Burner Building

Rev: ... 2002-12-15, 2003-03-14, -10-22; 2004-03-29; 2005-01-28, -30-31
2006-02-04, -03-06
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Making a Burner
Adapting a Blower
Mounting a Burner
Regulators, Tanks & Propane
Propane Pressures
Other MF Burners
Orifices
Drill Sizes
Pipe Sizes
Burner Discussion
Burner Tuning
Burner Book Review

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Burner Choices
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Furnace Building
Joppa Glass HP Propane Orifice Chart
Orifice Chart to buy
Reil Burner Notes
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If you are just beginning to consider making a burner, please check out Burner Choices before getting too involved with this page.

One well-known way to build a burner with a blower is with a pipe T. Furnace burner without blower with permanent copper gas connections

I have built 6 or 8 burners with various sized pipe, from 1/4" to 1-1/2" for various purposes. (See below.) I almost always build mine so the gas is injected on one side of the top of the T and the air is blown or sucked in the bottom. I try to build my blown burners so that if the power fails the jet is located so as to suck in enough air - using high pressure propane - to keep a reasonable heat up. This involves moving the intake pipe to the right position during construction. On an unblown burner, the same step must be taken just to make it work. [I was asked where the air comes from, since it seems closed, but when power fails, the valve is open (as shown at right) and thus air enters the intake of the blower, passes through the slots of the squirrel cage and up the pipe. Some kinds of blowers - expensive - would not pass air like this when stopped.]

Here are some specific directions for a full sized burner (like for a glory hole or furnace) using 1-1/2" NPT fittings for the T. The burner is shown on the right side of the glory hole shown below and in an image cut from the photo further down.

Cross sectional drawing of pipe T burner head

The burner is built as a T of the 1-1/2" fittings onto which are added the brass fittings for the gas, the blower adaptors and the feed to the furnace/glory hole. Not all details are shown in the drawing.

Adjusting the nipple -
Version 1 - Thread the brass adaptor into the iron adaptor. Tighten the brass adaptor moderately and move the 1/4" nipple in it until the end of the cap is still just visible (i.e. the pipe goes most of the way through the T) inside the T when looking through the base of the T opening. Mark the 1/4" nipple so it can be soldered. Remove the adaptor and use a torch to solder the nipple in the adaptor. (Epoxy can also be used as the fitting shouldn't get very hot.) Replace the brass fittings.
Version 2 - Connect the gas (so you might be doing this later in the process). With at least the base pipe attached and perhaps the blower if you want a better setup, but with the blower off, turn on the gas and light the burner (shall we discuss how you are holding this? Nope.) As the brass nipple is moved in and out, the burner will burn with more or less efficiency depending on how much air is dragged with the gas. The goal is to make a head the will work with the blower, but will also burn reasonably well during a power failure. It is unlikely you will get too much air (blue flame), but work from too much gas (yellow flame, poorly formed) to as lean as possible. When the nipple is adjusted, mark its location for soldering or epoxy.

Finishing the blower attachment
If using a 1 1/2" gate valve, attach it and its nipple. Thread on the 1 1/2" PVC adaptor and solvent weld on the 1 1/2" to 2" PVC adaptor. Cut the PVC pipe as needed. Use electrical sweep elbows (smoother curves) if bends are needed in the PVC.** Connect the end of the pipe to the blower.

* I previously recommended using a 1/4" IPT x 3/4" IPT brass adaptor. After attempting to work one of these after losing a useful tool and after pricing large drill bits and taper reamers and after having worked with the burner, I now feel that a slip fit with the larger hole and epoxy rather than braising is a much more economical choice.

** I am experimenting with metal flex tubing used with driers vents, 3" size. More later. [Later: Bad idea. Tubing is fragile - bends, kinks, comes apart.]

