Burners 101

[Goods]

Guys, consider this a very novice question, but for a given energy output, wouldn’t you need a set mass flow of gas (both fuel and oxidizer) resulting in a set mass flow of output gassed (CO2 and H2O)? Assuming the the forges are getting to the same temperature I would think you have to exhaust the same exhaust flow rate. In my head I see slow speed burns having large areas, but similar mass flow, so as long as a high speed burner creates enough swirl to slow down, should there really be a difference. I’m not a gas forge guy, so I can’t really see past my old engineering classes on this one.

Not meaning to stir the pot, but curious on your thoughts.

[Frosty]

Your arithmetic is close enough to right as makes no difference. 

What you "see" as the volume requirements fast vs. slow burners is an "of course."

The absolute temperature of a propane forge depends on one thing only. just how much flammable mix burns INSIDE the forge per second. Period. (picking a number for discussion that is irrelevant otherwise) To get say 10 cu/ft of mix through a 1/2" dia burner it MUST be moving 4x the velocity as necessary through a 1" burner.

The easy way to make a slow burner is enlarge the tube diameter, air intake and jet then lower the delivery PSI of the propane. The same amount of propane and air flow down the tube to the forge at  a lower velocity.

The ratio is by the square of the diameter. 2x the dia = 4x the volume at 1/4 the velocity.

The secret to getting the most out of your fuel dollar is to keep it IN the forge until combustion is complete so the forge walls can absorb the max energy. And as intuition says the faster the flame the less time it stays in the forge. One way to deal with this is by increasing the path the flame must travel before reaching a doorway. Swirling it around the interior. 

This last is what Mike and I were re-hashing a few posts ago. I prefer a hotter zone over an overall even forge temperature so I aim my burner flame at the floor perpendicularly making a hotter area on the floor and so hotter zone in the forge.

Frosty The Lucky.

[Mikey98118]

We like people who stir the pot. There is nothing wrong with anything you stated. Your engineering is right on; that said, take things a step further, because that is exactly what a forge is all about...taking things as far as you can, before giving up one erg of energy.

You are correct that there must be a minimum exchange of exhaust gases for every molecule of fuel and oxygen. The present topic on IFI is just what way is best at keeping the rate of exchange at that minimum. The problem is simple; the factors being manipulated are straight forward. However, an elegant solution (in the engineering sense); ah, there's the rub

 

[Mikey98118]

                                                                            Important retraction!

The instructions I wrote about using 6x4mm bras tubing as burner gas tubes for 3D printer nozzles will not work. You must employ 6.5mm tubing. Yes, I did do the work before writing the original instructions up, but did not realize that the M6 tap I purchased on Amazon.com was switched out with an M5 tap. By the time an M6 tap is run in the tube, no room will remain for external thread.

My sincere apologies.

 

[Mikey98118]

Stainless steel braided propane hose is sold in various lengths, up to sixteen feet. The longer this item has remained on the market the more its price has fallen; it can now be purchased for about the same price as twin torch hose. This armored hose is not quite as flexible as twin torch hose for use with hand held burners, but is a superior alternative for equipment use. Nearly all of these hoses come with standard (for propane equipment) 3/8” flare fittings; usually female at both ends, but some have a male fitting on one end.

    It is wise to buy your hose from a local supplier, rather than on line. It is even wiser to avoid Amazon ‘deals’ on hose and regulator combinations; most of those regulators have built in limiters, to reduce gas flow to barbecue volumes.

[Mikey98118]

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. Both 5/16-18 and 8mm rivet nuts and flange nuts.

[Mikey98118]

5/16”-3/16” and 8x5mm tubing can both be used to create gas tubes, which are screwed directly into (drill press drilled) ¼” thick aluminum mounting plates, 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).

[Mikey98118]

Slide-over stepped flame retention nozzles

So far, slide-over stepped flame retention nozzles do a much better job of controlling the flames of high-speed air/fuel burners than tapered nozzles ever did; they are a necessity for fan-induced linear burners.

    These nozzles consist of one pipe or tube, called a spacer ring, fitted into an outer stainless steel pipe or tube. You are likely to have to power sand the outer or pipe or tube, or the spacer ring, to get them to fit together. You might even end up slitting the spacer ring lengthwise, before pushing it into the rear section of the outer tube. Or, you could just as easily slit the spacer tube, and spring it apart, to provide a snug fit to the outer tube, and a sliding fit on your burner’s mixing tube.

    The spacer ring can be made of either stainless steel or mild steel, to suit your convenience. But the outer tube must be made of stainless; #316 stainless is better for the purpose than #304, as it does not oxidize away under high heat and live flame conditions as fast. However, #316 doesn’t last enough longer than #304 to put up with the high prices some sellers feel you should pay for it—just say NO to price gouging!

Note: These nozzles are kept in position with stainless steel socket-head screws. Do not use mild steel screws; they will oxidize in place after a few heats. It takes months to wear out a flame retention nozzle, but they are disposable parts, and frozen screws must be drilled out.

