My rule to thumb is that ANY blade, gets finished to AT LEAST 120 grit prior to heat treat. Experience has taught me that 120 grit is as coarse as I can go and eliminate the risk of stress risers. The "trick" is that you want to BE SURE that ALL coarser grit scratches are eliminated. Being able to spot those "leftover" heavier grit scratches just take a bit of time and experience...training your eyes to see those heavier grits scratches.

The way I did it was by using a large magic marker.....when I THOUGHT I had all the heavier grits scratches out.... I'd coat the blade with magic marker....then make a grinding pass...the marker makes and heavy grit scratches you miss, pop right out.

One of the biggest advantages to salts is the fact that blades don't scale, pit, etc. during hardening.....that means you can literally take a blade very close, or even to finished, and using salts, heat treat it, and go right to hand sanding afterwards.

I like Ed do AT least 120 pre-heat treat I will also take all of my profile grind lines length wise , nothing crossing the edge. I find this to be almost more important that the flats of the blade, in classes I have never seen even one blade crack if the edges had been profiled length wise no matter how poor the finish of the grind. running the lines length wise is cheep insurance.

MP

There are two aspects to the original question- what grit will contribute to stress risers, but also what grit will hold the clay the best. I found it interesting that the answers thus far coincide with both of my guidelines for hardening HT. I don't work with 120 belts but if I did that would definitely be the lowest grit I would go before hardening. But if you go much beyond 220X the clay has less to adhere to. In both concerns, 120X to 220X is the upper and lower limits I would work in.

Thank you Ed, Matthew, and Kevin,

I appreciate your responses and advice. I think it's pretty amazing that on this forum one can get such quick and thorough responses in such a short amount of time from some of the most knowledgable folks in this business. Very cool.

So, 120 machine grind it is...as long as I have a good finish and have taken care of the lateral profile scratches. That sharpie trick will save some time--I've been grinding out those lingering scratches by hand and that takes more time than I'd like to admit. And I have had trouble getting the clay to stick--probably due to me going too fine before hardening HT.

Again, thank you for responding so quickly and with good advice.

Steve

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There are two aspects to the original question- what grit will contribute to stress risers, but also what grit will hold the clay the best. I found it interesting that the answers thus far coincide with both of my guidelines for hardening HT. I don't work with 120 belts but if I did that would definitely be the lowest grit I would go before hardening. But if you go much beyond 220X the clay has less to adhere to. In both concerns, 120X to 220X is the upper and lower limits I would work in.

Kevin--what grit belts do you use? I've been using 36 or 40, 60, 120, 220, 320, and 400 and then doing hand finishing from there.

Steve

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Kevin--what grit belts do you use? I've been using 36 or 40, 60, 120, 220, 320, and 400 and then doing hand finishing from there.

Steve

I don't think there is a right or wrong with belts grits, and it is a matter of finding what sequence works best for your style of grinding. With your line up the only grit that is missing is 80X. With this many smaller steps I would definitely head Ed's advice with the marker, as those lines will be awful hard to distinguish from each other. I myself keep a tube of old ferric chloride next to the grinder for a quick dip between grits to darken the blade and all the scratches.

In my classes I teach that there are two categories of belts- grinding belts and polishing belts. Grinding belts are for shaping steel (removing metal), polishing belts are for removing scratches only and all shaping is done before moving to a polishing belt. I put the dividing line between the two at around 120X and one of the commandments of grinding in my class is that thou shalt not grind with a polishing belt.

Now once again I can’t tell you that your belt choices are wrong since it is whatever works for you, but in my class I know students would over-grind their blades working with that many grinding grits. Most folks start with a 40X or a 60X, I prefer to get the job done as quickly as possible without a lot of heat so I grind at 36X, but 40x would probably work for me if I tried it. I keep a stash of 80X belts around just for tweaking and fine tuning tricky grind areas when 36X is too much brute force; items such as the grind plunges, rolling edges or adjusting clips.

Years of teaching new bladesmiths has shown me that 220X is the most powerful polishing belt and thus the most dangerous to your blade; I have seen more students ruin blades at 220X than any other grit. This is because 220X seems so fine and is a polishing belt for sure, the problem is that it is still very capable of removing a lot of metal fast in places you didn’t mean to lose it. But I think 220x is the ideal grit to go to before heat treatment. Less than that and you have some fairly course texture to work out at 60+ HRC, any higher than 220X and you will just end up back at 220X (wasting belts) to get rid of scale and surface effects of hardening. This is what I recommend in a class, at home I go to a much higher finish because my heat treating equipment allows it.

From first approaching the grinder, to the final passes on a satin hand finish, the same rule applies- grinding is for removing metal, polishing is just removing scratches. If you get all of your grinding done properly, polishing, be it with a belt or by hand, should only take a couple of passes. If you find that you are taking longer than this it is because you are still trying to shape while polishing, i.e. working out dips, wobbles and facets that should have been fixed during grinding.

Following this rule allows me to personally use a dramatic sequence of belts- grinding at 36X with some optional light adjustments using 80X. Then I polished my ground blade with 220X (I rarely have to darken the blade as a 36X is VERY easy to see in a 220X finish). If I find ornery scratches that are not coming out it is because my grind is off, I stop and immediately go back to an 80X and fix it and then return to 220X because trying to grind with a 220X will only result in wasted belts and hot, faceted steel. Next is a couple of quick passes on a 400X (often dip in FeCl beforehand as 220X can hide in 400X). Finally I take about two or three passes across a 600X belt before hand finishing. If all is done right, the amount of passes drops dramatically on each belt until it becomes important not to pass over the blade with a 600X more than a few times or you will start getting orange peel and wobbles. Then when you sit down to hand rub the blade that perfectly flat plane will give up those 600X scratches to a 400X paper in just a couple of strokes, if you find a spot that doesn’t it is lower than the rest of the blade surface from an issue on the grinder.

