Formula for grind angles

Bill Thomas

Bill Thomas

Joined
Jul 7, 2013
Messages
64
As some of you have read my previous post you know I'm a rookie. My first batch of skinners are at heat treat and I'm ready to start a new batch. I have 52100 1/8 x 2 stock for chef knives. Is there a formula that will give me the grind angle using thickness and width to maximize the stock removal with out sacrificing any width? It's hard for me to explain but what I am looking for is a full V shape across the entire width width with little or no flats. When I did some practice blades with mild steel I tended to grind into the spine before I got to .025 on my edge for heat treat. There's got to be a formula to give me this angle so I can cut a block of wood to simulate the exact angle to get a feel for the grind. Thanks again in advance to those who respond and to those who have responded to my previous post.
 
I think there is too much interest in jigs, formulas and systems when learning to grind. It will take time to learn to use those crutches. Why not put that same time into learning how to grind freehand. The time spent will be a better investment. If you rely on a device to help you get the angle you need what happens when you need a different angle for a different kind of knife? What happens when you are getting unintended results for a particular style of knife for which your jig was designed? How do you fix it? Learn the feel of the blade in your hand against the belt. Learn how to read the grind as it progresses on the blade, where to apply pressure to move the grind this way or that. Learn when you are putting too much heat into the blade by the heat you feel in your fingers. Learn how to shift your weight and move your body to get smooth even grinds. Once you get good at freehand grinding then you can use jigs or other devices to help speed up production but at that point you will have the skills to fix problems should your grinding aids fail you.

Here is a chart developed by Steven Penner in another thread. Hope it helps.

 
Here's my advice Bill, don't make things more complicated than they need to be. In other words, don't worry about grind angles and what not. It takes some time and practice for your brain and hands to "sync" when you grind. To me, it sounds like you just need to get a feel for pressure. If your grind is moving towards the spine too quick, apply more pressure towards the edge. Also if you're wanting a full flat grind that dies out at the spine without cutting into it, you might want to leave a tiny amount of flat there pre-heat treat. You'll be able to take that tiny flat post heat treat when you have to thin the edge out anyway. Just stay focused and you'll get better with each blade.
 
Thanks i4marc for the advice and the chart. That is exactly what I was looking for. This site is great.
 
i4Marc said:
I think there is too much interest in jigs, formulas and systems when learning to grind. It will take time to learn to use those crutches. Why not put that same time into learning how to grind freehand. The time spent will be a better investment. If you rely on a device to help you get the angle you need what happens when you need a different angle for a different kind of knife? What happens when you are getting unintended results for a particular style of knife for which your jig was designed? How do you fix it? Learn the feel of the blade in your hand against the belt. Learn how to read the grind as it progresses on the blade, where to apply pressure to move the grind this way or that. Learn when you are putting too much heat into the blade by the heat you feel in your fingers. Learn how to shift your weight and move your body to get smooth even grinds. Once you get good at freehand grinding then you can use jigs or other devices to help speed up production but at that point you will have the skills to fix problems should your grinding aids fail you.

Here is a chart developed by Steven Penner in another thread. Hope it helps.

Click to expand...

I'm still trying to figure this chart out (I'm an eyeballer), but I think it's pretty cool. Especially when it finally clicks. :D
 
No problem Bill. That's what we're here for brother.


The top of the grind blending into the spine is a tricky detail. Adam has it right. Leave some flat at the top until after HT. Getting a nicely radiused transition from the plunge line into the spine is a delicate matter. Think of it like this: There are three things that affect that line - time, distance and pressure. If you press the blade straight into the belt then move it to the side you will get a square corner at the top. There are several ways to achieve a round corner, I would imagine. Others will offer their tips. This is how I do it. As your bevel grind progresses up the side of the blade have in your mind (or actually scribed on the blade) a point where you want that plunge line to start blending into the spine. Or if you are stopping your bevel someplace in the middle of the blade, maybe on a combat style knife, a place where you want to stop the bevel and run that grind line down to the tip. When your bevel gets to the height you want it is time to start the blend. Lay the blade GENTLY against the belt a short distance from the plunge. You are just feeling for the blade laying flat against the belt here but not applying any pressure. Move the blade slowly toward the plunge. When you get there, apply a bit of pressure at the spine of the blade as you are moving away from the plunge. You are actually feeding in pressure progressively harder as you move away from the plunge (not HARD hard, just harder as you go). You can start gently until you get the feel of it. It will take a few passes to build up the curve you want. Keep the blade moving smoothly. The more time you spend in one place the more material you're going to remove there. keep the motion fluid. Advice for grinding in general also applies here. Start with your weaker side. When you get the results you are happy with you can match those results on your stronger side. Practice on scrap.
 
