The On-Line Magazine of Rideable Model Railroading
© April 29, 2012
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Building Marty Burners
This is Marty Siegel giving my Locomotive a try at the Sacramento track.
I miss him and all his encouragement and good advice.
Written by Dave August
When people have ask me why my locomotive steams so well, my answer is always: "It has 'Marty Burners".
Marty Siegel was a very knowledgeable and friendly club member who was always ready to offer his advice on a good problem. Back in 1998 I was complaining to Marty that my 'Tube and Slot' propane burner just wasn't giving me enough BTUs. He suggested that I try a set of these burners.
As Marty told me, he was helping another club member, Jim Dameron, get the firing right on Jim's Pacific. Marty was so impressed with the simplicity and efficiency of the commercial burners in Jims engine that he took the time to make a set of drawings for them. Many club members have built variations of these burners and all of us have had good success. After a while we just started calling them 'Marty Burners'. This is a scan of Marty's original drawing and should print out at 8.5 x 11.
click to enlarge, then print the large version
click to enlarge, then print the large version
When I decided to build a set of these burners I didn't have the hex brass. Besides that, I couldn't bring myself to throw that much brass in the trash. I looked at the design and figured it was just a piece of brass pipe with a plug in it, so that's how I built mine. When I first looked at Marty's drawing the only thing that bothered me was the slot saw for the burner head. Dremel makes one that is 0.050, and it seems to work just fine. These slots are a bit shorter so being wider helps keep the area about the same. If they are properly built they will run at well over 15 PSI before the flame jumps from the head. That's quite a lot more than 6000 BTU. This is a drawing (left) is for my version of the burners.
What follows is the step by step construction procedure in photos.
That 3 inch long 1/8 brass pipe nipple cost $1.75. This will make two Burner Bodies. Around here the brass pipe caps are made from 9/16 hex brass. That makes it easy to index the piece when it come time to slot it. They each cost $1.50. That's a small chunk of brass from my scrap box to make the orifice plugs. The inside diameter of the brass pipe is nominally 9/32. That's not a common size for brass rod so I usually turn a piece scrap. I suggest that you anneal the brass before you turn it to size. I've broken the #71 drill going through hard brass. If you can get some 9/32 brass, it's one less thing to do. It will make a tight press since the end of the nipple gets compressed when it's threaded. We could be generous and say it cost 25 cents. Let's see, that's a total of 5 bucks in materials cost for 2 burners. They are not real budget busters.
Turn The Cap
First I turn the cap to about 0.450 for a length of 0.300. This diameter isn't a critical dimension. It just needs to be thin enough that the slot saw will cut all the way through it. If I can find a slightly bigger diameter saw I could eliminate this step.
Slot The Top
I use my milling maching to slot the top. If you don't have a mill, I'm sure you could build a simple fixture that would allow you to use the cross slide on your lathe to do this. Notice that I have a vice stop clamped in place. It both "backs up" the piece and makes it a simple matter to index the piece from the sides. Also notice how close the slot saw shaft is to the cap. The only critical thing here is to keep the distance between the tops of the slots bigger than 0.250. This is just under the 0.281 ID of the tube. DO NOT slice the top all the way through the center. The top of the cap deflects the gas mixture down and around the tube top.
Drill The Body
The first step in making the body is to drill the air mixture hole through the tube. The distance from the base of the Body isn't critical, I arrived at the 0.550 as a place where the bottom of the hole just touches the end of the 1/8 pipe threads. It could be closer to the end, I don't think I'd get it closer to the cap.
Ready to plug
I find it easier to plug the tube before I turn and tap the other end. I usually run a 9/32 drill all the way through the tube to clear out any leftovers from drilling the air mixture holes. Turn the brass for the plugs to 0.284 or so, for a nice tight press into the tube. If you get 9/32 brass rod I'd suggest not taking the drill all the way through the bottom to leave it small for a tight fit. The thickness of the plugs is not critical but don't make them too thin.
Press the plug
Insert a 0.250 piece of CRS through the air mixture holes and press the plug up to that. I try not to press the plug too tightly against the rod, just to make it easy to remove. It's OK if the plug is a bit from the bottom of the of the mixtures hole.
Drill the Orifice
This is probably the trickiest thing to do. I'm very gentle with the #71 drill and back it out several times in order to keep it cutting well. You want this hole as close to 0.026 as possible.
Turn the Tube
The length of the whole burner isn't really all that critical, but the length of this turned end is. It should be the full 0.200. It's diameter of 0.312 is fairly critical also and shouldn't be any thicker, although it could get as thin as 0.300.
Thread the Tube
This is probably the hardest thing to do. Notice that I slip the same piece of CRS in one air mixture hole to act as a "dog" and keep the pipe from slipping in the chuck. I hand thread the end for about 4 turns, that's usually more than enough.
Ready to Assemble
Here is a Burner Head and Body ready to assemble. All that needs to be done is to screw the Head onto the Body till the inside top of the Head is about 0.050 from the end of the tube. This dimension isn't critical, and I just eye ball it. But as a rule of thumb the further away it is, the lower the pressure will be where the flame jumps from the head. At 0.050 these will usually run all the way up to 15 PSI. I stick the same piece of CRS through the air mixture holes and use it to hold the body while I screw the head on with a wrench.
This is a finished Burner. You can see how close the Head and the top of the tube are. Don't be tempted to use a wrench on the Burner Head to screw it into your manifold. I use the same old piece of CRS through the air mixture holes. I usually test every Burner after I make a batch, just to see how things are going. It seems that in every batch I make, a few always burn a bit rich. See "Rich Idle" for more on this.
This is a pretty good photo of a Burner running at 10 PSI. Notice that the flame is less than 1/4 inch from the head and is totally blue. If the flame is jumping around or you loose one jet you may try screwing the head down a bit further, that usually cures the problem.
This is a Burner running at lower than 1 PSI. Notice that the flame is almost totally blue with just a hint of orange.
This is a Burner running at low pressure and burning a bit yellow. It seems that in every batch a few run a bit rich at idle. I've never had one that didn't burn totally blue at above 5 PSI though. If you do you can always press out the plug and replace it. I suspicion that the orifice drill cuts a bit wide now and then. This is a square law world and the change in area from 0.026 to 0.028 is quite a lot. If you consistently get rich ones you could use a #70 drill. Also make sure that the air mixture holes are completely de-burred.
Once you have the burners you'll need a manifold for them. Marty usually built his from pipe fittings. Several of us club members prefer to make then from square tube. This is a photograph of my (well used) Manifold and Burner assembly.
Marty suggested putting the burners on 2 inch centers and 1 inch from the fire box wall. I've found that you can tighten up the centers to 1.5 if you 'interlock' the flames.
Written by Dave August
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