Using Air/fuel torches as mini burners

There is a large variety of air/fuel torches, new and old, that can be re-tasked into  equipment burners. Recently, I have been seeing MAP gas hand torches marketed online (AKA dual-fuel torches) that are rated to burn propylene as well as propane); some of them feature a stainless steel flame tube, which makes them fit for use as equipment burners, with the addition of an external doubling tube to prevent their flame tubes from being rapidly oxidized away.

    Some air/fuel torches now come with a short fuel hose, instead of just being mounted directly on a 16 oz. fuel 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 is 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 are 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 cylinder; these allow you to use the torch of your choice to do the same jobs cylinder mounted torches.

 

    “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 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  doubling tubes onto. My burner's flame tube wall is only about .030" thick. When mounted in a forge or casting furnace, the superheated portion, even on stainless steel tubing, will 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 doesn't 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 chose this air/fuel torch, not because it would make the cheapest or hottest burner to build, but because it is a reliable model, and allows the easiest burner to construction. 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 than 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 actually 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 STK9 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.

 

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 a lot,  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 orifice, 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 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): Eventually 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 needed to retain the flame out in open air, it isn’t necessary when it 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.

    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 #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 area it occupies 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 for a snug sliding fit, allows it to slid over the flame tube, protecting it from  from being dented during mounting. The doubler tube is 1/2” longer than the flame tube, protecting its end, and 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 torches.

 

Caution:Always read and understand the manufacturer’s instructions before attempting to use an air/fuel torch.

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. canisters 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 cylinder to rest below most of a mini-forge or casting furnace’s body, it is safer still 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 at one end, and a male connector for a throwaway cylinder 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.

On 7/23/2018 at 3:20 PM, John in Oly, WA said:

Right off the bat, I started this process on the wrong foot. My simple calculation regarding the ratio between the fan opening in the funnel and the mixing tube diameter of 3:1 didn’t take into account the large hub in the middle of the fan blocking a good portion of the opening. So, the first two burners I made, one using the stainless steel plumbing reducer and the other, the sausage stuffer tube didn’t work so well. If I'd have listened to the 70mm part...

I think it is time I replied to John's concerns. If the fan used has impeller blades, the area it obstructs in the center portion of an intake funnel is of no concern. The blade configuration slings the incoming air to their tips, so the air being induced only inters near the funnel wall.

 

On 7/24/2018 at 11:27 AM, John in Oly, WA said:

Mikey, while the fan's hub doesn't appear to interfere with vortex formation, it does just generally block airflow - makes the opening smaller - which to my untrained eye made the flame look much richer (a lot of secondary flame). So I should have listened to your statement of using a 70mm fan. But I'd already purchased the parts for the 60mm fan, so I went down that road for a bit. Then switched horses mid stream.

I think what you will find is that you had too much of a good thing. All the factors in burner flow needs to be in balance with each other. Install a speed control circuit on the fan, so that the amount of vortex created is reduced enough not to over-match the rest of the factors in the burner's mixture flow, and your problem should suddenly vanish.

Aligning reducer, or “T” fittings, to mixing tubes: Most burner designs are considered easier to make with threaded plumbing parts; that can be true, or far from it; depending on the quality of those parts. Cheap imported fittings are becoming the rule as steel water pipe is marginalized by copper and plastic. Cheap pipe fittings are often made from marred castings, which don't thread properly, producing axially misaligned threading in the finish part; such parts make burners that cannot be properly tuned, and thus produce poor flames. Here are some answers to this problem:

(1) Avoid buying threaded fittings from large generic hardware stores. They don't have a good selection of fittings, and tend to use cheap imported stock. Look for regular plumbing supply stores or HVAC supply stores, instead.

(2) Hand screw fittings and pipes together, and inspect them before purchase; crooked fittings are easily spotted this way. Don’t stop with screwing the reducer to the smaller pipe that will be used as its mixing tube; add a larger pipe on its large opening and revolve the assembly in your hands. Whether the parts are axially true or not quickly becomes apparent.

(3) If you must buy your fittings online, consider using stainless steel instead of cast iron; stainless parts are likely to be much higher quality.