ADAPTING A BLOWER
Making a blower fit the pipe can be a challenge. The recommended blower has a flat flange. Similar blowers have a tubular outlet, the wrong size. A scrounged blower may have a square opening, flanged or unflanged. I recommend using a six inch piece of soft pine 2x6 as an adaptor. Check the next section on adding a gate valve. Drill or saw a hole through the wood matching the size of the PVC or the blower outlet ID, which ever is smaller. Then cut part way in the other side to match the larger diameter. If the blower is flanged, screw the blower in place. If it is not flanged, fit it into the opening, Taper the opening with a rasp for best air flow if needed. Use screws inside the outlet, through the sheet metal into the wood to hold the blower, with caulk if needed. Press fit the PVC and use silicone tub caulk (or epoxy) to hold it on the other side of the board.

Wooden Gate Valve

Blower & Valve after sanding & shellacking

While it is usually not difficult to scrounge a large (1 1/2" or 2") gate valve for controlling air flow, such a valve is heavy and costly if purchased ($24-48) Making one of wood is easy and if a 2x6 wooden block is used to adapt a blower to the pipe the gate can be built on the block. [The valve is shown in pictures above and a second one that is around, used on other burners. This is after a repair when it broke apart on being dropped. The grey PVC pipe was epoxied into place, the sides glued, but also screwed, and a crack glued. The slider then had to be sanded to fit and the whole was shellacked.]

Each installation will be different. Burners should be fairly firmly mounted, especially those which have white ceramic heads which are fairly fragile and should be mounted with a half inch space between the head and the burner port. My choice of mounts, used on both my furnace and glory hole, is to hang the burner below a support bar that can be shifted for correct lineup but which is unlikely to shift in normal use.
I have a rectangular frame fastened to the equipment which supports the door, etc. In the picture the frame has the round gloryhole under it and flat steel plates on top to the right. The square tubing just in front of the plates is bolted at the far end and can slide on the nearer rail. A simple flat of steel takes a bolt into the tubing at the top and into the burner at the bottom. The burner is threaded. Originally, I planned on mounting on the pipe, tapping a hole there but the balance was off creating awkward movement so I filled it with a short bolt visible on top and moved more directly above blower. I had to remount the tubing further out. 2005-01-28
Note the gauge at the left edge of the picture. This measures the back pressure on the orifice as the control valve below it opened. The pipe T below the gauge replaces the elbow in upper pictures. Originally, the gauge was mounted on a quick release stem, but I was reminded how little the gauges cost ($4-7) which is less than the quick release male and female, so just put gauges in place. The amount of gas flowing depends on the orifice size and the pressure and

Welding orifice cleaner (Sweethaven Publishing)

WHETHER THE ORIFICE IS CLEAN!! I reduced the size of the orifice to give me more control by braising over the nipple and re-drilling. On several occasions, I have found the pressure up and the gas flow down (the gloryhole not hot enough.) Disconnecting one of the copper flare fittings allowed me to unscrew the large iron adaptor and clean the orifice with a welding orifice cleaning tool while the glory hole was hot. Pressure dropped but there was more gas flow through cleared orifice. 2005-03-31

Sources: High pressure regulators, high pressure gas hoses, larger tanks - Most places selling a variety of propane cooking equipment will have the regulators for the high pressure burners used with large outdoor cookers. In Dallas, specific places are Elliott's Hardware (Motor & Maple off I-35) and NW Butane (11551 Harry Hines) the latter carrying the larger tanks as does U-Haul at I-30 and Furguson.. Note that some high pressure regulators are not adjustable - fixed at 10 or 12 psi. For future use, adjustable is nice.
Hardware - Brass fittings are available at most hardware stores. Pipe nipples are also, usually, although bigger sizes may require a visit to a specialized DIY plumbing shop.

