re Problem with Pencil Torch Flame

*** W. Curtiss Priest, Director, CITS Center for Information, Technology & Society 466 Pleasant St., Melrose, MA 02176 Voice: 781-662-4044 snipped-for-privacy@MIT.EDU

Chinese, Generic Pencil Torch Technical Note March 12, 2007

Failure Mode:

No flame No blue flame, torch flares, butane escapes very quickly

Keywords: repairing torches, fixing torches, problem with pencil torch, unable to light pencil torch

Introduction:

If you have found this note and have not tried to open the torch, you are probably in luck. If you have unscrewed the torch burner head, you most likely have lost the orifice.

Why?

I had to purchase a second torch just to see what comprises the orifice. It turns out that this is a thin sliver of a disk and demanding for even good eye sight.

Those who are used to standard BernzOmatic propane torches know that when the torch has low or no gas flow (no audible sound) and cannot be lit, that there is a brass orifice between the tube from the tank and the burner head. Further, the head has two flat spots, as the maker expects it to be disassembled when the orifice is clogged.

Included in most kits is a sheath of fine steel wires. To clear a clogged orifice, one pushes a wire through the center drilled hole in the orifice. The diameter of the wire is

9.5 mils, suggesting that the orifice is around 10 mils in diameter. Most importantly, the orifice is a largish object, about 1/4" long and a taper fits into the end of the tube and the face is rounded to create a seal with the head.

Decades ago BernzOmatic made a pencil torch, model TX. It used an earlier style stubby propane canister. However, it can be adapted to use with a standard 14.5 oz. propane tank by using a valve fitting to the tank that has a ribbed hose connection, a short piece of high pressure polyethylene tubing (the kind used to bring water to ice machines), and adding a ribbed hose connection at the torch end -- I cut the top of the empty tank so I could solder the hose connection to that. I see that BernzOmatic makes a similar hose connected miniature torch, the ST-900.

When the orifice on the TX clogs, the hole is only 2.5 mils in diameter and no common steel wire is easily available. The smallest such wire is a common part of a sewing kit -- it is the steel wire loop that is supplied to make threading needles easier. That wire is 5 mils in diameter. However, there is the alternative of using an ultrasonic cleaner and many people have one -- called a humidifier. The style that uses a tank placed on top of a white base uses a piezioelectric element to aggitate the water enough to create tiny droplets above the element. Those droplets are funnelled up and dispersed into the air. That element can easily be used as an ultrasonic cleaner.

To clean an orifice, or anything small, like a small mechanical watch or jewelry, remove the tank, clear away the salts that deposit around the element and then use an appropriate solvent. As the unit depends on the liquid (water) to cool the element, these units always have a sensor for water level. If it is a unit that senses conductivity from a pin to the element, just take a clip, a short piece of wire and clip to the pin and place the wire into a little puddle of water over the element. If it is a float, use string to lift it. Whatever, do not let the element run dry.

To clean an orifice, use water with a drop of detergent. First run the unit for a minute with just water/detergent to clear away anything soluble. Then rinse the area. Now place the orifice into the water/detergent puddle and turn the unit on for a minute. After rinsing and shaking the orifice, see if you now see a pin hole of light. If not, give it another treatment.

As for the orifice on the Chinese pencil torch, the orifice is incredibly small. From the factory it is a steel disk that is 2.45 mm. in diameter and .05 mm. thick. And the pin hole is about the same size as on the BenzOmatic TX, about 2 mils in diameter.

Repair if you have not lost or damaged the orifice:

If you still have the orifice, clearing the hole is simple but exacting. Most of us have no experience dealing with a disk this small. It can be bearly handled with fingers. It defies tweezers, wanting to fly out when pinched, as it is slightly tapered at the edges.

So, clear a table space and place a white fine cloth down. Now, if the disk falls, you'll see it. And the disk will not travel far if it tries to roll or skate.

