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belts not biting


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I've discussed this in another thread in the past, but I'm still kind of stymied...

When I'm making kitchen knives using 1095 and grinding post-heat treat, I usually use ceramic Norton belts from 35 --> 60 --> 80 and then switch the Trizact A160s (120 grit).

 

Next I work and finish up the edge on synthetic stones -- Namikawa binsui --> King 1000 --> King 6000.

Then I go back to the grinder, using Trizact A65 --> A45 --> and finally A30. Etch for hamon and then done.

My problem is that when I get to higher grits on the Trizacts, I often have a lot of trouble getting the belts to bite. For example, this time I had no problem with the Trizacts up to A160, but after I worked the blade edge on the stones, going back to the Trizacts, the A65s are very slow going. Not erasing the scratch marks, not throwing many sparks, and there's an almost slippery feel to the grinding. I've hit the belts with a wire brush and bought brand new ones, so it's not an issue of the belts clogging.

 

My latest theory is that the synthetic stones are doing something to the steel, like burnishing it so that the surface isn't receptive to the Trizacts. Or maybe small stone particles are getting into the steel grain somehow. I'm trying to remember, but maybe last time when I went back to ceramics before the Trizacts, it might have helped. Will have to experiment some more.

 

The thinness of the blades seems to be part of the problem -- if I don't pretty hard on the grinder platen, it's like the belt kind of skates off, but if I press harder, the steel heats up pretty quick. I don't have this problem on thicker blades.

Anyone have this experience or any advice?

 

 

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At a guess.. I think you may well be grinding through soft decarb and then hitting truly hard material...possibly.

Although this theory depends upon how you are Heat Treating?

Edited by owen bush
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Have you tried a rubber belt cleaner?

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Many abrasive belts must be used with the correct amount of pressure. Use too little pressure and the belts can "glaze" and stop cutting before the abrasive is used up. Are you using the recommended amount of pressure with your belts? Don't the Trizact Belts contain a dry, lubricant? Perhaps, in the higher grits, it is more noticeable? Have you thought about using either the cork or felt belts that are now available, instead of the Trizact? Another thought is to use higher pressure on the Trizacts with the addition of belt lubricant, this might allow you to use the correct pressure without excessive heat buildup.

 

~Bruce~

Edited by B. Norris
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good thoughts, but i don't think either is the problem.

 

when this first happened a while back, i figured the belts had simply dulled (even though they weren't that old) and i got some new ones. but those didn't help much either. i do hit them with a wire brush on occasion also. so i don't think it is a dulling or clogging problem.

 

certainly hardness might be part of the issue. but i'm working with knives with hamon and the lack of bite is not that different in the hard and soft areas of the blade. as for the heat treat, i have a very basic set up with limited ability to gauge temp, but i try to soak my 1095 at critical for 5 or 10 minutes and then quench in parks. i have no trouble with hamon formation. i may run a bit on the hard side because i just temper in toaster or kitchen ovens which cycle and probably average below 400'F.

anyway, i don't think it's a issue of removing soft decarb. the ceramic belts work just fine removing metal and even up to 120 on the Trizacts is okay. it really seems like the problem is at the higher grits (often the trouble really starts on the A45s).


honestly, i think the main problem is simply that the thinness, flexibility, and near flat grind of kitchen knives makes it hard to get a good bite from the Trizacts. but it does seem like the problem is worst when using the Trizacts after stones. it could be in my head, but it seems like the stones kind of lube up the steel making it almost slippery.

 

i'm going to go back to 80 grit ceramic today and work my way up again to see if that helps.

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i think bruce is on the money here. the Trizacts work great on my 1075 blades, but those do not have the flat geometry and thin flexibility of kitchen knives, so it's easier to press a bit harder.

 

once when i gave up trying to get the A30 Trizacts to bite, I ran the blade on them lengthwise on the grinder wheel. that seemed to work a whole lot better. but i still have to go through the A60s and A45s first, which can sometimes be very slow work.

 

maybe i'll try cork one day. i really love the Trizacts though, especially how they usually seem to be so great at biting and even at higher grits have almost no problems with bumping at the seam. it's just that they don't seem to work as well on my 1095 kitchen knives.