PRESSURE - Three different pressures are involved with propane: Tank pressure, high pressure regulated and low pressure regulated. "Hanson`s ASME propane tanks are built to 250# working pressure. Under normal circumstances, the vapor pressure at 100 F is 172 psi." "Tank Pressure-Unregulated pressure in any size propane tank or cylinder can range on average from 80 to 250 psi; High Pressure-Regulates pressure received from tank or cylinder pressure. Maintains a constant outlet pressure between 8 to 12 psi.; Low Pressure-Regulates pressure received from the high pressure regulator. Maintains a constant outlet pressure between 11 to 14 inches of water column. (28 inches=1 psi) " Stationary LP
Low pressure is similar to natural gas at the home. High pressure is similar to industrial supply natural gas.

First furnace setup with manifolded propane tanks on stand.

A standard 20# BBQ tank will freeze up when delivering enough gas to fire a full sized glory hole - either a bigger tank is needed - 100# (pound) is my choice - or a manifold with several tanks on it (at right in an early setup.) Freezing means literally that: when gas expands, it must absorb heat or it cools the remaining gas and tank. In humid conditions, the outside of the tank will be covered with 1/4" or more of ice. In cool conditions this happens faster. The propane does not convert from liquid to gas as quickly with the cooling and pressure drops. With small torch tanks, one will hear of putting the tank in a can of warm water. I have not tried anything to keep the tanks warm.

Propane is sold by the gallon for larger tanks, by the refill for smaller. Look under Propane (and/or Butane) in the Yellow Pages. For serious glassblowers (only in a non-urban environment?) the rate is negotiated with a company that delivers propane and a 250-500 pound tank is installed in the backyard away from the shop and plumbing run. A propane tank truck with a long hose comes somewhere between once a week and once a month (depending on usage) and refills the tank. In this case, the rate for tank rental, placement fee, and cost per gallon are all subject to negotiation. Once usage is proven, a lower rate can be negotiated - one rural glassblower is the highest summer user of propane for the delivery company and is well up the list in the winter.

Q#1: What are examples of high pressure and low pressure propane. Which is a 20lb bottle on the BBQ considered to be?
As it comes out of the bottle, very high pressure - 175-250 psi. You can buy either a high pressure regulator - 12 psi - (adjustable or not) or a low pressure regulator - 7 ounces. Unregulated high pressure is what is used in direct connect torches. Most cooking burners, like for deep frying turkeys or fish, have a high pressure regulator for even heat.

Q#2: What is the size of the gas bottle you use on the Hole and how long does it last? What is the cost to refill?
I use a 20# bottle (standard size) with the Fire Hole and I haven't run one dry in the times I have used it (or when melting aluminum) so probably it it will last 5-6 hours. I usually am running the hole and aluminum melter for about an hour at a time. For the glory hole, I use 100# (20 gallon) tanks with a high pressure regulator. If the weather is warm, I get 2 4-6 hour sessions out of a tank. If the weather is cold, the tanks tend to freeze up when sucking a lot of gas out of them and they are less than 1/3 full, so fewer sessions (freeze up means that ice forms on the outside and the propane inside wants to stay liquid, so pressure is lost. No, I haven't tried heating the tanks.) [Yes, I did later, with an industrial drum belt heater, which seems to work but may be risky.]
Around here there is normally a fixed fee for filling 20# bottles - like $9 now $6 in past - no matter how empty they are. The 100# tanks are charged by the gallon - was $1, now up to nearly $2/gallon. But I have found that if I take in the 100# almost empty and a couple of 20#, I am just charged for the total gallons - which makes filling the smaller ones cheaper. I buy at U-Haul, the closest place and usually with lowest or competitive rates. A full 100# tank weighs over 180# and I normally move them by putting an old quilt on the back seat of a car and sliding one in. [This is considered dangerous and one site has refused to refill the tank if I show up carrying it this way. Transport law to keep these things upright is being enforced.] I get it out of the car as soon as possible (i.e. I don't park the car in the Texas sun with a 100# tank of propane in the back seat! If I had a problem with the car, I would drag the tank out first thing.) At the house I use a hand truck to move the large tanks - I have two - through the yard. I built a trailer for my bike which works, but half kills me on the hill coming back.] 2005-02-11