The outer tube should be 1.125” longer than the distance of its inside diameter. The spacer ring should be 1” long. The nozzle is kept in position on the burner’s mixing tube with as little as a single screw, or as many as six screws, depending on how well it fits up to the mixing tube.

Caution: Stainless steel flame retention nozzles on a good burner design, will get to yellow heat in ambient air, if you burn propylene, and will quickly melt down in a forge. The same nozzle will get to orange heat in ambient air, burning propane, and will melt down in a forge, if they are not recessed back at least one-inch into the burner portal; do not position them close to the forge’s swirling super-heated atmosphere!

[Mikey98118]

                                                                                  Slit spacer rings

There are two different reasons to slit a slide-over stepped flame retention nozzle’s spacer ring: One is simply to decrease its diameter, so that it will fit within the flame nozzle’s outer tube; in that case the socket head set screws will be drilled and threaded through the outer tube and the spacer ring together, and then a set screw is screwed through both parts, one at a time, to keep the outer tube and spacer ring from moving out of position, during the work. Tolerances can leave you with loose fit-ups at times; in this case use electrical tape to center your parts within each other, and to keep them from slipping out of position while you drill and thread them for permanent fit-up. The tape will burn out of flame nozzle during the burner's first firing, changing nothing once the parts are trapped together by socket screws.

    The second reason is to allow it to become a constricting spacer ring, in which case the socket head screws are only drilled through the nozzle’s outer tube.

[Mikey98118]

                                                            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.

[Mikey98118]

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.

[Mikey98118]

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.

[Mikey98118]

                                                  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.

[Mikey98118]

    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.

[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).

[Mikey98118]

The British thermal unit (Btu) is a well-known unit of potential energy, which has long been used to compare fuels, and burner heating potentials; it is less legitimate for judging burner types. On top of this, you very rarely see it tied to burner turn down ranges, leaving us to ask questions like 140,000 Btu at what gas pressure; so far over a reasonable top pressure that that the burner's flame had long since started running rich?  

 

The problem is that actual heating potential is a slippery fish, even in a saint’s hands, let alone an ad manager’s.  Even if you do all the figuring for yourself, what does 140,000 Btu actually mean to YOU; at best it gives you a general impression of what a burner should be able to do; and that’s where you were when you came in!

 For instance, if two different burners are running the same gas pressure from the same gas orifice diameter, but one only puts out 2400 F flames, but the other one puts out 2800 F flames, their BTU consumption matches, but nothing else well.

[Mikey98118]

                                                         Go-to tool for burner construction

I may very some of the tools employed to build very different burner types, but a rotary tool is used on every one of them; a separate rotary accessories kit is highly recommended. If it comes down to a choice between buying a drill motor, or a rotary tool, go with the rotary tool. The cheap tool kit that comes with many rotary tool offers, will barely be able to successfully complete the work on one little burner, and those cheap accessories will not be pleasant to deal with. Much better accessories kits are offered through Amazon.com. I suggest the Populo 305 accessories kit, which has decent quality, and is only $15.90. Or, you could invest about the same amount of money on a Dremel EZ406-02, EZ-Lock Starter Kit, which includes their EZ–Lock mandrel, and four 1-1/2” cutting discs; this will do the best job of cutting pipe and tubing, which is where cheap accessories included with most rotary tool offers fail badly. So which choice is better? If you are a novice with rotary tools, I suggest going with the Dremel option, as you will need far more help with cutting than any other task (and their special mandrel is serious help).

Note: Some people have found that the sheet metal hub on one or more of their EZ-Lock cutting discs separated; if this happens, stop immediately and remove the disc. Use hardening thread-locker to glue the hub back onto the disc, and clamp it; then wait twenty-four hours for the glue to set hard, before using the disc again.

[Mikey98118]

                                                 Scoring and parting burner tubing

I previously recommended Rigid's miniature pipe cutter, as being the best choice available; well that was then, and this is now. A bunch of new pipe cutters are being offered on Amazon.com these days.

The Saillong Mini Steel Tube Cutter (No. 174-F), with two spare cutter wheels and “E” spring retaining clips, are now 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 the mixing tube, 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.

  Unlike my Rigid pipe cutter, the  No. 174-F cutter wheel 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 to leave a spiral score on the material, instead of immediately starting a proper cut.

 

[Mikey98118]

                                                                                 15/16" cutoff discs

Until recently, 1-1/4" cutoff discs were the smallest steel cutting discs that were commonly available. Dremel #420 15/16" discs were the only steel cutting discs available in this small diameter. All other  15/16" cutoff discs were the thinner garnet red discs, which are used by jewelers for cutting gold and silver rings.

    However, 15/16" steel cutting discs are becoming standard in accessories kits now. How to tell the difference? Steel cutting discs are dark gray. Jewelers' discs are garnet red, because garnet grit is what they are made from.

[Frosty]

Cool, thanks Mike.

Frosty The Lucky.

[Mikey98118]

You're welcome, Frosty.

