# Heat Treat Furnace Build



## jbolt

I have come to a point with a couple of projects that have parts that will need to be heat treated so it is time to build a furnace. This will be my version of the many examples out there on the interweb.

Specifications:

Heat chamber is 7" x 7" x 16"
Dual heating elements wired in series, 240v, 3100w
PID / SSR controller.
k-23 firebrick heat chamber wrapped with three layers of 2300 degree 1 mm ceramic paper.
1" angle iron frame & door skinned with .060 sheet metal

Here is the concept in CAD. 

Heat chamber.




With frame and door.





Before I can finalize the frame dimensions I need to get the heat chamber assembled. Today I cut all the bricks in preparation for assembling.

To cut the side and back bricks with the heating element grooves I made a jig out of 3/4" plywood. Time to put the CNC router to work.





Bricks in the Jig ready to cut. The bricks are clamped with screws against plastic shims. I put several coats of shellac on the edges of the plywood to firm up the wood a bit. The jig only needs to last for 10 bricks so this should be fine. 





Cutting was done with a hacksaw with a carbide grit blade. It makes short work of the soft bricks. Unfortunately the length of the brick combined with the 3/4" plywood took almost all the blade length leaving a very short stroke. 1/2" or 3/8" ply would have been better.





The jig is also setup to cut the rabbits. Here is the second op on the back bricks.





The way the bricks are laid out there is a 1.5" x 1.5" filler on the corners. I need 16 at 9" long and 8 at 1.5" long. Fortunately I still have the tile saw from my construction business. The bricks cut like butter on the wet saw.





Here are all the bricks cut.





Last thing to do before assembly is drill the holes for the heating element and the thermocouple and make the recess pockets for the bolts that the elements terminate to.

I have to say this is a first. Machining bricks!. I used a damaged 1/2" 4 flute carbide end mill for the pockets. Holes wire drilled with regular drill bits. 







Hopefully tomorrow I will get the heat chamber assembled and mortared.


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## Redmech

I'm enjoying this thread. I have a manual kiln that I'd like to put an automatic controller on to run my element. I'll be curious of he exact electrical pieces you use. Look forward to more posts.


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## jbolt

I got thinking last night I should pre-fit the heating elements before assembling. I'm glad I did. I had to make some adjustments where the element turns back on itself and my calculated length was short.

Here are the heating elements from Budget Casting Supply. Un-stretched the coils are 31". 





I attached a board to my workbench and marked it at the length it needed to be stretched. The opposite end is clamped in a vise at the end of the bench. It takes some force for the initial stretch but after that you don't need to pull as hard to make it stretch more so it would be easy to overshoot the length if your not careful. The supplier says you can cut the pigtails but not the coils otherwise overheating may occur. 





Hear is the element pre-fitted. I used a small flat bladed screw driver and a 1/2" wide wood chisel to hand carve the cutouts where the coils turn.  washed the brick last night and they soak up a tremendous amount of water. The firebrick is very easy to carve when damp as there is no dust. Having the bricks damp also helps with the mortar application and curing.





For assembly is screwed a couple of boards to my workbench using a framing square. I also attached a couple of 8" squares the the table as a guide to keep the first three course square. The bricks were assembled from front to back so the back could be installed at the same time. I only got two pounds of refractory mortar which was exactly enough. I plan on picking up another pound to make a slurry and detail all the outside joints. I will let the assembly cure for a couple of weeks while I work on the frame. Once it has had some time to cure I will block sand the sides and back to address any high spots. 






Once the ceramic paper arrives next week. I can cut some samples and stack it with the sheet metal to finalize the frame dimensions. I'm still debating adding a thicker insulating layer. Not sure yet. I have seen a number of builds with just a sheet metal skin over a single layer of bricks and other builds with a second thick layer of ceramic board or insulation. I suppose the worst case is if the outer shell gets unacceptably hot I could add a second skin with a layer of insulation in between.


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## jbolt

Hmmm... seems I missed a "R" in the thread title. Makes it sound like a medieval torture device....LOL


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## mikey

Very nice work, Jbolt! This should be an awesome addition to your capabilities.


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## Terrywerm

Title issue fixed.

Nice project!  Right up my alley also, so I will be following this one closely and hope to built a similar oven in the future.