Two specialized burners - tiny and side throw

The larger burner at right must be blower driven because of the location of the gas input [since rebuilt.] It is used with my aluminum melter and was built this way to fit inside the limits of the brick BBQ pit. The blower - attached to the white PVC pipe - and the gas - using the quick connect at a right angle to the T - are located outside and in front of the pit. The elbow in the larger pipe is propped up so the flame enters the side of the melter downward at a 45º angle. By using high temp anti-seize compound, I am able to keep the last nipple and flared piece removable so a nipple only can be installed for heating in the Fire Hole. The smaller burner uses a tiny copper tube and pipe cap with a drilled hole to make a small pre-heater burner, mostly for drying and preheating the glory hole sitting outside. A burner in between these two in size has also been used for preheating and for maintaining heat for cooking in the BBQ pit, where it is set on low flame and put through a hole in the bricks in the bottom of the back wall.

--- In glassblowing_topics@y..., fsankar10@h... wrote: > What does a burner head look like. In Mikes design it was an open > pipe (I think??) Is there a design where you used a flat cap on the > end and drill holes in the cap? > Newbie Almost all the burners I use have a bell shaped adaptor on the end to provide a swirl chamber that helps hold the flame, mixes the gases in the turbulence, makes a bigger flame, provides a thermal break from the hottest part of the flame, and provides a sacrificial element to throw away when badly damaged. There are burner head designs that use a ceramic head (Giberson and Wilton) and iron burner heads. For both of these the primary purpose is to provide more flame area and reduce burner noise (as does a ribbon burner) by breaking up the flame into smaller flames. Most burner heads are complex shapes to shape the gas into non-turbulent flow (which reduces noise) rather than just a bunch of holes drilled in a cap - which is why I don't use a cap, I am not into head design.

> Mike how did you know how far to slide in the brass nipple and why
> did you use a #50 hole?

Getting the burner to work sucking its own air in is a matter of setting everything up and lighting the burner and sliding the nipple in and out until the flame is most efficient. Then the nipple is marked, the flame shut down and it is soldered or epoxied into place.
Originally, the data for burner hole size came from Dudley Giberson's catalog. I will have to check my page. Dragging your own air only works for high pressure propane. With low pressure, you just hang the end of the nipple in about the right place and blow air past it.

Orifices
The amount of gas that can get into a burner is determined by the pressure of the gas and the size of the hole it is trying to squeeze through. The size of the hole is given most often by the size of the small bit used to drill it although the real determination is the area of the hole. Dudley Giberson, in his legendary catalog, gives recommended orifices for high pressure propane for the burner heads that he sells. From a practical point of view, if building a burner or modifying one to work from a different pressure or to deliver more gas, the easiest solution is to have modest variety of numbered bits in about the right range (say 55 to 70 in steps of 2 or 3 sizes) and use the bits to first measure the existing hole then select one to enlarge it. As mentioned below, these are very small bits and require a chuck that will go down to 0.0 to hold them.
If drilling a cap for an orifice it is best to drill from the inside as brass caps typically have a cone shape that centers the bit some what. If an orifice is found to be too big, the hole can be braised or silver soldered (not low temp soldered as sometimes the tip can get fairly hot) and drilled again.
If you are adjusting pressure with a regulator or a needle valve, it is possible to make a range of orifice sizes work, but if the orifice is too small, the maximum gas flow will be too low. If the orifice is too big, then the velocity of the gas may not be enough to pick up air for a good mix. Another odd requirement is being able to see the adjustment with a gauge, like the setup in the first picture on this page. If the orifice is too big, then the back pressure will be so low that moving the needle valve over a wide range produces a change from 4 psi to 3 psi. Making the orifice just large enough so that at full pressure the right full gas flow passes means that the gauge can be read from line pressure - say 12 psi - down to 2-3 psi for idling. 2006-03-06

