Heat Treat Then Start the Grind?

I've done both.
On larger and thicker blades, I'll typically do a fair portion of grinding before heat treat. On smaller and especially thinner knives (1/8" or less) I'll usually heat treat first, especially if I'm doing a scandi grind. That said, I will often bevel the corners pre-heat treat. I also make sure that I use sharp belts and dip on every pass or two if grinding after tempering, so that I don't raise the temp of the steel above tempering temps.

FWIW, I've had blades warp when grinding before OR after, just as I've had blades stay perfectly straight ground before or after. Thinner blades are easier to straighten unground, if needed, IMO.
 
I only grind after HT. I don't bother doing anything besides profiling and drilling before.

Soft steel gets gouged and smears too much. If I grind before HT, I'll just have to do it again (bevels and flats) post HT.

Some prefer to try and remove scale first, but I'd much rather clean off scale post HT and not chase deep scratches all day.

This saves me approx 50% time, frustration, and belts.
 
Mitchell Knives said:
95% of my knives are ground after heat treat.

If I'm going for a hamon, I'll obviously grind the blade prior to heat treat.

Grinding after heat treat greatly reduces any chance of warp, and saves time IMO.

Keeping the blade cool during the grinding process is easier than most people think.
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Hey guys, what's the best way to make a hammon? I know certain steels show hammon line better than others. I've read of the clay way, when you quench, you quench the clay too?
 
Joe Watson said:
I only grind after HT. I don't bother doing anything besides profiling and drilling before.

Soft steel gets gouged and smears too much. If I grind before HT, I'll just have to do it again (bevels and flats) post HT.

Some prefer to try and remove scale first, but I'd much rather clean off scale post HT and not chase deep scratches all day.

This saves me approx 50% time, frustration, and belts.
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can you elaborate on saving belts when grinding post ht? Thanks
 
You save belts by not doing repeat work and not having the chase as many scratches. With good ceramic belts designed for steel it's not really that much tougher to grind post ht so it works out. The exact belts you use shifts but I've found that I use fewer as well.

I find that I use more 36 grit belts and more 60 grit, but fewer of everything else. If I grind pre-ht I have to take it to a decent grit beforehand, then use the same grit again afterward and then work my way to a final finish anyway. By grinding post HT I find I can get much closer to the final grind using a coarser belt and then basically just refine the finish while fine tuning the exact lines. It's more controllable. With the ceramics you don't wear out belts THAT much faster on hardened than unhardened, to a great extent it seems to be just a matter of how much metal each belt will remove, hard or not.
 
Remyrw said:
You save belts by not doing repeat work and not having the chase as many scratches. With good ceramic belts designed for steel it's not really that much tougher to grind post ht so it works out. The exact belts you use shifts but I've found that I use fewer as well.

I find that I use more 36 grit belts and more 60 grit, but fewer of everything else. If I grind pre-ht I have to take it to a decent grit beforehand, then use the same grit again afterward and then work my way to a final finish anyway. By grinding post HT I find I can get much closer to the final grind using a coarser belt and then basically just refine the finish while fine tuning the exact lines. It's more controllable. With the ceramics you don't wear out belts THAT much faster on hardened than unhardened, to a great extent it seems to be just a matter of how much metal each belt will remove, hard or not.
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Thanks for the explanation.
 
I just started doing all my grinding post HT and I'm going to stick with it. Even though the steel is harder to grind, you have to consider that when you grind pre HT you need to take your blade up to 120 grit to avoid stress risers. Then when you get it back from HT you have to start at about 80 grit and work your way up to the final finish. It always bothered me when I did pre HT grinding that I basically had to grind the knife twice. It takes alot of time and in most cases just isn't worth it to me.

If you use ceramic belts, grinding hardened steel is not very difficult. Even 3V at 62 post HT isn't that bad. Grinding post HT also eliminates the chances of warpage and for me its nice to get started on a knife and finish it in a day or two versus getting it started then having to send it off for HT and wait 3 weeks. Another bonus is the savings in shipping if you use a water jet. If you are getting a big batch done, having them shipped directly to HT from the water jet saves alot of money in shipping costs, especially when you ship with insurance.

With the exception of 10V and a few other super high wear steels I'm going to be working with in the near future I don't see myself going back to grinding pre HT.
 
I will add one comment to the subject......safety.

