of the tuning process. The rivet nut is pushed into the washer, for silver brazing, silver soldering, or for setting in place (physically trapping by deformation). Mark out three equal spaces for air openings, between three ribs, using a divider (or just use the points of a hex bolt and plastic center finder to indicate where they should be). Drill holes between the the ribs, comfortably outside the area of the nut, and cut between them. Remember that there is no significant air flow in this central part of the opening, so do not shortchange yourself on rib width in this area. The ribs would be too weak, if you kept their lines parallel; that is not desirable. You want the three ribs narrower at their outer ends, and becoming wider toward the center of your disc, to balance maximum air induction with sufficient inflexibility. If you use a silver braze alloy with as high a melting range as you can find, along with black flux (which is rated for stainless-steel), it will provide a high temperature bond that requires less care to keep a brazed rivet nut in place, while brazing the ends of the mounting plate’s three ribs onto a funnel flange, with easy flow silver brazing wire and a lower temperature rated white flux (but still rated for stainless steel). Water-soaked rags, or blocking putty (ex. Wetrag) around the rivet nut, but kept away from the second area being joined, is another way to help protect existing silver brazed joints. Anti-flux can be placed around a joined area that is too close to the new joint for blocking putty to be used effectively; by resisting fluid flow out of the area of an existing joint, it will help you to protect it, when brazing a second joint, if you waste no time. Drilling and threading brass gas tubes: Most brass tubes and pipe fittings that you will buy and turn into burner parts are half-hard brass; this can be drilled and threaded more easily than stainless-steel alloys; however, it can be tricky to tap threads into, or run a die down; it tends to gum up tool edges on dies and taps. Half-hard brass alloys are inclined to compress during threading; this is a form of work hardening. Tapping fluid should be employed during threading; it can be purchased in amounts smaller than a pint). Even cooking oil is better than dry threading. Internal thread: Always tap the internal thread for whatever part you employ as a gas orifice first. Cut the external thread second. Tubing sizes may be a little small inside; in that case use the recommended drill size to enlarge it before running internal thread with a tap. If the tube is a few thousandths oversize, that is okay. Many novices lack a drill press, and see no use for one; they will be tempted to drill and thread by hand. However, a cheap drill press vice is only about ten dollars, and by placing your parts in the vice before you try hand drilling or threading with a tap, you will stay parallel with the tubing axis, far more easily (trapping your tube in the vice will also help you to correctly start a die down its exterior). Start threading with your tap as perpendicular 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 half-hard brass; instead, you must back off the tap 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 of M6x1 or ¼-27 and in size. Also back off the tap every full turn forward, and run it back over the thread you just made to clear burrs, and smooth up the new thread; otherwise, after a few extra twists, so much pressure will be needed to do this, that small taps will break off in the hole, as you attempt to back them out. Be liberal with your tapping oil. Dealing with a broken tap is no fun. Should you break a tap off in the tube, gently tap back and forth on its protruding point, to loosen it in the hole; then, try to back it out with pliers; if that does not work, cut away that section of tube, and try again with a new tap. You should have no need to use a drill bit inside 5/16”x3/16” brass tubing, unless your tubing isn’t actually 3/16” inside diameter; that is not very likely, but these are usually imported parts; you are probably going to be dealing with an ignorant drop- shipper (meaning they “don’t know or care” about actual sizes). External thread: Use the same care when threading with dies as with taps. Dies usually have their description written on the opposite side that is meant to face the work. Be careful to mount the die facing correctly, and grind a bevel on the tube’s end, to help get it started threading at true right angles; if you start the die threading close enough to perpendicular to the tube, it will finish truing itself up, within a twist or two. If the tube is a few thousandths small on the outside, that is okay. If the tube is the slightest amount oversize, your die will have far more work to do; spin the tube in a drill motor, and sand that extra diameter down to size; especially when running coarse thread, like 5/16-18. The coarser the thread the harder it is to run. But the courser the thread the less of it that needs to make contact. 75% contact may be needed in a fine thread, while 50% contact will work just as well in a coarse thread. Even the same outside diameter as the die can be hard to work with. If the first half-inch of thread is difficult to run, consider deliberately sanding the rest of the tube’s length a few thousandths of an inch undersize. Full contact in the first half-inch (at the tube’s end) helps to secure a gas tight joint with a hose fitting, but it is not needed (or especially desirable) on the rest of the gas tube. So why work that hard? After cutting the external thread, chase it thoroughly. Run the die back and forth over the new thread, until it moves easily. Otherwise, this part of your burner will be difficult to adjust for fine tuning. 5/16-18 screw-on flat mounting T-nuts can be reshaped and silver brazed, or silver soldered directly onto small funnel flanges; or they can be screwed onto large diameter metal plates, which are soldered, brazed, or screwed onto large funnel flanges. Rivet nuts (AKA Rivnuts) are internally threaded hollow rivets; they come in several different types, including round splined rivet nuts, which are your best choice for attaching externally threaded gas tubes onto metal mounting plates; they are press fit in place, through deformation, like solid rivets. The main difference is that they are designed to distort easily enough that they can be trapped in place with wrenches. A rivet nut gun is not needed, for mounting a few of these rivets; they will reshape and be trapped into place, centered and perpendicular, on thin sheet metal flat washers, or on cut out sheet metal. This creates a very strong joint that is always perfectly positioned on the mounting plate; they can also be silver brazed or silver soldered into position, if you prefer. Rivet nuts come in zinc plated mild steel, which is best for silver soldering unto mild steel mounting plates; stainless steel, which is best for silver brazing unto stainless steel mounting plates; and aluminum, which forms far more easily than stainless or mild steel, easing mechanical strain on a rivet nut setting tool’s bolt; aluminum is barely strong enough for use as rivet nuts. Materials needed to make your own rivet nut setting tool: (A) One grade #8 (SAE standard) steel socket head cap screw or bolt, of the same thread size as the rivet nut, and at least long enough to accommodate every part on the tool, and still engage all the threads on the rivet nut. The reason to use a high strength cap screw or bolt, is that it is much tougher than a low carbon mild steel cap screw; extra tensile strength is needed when using a small diameter cap screw or bolt as part of your rivet nut setting tool. Mild steel screws and bolts have about one-fourth the strength of high-grade screws and bolts, which are made of medium carbon content alloy steel, that has been quenched and tempered for maximum tensile strength. (B) A minimum of two brass flat washers, to sit next to the flange screw at the head of the bolt (and provide bearing surfaces). Some people even grease these washers. More washers will simply help the bolt to turn more easily. C) Two