Drill Bits- Drill bits come in two sets of sizes in the United States measure - fractional sizes and number/letter sizes also called wire sizes. Fractional drill bits are available in various materials in steps as small as 1/64" (0.015625") Number/letter size drills are based on holes in a plate matching dies for wire - gauges - originally. Today, the letter size are much less used than the number size because they overlap the fractional bits, while the number bits get much smaller than fractional drill bits. Click for a complete table The smallest bit I have seen in a good store is a #80 (0.0135 inch) while the table shows down to a #97 (0.0059") and a metric 0.010mm (0.0040). The #80 is so fine it will think about breaking if you look at it.:-) 1/64" is 0.015625" and is slightly smaller than a #78 bit (0.0160"). Lightweight aluminum foil is about 0.011mm or 0.0043". Most of the smaller bits will not fit in a standard chuck and require a pin vise or similar add-on chuck. Please note that wire size drills are NOT regularly spaced in their diameter - there is 0.0015" difference from an #80 to a #79 while only 0.0010" from a #79 to a #78 so even the difference varies.

Some Fractional Sizes [derived numbers]
in.	mm	Comment
[0.00040]	0.010	Smallest drill bit (metric)
[0.00043]	0.011	Light aluminum foil
0.001	[0.0254]	Thinnest commonly available shim stock
0.010	[0.254]	Ten Thousandths - "Quarter" Millimeter
.0135	[0.3429]	smallest commonly available bit #80
0.015625	[0.396875]	1/64 inch (one sixty-fourth)
[0.03937]	1	1 mm (1 millimeter) (5/128" or 1/25" closely)
0.0625	[1.5875]	1/16th inch (one sixteenth)
0.0598	[1.51892]	16 gauge steel (nominal)
0.2340	[5.94]	Smallest letter bit, #A
0.25	[6.35]	1/4 inch (one fourth)
[0.3937]	10.0	Ten millimeters = 1 Centimeter
1.000	25.40	Exact by legal definition 1 inch=25.4 mm

This page talks about home building burners. There are several ways of making burners which are more complicated and therefore are only for buying or for dedicated machinists.

VENTURI - A venturi burner uses a wasp waist shape to suck in air with high pressure gas providing the power - in other words it is a quality version of what is shown above. Of the greatest importance is that the air flow is much more proportional to the gas flow than the simple T pipe burner - increasing the gas flow increases the air flow while coming reasonably close to maintaining a constant proportion. The disadvantages of a venturi is that there are limits to its range - too little gas and no air is sucked in and too much gas means not enough air can fit through the throat. The biggest advantage is that it requires no electric power - as long as the gas flows, the flame will exist.

RIBBON - This is a term that is used for two different burners, unfortunately. The older use of the term is for a shape not unlike a pipe with a lot of holes drilled in one side. A mixer sends a gas/air mix down the pipe and out the holes. In tamer form these are used for heating BBQ's, ovens, etc. It hotshot forms, it is used for softening a length of tubing for bending in neon work.
Rather recently, it has been applied to a box of ceramic material, molded rather complexly inside in the best versions, so there are a lot holes on one side of the box and a pipe input on the other. It is claimed to be much quieter, because of all the small flames and more efficient. It is mostly used for glory holes and must be built into the wall.