The amount of sparks and the heat of those sparks created when grinding hardened steel is huge compared to grinding soft steel. Make sure you have all combustible materials far out of the area and a good spark trap of some sort. Even a 5 gallon bucket of water below the grinder is better than nothing. Also, remember that the sparks will be going back behind the grinder as well as toward the floor.
 
bladsmth said:
I will add one comment to the subject......safety.

The amount of sparks and the heat of those sparks created when grinding hardened steel is huge compared to grinding soft steel. Make sure you have all combustible materials far out of the area and a good spark trap of some sort. Even a 5 gallon bucket of water below the grinder is better than nothing. Also, remember that the sparks will be going back behind the grinder as well as toward the floor.
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One other point I would like to add to the safety notes that Stacy had mentioned.

NEVER grind steel & Aluminum without cleaning your collector and sweeping up in between.
The combo makes a form of Thermite. Spelling? A high temp burning explosive that was used by the military that will burn your shop and you to the ground in seconds.
I am not sure what is required to ignite it or if the sparks from harden steel will do it? But I don't want to find out! I have been told that water on burning Thermite makes it burn hotter.
 
Lots of interesting info in this thread! I've been debating for a long time about whether I should be grinding post heat-treat, and this thread has convinced me to try it!

Thanks for the safety heads-up on the grinder sparks Stacey, that is not a point that I had considered!
 
Quick question to all of you who are grinding after heat-treat: what steel are you grinding?

It just dawned on me that one benefit of secondary hardening steels like CPM3V is their high temper temperature, which would make it much harder to ruin the heat-treat while grinding. You would need to get the steel to 1000ºF to ruin the temper, as opposed to only 400ºF or so for most other steels.

I realize that it's hard to get an entire blade even up to 400ºF when grinding (provided you're careful) but I've always wondered what the temperature of the steel is at the face that's touching the belt... Given that heat is always diffusing and that steel is a relatively poor conductor of heat, if the back of the blade is 200ºF that means the front face has to be significantly higher. That the main reasoning for why I've shied away from grinding after heat-treat in the past.
 
aarongough said:
Quick question to all of you who are grinding after heat-treat: what steel are you grinding?

It just dawned on me that one benefit of secondary hardening steels like CPM3V is their high temper temperature, which would make it much harder to ruin the heat-treat while grinding. You would need to get the steel to 1000ºF to ruin the temper, as opposed to only 400ºF or so for most other steels.

I realize that it's hard to get an entire blade even up to 400ºF when grinding (provided you're careful) but I've always wondered what the temperature of the steel is at the face that's touching the belt... Given that heat is always diffusing and that steel is a relatively poor conductor of heat, if the back of the blade is 200ºF that means the front face has to be significantly higher. That the main reasoning for why I've shied away from grinding after heat-treat in the past.
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I have thought about the actual temperature of the facing side too while grinding HTed steel?
I keep the blade moving and really only get one maybe two knives per belt. I make large Culinary knives mostly.

A fresh Ceramic belt hardly makes any heat. As soon as things seem to be heating up quickly I then use that belt for profiling and other chores for the life of the grit.

I use CPM-154 & CPM-S35VN along with some 440C which are all air hardening with a last temper of appox, 350-400 degrees. I haven't used the CPM3V so I don't know anything about its temp ranges?
 
aarongough said:
Quick question to all of you who are grinding after heat-treat: what steel are you grinding?
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52100 is what I'm working with right now Aaron. Usually 1/8" or 5/32" stock. All bevel grinding is done post heat treat. Also, I grind free hand which allows me to feel with my fingers for any heat build up. And believe me, your fingers will let you know if you've stayed at the belt too long. I make ONE pass using moderate to heavy pressure and IMMEDIATELY dunk. I use ceramic belts up to 120 grit, so water all over the knife isn't an issue for those belts. I quickly learned to have my grind nearly complete at 120 grit. That way when I move up in grit, I can slow down my grinder if necessary and use lighter pressure which also helps to keep down the heat. At that point you're not removing much metal anyway. Just smoothing and refining the grind. This has all become routine for me now and I don't even think about it. To my knowledge, I've not had any issues thus far exceeding temper temps using this method.
 
It just depends. For small-to-medium blades that will have a machine finish (belt, scotchbrite, stonewash, etc) there's really no big reason to grind before HT. If you're using plates to quench, that will be a big factor, too. Plates are just going to cause problems if you've got a blade with FFG's, distal tapers and a tapered tang.

I agree that grinding hard steel is easier in a way... sometimes slower is better, mistake-wise.

