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View Full Version : Grindig after HT, pros and cons?



Nylund knives
05-03-2010, 10:29 AM
Hi,

I know some of you are grinding your bevels after ht. I've heard it's quite common for folder makers who usually make smaller blades.

I'm a scandi maker and make quite small blades compared to you guys. Most of my blades are 3''-4'' long.

I think I could save me some trouble with decarb layers if I do all the grinding after ht.

How much more wear on the belt will I notice when grinding after ht?
How many blades can I rough grind with a 36 grit belt?

I use mostly CPM steels...



Regards
Jakob

EdCaffreyMS
05-03-2010, 01:10 PM
Jakob,

The reason most folks that grind after heat treating is to prevent warping. Thinner cross sections of steel are much more prone to warping. If your using CPM stainless steels, I would think you could achieve the same thing by plate quenching.

OK, now to your questions....

If your using premium quality belts, you will notice more of a difference in how the belt grinds, more so than you will notice that the belt wears. I do a lot of after heat treat grinding with 50 grit "Blaze" belts, and am very pleased with the durability I get from them. With 36 grit, your likely going to notice a bit faster wear, simply because the larger grit will get knocked off the belt more easily when using it on hardened blades.

The question about how many blades you can rough grind with a 36 grit belt is a loaded question....that's going to depend a many factors....and to even attempt an answer would just be a shot in the dark.

I know folks have their own favorite progression of belts, but if I may make a suggestion......try using a 50 or 60 grit belt as your heavy grit, it will give you the ability to go to nearly finished dimensions, and then you can jump straight to a 400 grit belt and be done. I've been doing that for a number of years now, and it routinely cuts 45 mins to and hour off the time it would take me to finish grind a blade if I used 36 grit and then progressed to say 80, 120, 220, 400.

James Terrio
05-03-2010, 02:19 PM
I know folks have their own favorite progression of belts, but if I may make a suggestion......try using a 50 or 60 grit belt as your heavy grit, it will give you the ability to go to nearly finished dimensions, and then you can jump straight to a 400 grit belt and be done.

That sounds pretty interesting, I love the idea of saving time. What brand belts do you like for your 400 grit step?

Nylund knives
05-03-2010, 02:38 PM
Jakob,

The reason most folks that grind after heat treating is to prevent warping. Thinner cross sections of steel are much more prone to warping. If your using CPM stainless steels, I would think you could achieve the same thing by plate quenching.

OK, now to your questions....

If your using premium quality belts, you will notice more of a difference in how the belt grinds, more so than you will notice that the belt wears. I do a lot of after heat treat grinding with 50 grit "Blaze" belts, and am very pleased with the durability I get from them. With 36 grit, your likely going to notice a bit faster wear, simply because the larger grit will get knocked off the belt more easily when using it on hardened blades.

The question about how many blades you can rough grind with a 36 grit belt is a loaded question....that's going to depend a many factors....and to even attempt an answer would just be a shot in the dark.

I know folks have their own favorite progression of belts, but if I may make a suggestion......try using a 50 or 60 grit belt as your heavy grit, it will give you the ability to go to nearly finished dimensions, and then you can jump straight to a 400 grit belt and be done. I've been doing that for a number of years now, and it routinely cuts 45 mins to and hour off the time it would take me to finish grind a blade if I used 36 grit and then progressed to say 80, 120, 220, 400.

Thank you for your answer Ed!

Do you think that I would be better using high quality (ceramic?) 50/60 grits belt instead for the courser 36 or even 24 grit belts when grinding after ht?

Usually I use 36, 80, 320, 900 or just 60,320, 900 both metods are as fast as the other.

I'm using a big oven for ht and makes a lot of blades at a time so my heat treating have to be efficiant. I could send them away but I would like to figure out a way that works for me, my oven and the type of blades I make. I've tested many different ways...

I've heard of a guy who clamps blades with the same profile togeher side by side betwen steel plates and heat and quench them all att once. He gets good result with carbon steel. I was thinking about doing the same with cpm steels and use an anti scale coting on the edge side only.

I have no idea if it will work, but I don't see why it wouldn't... atleast so far:rolleyes:

The blade grinding after ht was one of my worries but I think I will handle that.



Regards
Jakob

EdCaffreyMS
05-03-2010, 04:37 PM
I learned of the belt grit trick from SR Johnson a number of years ago. At first I was skeptical, but gave it a try. I choose to use 50 grit Blaze for my heavy grit belts....it removes material rapidly, but does not leave such heavy, deep scratches that I can't get them out with a 400 grit belt.

After heat treat my method is to clean up all the "Flats" to 400 grit, then put a new 50 grit Blaze belt on the grinder, and grind the bevels to nearly finished dimensions. I then switch to a Norton Norax in X30 (400 grit). At first it seemed like I wasn't getting anywhere, but then I started keeping an eye on the clock. Although those last few scratches can sometimes be difficult to get out, I discovered that compared to using the 50, 120, 220, 400 sequence of belts, it saves me 45 mins to an hour on finish grinding a blade.
Once I finish with the Norax X30, I go to 600 grit on my disc grinder, and all but eliminate hand finishing. I still hand sand with 600 grit, but even on large blades it's generally no more that 15-20 mins to get the finish to where I want it.

So in the end I cut not only time off finish grinding a blade, but I skip 2-3 grit sizes of belts, which saves $$!

I've never tried ganging up blades for heat treat, but I have done a lot of it when I was using 15N20 for folder liners....and it worked great for that application.

Finally, my opinion is that there isn't much use for belts heavier than 50 grit....although some might use 36 grit, or even 24 grit, I think it just makes you have to use too many other grits to get to where you want to be in the end. In other words, I don't think the cost to savings ratio (in either money or time) is worth using a 36 or 24 grit belt.

James Terrio
05-03-2010, 05:07 PM
Ed, that sounds better and better the more you describe it. Thank you very much for your detailed explanation. The "romance" of hand-sanding wore off for me a long time ago. It sounds like your approach would work very well for me.


...At first it seemed like I wasn't getting anywhere, but then I started keeping an eye on the clock.

I have definitely noticed that myself. Seems like when you get things in order to begin, the later steps go a lot more smoothly... there's a "magic moment" when things suddenly seem to fall into place and make me smile.

I also agree that 50-grit is plenty coarse enough to hog steel (I'm a stock removal guy); in fact I've been letting my stock of cheap AO 50's run down and use the 80's in the early stages... nearly as fast and not as many deep scratches that take forever to get rid of. I'm pretty sure when I step up to better quality belts I'll be even happier.

Thank you Jakob for starting this thread! It's been a real eye-opener for me. I'm thinking I've wasted too much time and effort before and after HT up till now.

J. Doyle
05-03-2010, 10:00 PM
Ed explained this process to me a few weeks ago. I had never considered it before. I've been giving it a shot in the last week or so and it works good. I think that it will become my new method and I will save on the in between belt grits.

P J 234
05-04-2010, 07:03 AM
I used to do most/all of my grinding, and some hand sanding, before HT. Since I've gotten a variable speed quality grinder, my last few have been ground maybe 70% pre-HT and the rest afterwards. The only downside I've seen so far (and I may be doing something incorrectly) is that post HT grinding takes a LOT longer, since I'm running my grinder slower and dunking in water after nearly every pass to prevent overheating and ruining the HT.