flange nuts; one is screwed up tight against the bolt head, and a second flange nut that is drilled out or a larger size, to freely slide over the bolt’s thread (it is there to provide a bearing surface between the rivet nut and the turning bolt, with its locking surface on the side facing the rivet head (you do not want the rivet nut to turn in the hole, while being crushed into shape). (D) An open end wrench for the bolt or cap screw’s head, and a small crescent wrench for the flange nut. Drill a hole in the mounting plate that is as close to the rivet nut’s outside diameter as is feasible. A light friction fit would be ideal. The more gap there is between the rivet nut and the hole, the harder your job of riveting will become. The less gap there is between the rivet nut’s body and the hole it gets pushed into, the sooner it starts becoming trapped in place (and no longer able to turn under your tool). Screw the first flange nut tightly against the bolt head. Slide two or more flat washers onto the bolt, beside the first flange nut. Slide the drilled-out flange nut onto the bolt, with its locking side facing the rivet nut. Screw this assembly unto the rivet nut, just finger tight. Push the rivet nut into the hole in the mounting plate. Place the crescent wrench on the flange nut, and the open-end wrench on the bolt or cap screw head. Turn the bolt head until the rivet nut is securely fastened onto the mounting plate, using the wrench on the drilled-out flange nut to keep it from turning, too. You can find several videos of this process on the Net, with variations in nut and flat washer choices. Fender washers come in a limited number of center hole sizes, but it is not much work to drill or grind out a smaller hole to fit a 1/16” larger rivet nut diameter. This trick is even easier, when you need to increase a hole in a sheet metal mounting plate, a little larger than the largest bit that can be chucked in your drill motor. If you cannot find a high-grade cap screw or bolt to use as part of a homemade rivet nut setting tool, then employ aluminum rivet nuts, because 6mm rivets require equally small bolts. Even though small rivet nuts are easier to compress into shape, the problem of breakage grows as the bolt diameter shrinks. Unless they are high strength steel, ¼” and smaller mild steel bolts are likely to break off while being stressed by use as part of this hand tool. Then, malleable aluminum becomes the obvious choice for small rivet nuts. The same factors are present in commercial rivet nut setting tools, and show up as broken mandrels. Why does this happen? Because properly tempering mandrels calls for good quality control, and that is usually absent with cheap tools. For larger rivet nuts (8mm or 5/16” and up) you should choose steel rivet nuts, because, in the larger sizes, many people complain of stripping weak aluminum threads, while the rivet nut is being reshaped. Larger mandrels on the commercial tools (and larger bolts on home-built tools) are much less inclined to break. Note: High grade bolts are easier to find than imported rivet nut tools with properly hardened mandrels; these homemade tools are also inexpensive, and take up little room in a toolbox. Flange nuts: Are special nuts with a flange protruding beyond the width of the hex nut portion its bottom side, which functions as a built-in washer. Most of them also have teeth on the face of that flange, to look it in position (like a locking washer), although some have a smooth faced flange (like a flat washer), and a nylon ring inset into their hex head portion. Smoothed faced locking flange nuts are the best choice to use as the locking washer on a gas tube. You will use two flange nuts as part of your homemade rivet tool, and a third flange nut to tighten the gas tube into axially true position on the gas assembly’s mounting plate. Alternatively, two flange nuts can be used to secure the gas tube on a mounting plate without use of a rivet nut, if need be. One flange nut is silver brazed, or silver soldered to the forward-facing side of the mounting plate. The second nut is snugged up against the opposite face of the plate, to tightly trap the gas tube in an perpendicular position. 5/16”x 3/16” brass tube is 0.3125” outside diameter by 0.1875” inside diameter. 8-millimeter tubing is 0.312” outside diameter. 5-millimeter inside diameter is 0.195”. So, both 8x5mm and 5/16”x 3/16” brass tubing can be threaded for either MIG contact tips, or 3D printer nozzles. The importance of these tube sizes is, that they provide sufficient wall thickness to run exterior thread safely past the interior thread needed for a gas orifice, so that the gas tube can simply be unscrewed from a mounting plate, its gas orifice cleaned, and then replaced, without removing that mounting plate. Both 5/16-18 and M8x1 rivet nuts and flange nuts are readily available online. Thus, mounting plates can be silver brazed in place on any funnel. Your choice of funnels is greatly increased, by not requiring a built-in flange. Mig contact tips are the preferred choice for ¾” (and larger) burner sizes; with the addition of a short section of 0.020” I.D. capillary tube included, they also make the hottest ½” size burners. 3D printer nozzles are far more convenient than MIG tips with capillary tubes, for ½” and smaller burner sizes. 5/16”x 3/16” brass tube, and 8-millimeter tube, can both be internally threaded for 3D printer nozzles with an M6x1 tap; they can also be threaded for Tweco, Lincoln, Forney, and most other 200–400-amp MIG contact tips, with a 1/4-27 tap (the most common thread found in MIG contact tips). Either choice results in a streamlined gas flow between tube and orifice, permitting 2” long gas tubes to function as efficiently as 3-1/2” long 1/8” schedule #40 pipe did, previously. The tube exterior will accept 5/16-18 dies to create external thread for 5-18 rivet nuts (for use on mounting plates). However, 5/16” is only 0.0025” larger diameter than 8-millimeter, allowing it to also be externally threaded to match 8M, or 5/16-18 rivet nuts. 5/16”-3/16” and 8x5mm tubing can both be used to create gas tubes, which are screwed directly into (drilled and threaded on a drill press) ¼” thick aluminum mounting plate, and then locked in position with a flange nut. If you chose a nylon inserted locknut for this, it will stay in the correct position, without need for brazing, soldering, or gluing it on the gas tube, after the optimal distance between gas orifice and mixing tube opening is found (during tuning). Hose barb sizes for 5/16” tube: Barbed hose coupling sizes match the outer diameter of the narrowest portion of the barb; this leaves no room for threads of those same diameter. Therefore, 5/16” barbed couplings can be threaded to match up with 5/16” tube, only through their thickest section. You want to choose a hose barb that has enough length in that section to work well for threading. I suggest cutting short one leg of a straight hose barb; this should provide ½” of thread to engage the external thread on the gas tube, after sealing with thread-locker. Thread-locker comes in hardening and non-hardening types; both kinds are resistant to vibration, and the hardening type makes a stronger bond, but is not designed with the same flexibility in mind. So, be sure that the metals you bond with hardening type thread-locker are metals with similar coefficiencies of expansion; such as stainless to mild steels, or copper to brass, or to aluminum. Not, stainless or mild steel to aluminum, copper, or brass. You want all the parts to expand and contract from temperature changes at close to the same rate. Note: An aluminum mounting plate on a stainless-steel funnel, or vice versa calls for screws and nuts in slightly oversize holes, so that some part movement can be tolerated. Thread-locker for fuel lines, is rated for use with petroleum products, so you can use it to seal parts of your gas line (just remember that the hardening type of thread-locker, which makes such a convenient glue, also prevents the MIG contact tip from being unscrewed for cleaning, without first being heated up with a lighter or match).