Removing the disk:

1. hold the body of the torch in one hand and standard pliers in the other
2. lightly grip the head with the pliers, not too tightly, not too lightly
3. loosen the head
4. holding the unit horizontally over the white cloth unscrew the threaded tube to the head
5. the disk tends to stay inside the head, but, as you pull the two apart, look at the face of the threaded tube, you should see a fairly large hole ... if the disk is stuck over that, then brush it with your finger to get the disk onto the cloth
6. when the disk is inside the head, you can try to rap the disk out by tapping the threaded end of the head against the cloth
7. if the disk will not fall out or rap out, you need a pin that is less than .07" in diameter. A #52 drill bit will do, or a largish sewing needle

you press the pin into the center hole of the front of the burner head. You will feel it hit the disk, now slowly push the disk onto the cloth

1. you might wish to verify if you can see the clog, but, be warned -- holding the disk up to a light is pesky and be sure not to raise the disk, say, more than a foot above the white cloth
2. as the disk is so thin, the clog is easily removed using a fine sewing needle. Note, there are dozens of ways sewing needles are sized. Singer, for example, sizes them with the British gauge number. But, Dritz sizes them with a scale that runs about 3-10, where 10 is the finest

also ... important ... the sewing needle is much larger than this hole ... we are just using the sharp point on the tip of the needle. And, the size of the point does not always correspond to the size of the needle, but, in general, the finer needles have sharper points in the last 1 or 2 mils of their length

So, a Singer sized needle to use is a #26 or #27

And, a European sized needle to use is a #9 or #10

If you have a Jo-Ann's Fabric store, get the Dritz "20 Quilting Betweens" number 56B-10. "Betweens are only shorter in length than "Sharps" -- and both have the same points. The Betweens are available in the smaller size because working on fine quilts, the person wants a shorter needle for dexterity

1. with the needle on the cloth, just press the needle into the hole until it stops. Now flip the disk over and do that again. The clog should be cleared

[Note: some people lick their fingers to work with small things, such as thumbing pages. But, do not. You don't want to introduce junk. Natural levels of body oils on the finger tip will typically provide enough stick to pick the disk up if you scoot the disk as you try to raise it.]

1. to replace the disk do not attempt to either drop it into the hole in the head or use the threaded tube to place it into the head. If you drop the disk in, it will most likely not be flat and will be crushed. If you attempt to start screwing the threaded tube onto the head, with the disk balanced on the end of the tube, the disk can easily slip and get caught in the threads, and become pulverized
2. to replace the disk, you want to balance the disk on the end of thin rod with a flat end that just fits into the threaded region. A number 40 drill bit will do, or, you can use a common round tooth pick -- Diamond "Elegant tooth picks." This dowel is 2.1 mm. (.0825"). One end is slightly rounded -- carefully grind or sand that end flat

with the toothpick pointed up, with the disk centered, now just lower the threaded hole of the torch head down onto it ... the toothpick will go in about 1/4"

you can now hold the head horizontally and look at a lamp through this hole ... you should see a tiny pin hole of light

1. with the torch head pointed down, clear lose cement from the threaded tube and screw the tube in, hand tight. Now hold the body of the torch and with the pliers give the head a snug turn ... you are lightly crushing the copper onto the two brass surfaces ... now, the only opening will be the pin hole

Some might ask, is this worth it? Well, if you have only one pencil torch and are in the middle of a project that requires that one torch, then surely this is worth the twenty minutes to do this. And, while the #10 Dritz is the ideal point, probably almost any of the smallest needles in a pack will do, say, even a #23 (Singer size).

Now, what if you have lost or damaged the disk?

If you have time and are not interested in a "construction project" -- then stop here and order another torch. In that I sense that these torches are sold in the millions, perhaps a local hardware store or hobby shop has one, within driving distance (however, I do sense that small retail hobby shops are dying out ... several that I called had disconnected).

