Any interest in pics of a "Don-Fogg-esque" HT furnace?

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Any interest in pics of a "Don-Fogg-esque" HT furnace?

Knifesmith
Registered User
Joined: 25 Jan 2008, 21:09

03 Jan 2013, 02:38 #1

I've been working on a HT furnace (large open chamber, single venturi burner) made from a ~30 gal oil can.  Should be good for HT-ing everything from swords down the the little stuff. (probably overkill for the wee things).  If folks are interested, I can take pics of the interior before I weld the end on.  Taking pics after the end is on would result in bad pics as I'd be trying to take pics of a big chamber through a little 4X4" window. The main body and interior are finished, but I still need to weld the end on, fit the burner (and make a support for it), and rig up something to hold the readout for the thermocouple.

It's kind of too late to do a "build along", but from where I'm at now, it should be pretty easy to do a wee bit of reverse engineering if you wanted to build something similar.  I could also take pics of the steps from this point forward (or just a few pics of the exterior once I'm done, and explain how it was done).

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Eric Dobratz
Scarab Forge
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Don Abbott
Registered User
Joined: 28 Nov 2007, 21:52

03 Jan 2013, 13:07 #2

Pictures man! We need pictures.

I've got a 24 incher in the works.
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Knifesmith
Registered User
Joined: 25 Jan 2008, 21:09

03 Jan 2013, 16:54 #3

Alrighty then. I'll take pics of the interior when I get a chance, and take pics of the exterior when it's done.

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Eric Dobratz
Scarab Forge
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AboMatt
Registered User
Joined: 29 Apr 2008, 16:13

04 Jan 2013, 00:05 #4

I'd absolutely love to see some details !
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Knifesmith
Registered User
Joined: 25 Jan 2008, 21:09

05 Jan 2013, 01:02 #5

Ok, here goes.  Keep in mind that it stupidly didn't occur to me to take any pics until I was at this stage of the game, so if something's not clear, just ask questions.  In all honesty, the concept's pretty simple.  It's basically just a big insulated can that will eventually have a single propane burner going into it.  The idea being that the large interior will allow a more uniform heat with no real "hot spot".  Mine's going to be pretty simple.  The only thing that is an improvement over the basic design is that I've got it set up to take an industrial k-type thermocouple that I'll eventually have a readout for mounted to the side somehow, so I can know exactly what the temp inside is.  The interior dimensions of this particular can are about 16" diameter by ~26" long.

So, here it is without one of the ends on (the end that will have the access window as well as the burner input).  In this pic, you can see the bent rebar supports and ceramic kiln shelving that I've mounted as a support shelf.  I plan on making soft firebrick supports for blades to sit on pending size that will sit on this shelf during the HT process.  The lining is one thickness of 1" kaowool type insulation (the most expensive part of the whole shebang).



In this pic, you can see the shielded thermocouple (only about $35 off of eBay):



Here's a pic of the exterior showing the access/support for the thermocouple.  The 3/4" iron pipe is wider diameter than the hole in the body for the actual thermocouple probe (so there shouldn't be a problem with heat/gas jetting up through the probe hole).  And no mocking my crap-tastic welds.  I had the darnedest time welding thick rebar to the very thin material of the oil can wall.



And a pic with the thermocouple in place.  I think this particular thermocouple is made for industrial ceramic kilns.



Banged out a quick and ugly burner support made of rebar.  Here's a pic of the "face" of the furnace with the support in place:



And here's a pic with the burner in place:





And that's what I have for now.  Next, I've got to tack the end on, so that I can easily grind off the welds and access the interior at a later date for maintenance, problems, eventual replacement of shelving etc..., and figure out some sort of support system for the thermocouple readout.  More pics to come as I get a chance to work on this...
Last edited by Knifesmith on 21 May 2014, 02:40, edited 2 times in total.

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Eric Dobratz
Scarab Forge
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pfarneman
Registered User
Joined: 17 Mar 2012, 18:47

14 Jan 2013, 00:31 #6

Thanks Eric - this is great!

Patrick Farneman
N.E. Washington State, USA
http://www.betweentheriversgathering.com/
www.bridgestothepast.org
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Knifesmith
Registered User
Joined: 25 Jan 2008, 21:09

21 May 2014, 03:26 #7

So,

I slacked on finishing this thing forever, but I've got a longer blade that will really benefit from having this HT furnace completed, so I buckled down and finished it.



This is the finished furnace sealed up nice and tight with burner and thermocouple in place.  I realized that the thermocouple and the wires are long enough to allow me to rest the digital readout on the table rather than requiring it to mount somehow to the furnace itself as I had previously thought I'd have to do.  That combined with the fact that it was much easier to convert the thermocouple from a full size to "mini" type "k" plug, made this job a lot less daunting than it originally appeared to be.