RECUPERATIVE - Here the fuel is injected into the preheated air at the last instant, so the total design must reflect that fact. In a recuperative design, the exhaust gases of the furnace heat the incoming air either directly by having the outgoing passages and the incoming passages closely aligned and the air separated from the exhaust by pipe walls or panels that will withstand the heat or indirectly by having two piles of refractory heat storage (fire bricks) one of which is heated by the exhaust while incoming air passed over the previously heated other one - periodically the flows are exchanged. The former is more commonly used on small studio furnaces, the latter on very large industrial glass melters. The fuel is added to the heated air, which may be 500F degrees or more, just at the last moment in an all refractory nozzle, the air being driven by blowers located on the cool input side of the recuperative unit. 2005-12-16

BURNER TUNING Notes
I went and looked at the Reil burner site and added a link to my page. No, I don't think you can add a blower and the only reason for considering it would be to save wasting the more complicated hardware you have now.
The problem you having is common and has nothing to do with "cooling the tip". If a burner is working properly, the flame will stand just off the end, not heating the tip much at all. Part of burner design is to create turbulence or other complex flow at the end so the flame does not either blow off or burn back. Reil's bragging about being able to keep the flame on the burner with 25-30 pounds pressure is related to this. And it is why he shows pictures.
1. If gas pressure is very low in a venturi burner (which is what his burner and my T-type in back up mode are like) then the gas can actually start burning at the nozzle with just the air right there. Not good. Not efficient. May produce a noisy whistle.
2. With more gas pressure, the flame may be in throat where the air and gas is mixing. This is very roaring noisy and soon the entire burner body is glowing a bright red, not good.
3. With the beginning of proper pressure, the flame will be inside the mouth of the burner (the bell on mine), will be reasonably quiet and reasonably efficient. OK, but the bell gets red.
4. As more air flow is provided, the flame moves out of the mouth and stands at the end of the pipe, air being swept in past the mouth keeping it centered and turbulent. Great.
5. Eventually, if the fuel flow is increased beyond the capacity of the burner, the flame will start standing clear of end and it becomes unstable. In open air, the flame will literally blow off the burner

What happens if the pressure is too low for the size of the burner is that the flame works it way back down the list, trying to burn inside the pipe, etc. That is the pop pop. When you turned up the pressure and the flame moved out of the pipe, it was far enough out that it did not overheat the tip - no redness, lower noise.
If there is back pressure - not enough outflow from the forge/furnace - then the flame gets shorter and also starts to work back through the 5 steps.