So, just what advantages are gained in a burner from increased vorticity (which can be defined as velocity curl) First and foremost is good mixing of the fuel gas with incoming air. Propane takes a fair amount of mixing to burn completely in a primary flame envelope. A swirling motion provides the most mixing for the least drag on your burner’s air-gas mixture flow. Secondly, it speeds-up mixture flow rate through the burner, because the exit speed of air from the conical shaped air entrance, into the burner’s mixing tube, is approximately one-half of its rotational speed. Finally, vortex motion reduces the air flow’s pressure. The primary limit on flame intensity in a burner is how much it can be turned up, before being blown off the burner’s flame retention nozzle. So, lower flow pressure increases how intensely the flame can be run. Of course, a flame retention nozzle decreases mixture pressure in that area; however, the nozzle is limited in its ability to do so. A lower flow pressure into the nozzle greatly reduces the work it must accomplish.

You have it right. However, circumstances always alter cases, and we try to keep tweaking our advice to keep up with them. The latest circumstance to call along, is a flood of reasonably priced small commercial forges. What I view as first forges, because they are affordable, and small. For most of us, a larger forge isn't to far down the road, after some use with one of these beginner's models. This works out very well, because, no matter what forge people eventually think of as their ideal, that small forge will always be used whenever possible to keep the fuel bills down, and to keep the shop cooler in warm weather. But, the smaller the forge the more important those details, like floor thickness becomes; not just for cubic area, but also to keep enough room for combustion to complete before the flame impinges on the work. One of the changed circumstances, is a few vendors selling reasonably priced ceramic fiber board, to place beneath a Kastolite floor; this choice is timely, because my favorite choice of floor (a high alumina kiln shelf) has become overpriced.

