Minimum Heat Treat Thickness?

[Jason McEntee]

Hello,

 

Before I start grinding, I want to make sure that I don't remove too much material and end up with a warped blade after heat treat. Through searching here, I've come across the "thickness of a dime" a few times.

I send out for heat treat, as I don't have the means to do it myself. My previous project was triple normalized, oil quenched, then triple tempered.

This current blank (only the second one I've made, by stock removal) is 1075 steel, 3/16" thick, geared toward being a slicer. How thick should I leave it to ensure it remains straight throughout the heat treat process?

My apologies if this has been asked, but my search results were somewhat vague. --Jason

 

[Jerrod Miller]

There are actually a lot of variables that will lead to warping, most notably:

• Residual stresses
• Uneven heating
• Uneven cooling
• Creep (the part sagging under its own weight)

The great thing about leaving things thicker is that it adds thermal mass, thereby reducing the effects of the last 3. Proper normalizing/annealing takes care of the first. If your heat treater has really good control of the process 3/16 shouldn't be a problem. I've personally seen thicker stuff warp while heating in a forge with a single side-blast burner. Not really a direct answer to your question, but hopefully this gets you thinking about what is going on and where warps come from. I'd recommend talking to your heat treat provider and see what they suggest for thicknesses based on what they have successfully done in the past. And keep in mind that many (most, maybe?) swords warp upon quench, but subsequently get straightened with tempering (lots of posts about that on the forum).

[Doug Lester]

Some of the makers who make thin blades, like kitchen knives, will do their grinding after they are hardened and tempered. You do have to make sure that you don't overheat the steel while grinding. Grind holding the blade with bare hands only so that you'll feel the heat long before it gets hot enough to over draw the temper and dip in water often to cool it down. Speaking of water, 1075 might do better quenched in water or brine if your heat treater does not have access to a fast quenching commercial oil.

 

Doug

[Karim]

dont think you can speak of ensuring... But sins you are paying for the HT why not give them a call and ask ?

[GBrackett]

I regularly take my edge down to the thickness of a dime. Then after HT grind the rest dipping in water after each pass of the grinder.

 

I also use Parks 50 as my quenchant.

[Gabriel James]

i think you could easily grind the blade to half that thickness and still be ok. 3/16 is pretty thick....

[Jason McEntee]

Thanks guys, very helpful.

[Robert D.]

I once made a Kitchen knife for the girlfriend, that I forged out, then ground clean, and was probably at about half the thickness of a dime when I went to heat treat it at the edge, and about a dimes thickness at the spine.

Following advice from Alan, I started doing all my normalization and hardening heats in a pipe baffle ( I use a charcoal forge ) After the standard triple normalization and single hardening the blade developed the ever so slight warp in the first inch or so of the blade, Which was easily corrected during the temper cycles.

granted, I have only been doing this stuff for a little over a year, but the two things I have found to be the biggest causes for me with warping, is heat control and normalization processes, since you are sending out for heat treat, as long as they know what steel they are working with I would expect a respectable company to have these things dialed in quite well.

[Matthew Parkinson]

in respect to how thin.. I have found it is a bit of a ratio, the thickness the edge can be Vs the thickness or the spine as well as the overall cross section .

IE a chef knife at 0.090 spine can be 0.007 might be fine but a hollow ground hunter with a 0.125 spine and a 0.020 edge will ripple and warp all to hell as the edge heats. the rule of thumb of the thickness of dime at the edge is in general a pretty guide line for most flat ground blades as that thickness some warping can even be ground out.

MP

[Jason McEntee]

Thanks Matthew. I very much enjoyed watching you work in FIF S1/EP1, by the way. Beautiful work; you deserved the win.

[Jason McEntee]

I think I'm in business. Never done a flat grind before; this was a learn as I go experience. And, it turns out my heat treat guy includes any straightening if needed, so this should work out well.

 

Edited July 19, 2016 by Jason McEntee