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I'm looking for a good, used HT furnace. (Evenheat, etc) My budget is a little low (~$600 max). Anybody here have one they're letting sit around?

 

I may go the build vs. buy route, but I figured it wouldn't hurt to ask.

 

-d

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I'm of the opinion that if you make your own once you will never buy another one. They're too easy to make, even electric controlled ones. And much cheaper to make your own if you have the time to do so.

Edited by Tim Crocker

Crocker Knives

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I'm of the opinion that if you make your own once you will never buy another one. There too easy to make, even electric controlled ones. And much cheaper to make your own if you have the time to do so.

 

It's kind of looking that way to me as well. I'll probably be ordering a load of firebrick from Darren Ellis soon. I've also got my eye on a couple of process controllers on eBay.

 

Looks like I'm a-buildin' one!

 

 

thanks,

 

-d

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It's kind of looking that way to me as well. I'll probably be ordering a load of firebrick from Darren Ellis soon. I've also got my eye on a couple of process controllers on eBay.

 

Looks like I'm a-buildin' one!

thanks,

 

-d

I am not sure how hard/inconvenient it is but "how I built it" tutorial with lotsa pic's would

be nice :rolleyes:

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I am not sure how hard/inconvenient it is but "how I built it" tutorial with lotsa pic's would

be nice :rolleyes:

 

I already figured on that :) It'll be slightly specific to the process controller I'll be using, but not very much so. I'm guessing it'll cost about $400-500 from soup to nuts. the largest part of that cost will be firebrick! :o

 

-d

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Only needs to be brick on the bottom, and a few to support the element.

I've seen home-built ones with insboard used entirely and they worked fine.

 

I've thought about using insboard, but it's not all that much cheaper and it's a lot easier to replace a single damaged brick than to replace a section of board (if I build it right anyways). Plus, I figure there has to be a reason that evenheat/paragon/etc. all use firebrick...

 

 

I'll probably start a design thread in an appropriate forum to chat about my plans.

 

-d

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You might want to have a look at this site. He's done most of the work already, not that we wouldn't be pleased to see your work.

 

HT Oven

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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That is an interesting article, but I think he made it a bit more complicated than he needed to make it.. For a FURNACE that size (it is not an oven), only one zone is required. This drastically reduces cost, by reducing the process controllers required. I would also strongly suggest an excess temperature controller to shut off the heating elements should it get too hot. Instead of using bricks, you can buy the elements already in place, and just stack them together. Or you can cast the refractory and elements in place. Just watch the outside shell temperature to make sure you don't create a burn hazard. I can help with the electrical design and heat transfer design if you are interested....For something that small you can probably get away with using 110V or 220V single phase. I would also consider finding an inexpensive SCR for precise temperature control.

 

Scott

 

That is an interesting article, but I think he made it a bit more complicated than he needed to make it.. For a FURNACE that size (it is not an oven), only one zone is required. This drastically reduces cost, by reducing the process controllers required. I would also strongly suggest an excess temperature controller to shut off the heating elements should it get too hot. Instead of using bricks, you can buy the elements already in place, and just stack them together. Or you can cast the refractory and elements in place. Just watch the outside shell temperature to make sure you don't create a burn hazard. I can help with the electrical design and heat transfer design if you are interested....For something that small you can probably get away with using 110V or 220V single phase. I would also consider finding an inexpensive SCR for precise temperature control.

 

Scott

 

That was weird.....

D. Scott MacKenzie, PhD

Heat Treating (Aluminum and Steel)

Quenching (Water, Polymer, Oil, Salt and Mar-Tempering)

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That is an interesting article, but I think he made it a bit more complicated than he needed to make it.. For a FURNACE that size (it is not an oven), only one zone is required. This drastically reduces cost, by reducing the process controllers required. I would also strongly suggest an excess temperature controller to shut off the heating elements should it get too hot. Instead of using bricks, you can buy the elements already in place, and just stack them together. Or you can cast the refractory and elements in place. Just watch the outside shell temperature to make sure you don't create a burn hazard. I can help with the electrical design and heat transfer design if you are interested....For something that small you can probably get away with using 110V or 220V single phase. I would also consider finding an inexpensive SCR for precise temperature control.

 

Scott

 

 

I wonder if we can get this thread moved to the Tools section?

 

Anyways, I've seen that article and like soe of the physical set up and design bits, but for control I'm going a bit more high tech. I've got an Omron E5AX process controller on the way to run the elements and I've found software to run it (unless I write my own...which is a possibility...I'm cheap :) ) I've gotten a very generous offer for free Kanthal element wire (all I have to do is coil it...no biggie). I figure that using firebricks will keep things simple and clean (if not as cheap as possible). What would you recommend as a castable for something like this? The real bonus of using he 3" thick bricks in my mind is that they insulate REALLY well and so external heat isn't a real issue. The other bonus I see to not casting elements in place is that I can easily replace elements if I need to down the road.