So, what I'm getting at is that it's okay to watch the cartoons without your Warner Brothers hat. And by the way, just do what you need to, to reach your goal. When I wuz young and in my prime, I drunk that coffee, all the time. But now I'm old and very gray, I only slurps it once per day. The other two mugs is tea

Short answer? No; long answer is certainly not! But that is only my view. Query them about their reasons; perhaps they have good ones. Nobody knows everything. Or else we would have to call them a "know-it-all" (maybe that is a poor choice of subject for a know-it-all)...more coffee, yes, that will fix things up Okay, you are mostly dealing with hot-roding mad scientist types here; yes a bunch of them are sensible, but the rest of us try hard to ignore that, as much as we can. So, naturally our favorite answers tend to be extreme. In the real world, a made several casting furnaces from five-gallon propane cylinders, that had two-inch thick Kast-O-lite 30 linings; they work just fine, and heated up almost as quickly as the latter equipment that had 1/2" thick flame faces of Kast-O-lite 30, backed with 2" thick ceramic fiber insulation. They may take away my union card for saying so.

There are are three guys that I know of on this forum who have worked art in multiple materials. Although raised in an ornamental iron shop, I started deliberately mixing it with glass, once I rose to making design decisions; eventually, I blew glass into ornamental iron candle holders. One of the other guys on here spent years blowing glass (I think professionally). I don't know why guys on here don't talk much about it, but mixed-media was my passion, back when I was young enough to have any Frosty, I read your message, but when a paged back to the previous page, to see what guy you meant, your message disappeared. Being barely able to deal with computers at all, I have had to accept the glitches that happen on this forum

I don't have it posted, but you can buy or rent a used copy of the book Gas Burners for Forges, Furnaces, & Kilns; it has also been available for free downloads from various pirate sites for decades; and no, I have nothing against it being downloaded from such a source Yes, you definitely should use one of the burners that way. I suggest just such a course in the book.

It is good to finally see the "D." I am a fan of the oval, but despite my druthers, am forced to confess that the "D" rules

Safety limits for forced-flow burners Some part shapes used for air entrances on naturally aspirated linear burners, also work well with moving impeller blades, while others do not. However, the limits on shape and size imposed by use of moving blades, do not apply to motionless blades; these can be mounted on gas tubes without much forethought. Straight or curved wall pipe reducers, kitchen funnels, and other constricting tubular shapes, provide convenient ready-made entrances for incoming air to spiral its way through; and into the burner’s mixing tube. The air flow’s ever-smaller curve increases its rotational speed, along with forward velocity (by about one-half of the rotational speed). Also, the faster the incoming air’s rotational velocity, the lower the pressure of the incoming airflow through the mixing tube; these are all positive factors, but they require the mixing tube to be lengthened (about one-third more than with free-flow (naturally aspirated) burners) to stabilize the flame (by allowing fluid friction within the tube to slow the mixture’s swirl, before it exits into the flame retention nozzle). The first factor to keep in mind about funnels and other constrictive shapes, is the greater the ratio between the air opening’s diameter and the mixing tube’s diameter, the greater the vorticity created (the stronger the vortex). Secondly, the shorter the length of the cone shape the closer the gas jet is to the low-pressure area being created at its opening. This drop in the pressure of incoming air is not sufficient in free-flow (naturally aspirated) burners to create a problem, but the partial vacuum created at this point with the forced-flow of moving impeller blades, can draw some fuel gas back into the fan motor, if the gas orifice is close enough to it; then, the motor’s electrical sparks from brushed motors will ignite the fuel/air mixture. So, the first margin of safety in forced-flow burners is provided by sufficient length in the constrictor shape. Secondly, a maximum 3:1 ratio between the opening’s internal diameter to mixing tube’s internal diameter, helps to limit the strength of the partial vacuum created by these weak computer fans. Note: A low ratio (ex. 2:1) can be offset with a stronger fan. So, less than a 3:1 ratio in a part you are considering, need not automatically prevent you from using it. Help can also be provided by the addition of a short tube section between the funnel opening and the fan, producing the same effect as a longer funnel shape (in avoiding back-flow of fuel gas into the fan motor). Note: The moving fan blades you are concerned with here are impeller blades, which have become standard on axial computer fans; not the old-style flatter blades, which are meant to push air forward; those increase the pressure of incoming air. Impeller blades lower the pressure of incoming air. Be sure to seal the joint between the fan and and the funnel opening, to prevent air from being flung by the fan blades, through any gap; this will suck fuel gas through that gap, along with the air, and then into the fan entrance. Choose a brushless motor, if you can. Brushed motors constantly create electrical sparks between their two brushes and the commutator; they will ignite any fuel gas that enters the fan entrance. Brushless motors are very unlikely to create sparks. No sparks mean no ignition of stray fuel gas. The chance for sparking in a brushless motor is not zero, but it is close; good enough as one safety choice, among others. This leaves us wondering how much funnel length is long enough with impeller blades. Only experience can answer that question. Furthermore, fan strength, constrictor shape (straight, convex, or concave wall) all come into play. Add to that, how much curvature, at what point in a funnel shape, and we are reduced to trial and error. Always remember that, if the burner you design starts backfiring into its fan, there is very little work needed to change it over to a naturally aspirated design. You do not have to rebuild the whole burner; just stop the fan.

Dual 1/2" burners would be better, even if you had only used a 2" thick layer of ceramic fiber blanket. You apparently ended up with a 5" internal diameter in your forge; this means that its diameter to length ratio will encourage back pressure, so going with two half inch burners is now a necessity. I would advice two 3/8" burners instead, but half-inch "T" burners will turn down far enough to work handily.

