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grinding blades


Doug Adams

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Hello,

I am new at knife making and have only made 6 knives. The first several I profiled the blades on a bench grinder and then I filed the blades with a file and they turned out good. Lately I have been trying to hollow grind some blades. It is hard to me. How long does it usually take to get the hang of hollow grinding? Is flat grinding easier or harder?

 

Thanks,

Doug

Jn. 3: 16

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Hi Doug,

 

I am also "young" in the blade game, using a bench grinder then files/sen to refine any bevels. From my own personal experience, I would not even consider trying a hollow grind. It just seems more natural to me to have a flat or convex grind. Without getting into a discussion over the pros/cons of a given grind, I suspect it takes some skill or equipment to do up a good hollow grind, probably not with a bench grinder.

 

I believe most of the folks use a belt grinder with a contact wheel to get hollow grinds. Most likely, some kind of jig is employed to maintain a steady approach, but I'm sure somebody out there readily "wings it."

 

Thanks,

Brian K.

Brian K.

Rogue Amateur and Weekend Hobbyist

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Doug,

 

What size is your contact wheel and what type of grinder are you using? I used a Grizzly for many years and am just coming to terms with the new KMG. With the Grizzly, I could hollow grind but, the motor was in the way on one side and it made it almost impossible to get both sides the same. I think that I only attempted one hollow ground blade in all the years I had the Grizzly, when it first arrived.

 

I am new to hollow grinds as well but, have been playing around with them on the KMG. When you grind off of the wheel there is a smaller area of steel in contact with the belt and so material is removed more quickly. That, and the grain of the belt gets spread open as the belt bends over the wheel and so more abrasive is exposed. A blade will take shape much faster than when flat grinding, in fact I've been starting out hollow grinding for just this reason and then switching over to flat at the end. I can get a flat grind faster and more accurately doing it this way. My experience has been that it works much better if the wheel you are using is the right size for the width of the grind that you are making. Once you have the grind started, and get it centered, it is pretty simple to keep the wheel in the trough. The hard part is keeping both sides the same, I have a tendency to pull one elbow closer to my body when at the tip of the blade and have been working for a bit more consistency. Mostly, it just comes down to practice. Steel is cheap, cut some pieces off and try to grind multiple blades with the same shape and geometry. You will find that you improve as you go.

 

~Bruce~

“All work is empty save when there is love, for work is love made visible.” Kahlil Gibran

"It is easier to fight for one's principles than to live up to them." - Alfred Adler

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Doug --

 

Hollow grinding is frustrating and rewarding. It's a great way to really get to know the feel of your grinder. It is also a way to get a blade 90% done, then sneeze at the wrong moment and end up with a screwed up grind line.

 

I recommend using a work rest as you learn. It eliminates one variable (the Y axis . . . or how high/low you place the blade on the wheel).

 

Also, stick with drop points or clip points at first. The reason they are easier is that the grind is just straight on the X axis. Any blade with an upswept tip requires you to drop the handle of the blade toward the floor (assuming you are grinding edge up) as you approach the tip. That takes a lot of practice.

 

Keep your elbows close to your body while you grind.

 

Finally, the trick that I learned which really helped my hollow grinding is that you "lead" each pass of the blade with the edge. What I mean by this is that you tilt the very edge of the blade into the wheel first, such that it is the first part to make contact with the grinding wheel. Let it rest lightly against the wheel, then slowly bring the bottom of the blade towards wheel. The wheel should "click" into groove left by your last pass.

 

May the hollow grinding force be with you.

 

--Dave

-----------------------------------------------

"It is not the critic who counts; not the man who points out how the strong man stumbles, or where the doer of deeds could have done them better. The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood, who strives valiantly; who errs and comes short again and again; because there is not effort without error and shortcomings; but who does actually strive to do the deed; who knows the great enthusiasm, the great devotion, who spends himself in a worthy cause, who at the best knows in the end the triumph of high achievement and who at the worst, if he fails, at least he fails while daring greatly." -- Theodore Roosevelt

http://stephensforge.com

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Hi,

I was lucky to find an old bader from a knifemaker that retired. I ask him how old it was and he said he didn't even know he had had it so long. Bruce I have 4, 8, and 14" wheels. I have been trying the 8" wheel mostly. I think my steel has been a little too wide for that size wheel or either I am getting too high up on the blade. I am ending up with it too thin in the middle, between the spine and the edge. I need to find a chart and see what size wheel is for what size width steel.

 

Dave I think you are right, I believe I could do better with a rest. I have watched Johnny Stout dvd several times and he uses one too. I want to build a rest as soon as I can.

 

I am going to try the 14 inch wheel soon.

 

Doug

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I think Dave's advise is a very good way of going about it. I have 4 hollow ground blades that came out of heat treat and I will be working on them today, so maybe I can post some pictures later on.

 

Personally I don't use any kind of a rest, I free hand it. I will start out with a very steep angle, edge into the belt, this will cut in to where I want my edge line to be, make sure that this line is straight and even leaving 1mm - 1.5mm edge thickness. Also keep the edge straight across the wheels surface through your grind, this reference point helps me with the "dropping" of the handle to the ground. After your edge is cut in, drop your angle down and keep the same motion of keeping your edge straight across the wheel until your back bevel is where you want it and it meets the edge. Now comes the hard part, flip it over and make the second side look the same.

 

Go slow, use a lower speed if you can, and pay attention to what every pass has done.

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