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## kvt

I know a brick layer that use to wet all his bricks prior to use,  Ask why and it was so the mortar would stick better.        Quick question how long do you have to wait for the bricks to dry out before heating it fully.


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## jbolt

kvt said:


> I know a brick layer that use to wet all his bricks prior to use,  Ask why and it was so the mortar would stick better.        Quick question how long do you have to wait for the bricks to dry out before heating it fully.



I'm going to use a break-in heat up procedure posted by another forum member to get all the moisture out. http://www.hobby-machinist.com/threads/diy-heat-treat-furnace.34507/#post-291847


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## kvt

Thanks,   Ken


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## Silverbullet

This is an excellent build for us on this sight. I'm looking forward to doing one eventually. I enjoyed doing heat treatment and case coloring long ago.
Thanks


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## scwhite

jbolt said:


> I have come to a point with a couple of projects that have parts that will need to be heat treated so it is time to build a furnace. This will be my version of the many examples out there on the interweb.
> 
> Specifications:
> 
> Heat chamber is 7" x 7" x 16"
> Dual heating elements wired in series, 240v, 3100w
> PID / SSR controller.
> k-23 firebrick heat chamber wrapped with three layers of 2300 degree 1 mm ceramic paper.
> 1" angle iron frame & door skinned with .060 sheet metal
> 
> Here is the concept in CAD.
> 
> Heat chamber.
> 
> View attachment 234775
> 
> 
> With frame and door.
> 
> View attachment 234776
> 
> 
> 
> Before I can finalize the frame dimensions I need to get the heat chamber assembled. Today I cut all the bricks in preparation for assembling.
> 
> To cut the side and back bricks with the heating element grooves I made a jig out of 3/4" plywood. Time to put the CNC router to work.
> 
> View attachment 234777
> 
> 
> 
> Bricks in the Jig ready to cut. The bricks are clamped with screws against plastic shims. I put several coats of shellac on the edges of the plywood to firm up the wood a bit. The jig only needs to last for 10 bricks so this should be fine.
> 
> View attachment 234778
> 
> 
> 
> Cutting was done with a hacksaw with a carbide grit blade. It makes short work of the soft bricks. Unfortunately the length of the brick combined with the 3/4" plywood took almost all the blade length leaving a very short stroke. 1/2" or 3/8" ply would have been better.
> 
> View attachment 234779
> 
> 
> 
> The jig is also setup to cut the rabbits. Here is the second op on the back bricks.
> 
> View attachment 234781
> 
> 
> 
> The way the bricks are laid out there is a 1.5" x 1.5" filler on the corners. I need 16 at 9" long and 8 at 1.5" long. Fortunately I still have the tile saw from my construction business. The bricks cut like butter on the wet saw.
> 
> View attachment 234782
> 
> 
> 
> Here are all the bricks cut.
> 
> View attachment 234783
> 
> 
> 
> Last thing to do before assembly is drill the holes for the heating element and the thermocouple and make the recess pockets for the bolts that the elements terminate to.
> 
> I have to say this is a first. Machining bricks!. I used a damaged 1/2" 4 flute carbide end mill for the pockets. Holes wire drilled with regular drill bits.
> 
> View attachment 234786
> 
> View attachment 234784
> View attachment 234785
> 
> 
> Hopefully tomorrow I will get the heat chamber assembled and mortared.


I have a question I like your build by the way 
    My question is die you cut the bricks dry or 
Run water . 
     I was thinking not to run any water 
Because it would suck up the water like a sponge


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## jbolt

Most of the bricks I cut dry by hand using a hacksaw with a carbide grit blade. That would not work at all if they were wet. It would load up the saw and make it useless. 

The corner pieces I cut wet on my tile saw because I had it and saved me a lot of time. I washed all the bricks after cutting to get rid of the loose grit plus I wanted the bricks damp for mortaring. Its not necessary but if you use mortar on a bone dry brick it will quickly suck the moisture out of the mortar making it more difficult to work with and it can affect the cure strength. Cement products cure better damp. The bricks do soak up a tremendous amount of water. 