Taking your questions one by one, lets begin the the ceramic blanket. Lots of people decide to use the flame coating to push the blanket into shape. Some people are even sharp enough to mostly succeed with that move. But, as Frosty already pointed out the safe path is to use rigidizer to soak the blanket, and then mold it, before the water dries out of the solution, and turn the burners on for a couple of minutes to give it a permanent shape. Unlike many other tasks, this can be successfully done as easily piece meal, or all at once. You can even use a cardboard inner form, held together with tape to help you push the blanket where you want it to end up, before soaking with rigidizer, and heating the blanket, for it will freeze into the finish shape, before the cardboard burns up. Having shaped the blanket itself, holding, or even slightly improving that shape is far easier than trying to produce it as you put on the flame face. Always try; it doesn't matter what the outcome is, for you will learn something. Who knows, maybe things will be better than I predict. Then you can come back hear and say "See there mister smarty pants?" Personally, I think all us smarty pants need a sharp dressing down, frequently Good info, Tayor

The hex shaped shell of your forge, will allow you to mold the ceramic fiber and hard refractory coatings into an oval or "D" shape inside, which is fine. However,those burners look way too large for that size forge; their flame retention nozzles look to have oversized diameters for their mixing tubes. The photo appears to show something that might be a gas pipe running between them and into their nozzles, instead of being placed near the mixing tube openings; I will assume that it is not. But what it is, remains a mystery. I conclude that your forge is likely to suffer from a back pressure problem, resulting in poor combustion, low heat levels, and quite a lot of carbon monixied exiting both of its ends, as blue flame; is that correct? It does you now good to hear about your problems, without a reasonable solution. About now, what you find resonable is likely to be pretty restricted. Fortunately, those burners look like they can be aesily removed, and replaced by a single $25 Mister Volcano burner, which is all that forge can possibly use. Shove some leftover ceramic fiber in the front hole, stack a brick against the back opening, and use two or three bricks about 1" away from the front opening, to crontrol heat loss. No, those two burners aren't wasted, either. You will start wanting a larger forge in a few months, and they can be recyled into it. In the meantime, you will have lots of time to investigate, how to change them from poor to good burners; all the anwers you need are available right here on IFI. For instance, what to do about the oversized diameters on their flame retention nozzles? Insert stainless steel pipes inside of them, to reduce their diameters; this also solves the problem of oxidative loss, which would otherwise make them unusable in a few months. But how do you match the pipe that you buy with the exsiting inside diameters of those nozzles? Simply slit the pipe inserts along their inside weld beads, and compress them to fit. Don't forget to drill and thread holes for three little stainless steel socket set screws into the existing nozzles, to keep the inserts in place, when those nozzles heat up