(4) In the end, the surest answer to a problem, is to avoid it. Every threaded pipe fitting has a much higher quality butt-weld equivalent. Pipe can be used in the next smaller size to the fitting's opening, slid into position (after a little power  sanding, or grinding down, if it is oversize), and held in place with socket-head setscrews. This is a little more work than screwing together threaded fittings, but gives much better part control, and superior flow. Don’t forget to grind an internal bevel on the end of the pipe that slides into the reducer fitting.

 

                                                                                              Surprise

The more we know about any given topic the harder it is to learn something new. Chile Forge employs my high speed tube burner design (AKA "Mikey" burners). The thing is that all the Chili forges, are designed for rock and role; not for waltzing. Whether one or multiple burners, those forges only come in one burner size; and that is one-inch.

Furthermore, I designed all my burners for a minimum gas input of between four and seven PSI positive gauge pressure (the larger the burner the higher the minimum pressure).

While cruising the web, I stumbled across a discussion between some Chili Forge owners, who where having trouble getting their forges down to cool enough temperature for blade tempering. One of them came up with the idea of ordering the next size smaller MIG contact tip, then what came in his burner.

Now, as the guy who designed this burner; that would be the last choice I would ever make! Ordinarily, the smaller the gas orifice the leaner the burner will run, and those burners are already set to produce a perfect compact neutral flame.

However, circumstances alters cases, once again. It turns out that the undersized MIG tip was just the ticket to allow him to get away with turning a high speed tube burner down to one PSI gauge pressure, and tempering his blades.

Who'd a thunk it ?!?

Lots of folks are willing to build their own forge, but shy away from burner construction. "To each his own." However, while there are always lots of forges for sale, burners come and go on the market. Hybrid burners are gone. Mister Volcano burners are gone. The Burner Guru died, and his modified Mikey burners are gone. I'm not sure if Larry Zoeller of larry Zoeller Forge is still selling his "Z" burners or not.

This leaves various linear burners, a hand full of tube burners, or other jet-ejector burners around, at present. Good luck to the poor novice trying to  sorta good from just plain awful designs.

What to do? Here's a hint; the operative word is "design."

If the design permits small changes, you can probably improve the burner, should it turn out to look better than it runs; if it doesn't, then good luck; you're really gonna need it!

So, what to look for in a linear burner? An opening diameter that is at least 2.5 times that of the inside of its mixing tube. A 3:1 ratio would be ideal, but don't even bother looking for one of those. The smaller the opening to mixing tube ratio the weaker the burner will run. You can fix things like an over size gas orifice in a linear burner, but if you must change the funnel entrance, you would be better off to build a burner from scratch.

So, what do you look for in a tube style jet-ejector burner? Hopefully, rectangular air entrances; their actually are one or two of them on the market...presently. Most of those turkeys have enough air holes drilled in them to be reminiscent of a gum ball machine

However, there is at least one burner on the market presently that just has a few holes drilled in line with each other; this means that you can use a rotary tool and cutting discs to cut out the material between for and aft holes, turning them into slots. And, presto chango! Your rattle trap burner becomes a nitro dragster 

Could it really be that easy? Probably not; you will most likely need to change the gas orifice out for a different size, too; I think you can manage that.

Frosty "T" burners are being copied for sale by various people; most of them look like they could be tweaked to run correctly. Just ask Jerry for help with them. That's okay Jerry; no thanks needed (anything for a my good buddy) 

 

I imagine he would like that. Helping correct “his” burners that are built incorrectly even though the plans are free. I know Ron sure was a big fan of that. 

WHEW! Thanks for letting me off the hook for thanking you for that. . . Good Buddy.

Frosty The Lucky.

1 hour ago, Another FrankenBurner said:

I know Ron sure was a big fan of that. 

He was pretty sick of it by the time I met him

2 minutes ago, Frosty said:

WHEW! Thanks for letting me off the hook for thanking you for that. . . Good Buddy.

Thats quite all right Frosty. Having done my good deed for the day, I'll just slither off, back under my rock

He got sick of it the first time someone asked for help rather than reading the directions. They'd start out saying they just bought the plans and proceed to ask what to do point by point from the intro. 