I chose to use mortar on the joints to create the best seal I can to contain the heat as much as possible. I have read some reports of builds where no mortar was used along with no additional insulating layers which lead to overheating of the outer shell. I'm hoping my strategy of using mortar and multiple thin layers of insulating material will result in acceptable heat limit of the outer shell.

By the time I build the frame and control box I figure 3-4 weeks will pass and a lot of that moisture will have evaporated. The rest will come out during the break in. 

If I were to mortar dry bricks I would first apply a thin layer to each face to be mortared together, scrape that tight and then apply another thin layer to one side and then assemble. Scraping a thin layer on each face forces a mechanical bond and puts a little moisture into the brick. This will help the thin bond layer to better adhere and not dry out as fast.

If you do not use mortar then there is no reason to get them wet.


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## Groundhog

jbolt,
Please keep us posted (as to heating of the shell and anything else). I want to build a heat treating oven and don't know the first thing about masonry or most of the talents necessary to build a good one. Your thread has been very helpful and seems to be a good plan to follow. Thanks!


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## kvt

Jbolt,   Mine is the electrical side of it,  I can do basic electrical and could prob figure some of the other stuff out but would take a while.   Moisture can be a killer, as I did not get enough out of my small home made foundry the first time and it did pop a bunch of chunks and crack because of the moisture expanding .           I need to build a bigger one, along with a forge and a heat treat oven  Just more projects,   At this rate I will never reach the end of my list.


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## ezduzit

kvt said:


> ...At this rate I will never reach the end of my list.



This used to trouble me until I realized that there will always be a list of things to do, and that one must take pleasure in simply actively working on the list of projects.


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## jbolt

ezduzit said:


> This used to trouble me until I realized that there will always be a list of things to do, and that one must take pleasure in simply actively working on the list of projects.



Projects breed projects.........


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## jbolt

kvt said:


> Jbolt,   Mine is the electrical side of it,  I can do basic electrical and could prob figure some of the other stuff out but would take a while.   Moisture can be a killer, as I did not get enough out of my small home made foundry the first time and it did pop a bunch of chunks and crack because of the moisture expanding .           I need to build a bigger one, along with a forge and a heat treat oven  Just more projects,   At this rate I will never reach the end of my list.



Yes sir on moisture. At a house I built for a client we built a huge beautiful Rumford outdoor fireplace. My mason was really proud of it. He gave the owner all kinds of warnings and  instructions on how to season it properly by building several small fires over a period of time. They ignored him and at their house opening party they built a huge fire in it. Cracked the firebox, blew out the throat and damaged the chimney. One expensive party.


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## jbolt

mikey said:


> Very nice work, Jbolt! This should be an awesome addition to your capabilities.



This has been on my wish list for a very long time. Not sure where the heck I'm going to put it though.....LOL


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## scwhite

jbolt said:


> Most of the bricks I cut dry by hand using a hacksaw with a carbide grit blade. That would not work at all if they were wet. It would load up the saw and make it useless.
> 
> The corner pieces I cut wet on my tile saw because I had it and saved me a lot of time. I washed all the bricks after cutting to get rid of the loose grit plus I wanted the bricks damp for mortaring. Its not necessary but if you use mortar on a bone dry brick it will quickly suck the moisture out of the mortar making it more difficult to work with and it can affect the cure strength. Cement products cure better damp. The bricks do soak up a tremendous amount of water.
> 
> I chose to use mortar on the joints to create the best seal I can to contain the heat as much as possible. I have read some reports of builds where no mortar was used along with no additional insulating layers which lead to overheating of the outer shell. I'm hoping my strategy of using mortar and multiple thin layers of insulating material will result in acceptable heat limit of the outer shell.
> 
> By the time I build the frame and control box I figure 3-4 weeks will pass and a lot of that moisture will have evaporated. The rest will come out during the break in.
> 
> If I were to mortar dry bricks I would first apply a thin layer to each face to be mortared together, scrape that tight and then apply another thin layer to one side and then assemble. Scraping a thin layer on each face forces a mechanical bond and puts a little moisture into the brick. This will help the thin bond layer to better adhere and not dry out as fast.
> 
> If you do not use mortar then there is no reason to get them wet.


We had heat treat ovens Graves I think that was the name nether one had any mortar andd was put together dry . 
     We used some packing white packing in all the joints we could put it in . 
     The dry out  procedure is long it will take a week to do it . Slow  procedure  .


