PID Controlled Forge/Heat Treat oven plans & WIP

Quick update on this: the controller is finished as well as the A/B solenoid setup with the High mode and Low mode functioning. Since I've yet to complete the blown forge body to use this controller with, I've been using it with my venturi forge and it's a MAJOR upgrade to the shop. Even on my simple venturi forge, it's a complete game changer.

For heat treating in the venturi forge, I'm using a muffle, and can run the burners either using the high/low mode or just on/off mode (which gives a slight woof sound as it ignites, but it's quite minimal).

It can hold 1500f within just a few degrees already. If I place some heavy bars in the muffle along with the blade, it evens out the temperature even more. Great :)

I'll post pics of my current setup with the venturi forge and the controller with solenoid assembly since I still have a while before the blown forge is complete.
 
Probably answering my own question, but other than being able to use this to forge metal the advantages for HT over an oven are simply price?

Edit: Can't wait t see some images. I might go this route...
 
Pleasanthill, I'd say the advantage is that it's a multi-purpose tool and it's easier to build than an electric oven.

Additionally, the controller unit can be modular (as shown earlier in the thread) so can also be used on other devices if desired. Once you know how to build the controller you're half the way there on building any other temperature controlled tool in the shop


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Additionally, you can burn organic material in the muffle to create a highly reducing atmosphere which reduces decarb. It's actually quite effective.

Don't get me wrong, electric ovens seem to have more even heat throughout the chamber, but it's impressive how well the PID forge + muffle heat treatment works. For a lot of people who already have a gas forge, it's just a matter of building the controller and hooking it up.


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kdogmcg said:
I think a PID controlled oven will be easier to operate and hold a more exact temp
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I believe that as well, I was trying to get to other than being able to heat metal for forging which theoretically you can do with an oven but going this route vs an actual oven for the heat treatment purposes would simply be cost. You can build this a lot cheaper than you can buy or build an PID controlled oven and easier as well I believe. Well that and it had multiple purposes.

There is just something that intrigues me with this and the open flame vs the oven. I'm sure as I get down the road some more in the knife making arena I might gain more of a desire to make knives in a "laboratory" like completely precisely controlled environment with exact chemical compositions of metals and heats, but I still need to get to where i'm buying metal from an actual supplier. I'm still making then out of vintage Nicholson files.
 
If all you want to do is forge, or heat treat simple steels, I think a forge is fine. If you want to do stainless, that may require a 30 minute soak at 1900°+ then an oven may be more desirable.
 
Ah, I see you beat me to the post. Spent too long trying to word it. I have read about that "burning organic material". I really want to go the gas forge route and am just learning about the muffle and PID control. It's really caught my attention, as I'm already acquiring the materials to make the forge, and adding a controls to it was something I was wondering about and am learning OH people are already doing it...

My luck, thought I had an original idea..... No such luck..
 
If you plan to heat treat in your forge I highly recommend a larger interior chamber size than is sometimes standard for building a forge. My current Venturi forge is about 5x5" (square) inside and it's on the small side. Hence the reason for 8" diameter interior in the diagram, will allow for much more even heating during heat treatment


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nickandersonart said:
If you plan to heat treat in your forge I highly recommend a larger interior chamber size than is sometimes standard for building a forge. My current Venturi forge is about 5x5" (square) inside and it's on the small side. Hence the reason for 8" diameter interior in the diagram, will allow for much more even heating during heat treatment


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The piece of pipe currently have awaiting to build is 16" diameter X 24" in length X 3/8" thick. I was originally planning on going 3 burners.
 
pleasanthill said:
The piece of pipe currently have awaiting to build is 16" diameter X 24" in length X 3/8" thick. I was originally planning on going 3 burners.
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The 16 inch diameter pipe might be a bit large. It does offer the opportunity of an extra thick lining of wool. I run a 12 x 24 inch blown forge, using the A/B solenoid, its lined with 3000 degree Kaowool, one layer of 2" with a 1" layer of wool on top of that for a total of 3". This leaves an operating space of about 6 inches. In truth I work within the small area behind the flames coming from the 3 burners and up against the back wall of satinite clay coated wool. The blades lean up against the wall. This is my fifth blown forge build and I like this set up best of all of them.

These A/B forges are very stable temperature wise, being able to hold set point within 2 to 5 degrees. As Nick has discovered, forging in one of these forges is a whole new experience.
Glad its coming together for you Nick, Fred
 
Yea Fred for the forging as well, it's really amazing. Just set the PID to the top of the forging range (1900F / 1037C is what I set it to for for the O1) and then as soon as the metal color reaches the same color as the forge interior you know you're ready to forge. Stop when it's around 1600 and put it back in the forge...easy to stay within the safe zone of forging and welding temps!
 
Fred.Rowe said:
The 16 inch diameter pipe might be a bit large. It does offer the opportunity of an extra thick lining of wool. I run a 12 x 24 inch blown forge, using the A/B solenoid, its lined with 3000 degree Kaowool, one layer of 2" with a 1" layer of wool on top of that for a total of 3". This leaves an operating space of about 6 inches. In truth I work within the small area behind the flames coming from the 3 burners and up against the back wall of satinite clay coated wool. The blades lean up against the wall. This is my fifth blown forge build and I like this set up best of all of them.