I think his change of attitude is in part the result of being a retired school teacher.

Frosty The Lucky.

Good point; we all had enough of "special people" at work; it would just suck to come home for another round of the same old thing--ugh! What I liked best about being a welder, was flipping down my helmet, and saying good by to social interactions, for hours at a time.

 I liked being left alone in the drill shop for the most part. There were times I needed a hand but had to make do but for the most part it was worth not having to deal with the . . . 

Frosty The Lucky.

Somebody made a youtube on how to make the frosty burner.

But I get an error trying to link it, so I cannot

Jhttps://youtu.be/jjvPTHiwkYs?si=mG8Z-Oj25EAEcYOb

Ok, as a flat text it works. Must be the phone doing something weird.

There must be hundreds of video how tos making various qualities of T burner. In fact a friend sent me a link a couple days ago. They're often pretty educational, loaded with "DON'T DO THIS!" shop techniques. 

I rarely watch one and don't think I've seen one tune the burner. 

If you can't follow the directions posted here, you probably won't do as well copying someone else who can't follow them. 

One last word, NO I'm not going to watch let alone evaluate this or any t burner how to. 

Frosty The Lucky.

Gas valves: There are three kinds of gas valves that matter to you; needle valves, ball valves, and variable pressure regulators. Ball valves are meant to start and stop flow. In a burner system, they’re mainly used as emergency cutoff in case of fire; they are also used to divert flow from one pipe system to another. They can be used to control flow, but not in a satisfactory method. While the most dependable kind of gas valve, if they are cheaply made, expect them to leak, too. To find dependable ball valves, choose gas rated ball valves from the plumbing department of your local hardware store.

    Needle valves are best used to quickly fine tune flow in a gas system that already has a variable pressure regulator. A good quality valve, which is new, can be used to stop flow completely, but most needle valves sold in the propane fittings section of hardware stores, will begin to leak flow, eventually. What about air-propane cylinder mount torches; they only have a needle valve, right? Expect them to have, or develop, small leaks. To ensure acquiring high quality needle valves, purchase them from a welding supply store; they sell torch needle valves in “Y” fittings for torch leads, which last for decades without leaking.

Variable pressure regulators are used to limit the amount of pressure in a burner’s gas system to a little higher than the desired range you want to use; this allows rapid fine tuning of the burner with a needle valve, while protecting the hose and pipe connections from possible damage and leaking, from constant exposure to full cylinder pressure. Yes, it is possible to use the regulator to fine tune your burner, but if you have very much hose in your burner system, every change will be delayed; they are less likely to leak than needle valves, but once again, cheap regulators are not dependable, and are likely to leak.

 

Threaded parts seldom seal gas tight; especially when exposed to full cylinder pressures, as in the case of most cylinder-mount propane torches. The common fix is to use Teflon tape that is rated for fuel gas as a sealant, but such tape is meant for relatively low pressures encountered in household natural gas lines. So, Teflon tape is not likely to work well on lines without a pressure regulator installed. Even then, they must be turned in the right direction to avoid unraveling during installation, and the tape must be kept away from the last two pipe threads to avoid Teflon shreds from migrating into the gas line; inescapably plugging up the gas jet.

    A surer method is to apply gas rated gasket sealant on the threads of the male connection (kept away from the last two threads on the fitting’s end). You can also employ gas rated thread sealant (AKA Threadlocker). If you disassemble the fitting later, be sure to thoroughly wipe off excess sealant from internal threads first thing, lest some end up inside the gas orifice.

Always clean the gas system before assembly: Teflon shreds are not the only junk that can enter your gas system. Burrs from cutting, grinding, sanding and threading operations must be thoroughly cleaned from burner parts, and all lines and hoses cleaned out with compressed air, to avoid debris from accumulating in the small gas orifice of a burner. Debris could have collected in the fuel hose from the gas cylinder, if you rent cylinders from an exchange system, from junk in the hose, if you leave it off for a long time. Insects and spiders are attracted to fuel hoses, because of their stench of fuel vapor. Propane can leave a buildup of tar and wax in a burner's gas orifices; especially from poor quality fuel. The wrong kind of hose will rot out over time; only use LPG or multi-fuel rated hose. Never use acetylene hose! Never use air hose! Never use water hose!