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## scwhite

Jbolt you did a great job on your oven .


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## scwhite

Jbolt you did a great job on your oven .
    What controller did you buy ? I don't think I seen one in the pictures .


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## jbolt

scwhite said:


> Jbolt you did a great job on your oven .
> What controller did you buy ? I don't think I seen one in the pictures .



For the PID I got the SYL-2352P from Auberins on the recommendation from others.  I don't know much about these yet.


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## Eddyde

Awesome Build!
I have some experience around pottery kilns that are constructed similarly, fire brick with a metal skin. They get blazing hot on the outside, you may want to  consider adding a couple of inches of mineral wool insulation between the brick and casing, if excessive radiant heat is a concern.


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## jbolt

Thanks for the heads up Eddy. 

I think I am going to continue with my current plan and if it ends up not being acceptable I can modify it to add another insulating layer.


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## countryguy

Here was a post by Ray C (hope all is well w/ him btw if anyone's heard from him  of late).   I learned quite a bit from Ray and some of the textbooks he notes.  Passing the info.   CG 

http://www.hobby-machinist.com/threads/heat-treat-oven.9929/


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## jbolt

A little more progress on the build.

After much reflection I decided to do a redesign on the frame to accommodate a 1" layer of ceramic blanket. I would prefer to be able to use the oven inside my shop and with the limited space I have I'm hopeful it will keep the outer shell temps acceptable.

In addition I added a sub frame to the firebrick assembly. I had some concerns about braking the joints of the firebrick when handling and the way I assembled the bricks I wanted additional support on the bottom row. 

The sub-frame is made form some surplus 1 x 1 angle I had. The sub-frame is held together with 3/16" rods that I single point threaded on each end for a 10-32 nut. I could have used all-thread but what is the fun in that. 

Between the sub-frame and firebrick is a single layer of ceramic paper and a layer of steel mesh on the sides and top to provide some support. A piece of 22 ga. sheet metal on the bottom. I used the mesh to help with the break-in to let moisture out.


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## Mark_f

I notice the heating elements are too long in the picture once they were stretched. Can you cut the excess off or do you have to use the full length? ( I would think the length must be kept original). Also, how did you terminate the ends of the elements for connection? My questions are because this is on my short list of things to build.


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## jbolt

mark_f said:


> I notice the heating elements are too long in the picture once they were stretched. Can you cut the excess off or do you have to use the full length? ( I would think the length must be kept original). Also, how did you terminate the ends of the elements for connection? My questions are because this is on my short list of things to build.



The coils of the elements are not supposed to be cut, the pigtails can be trimmed. The extra length you see will turn along the back wall before the pigtails are run out the rear. 

The pig tail will be run out a small hole and then terminated on a stainless steel bolt. It is recommended to make the termination on the outside. Repeated heat cycles can loosen the connection if made on the interior side. I have also heard it is recommended to double back and twist the pigtail to reduce the amount of heat at the element termination.


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## jbolt

A little more progress this weekend. 

I'll start by saying I really dislike flux core wire welding. I can stick weld, tig weld and gas weld but for some reason I have a hard time seeing the weld joint with flux core wire. Nor does it help to not have a proper welding space and table. Working on a HF folding table out in the driveway stinks. I long for the day when I have a decent shop.

I got the frame mostly welded up and the door partially made and hinged. I also test the fit of the heat chamber to the frame. So far so good. My local metal supplier gave me some aluminum diamond plate cutoffs to use for the frame sides. Can't argue with free.


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## jbolt

Slowly but surely progress is being made. 

I have the heat chamber installed in the frame. The heat chamber is centered in the outer frame with jacking screws on the sub frame. I installed the diamond plate top and bottom and the 1" layer of Inswool ceramic blanket first and then used the jacking screws which are accessible through the open sides to center and lock the heat chamber in place. Once that was done the side insulation and panels were slid in place. The door was a little more complicated since I wanted to be able to service the innards if necessary so I didn't want to weld everything permanently inside. A smaller frame made from 1-1/2" angle slips inside the outer door fame from the front and is held in with screws from the side. Two jacking screws through the bottom of the door frame center and adjust the height of the door firebrick in the opening. It took a little more work but everything is adjustable so it fits together very well. 

