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Inside The Secret Underground Laboratory

#1,041
Sand Battery Furnace R & D testing report:

I worked out the technique for getting the charcoal lit, using some of the commercial FireStart product. Last night I burned 12 lumps of charcoal in it. The results were underwhelming. Piles of smoke, low heat, and it only got the sand up to about 140 degrees. I've realized that charcoal is the wrong fuel for this. The heat is too low and slow. I need a cleaner hotter fire for a shorter period of time.

Next up, I'm going to try straight hardwood scraps. I've got a bunch of thin strips of maple lying around here. I'm going to try cutting them about a foot long, and standing them up vertically in the furnace tube. About half the height. With some tinder underneath and the air bleed. A nice roaring column of flame.

The testing will continue this week, between the Santa gigs. And occasional Luthier work.
 
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#1,042
Bruce Johnson said:
Hello Rick!

Keith hadn't said anything to me, but okay, go ahead and send it to me. Although Keith has his own shop about 60 miles away these days, we still do some regular Luthier business. He comes up here once or twice a month to rent time on some of my specialty machines. And he routinely stops at Pat's shop. We help each other with different projects.
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Hey Bruce

Just a quick note to let you know I sent you my tracking number for the Les Paul bass via Private Message. It's scheduled to arrive via UPS early next week. Could you please confirm that you received the info from me? Happy to send the info again if it got waylaid....
 
#1,043
Sand Battery Furnace R & D Testing Report:

Unfortunately, this phase has to be written off as a Failure. I tried burning charcoal, then scraps of maple, and even hickory wood pellets. In all cases, it was too difficult to keep a hot flame burning steadily. The only way to keep it burning was to position the fire up high in the tube.....where most of the heat was lost out the top. I never got the sand above 160 degrees. I wasn't able to fully test out the sand battery part. I did roll it inside when it was at 160 and, it silently gave off some heat for an hour or two.

The basic idea of the sand battery works. I just need to find a better way to heat the sand. The tall slim furnace tube just doesn't work for burning wood. My thinking now is that I need to make the configuration more like a fireplace. Weld up a pyramid from triangles of steel plate, attached to a chimney pipe, maybe 2" square steel tube. That would be the bottom of the sand battery, with the sand on top of the pyramid and surrounding the chimney. For the fire, I'd get one of those small campsite wood pellet-burning stoves. The stove would sit on the concrete by itself, and the sand battery would be raised up on the casters, so it rolls over top of the stove, straddling it.

I think that would work, keeping a steady fire, and transferring most of the heat to the sand. But that's going to require a complete rebuild of the unit, and I probably won't get to it this season.

I'm also looking at two other options. One is to heat the sand with an oil fire, instead of wood. I'm thinking of a burner assembly that would drop down into the existing furnace tube. The oil would be in a small can nearby, elevated up, feeding down into the burner by gravity through a needle valve. That might work.

The other option I'm considering is electric heat. Embedding an electric heating coil in the sand to heat it. Some folks have made sand batteries heated by line power and/or solar panels. Here in Fillmore, "winter" days are usually clear skies and plenty of sunlight. It could be reasonable to roll the sand battery outside for the afternoon, hooked up to two solar panels. Then back inside to heat the shop all night. And, if I needed to, I could always plug it into line power to warm the sand up for a few hours.

I've got an electric heating coil coming in this week. I'm going to try embedding it in the sand of the existing sand battery and run some tests.
 
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#1,044
Bruce Johnson said:
The basic idea of the sand battery works. I just need to find a better way to heat the sand.
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What about a rocket stove sort of design? I have not tried one yet but seems like material feed / oxygen flow makes sense. Kind of like your air injection system. Draft is tricky.
I want to try something like this on my uncles double barrel wood stove design. He replaced the thin barrels with thick wall pipe years ago and the top barrel would be a perfect place for a sand battery.
Hope your next try works better. Thanks for posting results!
 
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#1,047
I would respectfully suggest that there is a LOT of practical engineering (and trial and failure and more trials and success as things were learned) that's been done on so called "rocket stoves" that would be highly applicable, but which I refrained from mentioning earlier since you entered into this with a entire combustion process worked out in theory, and I didn't want to be a naysayer without it having been tried as you envisioned it. At the opposite (wicked high tech/cost) end of the spectrum there's the fine folks in Beserkly at Applied Power Labs doing wood gasification. It's cool, some of the ideas turn out to shared, but probably not the way you'd want to go.

