Grinding after HT

Remy

Remy

Well-Known Member
I did things a bit differently than my usual this weekend and thought I'd discuss it here since some aspects of it surprised me.

I was grinding a fairly long blade from 1/8" 1084 and wanted to avoid having it bend on me during grinding and heat treating. The obvious solution was to profile it, drill everything needed then heat treat it before grinding. I'd never done things this way and expected a real hassle doing the actual grinding, probably wearing out a belt or two putting in bevels...

The profiling, drilling and heat treating went off without anything worth noting. I had 36 grit and 60 grit 984f cubitron II belts that I'd used to grind a 3/16" thick blade of similar size already, and that I'd used to profile this one. I sort of figured it would make a good test of how well the 984's hold up but didn't actually expect the results i got.

While I had to be careful of heat, the grinding didn't really seem that bad. The wear on the belts seemed fairly normal, if anything, and while it took significantly longer it wasn't a painful process. Ok, so it was painful, but that's because the spine corners were sharp and I slipped and managed to slice my index finger while grinding, youch. I'd say it took about twice as long to grind, but the wear on the belts seemed about the same as if I'd ground before HT. The extra grinding time is countered by not having the two step grinding process, I didn't have to start again cleaning up decarb and such after HT, worry about messing up my lines established before HT.... I'd say on balance it took a bit more time but was less work, if that makes sense. I can definitely see the appeal of this method for many knies and it makes more sense now.

Is this kind of belt activity normal or just something the 984's are particularly good at? I know a lot of folks that grind post ht use Blaze too.

Are some steels significantly harder or easier to do this with? I mean in comparison to their pre-ht properties. For example, if for argument's sake we say it is 75% longer to grind 1084 post HT and causes 10% more belt wear, are those numbers fairly consistent or would some other steel show 100% longer or 50% longer and different wear rate changes?
 
The steel that you used doesn't have much in the way of carbides and what it does is mostly cementite which is relatively soft as far as carbides go. I think that if you tried something like D2 or S30V then you would really notice the difference between grinding in the annealed state or after hardening and tempering, especially if you tempered for secondary hardening which will produce harder carbides in steels that you are able to use that procedure with.

Doug
 
Gotcha. Where does CPM154 fall in the carbide hardness range? I found tons of info about carbide size and distribution, but nothing on type/hardness. Assume a Paul Bos heat treat, since that's where I'm planning to send it.

I ask because I have a stack of profiled blades that I'd love to work with now and then, but I hate to send them out a couple at a time, the cost is prohibitive. If it's practical I'd rather drill the holes, grind the surface to a reasonable base point and then send them out without bevels. Then I can do the rest of it one or two at a time without needing to wait on a large batch to make sending them out worth while. I figure taking the sides to 220 or 320 will save me time afterward. I don't leave much in the way of visible flats on the blades I've got profiled, but it's got to be easier to get that baseline established beforehand.

ETA:
For the technical minded and picky. I understand that the blade still bent the same while I was grinding it, assuming I put sufficient pressure on it. The key was that it didn't set due to the HT. :happy: I know this is a pet peeve of some folks, and I do like to keep the science accurate.
 
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I only make liner locking blades, but I do the grinding after heat treat. I have just started to use the 984f belts. I think they are the best out there. I have blaze belts on hand in the same grit size I use and they give me about 1/3 the results. Frank
 
Go to www.trugrit.com, they have a data sheet for CPM154. They list it's grindability as better than D2 or even regular 154 but it's not contrasted against any simpler steels such as 1084. You will see that it does have a secondary hardening point though, except at 2000 degrees austinizing temperature, it's not as hard as tempering at 400 degrees, when subjected to cryotreatment. It requires a rather long soak time at temperature for austinizing which will mean that you will need a heat treating oven to do this in and a tank of liquid nitrogen for cryotreatment, if you want to go that route.

Doug
 
Doug, I'm sending them out to Paul Bos heat treating, I'm just not setup to do it myself and even if I had the equipment I think I'd send it out for now. That created the issue actually. Between shipping and the pricing schedule it makes sense to send out a decent batch of blades, not one or two at a time. It would make my life easier if I had all of them heat treated prior to doing bevels since that way I can work on them at my leisure and not have to finish a bunch before sending them out.

From what you and Frank said, and from what I've read, I'm going to give it a try. So now I have to get a bunch of holes drilled, cleanup the flats and get it all packaged up. Could be worse I guess. To me that's the boring part so I'll get that all out of the way and when they come back it'll be the part I enjoy. I think of it as watching the knife come out of the steel.
 