Next is getting the rear closure done and  the control box wired and installed.


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## Eddyde

Looks super solid, nice build!


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## brino

jbolt said:


> It took a little more work but everything is adjustable so it fits together very well.



Looking great, very nice design.
I appreciate you taking us along for the ride!

Thanks,
-brino


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## ezduzit

Almost like a professional job.  Seriously, I'm green with envy; would love to have this.


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## woodchucker

Nice work.  Looking good.


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## Desolus

This is why I get up in the morning.


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## jbolt

A little more progress now that the bathroom remodel is done.

I did the enclosure cutouts today on the CNC mill. Always fun to do setups on enclosures. This enclosure is small enough I could get it rigid enough to cut full depth with a 1/8" carbide end mill. 





I used some of the left over ceramic tile from the bath remodel to cover the back of the heat box where the elements terminate. The area around the tiled area will get a 1" layer of ceramic blanket.


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## jbolt

Here is the back panel construction and installation.

Back panel cutout on the CNC mill.




The only brake I have access to does not have any dies narrow enough to do the bend so I made up a redneck bender using angle iron and some door hinges. I used a crescent wrench has a handle. Worked perfect!








One layer of 1" ceramic blanket, back panel and the 1" angle iron retaining frame. The frame locks in with set screws in the corners.





To terminate and secure the ends of the heating elements I modified some 5/16" stainless steel bolts. The element passes through the middle of the bolt and is captured by the grooves. I put kinks in the pig tails of the element wire to create positive contact inside the hole to avoid potential arching. I don't know if that would have been an issue but the instructions for the heating elements required that the coils be stretched to create a gap between the coils to prevent arcing so I figured this was a good idea.





Heating elements and thermocouple installed.





Here is my first wiring configuration. I originally had the heating element setup with a SSR on each end of the element so it would be fully disconnected when off. I had a problem with the Auber PID controller. It would not give a consistent reading from the thermocouple and after a day and a half of trouble shooting I determined the unit was bad. 








I called Auber on the PID issue and they agreed it was faulty and sent me a return shipping label. That PID has been sent back for replacement. I posted about the PID  issue in the electrical forum looking for troubleshooting help and during those conversations another forum member, who has been an incredible help, suggested I use a single SSR and a double pole contactor. Apparently SSRs still leak some voltage when off. I also liked the idea of being able to switch the contactor to turn off the elements and still keep the PID under power for setups, troubleshooting etc. I also decided to order another PID from automation Direct. It has the ability to be programmed from a PC. 

Here is the revised electrical with a contactor, single SSR and a Solo SL4848-VR PID controller. The contactor is the type use in air conditioners. This one is 40 amp with a 240vac coil. The whole system is run on 3-wire 240vac. The PID provides up to 14vdc to trigger the SSR.








Here is a quick shot of the back panel with the elements terminated and hooked up. Last thing to make is a protective cage for the termination area. 






Today I powered it up and setup the PID. I did the initial setup with the elements disconnected and with a 75w light buld hooked up to the SSR. The PID manual is not very intuitive so it took some trial and error to figure out the settings. I'm not the sharpest tool in the shed when it comes to things like this but after pushing buttons for a while it starts to make more sense. 

After I was comfortable that the PID was operating correctly I hooked up the heating elements. The PID has 4 modes, PID, Manual, On/Off and Ramp/Soak. In PID mode you can auto tune the system to set the PID parameters. Currently the oven is on and set at 200 degs for the first part of the break in. The auto tune took about 10 minutes but once done the temp is holding rock steady. I will keep it at 200 overnight to burn off any excess moisture that may still be in the brick and then do the element break in and install the door gasket tomorrow.

Up and running! 

The toggle switch is for the contactor, the green light is on when the contacor is energized. The amber light shows when the SSR is on and the elements are heating. The two red indicators are lighted buzzers for Hi/Low alarms.


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## extropic

Just read this thread.

Nice work jbolt. Looking great.

Wondering if you're going to post a wiring diagram? It would be a help to the electronically challenged, like me.

I'm subscribing so I won't miss the Christening.