 

I'm open to any suggestions, provided I can understand them :)

 

-d

Edited by deker
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Burt Foster has a very cool, and accurate, HT oven using propane and a pipe burner (like the one's under bluing tanks, etc.). The bottom is partially open and the rest is a sheet metal box with firebricks. No need to mess with electrical elements. That said, Burt is a bladesmith/forger--I am not sure how well this design would work for 2,000F extended holds, etc.

 

John

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Burt Foster has a very cool, and accurate, HT oven using propane and a pipe burner (like the one's under bluing tanks, etc.). The bottom is partially open and the rest is a sheet metal box with firebricks. No need to mess with electrical elements. That said, Burt is a bladesmith/forger--I am not sure how well this design would work for 2,000F extended holds, etc.

 

I'd love to see the design. It would probably be really useful for salt pots as well. That said, I'm getting element wire for free and the electrical business doesn't scare me (as long as I'm careful). I can hold pretty consistant temps in my forge, but the bonus of an oven will be that it will allow me to do stuff like anneal O1 (which requires a 15 hour ramp down IIRC). It'll also let me HT stainless stuff if I ever do any stock removal (which I don't do now, though I'd like to do a few things in stainless like kitchen knives).

 

-d

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I'm about to build HT oven too. It's going to be sword length and I'm using kanthal elements from BCS. The internal chamber is going to be 40x4x4 inches and for temperature control I'm hooking it up to my Omega controller through a relay. I'm building it out of gas concrete bricks (hopefully they can handle the heat) that I'm going to coat with ITC-100. Think I'll weld a frame out of angle iron to hold it all together.

A very proud Say-Mak owner :D

 

My YouTube channel

 

www.leifern.com

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but the bonus of an oven will be that it will allow me to do stuff like anneal O1 (which requires a 15 hour ramp down IIRC).

 

-d

 

Sorry to butt in here, but you might want to try another method with O-1 and other moderately alloyed steels that can be problematic, like L-6, and stuff like that, and see how it works for you.

After normallizing, instead of the long anneal, try hardening the blade in oil, then immediately getting it into your oven for 1200F and an hour soak. In a blade section it'll mostly be "spherodized", which is a fancy way to say you used the upper end of the tempering range.... I personally think it works just as well and better than a process anneal for the kind of stuff we do. It'll be just as "soft" and easy to work with files and stuff as it will be with a full anneal.

 

Right now with my rather "primitive" set-up I do it in an open fire, harden the blade, then take it up to a dark red and hold it, even in the back-yard set-up like that it works really well.

 

Share some pics of the oven when you get it built, sounds like a cool project.

Randal

www.rhgraham.simpl.com

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Sorry to butt in here, but you might want to try another method with O-1 and other moderately alloyed steels that can be problematic, like L-6, and stuff like that, and see how it works for you.

After normallizing, instead of the long anneal, try hardening the blade in oil, then immediately getting it into your oven for 1200F and an hour soak. In a blade section it'll mostly be "spherodized", which is a fancy way to say you used the upper end of the tempering range.... I personally think it works just as well and better than a process anneal for the kind of stuff we do. It'll be just as "soft" and easy to work with files and stuff as it will be with a full anneal.

 

Right now with my rather "primitive" set-up I do it in an open fire, harden the blade, then take it up to a dark red and hold it, even in the back-yard set-up like that it works really well.

 

Share some pics of the oven when you get it built, sounds like a cool project.

 

Randall, could taking some of these moderately alloyed steels up to a stable austenitic condition and then bringing them down and holding at around 1200 degres until they decompose to pearlite work as well? Or is the sub-critical anneal of a martensitic structure a better starting place for a future hardening operation?

Edited by Guy Thomas

Guy Thomas

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Well, you can, but to do it right, you still need to have a controlled ramp-down rate and it still should have a fairly long soak to get the benifits from it, so in the end, you are still talking multiple hours, with L-6 and O-1 and the 41XX series in particular, which are the ones I have the most expierience with.

 

Just based on expierience, and this is an opinion so take it with a grain of salt, I've had much better luck overall with heat-treating and final grain size, toughness, everything, doing it this way than with process anneals, however, I've never really had the gear set-up to do hard-core process anneals to a super-accurate degree either.

 

L-6 can be so problematic in that area that it's given a lot of folks the idea that it air-hardens from normallizing... it doesn't, but an air-cool on L-6 makes it way coarse and brittle, and generally, just shitty.