Some of the core concepts are limiting the burn zone, and providing an area with high temperature refractory insulation to allow for complete combustion of the wood (and its gaseous pyrolitic breakdown products) before entering the heat exchange/mass heater part of the system. Those can be configured to exploit natural draft. I would suggest reviewing a lot of that information rather than reinventing it all as perhaps worth your time if you want to get your sand hot efficiently.
 
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#1,048
Yeah, I agree that a Rocket Stove type design in the middle of my sand battery would be an improvement over my current vertical tube furnace. It would make a better draft air flow and would keep a good steady flame going. But the thing is, a Rocket Stove is intended to blow most of its heat straight up. The thing you want to heat, like a pan of food, is placed over the top of the chimney, with an air gap. The flames apply most of their heat to the bottom of the pan. The Rocket Stove is like a naturally-aspirated torch. It creates a focused vertical flame, which you then apply to the underside of something.

If I put a Rocket Stove in the middle of my sand battery, like I have it configured now, it would just blow most of the heat out the top and wouldn't heat the sand very much. The more efficient solution would be to put the Rocket Stove underneath, and mount the sand battery above the chimney. Capture the heat on the bottom surface of the sand battery, letting the Rocket Stove have its own draft and air flow to keep it burning nicely.

And that's right along the lines of what several of you are suggesting, of putting a separate heat exchanger above the fire/burner. Like those classic double-barrel wood stoves. The lower barrel is a fireplace, with draft air venting and a chimney. The upper barrel acts as a heat exchanger, capturing the heat from the chimney air flow and letting much more of the heat out into the room, rather than heating the air above the house.

You could add sand to that upper barrel to hold the heat for a longer time. For example, mount a zig-zag steel plate horizontally through the barrel. Fill the space above it with sand, and let the hot chimney air pass under it.

And that's the general idea for my next-generation version. The welded steel plate pyramid with the smaller tube chimney, and the sand in the aluminum box above it and surrounding the chimney. The whole thing raised up with a separate burner/fire pit underneath it.
 
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#1,049
It's also pretty common to turn the output so it draws down (or off sideways, or both) though the mass when doing a "rocket mass heater" though most of those are not mobile and in parts. Getting it to draw with the downward turn is not impossible, just takes some tweaking of sizes. That might be less unweildly than hoisting 400 lb of sand up 4 feet...
 
#1,050
The last thing I need around here is another big old antique machine tool........But, how could I resist?

My buddy Thomas is reorganizing and shuffling his fabrication shop, and he had this beautiful old lathe......No place to put it, and it would have to go outdoors under a tarp. So he asked me if I could adopt it here in the Johnson's Shelter For Antique Machinery......

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Thomas and I moved it down into the basement this morning, using a drop-deck trailer, my crane and two of my pallet jacks. It's about 9' long, 3800 lbs. It's temporarily parked back here behind Unit 16. I'll be moving a couple of shelving units around, and then it will go into the Unit 14 bay with my other pre-1940 machines. It will be the centerpiece of my Old Time machine shop.

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It's a 1929 Hendey, 96 years old. It's kinda filthy, but in surprisingly good condition. It runs fine, and just about everything works. Nothing major is missing or broken. Thomas had been using it occasionally. It includes box loads of tooling and accessories, including two chucks and a faceplate.

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It's a fine old machine. Hendey was one of the top machine tool manufacturers in the US in the '20's and '30's.

I'll get it cleaned up and fully running. I don't really need it, but it will be useful to have around. It's a bit excessive for truss rod hardware and strap buttons...

Eventually, I may completely clean it off and repaint it. It was originally black from the factory.
 
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#1,055
Lo-E said:
You never know, Bruce…. You might need to fabricate a truss rod for a VERY stiff neck! From 4” shaft stock!
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Hey Ethan;

The Hendey is officially a 14" swing x 8' bed size. Realistically, it could machine a 8" dia x 5' long shaft. complete with precision threads and journals.
 
#1,058
CryingBass said:
But if you need to turn some very nice posts for your stairs or fence... :)
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Yeah, it could do that. A while back I made up some oak corner posts for a custom bed frame that a cabinet maker friend was building. They were about 5" diameter x 4' long. I used my other LeBlond Regal 13 lathe, mounting a small router on the tool post. It worked fine, but I'm not going to do another job like that. Very tedious and an awful mess to clean up. Turning wood on a metal lathe is generally not a good idea. Sawdust in oil can mess up machinery.
 
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