Edited by joe pierre
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spent a couple hours grinding today. some puzzling observations...

i went back to a ceramic 80 belt to clean up the surface of the steel and then started again with the Trizact A160 (120 grit). it took maybe an entire hour, or what seemed like an hour, using the Trizact to get one side of a large flat-ish grind gyuto done. the unetched hamon was not showing as well as it was previously at this grit, i think because the belt was basically burnishing the steel. in retrospect, that's simply a ridiculous amount of time for one side of a knife and one grit.

 

before i put the blade on the stones, i used this same belt and it didn't take nearly as long. also, the hamon was more evident without the burnishing effect.

maybe the steel is just extra hard. but the funny thing is the persistent scratches seem to lurk where the hamon isn't so if anything it's the softer steel that's not getting ground. like the softer steel is sitting in low spots.

 

hitting the belt with a wire brush does actually help, but not for very long. made me wonder this was just an effect of getting little grains of steel in the belt from the brush, that is, adding some abrasive, rather than unclogging the belt.

 

but the belt itself seems fine. i took a broken heat treated 1075 blade to it and it threw sparks and worked just fine. must be something about the hardness of the 1095 and the flat wide geometry of a gyuto.

 

i still have one more side (i'm working on two knives) and 3 more grits to go, but at this rate it will take an eternity, so i'm still hoping someone has some ideas.

Edited by joe pierre
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Is your platen flat and the belt tensioned so that it sits flat on it? Do you notice that the hardest surface to get to is in the center of the blade and that this problems happens with the thinner or more flexible belts?

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jesus, I did wonder about the platen yesterday, which is covered by ceramic glass. I took a look and it seems flat, but there is some friction residue on the glass, especially in the middle. maybe the belt could be tensioned more (I don't actually know where the tensioner is, but I did notice that my belts aren't as tight as they used to be). I'm just working on a grizzly grinder, so there's a certain amount of wobble. it does seem like the sides of the belt have more bite, but I figured that was just because there's more pressure when pressing due to the bending of the blade. but yes, it's worse as you go up in grit.

 

alan, the reason I love trizacts is that usually I have no problem skipping grits. heck, I used to go from 80 or 120 right up to the A65s no problem. the scratch marks usually appear like a paint brush with minimal contact. amazing things -- as I said they work just fine on a piece of heat treated 1075 that was lying around, but not so much on my kitchen knives.

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"it took maybe an entire hour, or what seemed like an hour, using the Trizact to get one side of a large flat-ish grind gyuto done. the unetched hamon was not showing as well as it was previously at this grit, i think because the belt was basically burnishing the steel. in retrospect, that's simply a ridiculous amount of time for one side of a knife and one grit."

 

Wide, flat, grinds are hell on belts. There is so much surface area, all in contact with the belt, that it is nearly impossible to bring adequate pressure to bear and keep the belts from glazing. More so the fine belts than the coarse ones because, the higher grits generate more heat and the instinct is to use less pressure. You can verify what I am saying by using a brand new belt on your blade, it will cut much better at first and then take longer and longer to get the scratches out. The same belts, on a contact wheel and hollow grinding, will not seem appreciably duller. The same belts on a smaller surface area will not seem dull because, more pressure can be used and the higher pressure will do what is intended for these belts and break away dull grit, exposing fresh, sharp, grit.

 

You can use belts up like they were free and slate the "dull" ones for some other purpose, such as hollow grinding - this approach will make the most of your time but, cost in belts. You can say "the heck with this" and just sand the blade out by hand - this will probably take less time than using the dull belts but, more than using belts like they were free. You could find a way to apply more pressure, without overheating the blade, either by using belt lubricant or wet grinding. Another option is finding a way to physically remove the "glaze" from the belts, the wire brush does not seem to be doing this. I have heard other knifemakers recommend using a brick (the high-fired ceramic ones, usually red) with as much pressure as possible, to remove dulled, "glazed", grit and expose the sharp, fresh, grit. I have done so myself and it does seem to work, though not as well a brand new belt and it needs to be repeated frequently and that uses a belt up at a much faster rate than otherwise.

 

"maybe the steel is just extra hard. but the funny thing is the persistent scratches seem to lurk where the hamon isn't so if anything it's the softer steel that's not getting ground. like the softer steel is sitting in low spots."

