kiln talk

[koyote]

I'm looking at making a couple major shop changes.

The big one is heat treating. I'm doing just fine with the steels I currently work using my forge and conalo oil/brin/copper plates. But... I'm lookign at a kiln and some houghton quenchant.

I'm having a few conceptual problems though. I'm familiar with what I can do with a kiln to expand my steel selection into O1, 3v, 154, and such.

My main concerns are batch size or large heat treat numbers, normalizing/straightening, and size selection.

Straightening and normalizing are things I often combine into the final stages just before heat treat, where I will run a blade up to heat and straighten, let air cool to black, and repeat so I get a blade that "wants" to be straight and has 3-4 normalizing cycles. I ave no idea how I want to run this process with a kiln.....

Heat treating multiples is another question area. This boils down to "how fast does a kiln lose heat when you open it to take a blade out?"

Size selection is a tough one. I'd say... 60% or so of what I do could fit in an 18 inch evenheat, 80% in a 22.5, and really right on 95% in a 27. But is a 27 going to be ridiculously expensive to run for the 10 inch knives?

I'd love to hear some methods people use with kilns....

 

[Mitchell Knives]

This boils down to "how fast does a kiln lose heat when you open it to take a blade out?"

But is a 27 going to be ridiculously expensive to run for the 10 inch knives?

I purchased a 27" Evenheat a few months ago.

Actually, it heats up quickly. I was a bit concerned about this before the purchase, but it has not been an issue. I can go from room temperature to 1500 degrees fahrenheit in about 30 - 35 minutes. I try to use the extra space to my advantage, and heat treat 5 or 6 blades at a time.

You might lose 40 degrees opening the door to remove a blade. By the time you quench, the oven is back to temperature.

 

[koyote]

That's the sort of thing that is hard to find in actual literature. thanks!

 

[Stacy E. Apelt - Bladesmith]

I can't find the thread right now, but this was discussed before.

The Cliff Notes version would be that if the oven has been allowed to fully soak the blades at target temp, there is no problem with the small temperature drop when the oven door is opened. Once closed it rebounds very fast, and the drop in temp will just be part of the overall drop in the quench. Until the blade drops below the critical temperature, no conversion will begin, so the internal changes made at 1450F will still be in effect if the blade cools for a short time to 1400F. It is in the drop from critical to below 1000F that things get serious.

Someone with a good oven and a Rc tester should do us a favor. Place five pieces of 1/8" 1095 ( marked 1,2,4,5) in the oven and soak at 1475F for 10 minutes. Remove #1 and quench in 120F fast oil, then do #2, and then #3, etc.. Test all for Rc and see if there is any difference as quenched. BTW, the door should be closed between quenches, and the quench oil should be of sufficient volume to prevent too much rise in temp. After these initial Rc tests, temper at 450F twice, then Rc test again.
My hypothesis is that there will be little or no difference.

 

[Tait]

I hope somebody tries this - it would be easy enough to do and use about $2 worth of steel.

Idon't have any 1095, and I'm not 100% sure my hardness tester reads perfectly, so I won't be able to do it.

A few months ago, I ran some experiments with A2. Although I didn't do enough pieces to be convincing in a statistical sense, there was no difference evident in hardness based on order removed from kiln.

 

[Bruce Culberson]

expand my steel selection into O1, 3v, 154,

3V & 154? Dude... are you switching over to the Dark Side?

Straightening and normalizing are things I often combine into the final stages just before heat treat, where I will run a blade up to heat and straighten, let air cool to black, and repeat so I get a blade that "wants" to be straight and has 3-4 normalizing cycles. I ave no idea how I want to run this process with a kiln.....

You could still use your forge for straightening & normalizing, then use the kiln for precision austinizing. That way you would only be half cheating

We should get Rob from knifemaker.ca to chime in since he offers heat treating services (that's where I...um...send my stainless blades for heat treating). I'll send him a link to this thread.

Bruce

 

[koyote]

3V & 154? Dude... are you switching over to the Dark Side?

Realistically, some form of stainless option is becoming necessary for some of my customers. I have some "when you get to it" orders for a rafting knife design I roughed out for someone on lc bar stock once to show some ideas, some saltwater guys have some wants...

The 3v has been requested a few times. My suspicion is that for the types of knives involved, running my 5160 will work out just fine. But I'm more than happy to give 3v a shot and compare them. It's expensive, and if it's anywhere near as hard to do final handrubbing on as people report, it'll just double the price of a given knife (5160 is bad enough). But I'll try it, it sounds interesting.

O1 and even 1095 will be much better with a kiln- I don't work O1 currently because I know very well that I can't make it do anything more than a decent stick of 1080 using my forge setup.

Of course, there's other stuff, like proper annealing of some of the whacky steels I get in from time to time.

But these things are pricey, I just want to make sure I got myself set up for this.

 

[Bruce Culberson]

Realistically, some form of stainless option is becoming necessary

I try to resist and say No, but about 10% of the knives I make are stainless.

With stainless you put the steel to the belt - no sparks fly, the belt gets dull, and very little steel gets ground off

Seriously though I recommend using sharp ceramic belts.

 

[KnifeMaker.ca]

Hi all

We do multiple baldes in the kiln quite frequently and, of course, with stainless its no problem at all. We do up to six at a time because thats generally about what our quech plates will hold comfortably. We hardness test every blade that leaves here (unless asked not to) and have seen no significant difference from first to last. (It's fairly common to see a +/- 0.5 range even on a single blade). We try not to imply undue accuracy.

We also do multiples for oil quench blades, but I prefer to keep that to 4 max, just because I don't want it to drop below critical. We quench one at a time with Marilyn closing the door as I turn the blade to the bucket (5 gallon, Houghton Quench K). I continue stabbing and slicing agitation (not side to side) for 60 to 90 seconds depending on blade thickness. By the time I'm ready for the next blade the oven has recovered to temperature. I'm not convinced the blade has fully recovered yet, because the handle may still be somewhat darker, but the blade end - deeper in the oven is less (or not) affected.

We recently did many batches of O1 Ulus and the maker wanted visible diamond penetrator marks. All were equal (+/- 0.5) in the blade area. Some of the handle ends were indeed up to 2 points softer.

I do as little 1095 as possible and do them as singles because Heat Treating 1095 just sucks! :grumpy: No point asking for more trouble than comes anyway.

Rob!