BURNER BOOK REVIEW
I have been sent a book on burners [Gas Burners for Forges, Furnaces, & Kilns, Michael Porter, Skipjack Press, Ocean Pines MD 2004, ISBN 1-879535203] to review. My overall reaction was positive at first, but I am rather more neutral on further reading. It took me a while to figure what was going on. At first I thought it gets a bit too focused on the particular design promoted in the book, which is built around using predrilled MIG and torch welding tips to produce a long narrow nozzle point.
After rereading, I found that the structure hides confusion. There is a good drawing of parts and the whole and a complete numbered parts list with matching numbers on the drawing. But as construction develops, it turns out that two parts have the same number and most parts have three names - the piece name (MIG tip), the group name within the burner (adjustable tip) and the major subpart within the burner (accelerator). Because a part number is assigned to the first name - we can have a sentence like this on page 42 "Screw the second contact tip into the other inverted female nut." Because the female nuts are assigned part 13, there is no good way of telling them apart, although they end up looking different after grinding.
Part of being too focused is failing to describe burners to begin with. My father used to teach experienced workers how to be teachers of their skill to new workers and one exercise he did was to take the teacher through the process of getting up, going to the door, and turning the handle - but doing it step-by-step without telling in advance what the overall goal was to be. Most adults want to fit their learning into their previous experience, so they want a framework or outline of the subject. This book launches with a description of some complicated parts without sketching the system they fit in.
Beginning with safety is a good idea and starting with a hand torch that can be used to build the other burners and, with a temporary mount, can be used to build itself is a terrific sequence. I see nothing wrong with the burner design although the fact that the orifices must each be built from scratch and can not easily be drilled out means the design must be taken on faith. While the use of a long thin tapering orifice clearly would increase the pickup of air, I do question the importance the designer places on gas flow inside the nozzles.
Chapter 1 is Safety, Chapter 2 is The Burner System and Its Fuel and Chapter 3 is Building the 1/2-inch Burner. (In total, there are 12 chapters, footnotes, glossary, resources and index.) Logically, one would expect Chapter 2 to draw the image of a burner system, mention the variations, and then go into the details. It just goes into the details and is very good at them. But I am sure someone with less experience with burners is going to be bewildered. It is not even clear what the shape of the burners in this book is going to be, much less how they fit in the design patterns of other burners a novice or intermediate equipment builder might have seen.
Throughout the book, the author pays good attention to safety, making it clear why propane tanks - which are used as shells for several of the projects - must be treated with considerable care while opening them up.
All of the burners in the book are high pressure propane, induced air flow, burners. Chapters 2, 3, 4, 7 & 8 are each devoted to the detailed steps of building gradually increasing burners based on the nominal pipe size - 1/2 to 1-1/4 inch. They cover every single piece needed and how it is drilled and assembled with good drawings and alternative choices in some cases. Some of the parts are specialized and it will certainly help to use the resources given, have a terrific junk bin, or know people who have cutoff pieces.
Chapters 5, 6, 9, 10, and 11 are devoted to equipment that can use the burners, starting with a forge (burner aimed down at a kiln shelf), then a forge cart (burner aimed up), a foundry furnace (aimed horizontally), a farrier's forge (smaller) and a glass furnace (a small unit that I have problems with.) Chapter 12 covers braising. Among the differences between the units is how various combinations of ceramic fiber, castable refractory, and Perlite enhanced refractory are used, with good and given reasons for doing so. Depending on the intensity of the flame and heat, the fiber is, in various units, rigidized, and coated. The author really likes ITC #100, but as far as I could find, never explains what it is, although on page 121, in a parts list it is finally described as "infrared reflective coating". It is, in fact, a fairly new product that has been discussed on glass forums with some question as to how well it works. The book does mention that it is expensive.
Considering the detail the author goes into (for example, reminding us to dry off a retractable measuring tape after using it as a dip stick to measure water depth in a tank), I am particularly bothered by the design of the foundry furnace. The lid hinge is built with one long arm that extends beyond the pivot bolt. In a caption for a picture of the shape of the parts, it is stated "It is not safe to use this extended hinge tab for a handle." Considering how much the lid is going to weigh, I would agree with that. But for the entire life of the unit, the long tab is going to be sticking out the back - what is its use? I expected it would be part of stop to keep the lid from falling back or a point to hang a counterweight. In fact, its only purpose is to hold a short length of chain with a pin on the end, keeping the pin far enough from the furnace to keep it cool. The pin is used to hold the lid open angled over the lower pot. So every time the furnace is to be accessed, someone is going to have to lift the lid, reach around under the hot lid, get the pin and put it in the holes in the hinge and later reach under the lid again to pull the lid out. I would have been much happier with a design that built a stop into the hinge design so that it could be opened from the front, not go too far and rest open. The author likes that the pin allows the lid to be tilted over the hot chamber.
The glass furnace design begins with the disclaimer that using a home made burner for a glass furnace is folly because it would not pass inspection so this is really a small foundry and glory hole. In fact, the burner design has little to do with inspection - the gas train, which is covered back in chapter 2, being more important. The other furnaces seem to be more based on experience, being mostly simple straight forward designs, while this one is complicated - pivoting in its frame with an expectation that for some uses, the frame will be filled with Perlite that will be removed for other uses. Sorry, but I think a design like my Fire Hole, with a rectangular frame around it so it can be set upright or horizontal is much easier than the pivot axle arrangement.
As I look at the burner designs in review, the burners seem pretty fragile across the air intake slots - there is a fair amount of weight hanging off the intake on thin metal supports. There are, in fact, warnings about torqueing the area when making connections. Since my blower based burners are working reasonably well, I don't know if working through one of the designs is something I want to do just to possibly disprove my doubts. 2004-03-29