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Burner Angle -- Am I Understanding This Correctly?


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Really great board, thank you to everyone who patiently answers questions and shares their experience. 

Doing my first forge build out of a propane cylinder and would like to make sure I have the burner angle correctly figured out before I weld everything together.  Been reading a few related topics and currently focused on the following as my guiding principles, which I found in a thread from March/April 2018:

Frosty: "I think you'll have better conditions in the forge if your burners are aimed at that angle short of the center of the floor rather than the far wall."
Mikey98118: "Mount the burner in position, and check to be sure the flame will impinge near tor the near end of the shelve, but clear of the wall."

I tried to draw this out to make sure I have the right understanding.  Is this correct?  

Attaching a pic of the tank with the cutouts and the legs on.  The second one has a swag at the angle these ports will sit at.  Heading out there this morning to start drilling/taping the burner ports. 

Please let me know if I'm way off.  Thank you in advance for any ideas.

 

 

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The center of the burner opening should be at ten o'clock, Do not attempt to position its angle in the shell, until you have the floor in place. Then measure the distance from the inside of the shell to the inner edge of the wall refractory. Add 1-1/4" to the distance, and aim the opening to center on that mark. Of course, you should be able to re-aim the burner flame, so long as you are in the ballpark. Most people falsely assume that atmospheric swirl takes a lot of angle; it doesn't. So, make your primary goal, for the flame to miss both the near side of the wall, and work peices in the center of the floor.

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Thank you for the replies.   A primary goal of missing both the near side of the wall and the work pieces in the center makes a lot of sense and clears it up for me.   

I was stuck on something else I read that suggested putting the burners at 10-15 degrees down from TDC.    Somewhere else had a suggestion of 2" down from TDC, which is what I have marked on there now.   I was having a hard time with the geometry with the ports that high on the shell and getting the flame to hit the near side of the floor at an angle that would also induce swirl (rather than splash, as Thomas noted).

Updated my diagram; is this "more correct" than before?   I do want to double check that 10 o'clock means about 6.25" from TDC (πd/(1/6 of a day) = π * 12/6 =~ 6.283”) for a standard 12" diameter propane cylinder. 

Thank you again for the help and patience.

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NO; what is wrong with this position is that it leaves very little distance for the flame to complete combustion before it will impinge on the work pieces. That is not ten o"clock; it is more like eight o'clock.

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Thank you, glad I asked and really glad I held off drilling holes this afternoon. I decided to mess with the bearings on my lathe instead ;-) . 

I guess I am not understanding the clock reference, as normally I think of 12 o'clock up, 6 o'clock down, 9 o'clock to the left and 3 o'clock to the right.   This is how I came up with 10 o'clock being about 1/3 of the way up from horizontal on the left.   This was about 6.25" along the arc from TDC when I did the math.    Apologies for not being clear on where to reference from.

Perhaps easier for me to understand if I could think in terms of degrees from TDC and/or just an absolute measurement since its a propane tank.   

Thank you again for your patience.  It's my first time building anything like this and I figured I'd ask questions to avoid making egregious mistakes.   I appreciate you taking time to point me in the right direction.   

I hope you have a Happy New Year. 

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So, likes look at this "failure to communicate" another way. Go back to your first drawing, and move the  the position of the burner opening down one-inch more, and call it Good :rolleyes:

But, do a good job of aiming the burner, before you weld up the burner opening.

Positioning the burner this way is effective, but subtle. The second best way is nine o'clock, and aimed at the far end of the floor; its not as effective, or any easier to accomplish, but it it isn't a bit subtle, so there's that :)

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Thank you, I really appreciate the response and clarification.

I moved it down 1" to 3" off of TDC and spent most of my afternoon getting it aimed to miss both the near side wall and the middle of the floor.  I actually used some longer sections of 3/4" PVC pipe as "aimers", as I was concerned about not only the radial angle but also the axial orientation (i.e. I wanted to avoid pointing the burner out of the front/back of the forge). Built a temporary fixture to keep everything straight. Definitely a case of measure twice (or 8 times) and weld once.  Pretty sure I'll be right at 1.25-1.5" off the near wall and little/no axial skew. My collars have two rows of offset adjusting screws which should make fine tuning possible. 

I'm very pleased with how everything welded up and I think I'm ready for paint now. I'll post more pictures after I get the paint on and probably more questions once I get to the insulation.