Threaded parts seldom seal gas tight; especially when exposed to full cylinder pressures, as in the case of most cylinder-mount propane torches. The common fix is to use Teflon tape that is rated for fuel gas as a sealant, but such tape is meant for relatively low pressures encountered in household natural gas lines. So, Teflon tape is not likely to work well on lines without a pressure regulator installed. Even then, they must be turned in the right direction to avoid unraveling during installation, and the tape must be kept away from the last two pipe threads to avoid Teflon shreds from migrating into the gas line; inescapably plugging up the gas jet.

    A surer method is to apply gas rated gasket sealant on the threads of the male connection (kept away from the last two threads on the fitting’s end). You can also employ gas rated thread sealant (AKA Threadlocker). If you disassemble the fitting later, be sure to thoroughly wipe off excess sealant from internal threads first thing, lest some end up inside the gas orifice.

Always clean the gas system before assembly: Teflon shreds are not the only junk that can enter your gas system. Burrs from cutting, grinding, sanding and threading operations must be thoroughly cleaned from burner parts, and all lines and hoses cleaned out with compressed air, to avoid debris from accumulating in the small gas orifice of a burner. Debris could have collected in the fuel hose from the gas cylinder, if you rent cylinders from an exchange system, from junk in the hose, if you leave it off for a long time. Insects and spiders are attracted to fuel hoses, because of their stench of fuel vapor. Propane can leave a buildup of tar and wax in a burner's gas orifices; especially from poor quality fuel. The wrong kind of hose will rot out over time; only use LPG or multi-fuel rated hose. Never use acetylene hose! Never use air hose! Never use water hose!

                                                                                  The Latest lab burners

It is always fun to look into lab burners; their manufacturers keep right up to the minute. Over the years, I have seen my own ideas on air entrances, and flame retention nozzles appear in their design. Now, they also include linear burner funnel entrances, and wast waist mixing tubes; they've come a long way in the last two decades.

Lab burners are actually harder to improve than our equipment burners, because they must output  soft flames.

                                                                                            Mixing tube hints

Thermal cycling is quite hard on mild steel; far less so for stainless steel. It makes sense to use mild steel for every part possible in large burner sizes, since prices go up rapidly by size. While handier over time, the only part that is vital to use stainless for is the outer tube of flame retention nozzles. However, there is little difference in price of stainless and mild steel in small pipe and tube. Also, stainless steel pipe and tubing is generally better quality than its mild steel equivalence. Finally stainless steel metric tubing is much easier to match up closely with stainless steel funnels.

                                                                                       Adding a locking screw

If you plan to mount a burner in your forge, and if it will be top mounted, facing down; then it is wise to include a locking screw to any slide-over flame retention nozzle. After tuning the burner completely, drill a hole completely through the nozzle, spacer ring, and mixing tube, between two of the rear set screws on the flame retention nozzle’s outer tube. Thread through both parts, locking them together, and screw in a long set screw. Ink-mark the protruding portion of screw inside the spacer ring, and remove the set screw. Employ the nut and Allen screw to help as you grind away excess thread. Run the nut over the end of the screw, and reinsert the screw. The nozzle is now locked in position, against dropping off during thermal cycling, and your work is done.

                                                         Drilling and in threading stainless-steel

Three-hundred series stainless tends to compress during drilling and/or threading, thus compacting its surface; this is a form of work hardening. What actually happens is the compressed surface becomes denser; this condensed layer begins to act like a bearing surface; dull cutting edges tend to ride on it ineffectually, instead of penetrating it, thus causing rapid heating of the cutting tool, which is why only very sharp drill bits should be used to drill stainless. The softer stainless alloys also tend to gum up tool edges, which then rapidly become dull. Stainless steel work hardens easily if a dull drill bit is used, if too little feed pressure is applied, or if drilling fluid isn’t used (tapping oil is perfect for this, and can be purchased in amounts smaller than a pint, but even kitchen oil is better than dry drilling).