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## Linghunt

Very nice.  I might have to try something like that for a long 6 foot furnace.  Low on my project list with so many things to do.


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## jbolt

Attached is the wiring diagram of how I wired this oven. ***USE AT OWN RISK!***


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## jbolt

Linghunt said:


> Very nice.  I might have to try something like that for a long 6 foot furnace.  Low on my project list with so many things to do.



Thanks Linghunt. I appreciate all your help!


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## jbolt

I installed the door gasket and did the burn in today.





The oven heats up very quickly. Took about 20 minutes to go from 200 to 1200. It could go faster but the controller starts pulsing before the set temp to not over shoot. I'm really pleased how well it works and how stable the temps are. Once up to temp the temp never varies more than a degree.

I did the burn-in outside under shade. The electrical enclosure started to get warm at the end of the 1200 deg period so I took the side panel off. I was concerned the controller might over heat. Factory spec is 122 deg F operating temp. I'm going to add a stand-off between the enclosure and the frame to give it a little more air space and since I am only using one SSR I will use the other SSR cutout for a case fan.

For those interested in the outside temps I recorded them at each setting at the end of each soak period. I took measurements at several locations. The door has the least amount of insulation with only 3 layers of 1 mm ceramic paper between the brick and frame. The highest temps were at the back of the oven at the ceramic tile back in the area around the upper heating element terminations.

Ambient Temp, deg F                                           87,          90,         93,         93,          93,         92,
Oven Temp, deg F                                                 1200 ,    1300,     1400,     1500,     1600,     1700,
Soak Time, Hrs                                                      2,            1,             1,            1,            1,            1,
*Temp Readings *
Top,                                                                          159,        185,       193,        198,        213,       222,
Upper right front corner of frame,                     164,       195,       205,        215,        236,       244,
Face of door,                                                            164,      184,       192,         199,        212,       216,
At upper element termination bolt,                   229,      248,       271,         262,        312,       321,
At tile between upper element terminations,   238,      259,       301,         313,        336,      406,
At PID case, (rated to 122 F)                                114,       110,        111,          105,        106,       105,


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## Linghunt

Add a vent for the fan,  think about a filter for the fan and suck in air . You don't want the enclosure to be a vacuum cleaner so pressure inside should be higher than outside.   You could make some little pagoda type top vent.  maybe a little screen or lip so bolts don't fall in, from future clutter.  

Example picture. 
http://www.newark.com/hoffman-enclosures/p2tp88/pagoda-top-800-x-800mm-grey/dp/79Y3261

Standoff  as you said is great idea. 

Use second measurement tool to profile different spots inside for temperature gradients.


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## jbolt

Linghunt said:


> Use second measurement tool to profile different spots inside for temperature gradients.



Inside the oven or the electronics enclosure?


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## Linghunt

jbolt said:


> Inside the oven or the electronics enclosure?



Inside the oven.


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## jbolt

Not sure how I could do that.


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## Linghunt

jbolt said:


> Not sure how I could do that.



Small gauged T / C wire thru the door seal , just for test.    Strip the insulation off and separate via air gap.  make T/C on end by twisting them together. ( it actually works that way, but has hillbilly look to it. )  

You could do a few and then swap meter from pair to pair.  perhaps one to a piece of scrape metal. 

Take some measurements, get a feel for how the Oven heats parts.  then pull all it off.  and call it done.  Don't go crazy on it.

Going crazy example:

I rented a datalogger deal with like 20 channels and used this to profile baffling designs and adjustments in a forced air annealing oven.   If you want to get fancier and think of a Ballast on the T/C.  

*Not saying to do this*, but just Food for thought. 

Heating in done by 3 methods:  Convection, Radiation, Conduction.  

Convection for this oven is main heat transfer method.  

To mimic the actual part temperature  You add a ballast part to the T/C. This will help display the actual part temperature vs air temperature inside the oven at one location.

Think of the Ballast part as a small piece of metal (same as what you heat treating ) with a hole in it slid over T/C.    This part will get scaling etc and mess up radiation heating and just be a mess. 

The Ballast concept is useful for heating in a vacuum chamber where all you got is radiation heat transfer method.  Different materials heat differently , so the Ballast is same as part. Dig into *black body radiation* if you want more.   