Properly securing and balancing rotary accessories: Fully insert accessories into the tool’s spindle, and just snug the collet nut; do not over tighten, or you might strip its threads, or worse, the spindle threads. There is a good reason why collet wrenches are so tiny. Take the hint. I have yet to buy an accessories kit that does not include a little rectangular silicon carbide dressing stone; they are used to help balance the softer aluminum oxide grinding stones, wheels, and cut-off discs. Employ that dressing stone to counter-balance accessories; keeping your rotary tool from suffering degradation from excessive vibration. Cheap rotary tools are likely to have spindles, which were machined significantly out of true with the tool’s axis; if you add unbalanced accessories to that, bent shanks and thrown accessories are the next trouble that will be flung your way. A few light touches, with a dressing stone, can save you a lot of grief. You can also buy inexpensive, larger, dressing stones, when it wears out. Rotate accessories that can’t be balanced with a dressing stone (like steel discs, brushes, and sanding drums) a quarter turn at a time (in the spindle), to improve balance. Accessory shank and collet diameters need to be properly matched. Some accessories being sold as 1/8” actually have 3/32” shanks (common with engraving, and nail grooming accessories that were designed for pencil rotary tools). An eighth of an inch is 0.125”; also 3.2mm (which commonly turns out to be only 3.17mm). But, 3/32” shanks are more than 0.031” smaller than 1/8”; they will end up loose enough to vibrate their way out of a 1/8” collet. What to do? Buy a cheap set of brass collets; there will be a 3/32” collet among them. 3/32” shank accessories were designed for use in pencil rotary tools; their weak motors slow down the minute the accessory starts being worked; thus, the weaker shank is no problem, but that that may not hold true in a 160-watt rotary tool. You should reduce speed a little, when using them. 3mm shank accessories: When you see an ad for 1/8” (which is 3.2mm) accessories, followed by a description change to 3mm, you can depend on them being only 0.118” diameter shanks; not 0.125”; this may not stay gripped by your tool’s 1/8” collet, but is too large to slip into a 3/32” collet. Millimeter collets are sometimes available, but it is simpler to employ a Dremel keyless rotary tool chuck, or a keyed chuck in a micro-drill to use 3mm shanks safely. Extended-shank accessories: Fully inserting extended-shank tungsten carbide rotary burrs isn’t sufficient to keep them from bending. You must also run 4” long rotary shanks (1/8” diameter) at half speed, or less. Also run 4” long die grinder (1/4” diameter) shanks at half speed or less. 6” long shanks should simply be avoided, or cut to 4” lengths). If extended shank burrs are spun too fast—or are cheap versions of legitimate burrs—they will certainly bend in seconds. Why are accessories made with “overlong” shanks in the first place? So that they can reach further into internal areas (as in pipes and tubes); they were manufactured as specialty accessories. Since speed must be reduced according to shank length, consider cutting extended shanks down to just what is needed to get a particular job done, and no longer, because the longer the shank the more the tool must be slowed. Freeing up jammed accessories: Collet nuts on rotary tools may need to be sharply rapped once or twice with the tool’s tiny wrench, to free up jammed accessories. Unscrew the nut a partial turn, so that the accessory can slide free; sometimes, they will revolve, but cannot be slid forward and removed. What has happened is that the collet, which the accessory’s shank slides into has jammed in place, locking the accessory’s shank together with the collet. Tap sharply, on the end of the nut with nothing larger than the tiny wrench that comes with your rotary tool; this will transmit just enough of a shock wave through the parts, to break the collet’s grip. Should a new tool come from the factory with the collet stuck in place, unscrew the nut a couple of turns, and poke the shank of an accessory against the top of the collet (at an angle), to break it loose. If you change accessories frequently, you may find relief from sticking collets with a brass collet nut; brass collet kits, which include 1/8” collets, sell for around $7.00 on eBay and Amazon.com. Just as some collets release better than others, some collet nuts are better too. Most collet nuts fit other spindles, so switching a better collet nut from a less used rotary tool to your favorite, should be an obvious move. Many people simply replace the collet nut (and its sticking collet) with a Dremel keyless chuck. Make sure to buy this attachment from Dremel; a cheap look alike won’t work very long, if it even works at all. How clever is this move? Enough that a few rotary tools are now being sold with this kind of chuck, instead of a collet and nut. Nothing succeeds like success. That said, even the Dremel chucks are not problem free. Keyless chucks cannot be tightened anywhere near as effectively as keyed chucks, or even collet chucks, and these tiny keyless chucks increase that problem; obviously, your whole hand can tighten a keyless chuck on a drill motor far better, than a finger and thumb can tighten one of these. Some people have ended up using pliers. A drop of oil or lithium grease in one of the jaw ways (the groove they ride in) will smooth performance. Run-out (AKA runout): Any rotating tool is meant to revolve on its center. If its spindle isn’t machined true (centered and parallel to its axis), accessories mounted in a rotary tool, or die grinder will orbit in a tiny circle around its axis, instead of revolving on it, producing heavy vibration; this is called run-out. In fact, it is inevitable that all rotating tools will have some run-out; just not a noticeable amount. If a micro drill’s keyed chuck is not mounted true on the motor’s spindle (usually because the tiny brass arbor that connects them is not machined true, or carefully mounted), the micro drill bits mounted in the tool will also orbit around a tiny circle, and quickly break. Any drill bit, or stone mounted in the tool will have the same problems as they do in rotary tools and die grinders with run-out, but to a lesser extent, because of the drill’s lower speed range. The larger an abrasive stone’s diameter the easier it is to break; especially in a tool with run-out. If you cannot deal with that, there are tungsten carbide burrs that won’t break anywhere near as easily; of course, a tool that is heavily vibrating from a run-out problem will tend to fling them about. But at least this will adequately demonstrate that the stones were never your problem. Diamond coated chainsaw burrs, don’t break apart; nor are they as inclined to be flung about, as tungsten carbide burrs. But, run-out will quickly dull the diamonds, and even knock patches of the diamond coating off. Abrasive stones versus wheels: Stones have advantages for working inside small tubes and pipes. Wheels grind faster than most stones, because their larger diameters create higher surface speeds, if the pipe or tube is large enough for their use; of course, a dressing stone can always make the wheel fit. All of these products consist of abrasive grit bonded together by resin. But stones are also glued onto their steel shanks, creating a separate failure point. Wheels have arbor holes that accept steel mandrels, so wheels are simply more durable than stones. Most wheels are ¾” to 7/8” diameters, with 3/32” or 1/8” arbor holes and 1/8” thickness; they can be used to finish grind small air openings; when they dwindle down to smaller diameters, they can be used to flatten internal weld beads and enlarge short areas of pipe and tubing for fit up.

Alternatives to high-speed steel drill bits: Why do those drill bits in your rotary tool accessories kit, always prove worthless? High speed steel drill bits, which lose their temper (hardness) at around 420 °F, have been used in rotary tools to drill wood, aluminum, brass, and plastic for decades. Mild steel, and especially stainless-steel alloys, are more easily drilled with cobalt drill bits, which are high speed steel with cobalt added (hold’s temper to 1100 °F), starting with M-35 (5% cobalt); the next higher grade is M-42 (8% cobalt); both grades have reasonable prices online, but not at hardware stores. M-42 has superior wear resistance. If M-35 is all you find offered, jump on them with a big toothy grin. While M42 is harder than M35, it is also more brittle. Sets of micro drill bits are usually made from tungsten steel (high-speed steel with tungsten added); these will hold their temper up to 932 °F. Tungsten steel is also tougher than plain high-speed steel; both important factors when drilling in stainless steel. Some sets of micro drill bits are tungsten carbide, which will take much more heat, but is also more inclined to break due to its increased brittleness. So, the point of tungsten steel, and cobalt steel drill bits in your rotary tool is less about their increased toughness, than how much heat they can withstand, while being spun at much higher speeds than is recommended for their size, when drilling steel.