 

    It only takes seconds to overheat a dull and dry drill bit in stainless, which rapidly results in melting temperatures on a drill bit’s leading edges, followed by transference of some of the bit’s high speed steel material to the stainless part’s surface; thereafter, no further drilling is possible, although the resulting mess can be removed with diamond coated burrs and patience. High speed steel lathe tools can suffer the same fate as drill bits.

    When a drill bit is about to exit the far side of a hole, feed pressure on the bit can cause the leading edges of its flutes to suddenly catch in the material’s thinning edge, and bind; small drill bits usually snap off at this point. To avoid breakage, ease up on feed pressure when you feel the bit “breaking through” the far side of a hole; this is true for any malleable metal--not just stainless steel. Larger bits may “grab” the part, causing it to spin around on the drill press, dangerously.

    It is generally a good idea to employ the drill bit recommended for a given tap in a given metal. However, the drill bit sizes listed in threading charts are normally meant for use on soft metals like brass or mild steel; they produce a 75% thread engagement. Only 50% thread engagement is recommended for stainleel-steel alloys, but the relatively few threads produced in most tubing/pipe products 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 burden, when using set screws in pipe or tube. But, threading through doubled layers of tubing or pipe used in some stainless steel burner nozzles is done with the recommended 50% thread engagement; also with schedule #80 pipe, when used as the nozzle’s outer tube. When schedule #40 pipe, or the equivalent wall thickness in tubing is used for a flame retention nozzle’s outer tube, but the threaded hole doesn’t include the nozzle’s spacer ring, it needs 75% thread engagement.

    “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 from, 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 drill 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 more 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 better market for these bits. M35 bits are good enough for this work, but you can find M-42 bits in the desired size at Panamericantool.com.

 Note: Sets of tungsten carbide micro drill bits embedded in 1/8” mild steel shanks are available online for low prices, and also of tungsten steel. 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 chamfered threads); and Taper taps (8 to10 chamfered 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. 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. 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.

    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 two are the most likely types to be offered online.

     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; as tjos indicates that the tap is starting to bind against chips, which need to be free to fall away from it. 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 outside or within the tube (with a rod, bolt, or piece of scrap metal), to loosen the embedded point or protrusion; then, try to back it out of the hole with pliers. Otherwise, you must grind out that piece of high-speed steel out with a diamond coated 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 is not enough thread left to properly engage the screw, you must start over by drilling and tapping for a larger screw.

    Any malleable metal will form a raised area on both the outer and inner 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 surfaces of tubes must be repeated back and forth, until all screws turn smoothly, and the part slides smoothly over other tubing.       

                                                Slide-over stepped flame retention nozzles

I am not certain if Ron Reil pioneered slide-over tapered flame retention nozzles, or if someone else did; I first came across them on his burner pages. The taper amounted to about a 1/8" increase in diameter over a distance of 1-1/2". The increased diameter was in addition to about 1/8" increase in diameter from the inside to the outside of a burner's mixing tube. What made them so convenient was that one-half the increased-cross section was variable in length; this allowed burner flames to be tuned somewhat. Thus, the importance of sliding flame retention nozzles.

    The next innovation was stepped slide-over flame retention nozzles, made by inserting a short length of pipe or tubing, as a spacer ring between an outer tube and the burner's mixing tube; these were also designed to slide back and forth on the mixing tube, to vary width to length increases in flame retention nozzles. However, they increased air induction by increasing turbulence (in the form of drag over the internal shoulder). This design was also much easier for newbies to produce.

    The idea came to me, while looking at various butane and propane torch-heads. It is a good design, but hardly the be-all and end-all final design for flame retention nozzles. The old tapered nozzles still work best on slower flow burner designs, such as "T" burners. And multi-lame retention nozzles will probably dominate future burners. Progress marches on.

Multi-lame retention nozzles… I think that was a YouTube invention.

They do seem to be dominating. Just look at most eBay and Amazon burners. 

I cheated. I used stepped tapered nozzles. A hybrid nozzle. Now we just need to park a hybrid nozzle on a hybrid burner, just to say we did.