Thank you again for taking time to help me. Very excited to get it in working shape.

Jason

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Thank you.  I really enjoy the equipment making part of hobbies, so it didn't feel like work at all putting it together.  The propane tank came up on CL for $5 and Everett Steel had everything else I needed in the scrap bin so achieving good economics so far.  

I am planning to use 2 x 3/4" 'frosty' burners with the 1" tee at the top.  Currently thinking 6" tubes on them to hit the 8-9x diameter to length suggestion .  The ports are big enough to accommodate larger burners and big flares but, since my interior is about 550 in^3, it seemed like the 2 x 3/4 was about right based on what I was able to find in other threads on the site.   Planning to stuff the ports with ceramic wool to keep the heat in and top it off with some fireplace door gasket.

Please let me know if I'm off.  Thank you again for the help and encouragement.

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That is way too much burner for two of them in that forge size. Fortunately, you have provided ample room for change with your burner openings. I will be making burners and equipment next summer. You can drop by my shop in Seattle, and get help. Or, you can downsized your plans to two 1/2" Frosty burners now :rolleyes:

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Pics of my shell with the paint on attached.  Got 3 good coats out of a fresh can of Krylon BBQ paint. 

Thank you for the suggestion on burner size. Looks like my total volume is right at 500 in^3 so I guess 2 x 3/4" burners would be more than I need.  I'll rejigger to 1/2" and read up some more. 

I drilled out / tapped a 1" x 3/4" tee the other day and that's when I figured out I needed to re-indicate my lathe.  Turns out my tailstock had drifted out laterally by about 0.010, which I corrected this morning. Everything is running tight again.  Screwing the tee onto a hex fitting I had laying around gave me a good way to grab onto it with a chuck. 

Definitely interested in your equipment build next summer. 

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I think you are right. 

I calculated it as 1/2 of a 6.5" cylinder (the top of the arc to the midpoint across the horizontal) plus a 2.75" x 6.5" box below that but along the entire 13.5" of cylinder (neglecting the curvature of the front and back).  I forgot to account for 2.25" insulation/refractory materials at each of the front and back, which makes the length about 9" (again, disregarding curvature). This gives me about 150 for the 1/2 cylinder + 160 for the box, 310 total. With the vagaries of the liner stack, it seems like 350 in^3 is a good design number. 

I'm going to roll with the 2 x 1/2" burners with equal parts confidence and naivety.

Thank you again.

 

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  • 3 weeks later...

Thought I'd follow up with a few pics of how my setup finished up.  Got a few pics of the liner going in also.  Left it in a bag with wet towels for 2 days.  I have had a lightbulb in it all week drying out the Kast-o-Lite 30 and am planning to fire it up this Saturday. 

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Nicely done, but you're not finished, yet. Those excellent burner portals, being oversize, will allow you a lot of leeway in burner positioning; they may also become unwanted exhaust exits, unless you make large flat washers to reduce the amount of flow through those openings, so that internal pressure doesn't promote flames shooting out of them. The washers will also limit the amount of secondary air that can enter your forge, lowering its temperature.

  I like to weld or braze nuts at right angles onto the washers, so that they can be raised exactly to the desired height on burner mixing tubes that you find to provide optimum air flow. Of course their are lots of way to do the same trick.

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I've been thinking about that potential issue and thank you for the suggestion on big washers. I'll see what I can come up with next time I get some shop time and will post back some pics.

I was initially concerned that my burner ports were too large but now that it is all put together I'm glad to have gone with 2" ID pipe.  They seem just right.

I was thinking I'd also use some left over ceramic wool dipped in rigidizer stuffed into the ports once I get them aimed.

The McClendons near me sells the rope seal for wood stove doors, which I thought might work well on top of the wool to keep it from getting unruly. I bought a foot of the 3/4" variety to try out and it seems to be doing a good job lowering heat loss with the 75W light bulb.  Obviously a different ball game with burning propane.

A final mechanical layer (i.e. oversized novelty washer) should create a good stacked solution.

Thank you again for the continued guidance and patience.

 

 

 

 

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McClendons Hardware; one of my favorite places :)

Not to nitpick, but you will probably end up needing a little bit of secondary air filtering in through those burner ports for complete combustion, once you start closing down the two exhaust ports somewhat. Everything ends up being a balancing act in forges.

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