Same with 4150, and O-1 can be not as bad but still pretty bitchy to work with after an air cool.

So I've gotten into normallizing twice with an air-cool just down to where the steel just has a red, then on the last one, I quench it in 120-150F oil, and then immediately bring it back up to a low red, around 1200-1250F, hold it, and then turn the fire off and let the blade cool in the forge.

It'll file really easy, it'll be fine-grained martensite, and when you go to heat-treat, it'll get even finer yet unless you blow the temps up too much.

 

When I had the full compliment of salt rigs I'd marquench it, let it cool, then bring it back up in the salts for the hour soak.

 

Mainly it was practicality, the process anneal needs a rig that can do it properly, and I never had the desire for that, or the need, and at least for what I was doing the spherodize anneal, or "soft-temper" as I heard it described as a kid, works just as well, if not better in my shop anyway.

 

Nothing wrong at all with a process anneal either if you got the gear and time for it, I've got a few buddies set-up to do it letter-by-letter and it's groovy... but I can't find a difference on the files bewteen the two, or in the heat-treatment after.

 

To do a full spherodizing requires an hour or more on a blade section.... but I don't find that nessecary either, in my open forge, I'll hold it for 10-15 minutes and as far as working it goes I find no difference, and when I destruction-tested a bunch of blades post-ht I found no detriments either, so I try not to call what I do "spherodizing", I think it's really more that "soft temper" I mentioned before.

 

Just something to try anyway, I like doing it that way and it works grand for me, other folks prefer the process anneal, and, why not. I'm just not that patient.

:D

Edited by RHGraham

Randal

www.rhgraham.simpl.com

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From my practical heat treating experience, I prefer what Mr. Graham suggests, and doing a sperodatization heat treatment...Personally I would use a longer time that an hour - preferably a lot more - look at a TTT diagram and it will determine how long.

 

I personally prefer electric heat to gas - I can control it much easier. I like the idea of computer control - it appeals to the geek in me. It is also relatively easiy to do nowadays - it used to be a royal pain back in the 80's.

 

Cant get much better than Kanthal - I would be curious which types of Kanthal. Some of it you have to real careful, and make sure you wear gloves after you use it, if you ever have to replace it, because the Moly DIsilicide in the elements forms a glass surface, that will cut your hand. It is also this glass that protects the elements from oxidation.

 

I am looking forward to seeing this project!

 

Scott

D. Scott MacKenzie, PhD

Heat Treating (Aluminum and Steel)

Quenching (Water, Polymer, Oil, Salt and Mar-Tempering)

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I've avoided the spheroidizing type process simply because it is a rather long process. Randall's post made me hit the books because I'd just read a section on the effects of tempering in the high ranges on various structures. Sure enough on a sample of .75 steel three structures, fine pearlite at 44.5 Rc, martensite at 64.6 Rc and bainite at 53.5 Rc all had dropped to the vicinity of 35 Rc after only 35 seconds at 1200 degrees F. and after another 16 minutes or so would drop down to around 27.5 Rc.

 

Not a spheroidizing operation by any means but a good quick way to get some of the trickier alloys soft enough for working with tools and a good place to start from for future thermal operations.

 

Edited to add: Since an I-T diagram is based on the isothermal transformation of austenite and is at least somewhat applicable to cooling operations how do you use it to determine how long to spheroidize other structures upon reheating?

Edited by Guy Thomas

Guy Thomas

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Well, like I mentioned, to do a proper spherodized anneal takes sometimes many hours to do properly, and there are cases where you'd want to do this, particularly if you are going to be machining the parts.

 

In the more practical side of things, in a simple shop-set-up, most of the steels run up to 1200 or therabouts for 15 min. or so gives you a great deal of workability in the steel as far as filing and grinding goes, and this suits an open-fire basic set-up well.

When I was running the full salt-rigs I usually did the hour soak since I could hang the blade and go do something else.

I think the main thing is to make adjustments as needed, in any case, if you are working a steel and do the the soft-temper gig, and it's not soft enough, or galls with the files, then you need to go longer.

And finally, I don't think that the final heat-treat will see much practical difference between a short soak or long soak really, I might be wrong, but I havn't seen any difference in physical testing, orther than much better grain than I could get with my given set-up than trying to essentially improvise a process anneal.

This way makes life easier for a simple forge and oil set-up like many of us use.

 

I still think highly of computer-controlled heat-treating equiptment though, so don't get me wrong, come late summer I'll have new salt-rigs running myself and I'll be back towards more processed thermal treatments when they're needed. WE all don't have that kind of gear though and I just wanted to point out a method that could be tried. It'll work for ya or not, if it does, it could save some time and kilowatts.

Randal

www.rhgraham.simpl.com

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