We all remember how our first knives took days in front of the television, with sandpaper in hand, to finish. That was because we were still trying to grind that blade flat with our fingers. And we really didn’t get it flat because without a flat backing our fingers eventually allowed the paper to get down into the wobbles and get the scratches, so we had a very well polished wobbly grind. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//biggrin.gi f' class='bbc_emoticon' alt=':D' />

Thank you, Kevin, for the info on grinding. So your sequence is:

36, 80 (a bit, sometimes), 220, 400, 600, then hand polishing. I can see that if you've got very flat flats and nice clean lines, using fewer grits and taking bigger steps works well. As I get better at grinding I'll move in that direction.

I'm finding the 40 grit are good for me for now, but I'll keep my mind flexible and keep trying out different sequences to find what works for me as my skills develop.

Thanks for all the advice and information. Very helpful.

Steve

Love reading post like these. Learn something helpful everytime, paticularly Kevins contributions. I learned a long time ago that I was spinning my wheels and wasting my time, not to mention a blade or two, by using every single grit available to get from a forge scaled blank to a prepped for ht blade, and the cost of those belts could send you right back to the draw filing board. I've learned through the years to forge fairly well to shape and dimension with just a bit of oversizing for material removal. I start off by using a small angle grinder with a coarse wheel to just remove forge scale so that I can go to a 60 grit belt and set all dimensions. After that I go to a 120 and 280, at which time I hot stamp my name. I go to this grit because I get a cleaner stamping without course lines leading into the impression. After that I'll go over it again real quick with the 280 and HT. I don't yet have a salt pot setup so I use an antiscale compound that works really well and leaves a smooth gray finish. After tempering I go back to a 120 grit to just bevel the edge down to sharp, with a quick clean up on the 280 (I like the gator belts in the finer grits except for the dust they throw),and then to a 500 grit belt, followed by a 600 grit cork belt. I've found I can start my hand sanding with 400 grit w/d and then 600 if the blade calls for it. The big thing is knowing you have gotten all the previous grit scratch's before going to the next grit. I know I've read a lot of this on this forum before down through the years so my apologize for the repetition. I forgot to mention one thing, and that is that I generally wait until after H/T (between the 280 grit clean up and the 400 polish belts to cut the shoulders of the ricasso for the guard. I do not like for my ricasso to be hardened, at least not fully hardened and tempered the same as the edge. Some, maybe many, makers do, but I choose not to because it makes it so much more difficult to work (for me anyway) and I like toughness in this area rather than extra rigidity. Wes

Thanks for the feedback, Wes.

It sounds like you go to 280 before going into hardening HT, in part because you hot stamp your mark.

Knowing that 120 grit is the minimum grit to go to (lowest number belt) before hardening is really helpful--as well as knowing that it is not important to hand sand lengthwise before hardening HT, as long as you are sure you don't have bumps and bigger scratches hiding in the background.

It's also helpful hearing what folks do for their grinding sequence in general. It seems that the more experienced smiths (and others who can get really flat, even grinds) take bigger jumps between grits. I'm definitely going to work towards that, as my grinding skills improve.

Steve

Steve, it's difficult to include every single detail when giving a rundown because not everything comes to mind just when ya need them too. That's how it is for me anyway(must be getting old), I didn't think to add this detail that I follow and I see Ed mentioned it too in that at the 280 grit I heat treat at, I will carefully (even under magnification) look for deeper scratch's at the very edge of the blade, I'm actually anal about this and I'll take that 280 or even 320 on a sanding stick and I'll polish just the edge area length ways, I'll even round the edge off a bit since I've experienced a micro crack due to this once, and I do mean once, as I've never let it happen since due to this. A 120 grit finish will work but I'd feel better with say a 150 or 180 grit since there still is your concern for clay adhesion. I'll also throw in here that I go to a 280 grit before H/T because I do use the anti scale compound as it aids in there being less backtracking to finish out a blade. Seems like everything boils down to saving on steps, and thus grinding belts. After 29 years of making knives I'm still guilty as hell when it comes to stretching all I can out of a belt and then some, and I'll be the first to admit that I make a much better knife, with less effort and mistakes, when a new batch of belts come into the shop. Wes

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...I will carefully (even under magnification) look for deeper scratch's at the very edge of the blade, I'm actually anal about this and I'll take that 280 or even 320 on a sanding stick and I'll polish just the edge area length ways, I'll even round the edge off a bit ...

Amen to that. I always run my very edge lengthwise on a 220X or finer belt to eliminate any scratches that could be left going perpendicular across the edge.

I've been experimenting with this a lot the last couple months trying to figure out what works best for me. I finish as much as I'm comfortable before heat treat. If the blade is thick enough to heat treat without re-shaping, you might as well take it up to 400 by belt or by hand. 400 will take scale off just fine. You're going to have to do it anyway, and the less you need to rub out with a hard blade the better. If I plan on still walking up the bevel after heat treat, I find it easier to make sure I graduate the belts to higher grits sooner. Those 36 to 80s will hide under 220's on the belt grinder sometimes, and in my limited newbie experience, hate polishing them out by hand haha.

I drawfile the edge with a 6" fine file. I haven't lost any since doing this and using Parks, or slower oil if the steel will tolerate it.

I just like drawfiling, and a small file, with fine cut, seems to do it well enough. I drawfile the spine, too. So, I just flip the blade over and hit the edge with short draw strokes to keep the file from galling. It is about the same as using 220x paper, just simpler.

Another way to accomplish about the same thing.

On anything less than about 12" long, I also use the disk grinder with 80 grit to get out the dips and wobbles from the belt. Or drawfiling.