Reasons for heat treating before/after grinding main bevels

DrubieG__MimicKnives

DrubieG__MimicKnives

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I noticed in seeing conversations and watching videos of makers, that some people heat treat their blades before they grind the majority of their main bevels. Others do it after. I’m still new to this stuff and have somewhat of an idea about the whys… but I don’t want to leave that in abstraction.

Can some of you makers weigh in on the reasons you do one or the other?
 
Hand sanding hardened steel is a lot harder then soft steel, also you don't have to worry about ruining the HT.

Grinding post HT gives better grind lines and there is no warping during HT.
Altho I never had any warping of ground blades, even thin blades.
Sanding stones make "hand sanding" hardened steel easier then sandpaper
 
It depends on the alloy for me.

I grind 90% of my blades pre HT, as I primarily use high wear resistant steels, like S90V, 10V, etc. Grinding and finishing these steels post-HT is an exercise in futility. I use an outside heat treat service that reduces my anxiety over warped blades or bacon edges (even at .010 edge thickness.)

the other 10% are steels such as AEBL that are easier to grind and finish post HT and actually seem to act "better" (less gummy) while grinding post HT.
 
When grinding post HT do you always have to use a water sprayer or something like dip the blade in water after each pass? Maybe some steels are more susceptible to being further tempered when grinding hot?
 
pro-tip...add a few drops of dish soap to the water, will diffuse surface tension and allow metal dust to settle to the bottom easier.
 
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A misting/spray setup is a great advantage for any knife shop. Dipping every pass also works.

You should always be aware not to heat the steel over 400°F to avoid ruining the temper. That is a LOT hotter than "too hot to hold" if you grind bare-handed, but when using grinding magnets, you can easily get it too hot.

If you use steels with a high temper range around 900-1000°F you can eliminate the concern over damaging the temper. Depending on the blade use and steel type this may be an option if no cooling method is available.
 
Spoken from somebody who makes only a dozen or so knives per year - it depends on the thickness of the blade. Anything <.125" I'll for sure grind post HT, thicker than 1/8" it's sorta your choice even with AEB-L which is known for being "warpy". I ground dry belt for several years. As navman says you dip in water each pass and keep the blade moving across the belt - don't linger at one spot. Not too much of a problem keeping blade from turning color.

Lately I've started using a mister system to put a water mist on the blade while grinding - that works really good. Allows a bit faster bevel grinding without overheating. I'll still dip in water after several passes because a blade can still get that nasty blue color, especially the tip. With the footswitch I added to mister I really wish I'd had the mister setup years ago. If you've already got an air compressor a nice mister system can be setup around $50 including the footswitch. The footswitch allows the mist only as the blade is in contact with belt so no so much wasted water and not near so messy.

I don't think the type of steel matters when grinding post-HT - heat is created when grinding and if any portion of the blade turns brown (light brown around 400°F) while grinding the HT is affected. If you see a dark blue, HT is ruined as dark blue is over 500°F. The problem of overheating isn't much of a problem until the bevel starts getting down to the thin edge. A thin edge can overheat so easy. The trick is to grind light pressure, move quickly across a "sharp" belt, and dip in water every pass.

navman, good time, but a few drops of what? {g}

Stacy, you got your post in as I was hitting "post". Good idea on using a high temperature temper steel. If it's tempered at 1,000°F not much danger of overheating while grinding bevels.
 
I'd like the experts to chime in here. It seems you can get a more 'active' hamon, if you grind what you can pre-heat treat.
 
I do only stainless now. Grind after HT and accept all nerv training, thru suffering working with it, as just another day (S90V, M398 mostly). I HT myself so to avoid warping, plate quench is dominant and achieves uniform hardening. Warning: belt life is from 3:1 to 5:1 per knife. So, think it thru.
 
Ken H> said:
Is that from 3 belts to 1 knife? All the same grit? or going from larger grit to smaller grit?
Click to expand...
Grinding carbide monsters before HT will save you belts 3:1. With one 40 grit I could grind pre HT 3 knives, while grinding post HT one belt barely makes it. Then goes 80, 120, etc...
On a S90V 12cm blade I use 1x40, 0.7x80, 1x120, after that ironing up with Trizacts. If I don't feel right and want to go faster it's 2x40, 1x80 and 2x120 and inevitable ironing with Trizact. If after that I have some 14C28N to work with it seems like wood, not steel. S90V to 14C28N is 5-8:1 in belts. Diamonds could help but I don't have a third kidney to sell.
 
I have done some testing on carbon steel,
Depending on the HT regimen, decarb from my process can be up to 15 thou per side.
Based on my testing, 2-3mm thick steel I grind after HT, over that thickness an obtuse angle to 1mm either side of CL and then grind rest after.

I an only a beginner and made a handfull of knives but those are my observations to date.
 
To grind or not grind pre heat treat depends on the steel.

I’ve had blade that are unground still warp in heat treat.

If I’m using a higher alloy steel with a decent amount of vanadium in it I’ll grind about half my bevel or more depending on the knife the steel and the stock thickness.

Pre heat treat grinding saves a lot of time vs grinding post heat treat and a decent amount of abrasives. I can grind a few magnacut blades post heat treat with one 60 grit belt before it starts to dull beyond what is efficient to use. However if I pre heat treat grind with that same belt can do 15-20 blades maybe.
 
A misting/spray setup is a great advantage for any knife shop. Dipping every pass also works.

You will always have to be aware not to heat the steel over 400°F to avoid ruining the temper. That is a LOT hotter than "too hot to hold" if you grind bare-handed, but when using grinding magnets, you can easily get it too hot.

If you use steels with a high temper range around 900-1000°F you can eliminate the concern over damaging the temperpost-HT. Depending on the blade use and steel type this may be an option if no cooling method is available.
 
Stacy E. Apelt - Bladesmith said:
If you use steels with a high temper range around 900-1000°F you can eliminate the concern over damaging the temperpost-HT. Depending on the blade use and steel type this may be an option if no cooling method is available.
Click to expand...
I thought I'd replied to this yesterday - but that's a GREAT idea. If the steel is tempered at °F not much danger of overheating during grinding.
 
Stacy E. Apelt - Bladesmith said:
A misting/spray setup is a great advantage for any knife shop. Dipping every pass also works.

You will always have to be aware not to heat the steel over 400°F to avoid ruining the temper. That is a LOT hotter than "too hot to hold" if you grind bare-handed, but when using grinding magnets, you can easily get it too hot.

If you use steels with a high temper range around 900-1000°F you can eliminate the concern over damaging the temperpost-HT. Depending on the blade use and steel type this may be an option if no cooling method is available.
Click to expand...
Using the lower tempering range 300-450 improves toughness and corrosion resistance.
 
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