Baffled by my baffle

[Steve Voigt]

Hi all, I could use a little help here. I've been using the charcoal forge below, powered by a woodstove fan, for a couple years. It's a pretty big drum, 14" diameter, and the the inlet in the bottom is 2-1/2" pipe, so there's plenty of air and a good sized hot spot. I use this for heat treating woodworking tools and don't have much trouble getting up to critical temp.

I decided to try adding a baffle, as shown in the pic. It's a piece of 2-1/2" sched. 40 with 1/4" plate welded to one end. I tried to heat up a planemaker's edge float (1/8" thick O1, and similar in size and shape to a knife). I was completely unable to get up to temperature. The best I could get was a dull red. After half an hour and half a bag of charcoal, I gave up, knocked out the baffle and just heated the work on the coals.

Is there any way I can get things hot enough to make the baffle work with the set up I have? Or do I need to ditch the brake drum?

Any advice is much appreciated. Thanks all.

 

[TwistedCustoms]

I would raise the baffle to get the fire under it. the way it looks in the photo you have fire on the sides of the baffle. Try building your fire the way you normally do and laying the baffle across the hot spot on top of the fire. I use 2" sch 40 open on both ends on top of a coal fire and have no problem getting crit temp inside the pipe. I actually have to rotate the pipe while building up heat to keep from burning the pipe. You can bank coals up all the way around the pipe for insulation but you need a hot fire under the chamber.

[Frosty]

You had me wondering and looking for the "Baffle". I think most of us call that a "muffle".

I think I'd lose that WAY too big brake drum, I think everybody who built a brake drum forge has a great big one collecting dust somewhere. Check out Charles Stevens' side blast forge posts. Charcoal really does work better with a side blast. The Lively, wash tub forge is a good charcoal forge as well.

Myself I like a "Duck's Nest" pan forge over any kind of fire pot, it lets me size and shape the fire as necessary. The duck's nest is just a depression in a layer of compacted sand, clay mix or damp earth, around the air grate. The fire brick is laid around the air grate in whatever size, shape, depth, etc. you need. 

Were I doing what you are in this situation, I'd lay a piece of flat stock over the air grate to direct the blast sideways and prevent flame being directed straight up, Then the bricks get laid 2 end to end, about 9" apart. The bottom layer on the flat, the second on edge to form a trench about 6" deep. Then cover the trench with more bricks. Load your "baffle" and start the fire and preheat the oven. When it's hot spread the fire evenly, full length lay a bed of fresh fuel down, lay your baffle and cover it with more fuel. Close the ends and maintain careful control of the blast. Re stoke the fire as necessary of course. A piece of small dia. pipe split lengthwise makes a good fuel charger, you can insert it all the way in and turn it to dump the charge.

Forcing air into a closed wood furnace like this will disperse the heat pretty darned evenly, the muffle will do the rest. 

Frosty The Lucky.

[Steve Voigt]

Hi guys, thanks for the feedback so far. Frosty, you're right of course, I meant muffle and somehow turned it into baffle.

Frosty, I'm having a hard time picturing what you mean with the bricks. Are you saying I should build an enclosure around the brake drum with the bricks?

Thanks again.

[ThomasPowers]

I'm with TC; it looks like your pipe is having COLD air blown directly on it from the tuyere and the charcoal is only on the sides and top.

[Frosty]

On 9/10/2017 at 9:45 AM, Steve Voigt said:

Hi guys, thanks for the feedback so far. Frosty, you're right of course, I meant muffle and somehow turned it into baffle.

It happens I've seen baffle used before, I'm always willing to blame Autocorrect and inertia.

Making a brick furnace won't work in a brake drum. I'd lose the drum and replace it with something a LOT smaller Disk rotors work much better. The brick oven I described works on a Duck's Nest forge. Basically a shallow pan with an air grate in the center. You pack an inch or so of damp earth over the pan to help prevent localized heat from warping a steel pan or cracking a cast iron one. 

What I like about my old rivet forge is how versatile it is as opposed to a fire pot forge. I can  make any size or shape "pot" I want or need by arranging the bricks to suit. 

If I had to use that big drum I'd be burying the muffle in charcoal and watching it like a hawk.

Frosty The Lucky.

[Steve Voigt]

Hi all, it's been a while, but I wanted to update my post with some good news--victory!

I wanted to follow Twisted Customs and Thomas Powers' advice, and raise up the muffle pipe, but I already had the deep cutouts in the brake drum. I decided to kill two birds with one stone. I clayed the drum, inserting mending plates between the clay and the cutouts. That allowed me to raise the muffle pipe about two inches.

I am not sure which made a bigger difference, the height adjustment or the clay--maybe you guys can tell me. But it is a big difference. In addition to getting plenty hot enough, fire management is easier--when the fire gets hollowed out, I just push a little and fresh coals slide down the sides of the cone to where they're needed. And, I'm probably using half the fuel I used before. It's like getting a free drink with a free meal.

If anyone wants to waste 15 seconds of their life checking it out, I posted it on my Instagram feed, embedded below. Thanks again, so much, to everybody who helped out!