On the other hand, I'd rather not grind a 10" chopper hard, and there's no way on earth you can convince me to hand-sand a hardened blade of CPM-154, CPM-3V or Elmax to 2000 grit... so obviously that's all going to be done pre-HT when it's called for. Interestingly, the only fully-ground blades I've had warpage issues with were O1. (I don't do hollows; my HT is done by Peters')

When grinding or even sharpening hard steel, you don't have to get the whole blade hot - or even warm to the touch - to foul up the temper at the edge. Take a piece of scrap and try it yourself... it only takes a second to turn a thin tip or edge completely blue if you lean in too hard. Damage to temper can occur before oxide colors form, as well... it depends on the alloy. Google Roman Landes' experiments in this area for more info.

That's why the guys who grind post-HT talk about doing one smooth pass, cool, one pass, cool, etc. If you can feel the back of the blade getting hot in your fingers, it's probably way too hot at the edge.

A skilled independent maker is pretty likely to understand this... the guy setting up a robot, or an hourly-wage-worker at a factory (both of whom have quotas to fill) may not know or care. I suspect that's a big factor in the stories about "inconsistent HT" in factory/mid-tech knives like those mentioned earlier.
 
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Thanks for the responses guys! I like the idea of grinding post heat-treat, but given that I don't do hollow grinds and my blades are fairly stout (compared to kitchen knives at least) perhaps it's not necessary for the moment. I'd like to look at it in the future, but I think perhaps a wet grinding setup would be what I would like to take away the issue of potentially ruined tempers.

I'll try one at some point anyway, just to see how I like it. Given that so many makers do it and like it I think it's worth at least looking at.
 
james terrio said:
A skilled independent maker is pretty likely to understand this... the guy setting up a robot, or an hourly-wage-worker at a factory (both of whom have quotas to fill) may not know or care. I suspect that's a big factor in the stories about "inconsistent HT" in factory/mid-tech knives like those mentioned earlier.
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I'm glad you mentioned that James. On the first page of this thread, Bark River Knives was mentioned. First let me say, that I own a couple Bark River knives and enjoy using them. There has been much discussion, right here on BF, about some of these knives having issues with heat treat. I don't personally think it's the heat treat at all....or the knives being ground too thin. They are considered "semi-custom production knives" with, IMO, an emphasis on production. And although Mr. Stewart is not likely to ever admit it, I'm convinced these occasional "bad knives" are caused by exceeding temper temps when grinding. I know they grind knives post heat treat and I've watched video of them doing it. In the video, a worker made probably 5 passes before cooling the blade and I think that it can sometimes lead to problems for the end user. As you said though, for those of us not trying to produce 1000's of blades a year, we can pay closer attention and put more care into assuring that this doesn't happen.
 
Adam Buttry said:
There has been much discussion, right here on BF, about some of these knives having issues with heat treat. I don't personally think it's the heat treat at all....or the knives being ground too thin.
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I don't want to speak for them or tell tales out of class, but I can say for a fact that I know who does their HT... and I'm 99.9% sure, that's not the problem. ;)
 
james terrio said:
When grinding or even sharpening hard steel, you don't have to get the whole blade hot - or even warm to the touch - to foul up the temper at the edge. Take a piece of scrap and try it yourself... it only takes a second to turn a thin tip or edge completely blue if you lean in too hard. Damage to temper can occur before oxide colors form, as well... it depends on the alloy. Google Roman Landes' experiments in this area for more info.

That's why the guys who grind post-HT talk about doing one smooth pass, cool, one pass, cool, etc. If you can feel the back of the blade getting hot in your fingers, it's probably way too hot at the edge.

A skilled independent maker is pretty likely to understand this... the guy setting up a robot, or an hourly-wage-worker at a factory (both of whom have quotas to fill) may not know or care. I suspect that's a big factor in the stories about "inconsistent HT" in factory/mid-tech knives like those mentioned earlier.
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Yes sir! I agree completely. Any of us who have burned a tip should get this, used to happen all the time to me on the Craftsman!

Still many variables in how fast heat builds up, material, its thickness, abrasive type and condition, platen types and temps... you just have to figure it out.

As for the 3-V temps, I still don't want it getting warm. There are ways to temper with high or lower heat depending on what you want out of the steel.

Someday, I'll be able to grind like Ray Ennis, I hope:http://www.youtube.com/watch?v=kvlKfzW12d0&list=PL2A1405CB597714D4
 
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