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Building a heat treat oven need advice Part 1--Ramp Soak??

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I have pored over home built heat treat oven plans from all over.


1st question:  Can someone explain RAMP/SOAK and what might I need it for in the future.  I ask because a PID controller with it runs about twice the price as one without it.  Not sure I need it now, but may later on.


Currently just starting to make file and rasp knives, leaf springs soon to come, then likely 1084.  Down the road.....who knows...




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What are you using for your Heat treat manual?  I use the ASM handbook.  Some alloys with lots of carbide formers take extended times at temperature to put the carbon locked in the carbides back in solution: this time is the SOAK  Ramping is changing the temp at a controlled rate to allow certain things to happen---again often for very high alloy steels.  Some steels won't anneal without a very controlled ramping down.


If you are just using simple alloys it's not that important.  If you will be getting to the superstar prima donna alloys it may be very important

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Thank you Thomas.  That makes some sense.  Can you give examples of some common blade alloys that require soaking? 




Mostly so I will know what I may or may now want to deal with down the road.  Not too sure what prima donna alloys might be.



Moving this to Blade section since this seems to be more accutate for the question being asked

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A PID controller is designed to stop temperature overshoot, as it gets close to the target temperature it uses data from a calibration setup heat to pulse the heating elements. this is usually through a relay for slow pulsing or SSR (solid state relay) for fast pulsing.


Not much call for slow ramping with heat treating metals, unless you are using something with a lot of grunt and the PID function gets less useful as the temperature rises. it is possible to overshoot while tempering, not likely at a red heat.


A ramp soak controller lets you program an oven from start to finish so that you dont have to hang around while it is doing its thing.


I had a browse on the internet. A ramp soak 50 step controller with ceramic K type thermocouple and SSR + heatsink is about $150


All correctly wired up in an enclosure with breakers is about $100 extra. That seems like good value to me.

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High alloy ones and lets not get into HSS like M-2; but few knives get made from the stranger alloys just because they are quite expensive and require "professional" heat treating.  (I worked with a swordmaker who had a custom built electric vertical heat treat furnace with ramping controls and inert atmosphere---he liked D2...and his father was a research metallurgist)

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Alright!! That sounds good and explains much.

I suspect I may build the oven with a standard controller and SSR pkg and work on my basic skills.

If I decide to do stainless steel at some time, that may be the time to either build a new oven or upgrade the PID controller.

I am not one to just leave a super hot oven running and not hang around.

Thanks guys. I appreciate the advice.

Part 2 coming up soon.

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I suspect you will find all the controllers in a range will be the roughly the same price, just with slightly different software for each application unless you are looking at something that has a custom user interface or a fancy data logger.


A ramp/soak controller is a must for me, I have to leave myself large notes and alarm clocks to remember start times ETC, I have a shocking memory for times. Plus you can pack a heap of stuff in a tray of sand and temper it overnight if you get cheap power after midnight or while the solar panels are producing power in the afternoon.


A 50 step controller should hold 2-4 programs in its memory so you can choose the cycle and press start, no need to program it every time. Should really download the user manual and check before buying one as they are not all the same.

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maybe we are not clear enough as to how we use ramp and dwell functions.  O1 likes to take a rest at 1200F when heating from room temp.  Also its a problem just sticking it in a hot forge, I shattered one by forgetting to preheat a blade. 


So *** Starting O1 blade ***

insert blade

ramp to 1200F

dwell 10 minutes

ramp up to to 1700F

dwell infinity


**** Annealing O1 forging ****

ramp -40 to -50 degrees over 1 hour each drop till below 900F then allow to cool in forge. its annealed!

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For Carbon steels, you should be fine with a basic PID controller. For anything that calls for a hold on the way up, you can just change the setpoint at the appropriate time.


Once you get to some of the stainless steels, ramp and soak is very nice to have, especially for slow ramp down when annealing.


Stick with a 48mm x 48mm (1/16th DIN) controller and leave a little slack in the wires (the terminal positions change on different controllers) to leave an upgrade path for the future.


Ramp is also nice for tempering as a small overshoot can lose a Rockwell point or more and radiated heat from the elements can make it much more. Temper in a tray of dry sand and you'll have no problem.

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Thank you gentlemen. Steve, you were right, I didn't understand the concepts very well thank you for the explanation.

Tim, glad you chimed in. I see your name everywhere in heat treating oven talk.

My next question is about plans for an oven wired for American electricity.

I will have 110v at 20A dedicated and 220v at 50A as well in my garage. I would love to hear opinions on both and plans.

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If you need it to be mobile for use anywhere there's power, the 110V may be worth considering.


Otherwise, 220V knocks it into a cocked hat. It's definitely the better way to go if you have the supply. Being able to use an off-the-shelf 110V element on each side and connect them in series for 220V makes sourcing the elements easier.


The oven power requirement for multiple workpieces tends not to be significanly different to that for a single slipjoint blade; the thermal mass of the oven itself is much greater than any collection of blades most of us would want to load in one hit. Even if you are making small anvils, it will just slow things down slightly.


More significant to my mind is the length of workpiece you want to accommodate. An extra 4 1/2" (the width of a brick) adds about 20-30 bucks to the build cost. 


Assuming the same materials, the surface area is the main thing that determines how much power is needed.  I built my first 4 ovens 18" long with 3 kW of elements. My latest is 22 1/2" long, also with 3 kW of elements. All will comfortably run to 1205 degC (2201 degF) with power to spare and I'm reasonably sure 27" would work fine on 3 kW.


I also built a 42" sword oven with 6 kW of elements, just for fun. I am told it works reasonably well.


We have 13A, 230V domestic sockets in the UK, which is why I use 3 kW. The sword oven uses a separate supply for each side's element.


There are some quite significant differences between your power systems and ours. We only have one hot wire to contend with, but it is at 230V to ground. I am happy I build my ovens so they are as safe as they can reasonably be, but I don't think they would necessarily work, or meet code, over there.


There are homebuild HT oven wiring diagrams from the US and Canada out there on the web and you are better off using one of them as a starting point, rather than a European one.

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Thanks Tim and thingmaker.  Definitely ideas to consider.


My big problem, Tim, is that I can't seem to find a good and clear wiring diagram for a US 220V system.  I have seen several, but the minute details seem to be absent and I don't want to take a chance on something bad happening.


If anyone on here can provide a good source for a 220V oven I would be indebted.


Thanks all.

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That helps. Thanks Thingmaker.


Mike, I am not a qualified electrician, even over here, so please get an opinion from someone competent and familiar with your system.


It looks like my wiring would probably work OK with the addition of a second SSR in the other hot leg. The AutomationDirect Solo/Omega CN7823 controller I use has a pulsed DC output rated at 40 mA, so will happily run 2 SSRs. I use a contactor to break both the live and Neutral of our supply. It would break both hots on yours.


Protective grounding and a GFCI should take care of the safety concerns whilst it is running.





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