I left out a lot.   

I stuck a big chunk of SS in my little oven.  It's like 4"x4"x2".   ( thermal mass that will not change in temperature much form Oven heaters cycling on and off). Setpoint at 900 and 990 F for the most part.  

I sit my parts on top of it in a SS basket I made.  I used the thick Foil that you seal the parts in with some paper to prevent scaling. 

If I wanted a better system,  I would buy an isolated T/C  install it in that chunk of SS with a setscrew and hole.   But when I do larger parts I take it out so then I would have to mess with T/C location.   Takes you back to KISS method, and don't go crazy.


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## Groundhog

I hope this thread doesn't go away. I really want to build an oven but it will be awhile. Although I haven't read this through from end to end yet there seems to be a lot of useful info here. Looks like an exact copy might be an easy (for me) way to go (especially if you keep tweaking it).
I know pictures and write-ups along the way are a real pain. Thanks so much for sharing.


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## dulltool17

I gotta build one!   I see you bought from Automation Direct....it's a pleasure working with these folks.
Actually, we build ovens where I work, but he chances of acquiring one "on the cheap" are nil.


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## Linghunt

dulltool17 said:


> I gotta build one!   I see you bought from Automation Direct....it's a pleasure working with these folks.
> Actually, we build ovens where I work, but the chances of acquiring one "on the cheap" are nil.



What company and size of Ovens?  Do they sell scratch and dents maybe?   Looking for a long 6 footer x 5" x 5"   for treating long rods.  I'm limited to 37 inches now.


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## dulltool17

Thermo Fisher SCIENTIFIC.   I'm the Manufacturing Engineer for Chiller Production, but spent a bit of time this afternoon with the MFE for the Furnace line.  They build a long one with a chamber I'd estimate at 6" diameter x 50" long.  It has three separate elements.   I have no idea what the specs are or pricing.    I was told that the smallest, with about a 5 x 5 x 5 interior goes for a grand.  I've not seen Scratch & Dent items.  YOu might find one on E-bay.

If you're going for 6' long, maybe the JBolt route would be viable.  Definitely needs multiple elements, probably with independent control.  Not an undertaking for the faint of heart...


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## Linghunt

dulltool17 said:


> Thermo Fisher SCIENTIFIC.   I'm the Manufacturing Engineer for Chiller Production, but spent a bit of time this afternoon with the MFE for the Furnace line.  They build a long one with a chamber I'd estimate at 6" diameter x 50" long.  It has three separate elements.   I have no idea what the specs are or pricing.    I was told that the smallest, with about a 5 x 5 x 5 interior goes for a grand.  I've not seen Scratch & Dent items.  You might find one on E-bay.
> 
> If you're going for 6' long, maybe the JBolt route would be viable.  Definitely needs multiple elements, probably with independent control.  Not an undertaking for the faint of heart...



*Thanks for the info*. The JBolt direction is probably the most economical method. I keep an eye out on used equipment site when I remember.  That is how I got my current tube furnace that is 37" length capacity x 3 inch diameter.  I recall getting it for about $1K without controls.  This one has 3 thermocouples, but only need to control off of one from measurements and testing. I had the controls already from my attempt to building one from an old tool box inside a salvaged Hoffman cabinet.  

Multi-section ovens and controls can be tricky.  I had project with an inline continuous feed 3 section furnace used to heat large glass circles around 24 inch diameter that were pressed to a spherical curves for computer monitors.  This was pre autotune days.  I sure learned a lot about PID loops on that job. I bought and studied a book just on PID's. The biggest fix I did was changing out the K thermocouple wiring.  I discovered they used multiple types of wire and also aluminum terminal box in various locations.  It was a great learning project, but a nightmare of a job.  I was total cherry back then too that didn't help.   

Today's controls are so much better.  I got stuck with a PID tuning application that other engineers gave up on. I messed with it for a while and didn't get anywhere.  I figured I needed to try anything as long with it was different.  My fix was to make the bandwidth ranges of the PID variables vs constants and I changed those at diffferent stages of the ramp and steady state.  It worked and surprised them that I fixed it.


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## jbolt

I did a few more tweaks to help with the electronics enclosure cooling.