I understand you. To me, it's the grinding that is boring. I love shaping the steel with a hammer. I sometimes have to tape notes to the computer reminding myself that I need to get down into the basement to grind or finish a knife.

Doug
 
Remy,
i profile and put a bevel on the edge before HT. batch them at about 20 + blades and off too Paul Bos.

Cpm-154 does well at 58-60 Rc Or you can call and talk with the Paul that runs it now and discuss it with him?

Laurence

Www.rhinoknives.com
 
Good point, I had forgotten about doing a partial bevel in to help the belt with that start. I'm thinking 60RC, since none of the blades are meant to be chopper types or rough use designs. I'll be giving them a call before sending in but I think I've got that part pretty well figured out. :)
 
I started grinding after HT a while back, mostly 1084 and 01. I didn't notice that much difference other than I had to dip the blade more often to keep it cool while grinding (I have a 2x42). I mainly use Norton Ceramic belts and Gators.

Then I got the bright idea to try some CPM 154 for a couple Kitchen sets that I was going to give away as Christmas presents. The sets consisted of a cleaver, 8" chef knife and a paring knife in a custom made knife block.

I was in a bit of a rush because some materials got delayed so I figured I'd just rough grind the profiles and send them out to HT and grind them afterwards I just hit the flats a little and to be honest, I'm not sure I got all the mill scale off. That stuff was hard! I sent these out to Texas Knife due to their quick turnaround. I had them Cryo'd as well. I think they treat them in the 57 to 59 range.

Anyway, when they got back I took one of the cleavers and put on a fresh Norton 60 grit belt and went to town....or so I thought. The Nortons hardly touched that stuff! I tried the Chef knives and the paring knives and had the same result. Lots of grinding but little progress. I actually had to set them aside while I ordered some Blaze belts. Once they arrived I went about trying to grind them again. They did make a difference, but it still took over an hour to grind the Chef knife and paring knives! I'm not sure how long it took to grind the Cleavers as I just would do them in shifts. In fact, it got so bad I actually thought about throwing all of it in the scrap pile, but then realized how much time and money I already had invested in these Kitchen sets.

I learned two important lessons. 1. Grind CPM 154 (and probably most stainless) prior to heat treat. 2. Order CPM 154 already surface ground. That mill scale is some unbelievably hard stuff!!!

I love the CPM 154 after I finally got it finished, but man what a journey it was. In fact, I still have one more set that I haven't finished. Every time I look at it, I just think I'm not ready for that kind of abuse any time soon. Probably after I get a 2x72 I'll tackle them.
 
This was just the type of thread I was looking for... I've got 2 kitchen knives in the works, both 1/8" 440C from Aldo, an 8" chef and a 7" santoku. And I'm torn on grinding them now on my 2x42, or sending out for HT and grinding after. Thinking about the volumetric amount of steel that needs to be removed from these 2" deep blades, is really making me want to grind them NOW, and then send off for HT. At least rough ground...
 
on the 2x42 I'd at least get the bevels halfway done before sending them out, not the best machine for post ht grinding. It's FAST but low HP, so you'd just generate a lot of heat and not get anywhere. I used to do a little post HT grinding to fine tune things on 1080 and 1084 and it always took forever and was a struggle to not overheat things. I'd hate to be doing any serious grinding with it. No comparison with the variable speed 2x72.
 
Good info as well. A bigger "real" grinder is certainly on my wish list... but you know how that goes.... :( Finish paying alimony, get some debt eliminated, stop going 'out' so much and sell some knives... one of these days I'll have that variable 2x72! :)
 
Yup, step by step, just keep plugging away at it. I figured I'd give you the heads up on the 2x42 though. It's not that you couldn't do it, but it's a real struggle on that machine. If you decide to give it a try on one, try the blaze belts. From the looks of it they're the best option in 2x42 for the job. If someone had them in 2x42 I'd suggest the cubitron II's 984F, but I don't think they're available in the smaller size normally.
 
Ok, got the steel back and did some grinding. no problems at all. I started with a 36 grit 984f belt and then a 60 grit, quick and easy grinding. I removed the 60 grit grind lines with a 120 grit j-flex but not entirely and have stopped there for the day. I will start back up with gators tomorrow to finish the blade and get it ready for a handle. So far, no issues, I'm very happy with how it works. It's also a nice feeling knowing that what I see is what I get, no need to go back to the grinder later and clean up, I can grind it to exactly where I want it and be done.

I can't recommend it for everyone, but if you're using 3/16 or thinner stock it's probably worth trying. Just make sure you have good belts, I can't imagine what this would be like without the proper belts.
 
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