I was going to say just under 2 degrees before I read the chart so I was pretty well right on. :cool:

Chris
 
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Don't worry about formulas.
Spend time at the grinder instead of your calculator.
If you don't want to grind into your spine - stop before you get there.
It's no more complicated than that.
At some point you will become "one" with your blade and the belt and you'll be able to feel what's going on.
Make a grind.
Take a look.
Use some lay-out dye or use a wide marker.
Slow down.
Learn by doing.
We all did.
By the time you get to the point where you'll walk up to the grinder and make exactly the kind of grind you want, you will have ground many, many, many blades. Dozens and dozens? Hundreds?
Yes.
And just so you know, the first knife you make that turns out exactly like you want it and to the high standards you want to achieve will cost you thousands of dollars in time, steel, materials, belts, etc.
 
+1 to Karl. I am new too and I went through the same obsession. I didn't think I could grind free hand with any accuracy after just a few attempts so I searched for the perfect jig to help me. I went through some variations and the best one still turned out a different bevel on each side. I tossed them all and went free hand and never looked back. It really isn't that hard to get results better than a jig or a formula once you get good platen and good belts. It's all about putting pressure on the side of the bevel you want to remove material from and "walk" the bevel up towards the spine. I'd say it only took me about ten blades to feel like I can achieve what I set out to do. Go free hand and never look back.
 
As far as chefs knives are concerned, as fun as it is to do freehand, if you are doing volume runs and want consistency and quality use a jig. If you have a fast machine say a craftsman 2x42, and are freehanding, you are bumping your learning curve immensely. Its a pain in the ass freehanding on a machine running 3.4k sfpm. Granted you will develop a "light touch" which will come handy when your are using a slower machine, it still sucks.

Using a jig, Just remember when to double your bevel angle on the opposite side. That is if you grind a 1.5 degree on one side, you have to grind 3 deg. To meet the apex on the opposite side.
 
I have learned more while filing blades than when I grind them. The motion and violence of the grinder throw off my rookie feelings.

Practice filing until you see your high spots and can feel which metal you bent to make them. Your file or your blade.

Then move to transition to a power grinder. I think that was the way I needed to do it.
 
If you are interested in producing quality flat grinds over a wide range with the ability to produce the same grind consistently over time; read some of the material around on the Bubble Jig.
If your interest is just turning out the blades and not really learning about grinding, get a sled jig; if you are interested in learning to grind with exact angles take a look at the Bubble Jig.

Fred
 
Karburized said:
Using a jig, Just remember when to double your bevel angle on the opposite side. That is if you grind a 1.5 degree on one side, you have to grind 3 deg. To meet the apex on the opposite side.
Click to expand...

Im not sure I understand this. I use a jig that i squared up in the mill so both sides would be ground at the same angle. To me if you grind both sides at say 5* you end up with a 10* angle. am I missing something, it looks like if you double the angle your grind line would be shorter on one side.
 
I ground freehand since the start. Struggled for a while. Then got Fred Rowes bubble jig, its a freehand jig and it works. I only used it to grind 3 or 4 blades and haven't needed it since . I still use it for swedges. In now grinding freehand, in a free country, listening to Freebird!
 
Theiskell said:
Im not sure I understand this. I use a jig that i squared up in the mill so both sides would be ground at the same angle. To me if you grind both sides at say 5* you end up with a 10* angle. am I missing something, it looks like if you double the angle your grind line would be shorter on one side.
Click to expand...

How I am reading it is if your knife rests on its ricasso or tang flats where it attaches to the jig, then you want the same angle for each side. If your jig attaches on the bevel, you will need to double the angle on the 2nd side.

Chris
 
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