I added 1" standoffs between the enclosure and the enclosure mounting straps.




I also added a 60mm 220vac fan to the bottom of the enclosure. A 80mm fan filter cover covers the 70mm x 50mm cutout for the SSR I did not use. The fan comes on with the contactor. 
I got the fan from mouser electronics. p/n OA60AP-22-1WB


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## jbolt

Attached is an initial setup and quick start guide for the SOLO SL4848-VR controller. I didn't find the manual very intuitive for someone not familiar with PID controllers so I'm passing along what took me a few sessions to figure out.


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## Linghunt

Is the fan blowing out of the box or sucking air in?   

My "general" picky thought process for cooling fans:  Suck air into the enclosure, you now have a slight pressure gradient in the box, cracks or gaps from different holes or the door will have air flow out of these.  Most of the air will  go out the vent, so this is being real picky.  Filter the fan so you don't suck "dirty" air into box.  Heat rises, so fan on bottom, vent on top.  Don't forget to change filter or blow it out on some schedule. 

What you have here is *more than good enough*.  My Oven has no filter , and the vent is on the side, I built with what I had. My box does collects dirt, I blow it out when I remember

Aside: I got an extra cooling fan on my phase perfect converter and no filter. I didn't have one to fit the fan I had from salvage and just went with it.   Manufacturer has a fan as well hooked to a thermal switch, and no filter.


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## jbolt

The fan draws air into the enclosure.

Sent from my SM-G955U using Tapatalk


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## brino

Linghunt said:


> I bought and studied a book just on PID's.



Is it a book you'd recommend?
Or do you have other resources you could point to?
Thanks,
-brino


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## Linghunt

brino said:


> Is it a book you'd recommend?
> Or do you have other resources you could point to?
> Thanks,
> -brino



Let me look,  I got it here on my shelf.


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## Linghunt

brino said:


> Is it a book you'd recommend?
> Or do you have other resources you could point to?
> Thanks,
> -brino



If you have a technical background and understand Laplace transforms etc, then it's good. Without the a high level of mathematics it will read Greek.  The Math is not hard and illustrated well, but without having seen them before is the point.

Here are some samples of the authors writing style.      There are 4 old controller referenced in the book,  That section is interesting but junk. Book is 1988.








































Found this one , (my 1st EE boss gave it to me when he retired)   This is a small handbook from 1980. Still good today since math and physics doesn't change.  I took one internal page picture.  This type stuff is hard to read. 





http://www.linghunt.com/ForumPosts/books/EM_SHIELDING_BOOK1.jpg




http://www.linghunt.com/ForumPosts/books/EM_SHIELDING_BOOK1.jpg




http://www.linghunt.com/ForumPosts/books/EM_SHIELDING_BOOK1.jpg
I think I have some other material not so Math based.  Let me know how this reads for you.


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## brino

Thanks @Linghunt 
Electromagnetics was my most difficult class.
PID looks interesting. I wish I knew more control systems theory.
-brino


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## Linghunt

brino said:


> Thanks @Linghunt
> Electromagnetics was my most difficult class.
> PID looks interesting. I wish I knew more control systems theory.
> -brino



EM classes were interesting and tied so many of the other classes together for me.  The picture I selected was a typical boundary value problem.  No only does it work for EM, but same material for light.  It was a big help for me working for a thin film company.  It the fundamentals for everything we did.  Some products had 100's of layers and each one was used to reflect or block a portion of the light.  anyway...

Control theory is tough area as a well.  Have a feel for negative feedback is critical to build on.  Feedback in simple transistor circuits is a good starting point.  Mechanical examples like a toilet float work too.

Check out this link on PID's available today.  Note more different *"knobs"* you can change.  That can get you in big trouble too.

https://cache.industry.siemens.com/...t_76099/v1/Ex_StdPID_ModPIDenUS.pdf_en-US.pdf

I'm far from an expert on that, I know just enough to be dangerous.


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## jbolt

I went to use the oven today and had forgotten how to program the Ramp/Soak so I updated the SOLO 4848-VR Setuo & Quick Start Guide I posted in post #56 to include Ramp/Soak programming. Also attached to this post.

https://www.hobby-machinist.com/threads/heat-treat-furnace-build.59556/post-510673


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