[Mikey98118]

Printer Nozzle Gas Orifices

The gas orifice on a naturally aspirated burner must closely match its diameter in relation with the diameter of the narrowest point of constriction, no matter what the inside diameter of a burner’s mixing tube is. On 3/4” and larger burners, this is best accomplished with a MIG contact tip. On burners 3/8” size and smaller, 3D printer nozzles have every advantage over MIG tips (even with capillary tube trapped in them as precise gas orifices); this is because the greatly increased friction of the gas molecules through smaller orifices make it necessary to shorten the length of capillary tubes down to that of printer nozzles. So, in smaller burners, capillary tubing used for gas orifices give little advantage, while printer nozzles are cheaper, more easily acquired, and far simpler to mount. Right in the middle of these ranges are 1/2” burners, which can benefit from a correct size and length of capillary tube in a MIG tip, but with printer nozzles do nearly as well (with less work and expense).

MK8 Ender 3 extruder nozzles are available through Amazon.com); they have M6x1 male thread. The markings on each of these nozzles stands for the orifice diameter in millimeters:

 0.3 (millimeter) is 0.0117” orifice diameter is a good gas orifice size on a 1/8” burner.

0.4 (millimeter) is 0.0156” diameter is a good gas orifice size on a 1/4” burner.

0.5 (millimeter) is 0.0195” diameter is a good gas orifice size on a 3/8” burner.

0.6 (millimeter) is 0.0234” diameter is a barely workable gas orifice size on a 1/2” burner.

0.7 (millimeter) is 0.0273” orifice diameter is a suitable gas orifice size on a 1/2” burner, but a capillary tube can be tuned for performance by varying its length; thus, the right orifice diameter capillary tube can give a little better performance than just a printer nozzle.

Printer nozzles generally have M6x1 thread, but there is another difference to look for; they have grown longer. The latest models feature 5/8” of thread length; this is important, because you need the gas orifice to run parallel to the axis of the gas tube. The older printer nozzles had as few as three threads, which were far harder to ensure a proper aim with.

[Mikey98118]

                                                            Fine tuning the forge

Fine-tuning burner performance completely  is usually done while running it in its intended equipment, and only after adding finish coatings, and a front baffle plate or brick wall for an adjustable exhaust opening to the forge, along with an adjustable secondary air choke installed on the burner’s mixing tube. These things are needed in order to raise internal temperatures high enough to better judge flame performance. Sounds backward, doesn't it? But the thing is that the best evaluation only comes in equipment that has been turned into a “radiant oven.”

 The burner is merely part of the forge; if performance only revolved around the burner, most of what we've learned about constructing heating equipment would be "gilding the lily"; it’s not.

 

Clear back when I was still writing Gas Burners, I raised the temperatures in my forge from orange to lemon yellow, merely by refining the high-emission coating it was painted with, from the stuff that came out of the jar to colloidal grade particles. I A few weeks later lemon yellow jumped up to yellow white by stopping all secondary air from entering the burner port; this has been further refined by the addition of a sliding secondary air choke on the burner's mixing tube. t has been stated that good burner performance requires a delicate dance of several factors; ditto for the equipment it heats.

[Mikey98118]

Drilling holes with rotary tools for 10-32 taps that are being used on small flame retention nozzles to thread holes for their socket set screws cab be done, if you are careful; these taps call for a #21 numbered drill bit, which is 0.1563” diameter; this is 0.030” larger diameter than the 1/8” shank limits of rotary tool chucks, so you need to enlarge the holes left by a 1/8” cobalt drill bit. Drill, and then file or grind, at one-half speed in a rotary tool.

    Enlarge the hole a little bit with a diamond coated rotary burr (safest) or a 1/8 single cut tungsten carbide rotary file (fast but tricky). You are removing only 0015” all the way around the hole’s periphery. So, you want a tool that works smoothly, and slow enough to keep control of the process. Swing the diamond coated burr lightly around the hole, and check to see if a taper tap will thread in the hole easily. If not repeat enlarging and checking. Be sure to keep track of how many passes produce the desired result. It is wise to perfect your technique on scrap tubing, before enlarging holes in your flame retention nozzle parts—especially if you choose to employ the rotary file.

[Mikey98118]

                                                        From mini 12V angle grinders to rotary tools

About three years back, Milwaukee came out with a 3" battery powered angle grinder, which they had built in China; it was a ridiculously overpriced and glitch filled design--since then the design as been improved, and it is only seriously overpriced. In the meantime, other China OEMs redesigned  their own versions of that tool, which are marketed for around $50. Their tools feature 12V interchangeable batteries and high torque brushless motors. The main point of these tools isn't grinding, but surface cutting.

I have wondered every since then, when the Chinese would make the obvious move, and come out with the same combination in a rotary tool, so that a battery powered rotary would finally be practical. There are now such rotary tools advertised on Amazon.com, by three different manufacturers; none of them feature a brushless motor, yet. But this upgrade is only a question of time; in the meantime swapping out the motor is just an additional twenty bucks and some wiring work