Mikey98118

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

Also, the coffee hasn't had much time to circulate in my brain, and various other excuses...

On 11/14/2023 at 2:27 PM, Pigsticker said:

Do you have a start to finish forge posted?

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

23 hours ago, Pigsticker said:

Also wondering do you think if only thing i have for any real heat is the forges big burner should i burn in rigidizer.

Yes, you definitely should use one of the burners that way. I suggest just such a course in the book.

And there are complete instructions on how to build a gas forge, from a used five-gallon propane cylinder in the book; these old cylinders are given away at various propane supply sources.

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.

1 hour ago, Pigsticker said:

Wow. Thanks so so much.  If i make a d or oval, will i be bringing the back of the blanket into play?

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.

2 hours ago, Pigsticker said:

Should i try it 2 burner to see or not even try.

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

1 hour ago, wirerabbit said:

This is a Vevor forge and will work just fine.

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.

5 hours ago, OlavFairhair said:

And besides, from what I've read, brick forges will always slower to warm up, or somehow less efficient.

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

Hi, Guillaume

Love to see your use of sheet metal in forge construction. I just advice guys to use old gas cylinders, tin cans, and pots. But that is only because, sheet metal is very expensive for an American who doesn't live near a scrap yard, so learning how to use sheet metal isn't an inviting prospect these days.

As to the photo showing the air entrances and gas tube on your burner. One of the earliest improvements made on burners, was to square up the forward and rear ends of slot shaped air openings. The second improvement was to bevel the forward and rear edges of those openings; both changes greatly increase air induction into tube burners. The result is way hotter burner flames. The thicker the tube wall the more important beveling is...

Your gas tube looks way too long. While some tube length is needed to increase the speed of gas molecules leaving the gas orifice, how long that needs to be depends on orifice size; the smaller the gas orifice the shorter the gas tube needed. Also the smaller the inside diameter of the gas tube the smaller the tube can be. However, there is a "sweet spot" where the gas orifice is at the best distance away from the forward end of the air entrances to induce maximum air into the burner. I estimate that to be about 3/16" on that burner size.

Are you employing a .3mm 3D printer nozzle as a gas orifice, or some other size?

It should be about time for people to ask some questions, to help them finish their garage and barn warmers...er, I mean forges, before icicles start forming on the eves

                                                                  Why 1/4" and 3/8" burners?

The only equivalent commercial source to small burners are standard dual-fuel torch-heads, which will last fast as a hand torch being run on  MAP fuel (polypropylene), and even faster mounted in heating equipment, even when only run on propane; the problem in both instances is their paper-thin flame retention nozzles. At high heat levels, which are obtained with  (polypropylene) burning in the open air, and with propane burning in a forge or casting furnace, even a stainless steel flame retention nozzle will oxidize away over time; the thinner the nozzle the less time that takes. Flame retention nozzles must be considered as a consumable item; the thicker they are the better. The thin none-replaceable nozzles on commercial dual-fuel torch-heads are simply a rip-off.

    So, using a dual-fuel torch head in your two-brick or coffee-can forge isn't going to be the cheap and easy path, unless you think replacing them, instead of just a flame retention nozzle is going to save time and money!

  An even worse choice, is using one of the older propane torch-heads, with a brass flame retention nozzle, laid in an over-size burner opening (to keep it from melting); this saveS the torch will wasting lots of expensive fuel.

                           What does a hot efficient forge take?

(1) Good design; this starts with size. Make the forge no larger than your present needs--not as large as you suppose you could need, eventually. Shape is also a concern. Your forge should be no longer than one and a half times its width, and about two thirds as high as its width; these proportions apply to tunnel, "D", oval, and box forges. The best shape for a first forge is variable (brick pile forges). Burners should have sliding air chokes on their mixing tubes, so that the amount of secondary incoming air, which the burner's flame is inducing, can be controlled. The speed of exhaust gases exiting the forge should be controlled with a baffle wall, while radiant energy is reflected back into the forge.

(2) A hot and efficient burner; while this is certainly an important part of any forge, you will note that it is secondary to good forge design. A miserable burner cannot properly heat the best gas forge; but a merely average burner can do so.

How is this possible? A proper gas forge becomes a radiant oven, once heated. Any carbon monoxide  gas (secondary flame) Is quickly consumed within the forge, so that only hot exhaust gases escape the forge--not flame.

Frosty covered things pretty well. I would only add that your next step should be a brick baffle wall in front of the forge, to allow stock to pass through, and exhaust fumes to escape upward between its near side and the forge, while bouncing back radiant energy into the forge's interior. You will find that it saves you plenty of fuel, and glare in your eyes.

For this wall, you are better off to use plain old hard clay firebricks, and coat their forge facing sides, just like the forge interior.

Once you add a baffle wall, that forge should use about one-third gallon of propane per hour, at welding heat. There are other steps you can take to reduce fuel used, like adding an idler circuit to your forge. However, most people with a small efficient forge, just don't bother going that far