need advice for homade propane furnace

Bigger outlet hole in the lid.

Cheers Trevor Jones

Some pics may help, I just removed the burner, put the flare on a temporarily rigged it to a metal stand just to see how hot I could go. It couldn't get hot enough to melt sterling but was right there (orange glow it gets right before it gives it up). Can't get any hotter with the open flame which is why I built the furnace.

Here's the burner rig:

=B

Bigger so it does not choke off your fire. You can try just setting the lid on crooked and adjusting the exit size a bit to see what works.

Cheers Trevor Jones

That sounds like a good idea. YOu also might try forcing air, with a blower, down your air intake to see how much that helps, which I suspect it will. If it does, try something bigger than your 1" to 3/4 inch reducer as your venturi. Just removing the 1" pipe might help. a 1/16 "orifice" seems a little large to me too.

jk

Hi Trevor, I don't think that's the issue. As you can see here I have a fairly low flame and if I even cover it half way the flame rises above the furnace.

Stuck man, any help? Even tried a blower on the back end but as expected, blew the flame out.

=B

I have a propane furnace setup that is based on a set of plans that was offered in Home Shop Machinist a number of years ago. It's uses a forced air burner that's always worked very dependably and is a bit different from the design that you describe. If you'd like to see the burner design, or whole set of plans, send me your email address offline.

Do a bit of reading about the Mongo and mini-mongo burners. Rupert Wenig is a friend of mine. He melts cast iron on a naturally aspirated burner.

Your flame looks way to fuel rich. Balancing the amount of fuel to the amount of air, in a naturally aspirated burner, is critical. Better to have a small hole and drive the fuel through at a higher pressure, then choke off the air as required, IMO, but balanced is best. For a given size pipe burner, there is going to be a optimum size gas orifice, and that one is HUGE compared to the ones I have seen , made or used. Try working up from a number 60 drill bit, one drill bit at a time.

A naturally aspirated burner is going to be a bit more sensitive to back pressure from too small a exit as well.

A simple forced air set-up with a choke plate on the inlet is a easy way out. Simply add fuel, then adjust the air until there is just a hint of flame coming out of the top. More fire than that means too much unburnt fuel and a cold fire. Those flames look like a chafing dish burner. OK for heating the lunch line, but not really very hot in the scheme of things.

Cheers Trevor Jones

I built a furnace one time long ago using just a five gallon metal bucket lined with firebrick and morter with two ( I think) half inch x 1 inch tees and a pipe mounted in two holes on each side on the bottom of the burner. I used an old vacuum cleaner to blow air in each of the one inch pipes coming out of the tee with the gas from a hose connected to the stove going into each of the half inch fittings of the tee. A stub from the other side of the 1 inch opening of the tee went into the burner bucket. The gas pressure out of the stove fitting,( I took the burner off the orifice right after the valve and shoved a hose on the stub. That furnace would melt aluminum and would almost melt brass. I bet if I opened the orifice up on the stove it would have melted it. I was only

John

Your probably not getting enough air in at the burner. First thing I noticed looking at the design page vs your pictures is that you seem to be missing the air intake holes after the propane.

I would use a longer tube and drill holes/mill slots. Many of the designs out there use a sliding choke to partially cover the holes depending on the setup (pressure from the propane).

Sounds like too much fuel for the air. The oliver design doesn't allow enough outside air into the burner, IMHO. Try making the holes into slots.

See the link below to the castinghobby group. We'd love to have you join.

Thanks Marc, as I mentioned in orig post I have several configs. The one show is a downwind setup where the air is pulled from the back. I also have the exact upwind setup with 6, 3/8" holes as well as another larger downwind setup using a 1.5 inch to 1 inch intake. *All* fail when capped.

It appears my problem isn't air but fuel. I couldn't find a drill bit smaller than 1/16" so that's what size hole I have for fuel jet. Their saying too big unless I use forced air. Using forced air is a possibility but I'm going for a naturally aspirated config so am going to attempt to use a "vamp-clamp" to pierce a smaller hole in brass today. I know I'm shooting for about 3/4 millimeter vs what I have now which is about 1.5 millimeters.

Hey if you know of a common place to get a #57 or #60 drill bit please let me know.

Thanks for the reply.

=B

You can regulate the blower air with a blast gate or possibly (depending on the motor) a router speed control.

If you have gas exiting the side air holes, move the orifice further into the burner until it stops.

Virtually and good hardware store or even Home Depot ,Lowes and Harbor Freight have sets with numbered bits. Or go online and order from any number of places.

Ben wrote: ...

...

An alternative to drilling a small hole is using a mig-welding contact tip as a nozzle. Common mig wire diameters include .030, .035, .045 etc, [vs. #57 0.043" or #60 0.040"] with the hole diameter slightly larger than the wire diameter, of course. I think the tips I used have a 5x1 mm threaded shank. If you don't have metric taps, that's close enough to 3/16"-24 to turn in a few turns. Any welding store will have a variety of these contact tips at a variety of prices. See pictures at eg

A real hardware store ought to handle number bits at least to #60, some even have the weenie #61-80 sets. Some of the forge burner makers are using MIG welding tips for fuel jets, the part of the MIG handle that the wire feeds through. These are relatively cheap and available in several hole diameters, check with a local welding supply. If you screw up with redrilling, they're cheap enough to discard and get another.

Stan

James/Stan, thanks I will definitely pick up some tips. The next step is likely another drilled hole but as you can see I like to have several options as far as config goes.

Thanks again,

- Ben

A lot of burner designs use a mig tip for the orifice. They are easy to swap for tuning.

The mig tips I have found are threaded 1/4-fine

Kind of the same problem. Its not one or the other, but the proper mixture of both.

I bought one of those 115 drill bit kits from HF for this. I've been slowly replacing the high use bits with good bits, but its nice to have one of everything.