Here's a closeup of the el-cheapo digital readout that I got (which actually seems fairly nice) attached to the shielded thermocouple.  It's reading a bit higher than garage-temp as I had just had it in the furnace with a torch heating things up to see how accurate the thermocouple/digital thermometer setup was.

Last edited by Knifesmith on 21 May 2014, 03:32, edited 1 time in total.

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Eric Dobratz
Scarab Forge
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Mick777Oz
Registered User
Joined: 18 Nov 2012, 00:21

21 May 2014, 08:40 #8

This is aimed at tempering process? Or will it get hot enough for a quench?
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Knifesmith
Registered User
Joined: 25 Jan 2008, 21:09

21 May 2014, 19:02 #9

This is aimed at a very accurate normalizing and heating to quench processes. This will make "soaking" certain steels at temp. much easier (1095, 5160, etc...) as well as hopefully making exact quench temps very repeatable. With the hamon that I usually do, how "active" a pattern you get depends on a lot of things, the most sensitive of which is probably the exact temp you quench from. Eyeballing 1450F from 1550F isn't impossible, but it's a sensitive thing, and I'd like to take "operator" error out of the loop as much as possible.

The low temp on the exposed thermocouple is just because I had been playing around with running a propane torch in the thing to see how quickly a bulky shielded thermocouple responded to temp. changes, and to see if there was any lag (when compared to a standard dial oven thermometer). The big thing is surprisingly responsive and accurate. I suppose it would have to be being a ceramics thermocouple. Cone 6 isn't too far from cone 7, and some glazes are really touchy...

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Eric Dobratz
Scarab Forge
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Mick777Oz
Registered User
Joined: 18 Nov 2012, 00:21

21 May 2014, 20:44 #10

That is a big volume to heat. But there's only a very small opening so i guess it should be efficient to hold at temp. Looking forward to see it working.
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Alexander13
Registered User
Joined: 23 Jan 2014, 13:31

22 May 2014, 15:31 #11

It's very much like a portable raku kiln that I built a few years ago and it works great. It should have no problem reaching your required temps. Looking forward to seeing pics of it in action.


Cheers
Joel
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Knifesmith
Registered User
Joined: 25 Jan 2008, 21:09

22 May 2014, 23:15 #12

Very similar concept to a raku kiln (except wee little window access rather than a big swinging door to open at heat).

Now I guess I have to try to get some good "in-use" pics eh?

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Eric Dobratz
Scarab Forge
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Mick777Oz
Registered User
Joined: 18 Nov 2012, 00:21

23 May 2014, 01:15 #13

Ahh, yes!
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Knifesmith
Registered User
Joined: 25 Jan 2008, 21:09

01 Jun 2014, 04:44 #14

Well, I had some time to do a "quick" green fire of the furnace this evening.  Heating the darn thing took a while (which is to be expected I guess with a single burner in such a large space).  Slow and controllable temperature rise though.  I wasn't able to take it up as high as quenching temps unfortunately as I got called off to storytime and bedtime, but it was still climbing nicely at the temp. where I took the pics, so I have no doubt it'll reach the ~1500F I want.

Looking cool without a flash:



and one with a flash to better show the thermocouple and readout:



(yeah, it's on in this pic.  Amazing how much the flash counters out the flare from the furnace.)

That's about it.  One thing that I'm going to have to modify is to add a stainless flare to the burner.  The window is so small that the interior of the furnace is pretty oxygen free running at temp. (which is great for preventing scale, not so good for maintaining a burner flame).  Add to that the fact that the burner flame is running along the bottom (not directly impacting the insulation), so there's no "hot spot" helping keep the gas ignited at the lower temps.  It needs a way for the burner flame to be independent of the interior of the furnace as regards to staying ignited.  Other than that, it works exactly as planned.

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Eric Dobratz
Scarab Forge
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toxophileken
Registered User
Joined: 15 Jan 2006, 04:55

03 Jun 2014, 08:58 #15

Looking really great, Eric! Thanks so much for sharing this! If I hadn't just purchased an Even Heat kiln, I'd be all over making one of these…

Those home made burners work great, don't they? I've been running mine at 2 psi for forging, and 1 psi or less for heat treating.

On the welds, don't sweat it, they will work fine. One tip - I've found that when welding thinner material to thicker, a thing that helps is to start the weld on the thicker material, and push the puddle onto the thinner, letting it carry the heat, rather than the arc, if that makes sense. Another trick on very thin stuff is to reverse the polarity on your MIG welder, so that the electrons are coming off the thin material, rather than running at it. Don't know if that makes sense. I've spent a lot of time closing up holes I burnt in thin material… Ha ha.

I think I'd like to hook up one of those thermocouples to my forge, just to see what temps I'm running at. Like I need another project… Well, I'll get to it eventually…

Thanks for sharing your R&D, and for the inspiration!

Ken
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