 

Sharp abrasives will cut the hard or the soft steel equally well. Dull abrasives will not cut the hard steel as well as the soft and you will have problems like you mentioned above. It is exactly the same as trying to sand metal pins in a wood handle, you have to use sharp paper (and a hard, flat, backing) or else the wood goes away and the metal does not.

 

~Bruce~

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sounds very reasonable.

 

the only things that remain puzzling are that the first time this happened, I bought a new set of belts and it really didn't seem to make much difference. so i do have two sets now -- in theory the old dull and new sharp -- but i've gotten then mixed up and it's hard to tell them apart.

also, i didn't have much trouble with the A160s before the stones, whereas now they're very slow going. of course, it could just be that they got dulled the first time, but it's still hard not to believe that using the stones did something to them and so i still wonder whether the belts somehow get clogged or dulled with the synthetic stone material in some way.

 

and i still don't understand why the belts seem to be less effective in the non-hamon areas. you'd think they'd be duller in the hardened areas of the hamon, but strangely it seemed to be the opposite.

 

as far as deglazing, maybe the wire brush is working to rough up the belts (rather than adding abrasive from the ground wire). as i said, it does seem to work, but only for a bit. maybe at the higher grit it will be more obvious whether it's working because the belt is getting deglazed or because of microparticles from the wire brush. or maybe i'll try using the brick.

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are you using something to carefully push (hard) just opposite of the place you want to grind? if you are holding the blade by the ends, then the flexibility can make it not bite except on the edges. I had to start taping my thumb to deal with heat, and then pushing with it in the middle of the blade flat to get rid of the final scratches.

 

This is worse with a hamon, because the harder material on the edges (the back edge hardens just a tad most of the time, where the spine doesn't have clay) tends to shield the softer material. Especially so when they are first heat treated, because the martensite will stand proud of the pearlite/cementite.

 

Just ideas. It still comes back to pressure, belt tension, and a flat platen.

 

kc

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I have experimented with that approach in the past. Unfortunately, most tools (like a small piece of wood) seemed to remove my ability for fine control of placement of the blade. Or, when I tried something like tape or a surgical glove, it melted with the heat!

 

Best thing would probably be something like a wooden thimble for the thumb.

 

Now, belt tension... you think that tightening will help? It seems pretty tight to me already, but I could try for a bit more...

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  • 4 weeks later...

I tape my thumbs with several layers sometimes and just push with them (on kitchen knives, especially). I know exactly what you mean about losing a bit of fine control with the push sticks.

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yep, that's the ticket. at a fish and tackle shop, i recently saw a kind of thumb cover made of suede used to hold the fishing line and i thought about using a cut off finger from a glove over my thumb. i experimented with different approaches and ended up just using a small piece of cork to shim between my thumb and the metal to help apply pressure.

 

i think you're right and that my problem involved pressing with both hands on either side of the blade causing the metal to bow away from the grinder. pressing on the cork with my thumb directly over the platen was a definite improvement.

 

i still think there's something a little weird about trying to grind with trizacts right after the namikawa binsui stone though -- maybe some kind of lubricating effect that reduces the bite of the trizacts. so using a coarser grit first and then moving to trizacts with the cork thumb guard seemed to improve things quite a bit.

 

so mystery mostly solved. thanks all!

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i think you're right and that my problem involved pressing with both hands on either side of the blade causing the metal to bow away from the grinder. pressing on the cork with my thumb directly over the platen was a definite improvement.

 

Sometimes I will grab the backside of the platen with my hand and then use my thumb to press the blade into the belt. Only works until the platen heats up! Until then, it sure works well.

 

~Bruce~

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great detective work. I am no help with Japanese stones or trizacts. I need to get some trizacts, actually. They obviously work well, but I haven't bought belts since I have been hearing so much good stuff about them.

 

cork is a good idea, I may try that, or the piece of glove.

 

kc

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I'm going to go out on a limb here and suggest you remove the stones from your process and grind through the selection of belts and see if they bite the way that you want.

You can hand finish form there or use the stones to sharpen after wards.

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interesting thread, not much to add but thought I'd throw this out there. Are you drying your blade after cooling it? I think the trizacts have a water soluble resin and will crap out quickly if used on a wet blade.

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