However, if you enjoy projects, as a hobby, then it is a fairly easy matter to make a disk, or many disks :)

To make a disk we fabricate a custom punch for copper and we use the above Dritz needle to create the 2 mil. diameter hole.

Copper flashing is commonly available. Also often the interior of PC monitors are lined with a copper sheet for RF interference protection. The following instructions are for 3 mil. copper. If the copper is thicker or thinner, you will have to adjust the piercing force (below) as appropriate.

Fabricating the punch:

I pondered how to make this tiny disk and I realized that the only practical way to make a "perfect" round disk of this size is with a punch. If you are a hobbiest, then you may have already acquired a punch set for cloth, rubber, or soft metals ... mine is called a "Maxi Punch Set" and has a handle and six punches ranging in size from 8 mm. down to 4.8 mm. But, of course, not 2.45 mm.

And, to punch copper, we can make a punch with soft steel. It turns out that an 8-32 steel screw is a usable size, so we machine one that is 1" long.

You need, at least, a drill (preferably a drill press), a number drill set, and a rotary grinder (preferably a Dremel-like with a cutoff wheel). We will drill a hole down the center of the screw and then taper the screw from the outside with the cutoff wheel at an angle, thus creating the cutting edge.

Steps:

1. cut the head of the screw off with a hack saw or cutoff wheel
2. to accurately centerpunch one end of the screw, place the screw in the drill, and, with it turning, take the rotary tool with a carbide cutter -- such as a chishel tooth and holding the bit in the plane of the screw, remove the threads on the part of the screw protruding from the chuck

as soon as you see no threads, you are done, and it does not matter if you were perfectly parallel -- we are just clearing the threads to see the end. Do not remove material further, we need the remaining wall size

1. carefully locate the center and centerpunch
2. with a #45 drill, place the screw in a machinest vise (there are "V"s to hold round objects straight) and drill in about 1/4"
3. we want to finish with a #41 drill, but, because that size drill bit gets close to the outer diameter of this trimmed screw

at this point I never trust that the final drill will be centered if I see that the current hole is not perfectly centered

my way of assuring centricity is to eye the hole and with a carbide chishel bit of a size smaller than the current hole (or any burr or diamond coated bit) I carefully remove material on the inside wall that is "too far in." You are "walking the hole out." And, as you do, you are also getting it closer to .096" diameter -- the size of the hole a #41 drill cuts.

now drill the end with the #41. If you break through the wall, you must start over

1. tapering the outside is fairly quick and easy. You again turn the screw with the threaded end in the chuck. As you turn, you angle the cutoff wheel at about 45 degrees to the end of the screw/punch

if the result is a punch with a ragged end, just square the end off by pressing it against the side of a spinning cutoff wheel, and then angle the end again

1. to permit removing a punched disk we need to create a hole to the other end of the punch. Take a #50 drill, place the punch in the bench vise, and drill from the punch end through to the other end. As this is nearly an inch long hole, be sure to raise the bit every few seconds so that the cut metal is released and the bit does not bind

When done, the punch can be held with vise grips as described below.

Fabricating the torch orifice:

One is making a very small disk which is difficult to handle because it is also thin. Work in a contained clear area with bright light.

Tools:

1. small bench vise with a 3/8 inch brass nut, with a side face, facing upwards 2. 2 small vise grips 3. one shortened #10 Dritz sewing needle 4. one home made copper punch 5. one postal scale (or, ideally, a slide spring scale) 6. one block of wood 7. a number 52 drill bit 8. a number 40 drill bit 9. a flat punch -- around 1/4" diameter

Materials:

3 mil copper (for other thicknesses you'll have to adjust the force on the piercing needle)

Preparation:

As one will put the orifice into a copper disk, the scale will push on the end of the needle with a selected force. As the #10 needle is only .0180" in diameter, it is easily bent.