I think that fan-blown burners will also be making a comeback. Since multi-flame ceramic heads, and also multi-flame ribbon burners have a much greater cubic area than typical flame retention nozzles, limited increased flow pressure is a positive, rather than a negative. However, the oversized fans of the past, being a great example of "too much of a good thing," will probably be replaced with 12V to 24V fans. All things in balance, is key.

                                 All miniature pipe cutters aren't created equal

     The Saillong Mini Steel Tube Cutter (No. 174-F), with two spare cutter wheels and “E” spring retaining clips, are recommended for tube diameters from 1/8” to 1-1/8” (3-28mm); it is used for parting copper, brass, aluminum, and thin stainless steel tube (up to1/16” thick); $10 from Amazon.com. This cutter is not a necessity, but is quite handy, both for parting tubing, and for scribing perpendicular lines, (for cutoff discs) in the larger tubes or pipes chosen for flame retention nozzles in 1/4”, 3/8”, and ½” burners. This is the best quality I have found in a miniature pipe cutter, and yet it is offered at a low price. The cutter wheel on my 174-F, tracks perfectly (no wobble), and so it takes no special care to maintain a single cut line in the material, rather than fighting a tendency for its wheel to leave a spiral score on the material, instead of immediately starting a proper cutting path.

                         Why small, why stainless steel, & why linear burners?

Why small burners? Combustion gases begin to slow, as soon as they leave the flame envelope. The flames of two 1/2" burners will use the same amount of fuel to produce an equal amount of heat as a single 3/4” burner; but they will drop velocity much faster in a five-gallon forge or casting furnace, increasing efficiency, because their flames can burn faster/hotter without creating a wasteful tongue of fire out the equipment’s exhaust opening. Ditto for two 3/8” burners versus a single ½” burner in a two-gallon combination forge/furnace, or two ¼” versus a single 3/8” burner in a one/gallon forge/furnace. Because the parts and tubing these burners are built from, cost less as their sizes reduce; it costs little or no more to make two smaller burners than a single larger burner; only the price of an additional funnel shaped air entrance is added on smaller burners, along with the cost of a second mixing tube on larger burners. When buying from online sources, it is usual to find two or three small tubes offered for very little more than a single part of the same size.

Why stainless steel? Once again, the sellers are determined to make a certain amount out of each sale, so you will find stainless costs little or nothing more than mild steel, but is of far better quality. Several years down the road, your stainless steel burner will still be in fine shape; not necessarily so, with a mild steel burner.

Why linear? My reasons for choosing linear burners are complicated, but the bottom line for you is simple; as burner sizes decrease, linear burners run more smoothly than any other design. Considering who just made this statement, maybe it deserves some consideration...

Plugs and inclusions: Propane comes in widely varying quality from different sources, but even the best of it is not perfectly clean (we aren’t talking about triple refined butane lighter fuel here). The waxes and tars that all commercial propane contains, can plug small orifices on MIG contact tips, and the even the smaller orifices of 3D printer nozzles; ruining burner performance, while rapidly increasing pressures on gas hose and gas fittings to full cylinder pressure, unless a proper regulator—not just a needle valve—is employed. Poor quality “bargain” propane can form tar balls quite rapidly.

    It then becomes necessary to shut down and clean the burner by poking the tar ball out of its gas jet with a set of torch tip cleaners (or piano wire for very small orifices), and blowing it back out through the larger diameter gas tube with air pressure; canned air is fine for this, if you do not own a compressor.

    How likely is this problem to happen? The answer has more to do with your burner's gas orifice diameter than to propane quality. I only know of one instance of low-quality propane plugging a MIG tip orifice (with a 0.031" through hole. On the other hand, small commercial propane torch-heads, which depend on tiny gas orifices to work (0.004" and less), are commonly plugged shut by as little as two or three 16 oz. canisters of propane.

    Newly constructed burners must have their gas systems thoroughly cleaned from all construction debris, dust, etc. Otherwise, it will inevitably end up plugging the gas orifice. Once, propane has been run through gas hoses, and regulators, they should be kept on the heating equipment, or have their ends should be capped. Insects and spiders are attracted by its odorant.

Mike: Do you know of a commercially made propane filter?

Frosty The Lucky.