These A/B forges are very stable temperature wise, being able to hold set point within 2 to 5 degrees. As Nick has discovered, forging in one of these forges is a whole new experience.
Glad its coming together for you Nick, Fred
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Would a 12" x 17" be too small? Buddy had a piece laying around I can get but probably limiting my length too much. Might be better off sacrificing one of the 30lb propane tanks I have.
 
I think it could work...though for me I really want the option to be able to heat treat longer blades as well...short swords and the like


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A 12X17" pipe will make a very good forge. With 2" wool, it makes for a good size 7" chamber. With 3" of wool ( 2" of regular wool and an inner 1" Hi-Z layer) it makes for a 5" chamber. One blown burner will run it nicely.

Longer forges are not needed for 99% of most knifemakers. A 36" sword can be HTed in a 16" forge.
 
I think I may either use the larger one of the propane tank. I will be doing some larger knives as well. Actually about to make a new thread about the steel the guy (friend) is insisting he wants to use for a custom hog hunting knife. it's going to be in the range of 12" - 14". Were going to go get the steel when the weather cools as it way out in the woods. Hopefully have the forge built (excluding PID) by then as I will definitely be needing it. Hoping JTKnives will chime in on the thread once I post as he is the only one I've seen on here who's actually attempted what I'm about to.
 
I'm a newbie here but would like to share some observations I've made so far with regard to heat treating. Please anyone chime in if you have a comment. I went from heat treating carbon steels by determining temp via magnet,to using a c. 1970's Thermolyne analog muffle furnace. When I first started,It was the magnet technique for a while,then I bought a long K type thermocouple with a PID attached to stick in my small forge and couldnt believe the variation in temp. In 1.5 by 9" hole! Shortly after this I got a really good deal on the aforementioned muffle furnace and a slightly smaller one from a going out of business machine shop liquidation. Still though, I wondered how I could check to see if the thermocouple and pyrometer in the furnace where accurate. Today i realized I could drill a hole in the back wall of the furnace and put my PID connected thermocouple at the bottom of the chamber and compare the readouts. AND AFTER ALL THAT,HERE IS MY QUESTION! From I've been reading about K type TCs,they can vary as much as 25 degrees +- F over 1200 degrees! This can be a biggish deal when working with 1095 steel.if all the major manufacturers rely on this K type TC whats the point of spending over a thousand dollars on a kiln that cant guarantee accuracy? And again from what I've read,the readings wander more with each use! WHAT THE FRENCH FRY is going on? Also,in order to avoid having the ceramic tube encased new thermocouple be too near any of the heating elements entering from the back,can a length of protected thermocouple stick out the back an inch or two provided the tip is where its supposed to be in the chamber? THANKS ANY AND EVERYONE. If I've posted this in the wrong place,I apologise and will welcome correction.
 
That Moron said:
(...)From I've been reading about K type TCs,they can vary as much as 25 degrees +- F over 1200 degrees! This can be a biggish deal when working with 1095 steel.if all the major manufacturers rely on this K type TC whats the point of spending over a thousand dollars on a kiln that cant guarantee accuracy?(...)
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This is probably worth another thread...
The equipment does not warrantee accuracy at that level on it's own. But it does warrantee much tighter _repeatability_. This means you cannot follow blindly posted recipes, but you can use them as great starting points for your experiments. You'll have to try, measure and adjust. And even after you found the right formula for your set-up, you need to measure again from time to time for QA purposes.

Also, if you wanted to, you can significantly reduce the errors with calibration. But that's a discipline on itself, and requires a lot of work, and a lot of knowledge. But even with simple calibration techniques you should be able to reduce the error to a few degrees at a single temperature.

Finally, keep in mind that neither the composition as per the specification, nor the transformation temperatures are so specific. The former has ranges for most elements, and these ranges affect most of the relevant temperatures. The latter varies tens of degrees even for modest heating/cooling rates.
 
Yea I'd just get some temperature crayons, silver or something that is known to melt at an exact temp and use that to calibrate your TC if desired. After that, IIRC, I think as long as they're used within the recommended temp range they shouldn't lose a whole lot more than 1% accuracy over time.

Stacy had previously suggested replacing every year which, given that this is the most important part in a heat treating apparatus, is probably a good idea to ensure that they stay accurate.


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Nick, contrary to belief's I still am a member of this forum and I do occasionally post. I am more of an observer these days when it comes to this forum but that is neither here nor there in connection to your question.

You have already talked with Fred Rowe and he is the man when it comes to this set-up and making it work. Fred is one of the few to encourage me when everyone else said it can't be done! He was also very helpful in feeling out some problems that I was having with my set-up.

At present my forge is down and haven't had time to get back to it! I am unable to answer the questions concerning setting up a forge as you speak off, as I am dealing with a lot of health issues with my wife!! All my time has been rerouted to care for her and even though I still read on the forums I don't have the time to frequent them as much as I use to! G

Good luck!!
 
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