One of the vise grips should be a pair with either a smooth or serrated jaw at its end, say, 3/8" of jaw width. The sewing needle is shortened such that its point comes out one end of the jaws about 1/16" and does not come out the other end. (Now, pressure on the side of the vise grip will press the needle into the copper foil.)

With practise, it takes about four minutes to punch and prepare the copper disk. It takes about one minute to press the hole.

Steps:

1. With the punch in a "needle nosed" vise grip, pointing out the front of the pliers, place the copper sheet over the wood block, press the punch, and rotate about half a turn left and right with constant pressure

Too little pressure, you will not press through to the wood.

1. Press the copper disk out, using a #52 drill through the far end of the punch onto the brass nut. Surround the area with your fingers, as when the disk pops, it can fly. (you can always punch another one :)

1. The disk will have an edge curl. This must be removed. Take the end of a flat punch (or almost anything with a flat end) and press down on the disk, evenly. Look and assure yourself that you flattened the disk evenly. Press with a slight circular action -- this will assure contact with all edges.

2. Take a black permanent marker and roll it on the disk to mark that side. Roll off of the disk, as, just lifting will take the disk with the pen.

1. Eyeball the center of the disk (not critical). Place the point of the Dritz #10 needle/vise grip in the center and hold those pliers so that the needle is straight up.

2. A number 7 Petersen Vise Grip weights 160 grams. With your scale you need to add somewhere around 1200-1500 grams.

This is sufficient force to drive the point of the needle through the disk and into the brass. But, it pushes only the needle end which is about 2 mils diameter and not the entire needle which is 18 mils in diameter.

You should be able to pick up the disk by just raising the vise grips. You should see the point end of the needle, just coming out the other side of the disk.

1. Inserting the disk is touchy. It cannot just be dropped into the torch end of the unit because it will not lie flat and screwing in the torch body will crush the disk.

So, you need to do a balancing act. And do this close to the table so when the disk falls, you can easily recover it. Note: the disk is light enough that the oils on your finger tip is enough to pick it up from a flat surface. Do not lick your finger -- that would leave material that could clog the orifice. You will find that pressing your finger on the disk, with a slight sideward swiping action will pick it up reliably.

One places the disk on the flat end of a #40 drill bit with the black side facing the bit. Why? You have not drilled a hole, you have pierced one. So, there is a tiny copper coller around the hole on the side the needle came out. If you point that towards the butane source, it will more easily clog, so we point it away.

You have the disk/bit in one hand and the torch head in the other, you carefully line the end of the bit up with the screw threaded hole in the torch head and push it in (about 3/8"). You should be able to hold the torch head towards a light (keep the head horizontal to keep the disk in) and see a tiny, tiny pin hole of light.

If you see no pin hole, start over and press the needle with another 200 grams of force.

1. Clear the threaded end of the torch body of lose cement

1. Screw the thread into the torch head until it stops turning

2. Take regular pliers. Hold the torch body in one hand, apply the pliers to the torch head, lightly. Too hard, you'll score the head. Too soft, you'll skate. Now just give the head a snug turn. This compresses the disk/washer around its edges so that the orifice is now the only passage for the butane into the head

If you have a microscope you can view your result. Use a 30x magnification. To determine the size of your hole, place the disk with the black side down. Now take the needle threading wire (measure its thickness with a caliper or micrometer; they tend to be 5 mils) and place the wire next to the hole. You should see a hole that has a diameter about half that of the wire -- i.e., the pierced hole is about 2.0 mils.

This size -- 2.0 mils. -- is about as large as the hole should be. The flame size will be somewhat greater than the original.

One interesting side-effect of being able to make these orifices is that you now have the ability to make the torch cooler or hotter. The smaller the hole, of course, the smaller and thus cooler the flame. (This can also be done by adjusting the gas flow from the body, but, this behaves differently, and requires fussing. If you are, say, a jeweler, you can tame the flame to a known setting. If you have two torches, you can set one for a small flame and another for a larger flame.