Miniature adjustable three-jaw rotary chucks: A keyed chuck needs to have reasonable quality to successfully spin an accessory, or drill bit, at high speed. So, what about key-less chucks (finger & thumb tightened) for rotary tools, sold online and through jeweler’s supply stores; the kind that has three independent moving jaws? I bought three of these cheap imports, before giving up; they all froze, and broke during their first attempted use. Why? It turns out that none of them were a Dremel 4486 Keyless Chuck. Dremel has their brand name to protect; anonymous drop shippers do not. Make sure that you are purchasing your “Dremel” chuck from Dremel. What is clever about this chuck is that they designed it to thread directly unto a standard rotary tool’s 9/32-40 threaded spindle, greatly increasing its stability, by making an end run around the weak spot in most rotary tool chucks—their skinny shanks. While better than no-name chucks, it is still not anywhere near as good as a miniature keyed chuck (used on DC motors to make micro-drills). However miniature keyed chucks often suffer from the poorly machined brass arbors that come with them. It is better to buy a steel JT0 arbor for them, to avoid run-out problems. An inexpensive keyed chuck and steel JTO arbor, that is made for use on DC motors, is sold by Walmart. Foredom A-MC2 Micro Chuck: Foredom makes a rotary tool chuck from high-speed steel, which is just okay; it is a jeweler type, which employs an integral castellated collet that squeezes all four jaws closed as a single unit, to create a type of variable diameter collet chuck; it still isn’t as smooth as a set of brass drill bit collets. Why not? It is machined to about 0.001" (one thousandths of an inch) tolerance, and extends well beyond the spindle’s end. Really smooth performance in this instance would probably require 0.0002" (two ten-thousandths of an inch) tolerances; producing that level of quality would price it out of the market. What this chuck does do well is act as a protrusion, to help extend the reach of grind stones and drum sanders deeper into small tubes (which need to be increased a few thousandths of an inch in diameter for fit-up). Remember to dress any stone, or rotate any drum you spin in it (to offset run-out), before inserting it into the work piece. Accessories with 1/8” shafts are cheap and easy to find; this variable chuck is also used to accept micro drill bits, which have varied shaft diameters. Google “adapter chuck for drill bits” or Foredom® A-MC2 Micro Chuck to see what is currently available. Do be sure to read customer feedback about any chuck you find tempting; good designs don’t count for much, without sufficient quality control.

“Just buy a Dremel” can be sound advice when it comes to some of their rotary tool accessories, and attachments. If you do not want to pay close attention before every purchase; if you would rather “just get on with the job,” then paying their top prices for consistent (not necessarily best) quality is a practical choice. As you get comfortable using rotary tools, you will inevitably modify that choice a lot. With sixty-five years “on the tools,” I still choose to pay Dremel prices at times; but never out of brand loyalty. I think that the Dremel 575 Right Angle Attachment, 4486 Keyless Chuck, and A550 Shield are worth their prices, and will greatly aid you to do build your forge. The EZ Lock mandrel and abrasive cutoff discs are worth every penny; so are Dremel’s 420 cutoff discs; their model #100 and #200 rotary tools are worth their cost. But, paying Dremel prices for their other stuff? Not these days.

Burner sizes: The first thing you must decide about your burner is what size it is going to be. Home-built burner sizes are given according to schedule #40 pipe sizes (or its equivalent inside diameters in round tubing) that is used as the burner’s mixing tube. These burners were built from fractional pipe for many years (and most still are). So, it is handy to know what actual inside diameters these nominal pipe sizes have, since it is the inside diameter, you are trying to match in a gas orifice diameter, and to whatever you use for a conical air entrance. Actual Imperial (fractional) pipe diameters are larger than their nominal pipe sizes, both outside and inside. If you choose tubing instead, it will seldom be an exact match with pipe, so choose a little larger inside diameter, when possible (rather than a little smaller), for your burner’s mixing tube, or the flame retention nozzle’s spacer ring, and outer tube. Imported stainless-steel tube can be a handy alternative to fractional tube in the smaller sizes, and is more likely to match up well with most stainless-steel funnel shapes. Imported cast stainless steel pipe, while being advertised in inches on Amazon.com, are nearly all made to metric dimensions. Schedule #40 pipe dimensions: Nearest metric tube & pipe sizes: (A) 1/8” pipe is 0.405” O.D. x 0.270” I.D. 10x8mm (0.390” O.D. x 0.312” I.D.) tube. (B) 1/4” pipe is 0.540” O.D. x 0.364” I.D. 12x10mm (0.468” O.D. x 0.390” I.D.) tube. (C) 3/8” pipe is 0.675” O.D. x 0.493” I.D. 14x12mm (0.546” O.D. x 0.468” I.D. tube. (D) 1/2” pipe is 0.840” O.D. x 0.622” I.D. 18x16mm 0.702” O.D. x 0.624”) I.D.) tube. (E) 3/4” pipe is 1.050” O.D. x 0.824” I.D. 20mm pipe nipples, couplers. (F) 1” pipe is 1.315” O.D. x 1.049” I.D. 25mm pipe nipples, couplers. (G) 1-1/4” pipe is 1.66” O.D. x 1.38” I.D. No equivalent pipe. Nearest size is 40mm. Be advised that imported cast stainless steel pipe fittings are very likely to be metric; not Imperial, no matter what their advertisements on Amazon.com states. Stainless steel tube is the simplest choice to work with for any tubing part (although schedule #40 stainless steel pipe nipples purchased online may be cheaper); and it is the choice that is demanded for at least the outer tube of your burner’s flame retention nozzle.

