Why Grind Bevels Many Times?

H

Hugh Buchanan

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Aug 24, 2017
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I tried an experiment last week. I profiled a blade and immediately heat treated and tempered it. I polished the edges and the flats with 320/600 grit belts. I would have gone farther if I had higher belt grits. The 600 grit belt left the blade shiny, almost mirrored, but with streaks, I hand sanded with 1000 grit paper, but decided that it looked better after the 600 grit belt.

After getting the flats to what I was going to consider finished for this experiment, I ground the bevels with a 320 grit belt. By finishing the flats before grinding the bevels, the grind lines and plunge lines remained sharp and crisp. The results were better than anything else I have done (I've been making blades for two years) and I think you would find the blade to be acceptable in every way. I don't think that I spent more time at the grinder because of the high grit. The steel came off the blade quickly. I only touched the bevels one time in the process. The aluminum oxide abrasive doesn't seem to be phased by hardened steel.

The conventional process begins before hardening, with belts containing grit you could use to pave your driveway. I am wondering if there is a good reason to start coarse, before heat treating, going up to finer grits in stages before and after HT.

I am using an Origin Blademaker Grinder with a 1 hp motor and Combat Abrasives aluminum oxide belts. I use jigs for grinding flats and bevels.

What am I missing?
 
The grit used depends a lot on the thickness of the blade. A fine grit will work on a really thin blade since there's not much metal to remove. If you've got a thick blade that's a LOT of metal to remove with a 320 grit belt.

I like making my first grind on a HT'd profiled blade with perhaps 80 (perhaps 120 grit for a .060" thick blade and 50 grit for a 1/4" thick blade?) grit to remove a good bit of the metal. That will allow faster metal removal without generating so much heat. Then move up the grits to remove the coarse grind lines.
 
i start with very coarse because a 36 grinds a lot faster than a 320. there is also less friction/heat with a lower grit belt, and the lower the grit the belt is, the longer the belt usually lasts.
 
I am in total agreement about grinding the bevels as little as you can. But, using a 320g to do the grinding is silly and not an efficient use of time or belts. A lower grit belt will grind faster, with less heat. Super important if grinding after HT.
 
Grinding with a higher grit can certainly be done, but heat, belt life, and time will be your enemy. If you're only doing one blade once in a while, and if you have the free time / patience it takes, there's really no harm in it. Just keep your blade cool enough to touch, especially along the edge and near the tip. However, when you're trying to remove a significant amount of metal, or grinding dozens of knives each day, week, etc., the number of belts used up, the time wasted, and the time spent cooling a blade down adds up fast.

I personally don't make enough knives (yet) where I'd notice a big difference, but I have ground larger items like hardy tools and axes. Doing those on a 320 grit belt would be like pulling teeth - it can be done, but you're not going to have a good time.
 
Ken H> said:
The grit used depends a lot on the thickness of the blade. A fine grit will work on a really thin blade since there's not much metal to remove. If you've got a thick blade that's a LOT of metal to remove with a 320 grit belt.

I like making my first grind on a HT'd profiled blade with perhaps 80 (perhaps 120 grit for a .060" thick blade and 50 grit for a 1/4" thick blade?) grit to remove a good bit of the metal. That will allow faster metal removal without generating so much heat. Then move up the grits to remove the coarse grind lines.
Click to expand...
 
I'm using .125 O1 steel. If the 320 grit is slower than a coarser belt, I'm making up for it by grinding in only one pass. I don't think it is very much slower. I cool the blade frequently in a bucket of water.
 
The stock is .125. I think that my bevel angle is about 9 degrees. This gives me a bevel that is about 3/4" in height. I had my jig set at about 6 degrees, but it was difficult to control the height of the grind lines. I went to the spine of the knife on several occasions. My grind lines are more Dan Berg than Walter Sorrells at this point. They follow the curve of the blade's edge.

I have had to study all kinds of math: Algebra, analytic geometry, trigonometry, calculus. I never used any of it until I began making knives. I have used trig a little in order to calculate the height of the grind line as a function of the grind angle.
 
bmilleker said:
I am in total agreement about grinding the bevels as little as you can. But, using a 320g to do the grinding is silly and not an efficient use of time or belts. A lower grit belt will grind faster, with less heat. Super important if grinding after HT.
Click to expand...
 
I appreciate what you are saying, but my point is that it is not much slower. I keep the water bucket close by. You make up the time lost, if any, by grinding only once.
 
320? I use 400 grit on my slip joints to dial in the tang dimension because it remove so little material.

320 grit is more of a finishing grit and designed to remove very little steel.

Now some makers will start with 50 grit and complete the grind then remove the scratches with 320-400 grit

Using 320 would be a very inefficient way to remove steel in for main bevels
 
If you're using a fixed speed grinder I think it's a great way to go.

It slows you down and you can watch the progression.
 
Hugh Buchanan said:
I'm using .125 O1 steel. If the 320 grit is slower than a coarser belt, I'm making up for it by grinding in only one pass. I don't think it is very much slower. I cool the blade frequently in a bucket of water.
Click to expand...
Are you saying you take the bevel from start to finish in only one pass? You grind at same spot until the bevel is complete, then move a bit more? Am I understanding this correctly?
 
how long did it take you to grind with your method?
how many 320 grit belts did you use?
how can you grind in one pass with a 320 belt? without it overheating...

I'm not trying to be rude or harsh, but it seems like "bobbing for french fries"....
 
Hugh Buchanan said:
I'm using .125 O1 steel. If the 320 grit is slower than a coarser belt, I'm making up for it by grinding in only one pass. I don't think it is very much slower. I cool the blade frequently in a bucket of water.
Click to expand...

Well , I think ! If you menage to grind one side of your knife in ten minutes I will grind same in half minute with 40 grit:D
I wouldn't dare to try it with 100 grit ceramic belt .....and you can do that with 320 AO belt ??? Which speed you use and how much time you need to grind one side ?
One of the problem with very fine grit belts is that there is to much grain on square inch so we can not put enough pressure with hand on steel belt to grind properly ...... that s why we get heat fast , most time belt is rubbing instead of cutting ,but that s good leave nice finish :)
 
I'm a newbie, so I spend a lot of time grinding bevels. I go slowly and I don't remove a lot of steel quickly. I'm more concerned with making good plunge lines and crisp grind lines. I cool frequently in a bucket of water. If you take the flats to their finished state before you begin grinding the bevels, the grind lines look much better.

Yes, you can grind faster with 40 grit, but then you are not finished. You must repeat the procedure with two or three other belts. Every time you put your blade on a different belt, you risk making a mistake.

Having tried this new process, I am very happy with the results and I will be using this method on every blade I make from now on.

Thanks for your reply.
 
HSC /// said:
how long did it take you to grind with your method?
how many 320 grit belts did you use?
how can you grind in one pass with a 320 belt? without it overheating...

I'm not trying to be rude or harsh, but it seems like "bobbing for french fries"....
Click to expand...
 
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