Why speak of small drum sleeves needing a better grade of mandrel? Because the smaller the mandrel the harder it is to keep a sanding sleeve in place; this is why 1/2" mandrels are used in video commercials; not 1/4" mandrels. So, not being able to keep the sleeves in place, is always a problem with the mandrel, although most people curse the sleeves. Junk sleeves are the problem, only when they burst apart or unwind during use. Often, there is nothing wrong with the sleeve's quality control. The problem is that garnet coated sleeves, which are meant for wood working, are sold in accessories kits, instead of sleeves with the more expensive carborundum grit coatings, meant for steel work; these must be purchased separately, after you quickly where out the wood working sleeves.

Unless you plan to do hundreds of experiments, where you are is likely to be as good as it gets

Actually, the photo says it all; this will never be more than a second rate burner. Why? Because the pipe reducer being used as its conical shaped air intake does not even provide a two to one reduction in diameter with the inside of the pipe being used as the burner's mixing tube. You need at least a two and one half reduction in diameter for a linear burner to come alive, and a three to one reduction is desirable.

More on rotary tools Hand held rotary tools become more valuable all the time, but, avoid their variable speed versions like the plague. Yes, it is handy to be able to vary the RPM on a rotary tool, but you want to do that trick by plugging it into a separate speed controller, like those made for routers; the reason is that the circuitry is too delicate when they are mounted in the rotary tool itself, and so they burn out quite easily. Single speed rotary tools cost so much less that you can often buy the router control for the price difference, and not only end up with a much tougher tool, but one that has a wider speed range to boot. If you cannot avoid buying a variable speed version, you are still better off to run it at full power and use a router control to vary its speed; saving wear and tear on the tool’s own circuitry, and better controlling its speed in the lower RPM range. Accessories have been improved even more than the rotary tools have. Cutting disks were originally made to create very thin cuts in rings and other soft jewelry items; many still are, but steel cutting friction discs have been perfected, along with the spring loaded mandrels they mount on. Dremel’s EZ Lock mandrel, and EZ Lock 1-1/2” cutting disks allow you to make delicate internal cuts for air openings in burners, and quickly do all the cutting needed while shaping forge shells, or cut angle iron for equipment stands. A Set of diamond coated burrs replaces hand files; they are fast, easily controlled, economical. Unlike rotary files they do not fling needle sharp debris. Drum sanders (the mandrels) use abrasive sleeves to slip over an expandable rubber drum; they are hard to beat for smoothly removing a few thousandths of an inch, to make tubing or pipe parts fit. The best design for small drum sanders use a bottom nut for tightening instead of a top screw.

Well, yes and no. Mostly no; that view is mostly incorrect. Can I always create an oval, "D", oe tunnel forge that is more efficient than a box forge? Yes; however, will it be a lot more efficient? NO! Will it be superior enough to offset the limitations built into those other designs? Probably not for a shop forge. If the forge is indended to be move to job sites, they would be. The biggest problem with your present forge is its burner. The second big problem is a hard firebrick floor. Change the burner first, and the floor next. By the time you get around to looking for more improvements, your dissatisfaction will probably not justify bothering with anything further As to your forge burner, what Frosty said sums it up; "They aren't very good but not awful." It would be easier to explain what is especially right with this burner, rather than list everything they got wrong: nothing is right! No, it isn't awful, but it will never put out those critical last five-hundred degrees needed to bring your forge interior into high incandescence. Without that added input, your forge will remain a mere gas oven; not a radiant oven. That last twenty percent of heat input will double the forge's working output.

Your photo makes what is wrong with that forge obvious, and it is the burner. Either buying or building a burner is the first step to improving this forge, or replacing it with a better one. However, a proper burner is likely to solve most of your problems with the present forge. So, get smart and stop thinking about replacing the forge, without knowing that you actually need too. Think "better burner for my forge."

Well, yes, but within limits. More than a three to one constriction ratio between funnel entrance and the mixing tube's internal diameter is problematic. The limits also apply to shortening the conical air entrance. A sixty degree cone is a better shape than a forty-five degree cone. The shorter the cone the worse the problem. So, why say probably? I have observed the problems that accumulate with forced-flow burners, but free-flow burners are more subtle; nevertheless, an obvious, repeatable, event in one type is likely to show up in some degree in the other type.

Do not feel lost,Guillaume. Your friends have the right idea, but "the devil is in the details." I don't want to devil you, so I will admit that I got one of those details wrong; that would be the size of your burner. So, just ignore my question, and wrestle with less pesky details. If you're happy with the burner, than so am I