Bevel grinding questions

Sean Yaw

Sean Yaw

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Feb 26, 2019
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Hi. I am going to be grinding bevels on a Lanny's clip slipjoint blade and have two questions:
1 - How do I get the top grind line parallel with the top of the blade instead of the edge? All of the blades I have ground so far have had the top of the grind parallel with the edge, so I have not had to worry about thinning the edge by differing amounts over its length. As you can see from the photo, the distance between the grind line I am aiming for and the blade edge varies across the length of the blade. The geometer in me concludes that if I keep the blade at the same angle throughout the grinding, the final edge at the belly of the blade will be thinner than it is at the base of the blade. This would suggest that ending with a consistent blade thickness would require decreasing the angle while grinding the belly. Is that correct? Any tips for how to do that? I have been using a bubble jig to keep the same angle but reliably varying the angle seems much more finicky.

2 - How do I get a crisp top grind line? The top of my grind lines never end up exactly where I want and are (to varying degrees) kind of wavy. Are there any tips to getting crips lines beyond practice? I am grinding bevels on a 1x30, so I imagine a wider belt would help, but more skill and knowledge would probably help even more...

Thank you for the advice.

IMG_06781.jpg
 
I thought that perhaps I could be exaggerating the effect of grinding with the top of the blade (instead of the edge) perpendicular to the belt on uniform edge thickness, so I calculated (he says confidently) what the variation would theoretically be. The difference in edge thickness would be about 0.014" between the narrowest part of the blade (base) and widest (belly) if I just ignored my concern and ground with a uniform angle and the top of the blade perpendicular to the belt. So it does seem as though it would be a bad idea to grind with the same angle throughout. Thanks. I am eagerly awaiting wisdom.
 
If you want the top grind line parallel to the spine, then make the edge profile parallel to the spine.

If you want your grind lines crisp, slow down the grinder and refine it with a 220 belt and do not go past that with your 400 grit and above belts.
 
Thanks, Adam. That makes sense that making the edge parallel to the spine would fix the issue I am talking about. What do people do when their edges are not parallel to the spine? There are quite a few knives I have seen that do not fit that description (bulbous tips). Do the makers modify the grinding angle to grind those knives?
 
Put up a picture.
Chance are they are doing the grind for the edge, and then blending it the top edge to where you want. Doing it equally on both sides takes experience.
 
These pictures not mine, unfortunately. I pulled them off the internet. If Bill and Enrique can do it, I should be able to, right? :)
couteau-lannys-clip-pena-tit-1-z.jpg
ruplesinglebladetrapper-01.jpg
 
AVigil said:
Put up a picture.
Chance are they are doing the grind for the edge, and then blending it the top edge to where you want. Doing it equally on both sides takes experience.
Click to expand...
Thats what I was going to write, but opposite. Concentrate on getting your top line straight and then grind and blend the edge to same thickness. Deffinently needs some practice and feel for the grind. Jig would make it easier.
 
You could also overlay you blank over piece of mild steel and cut out a practice piece and practice your grind on that. No amout of explanation can substitute actually doing it.
 
Yeah, luckily I screwed up the back square on the first attempt fitting up the blade, so I have a spare to practice the grind on first!
 
I'm interested to see how this progresses and what you come up with. To me one of the most aesthetically pleasing knives is the Randall 27. The top of the bevel doesnt follow the edge. I want to try something similar.
 
yaw said:
Really? I would have guessed it was even harder, since I would imagine you would want the hollow to span the whole surface of the grind.
Click to expand...
You can walk a hollow grind up. It doesn’t have to follow the shape of the blade to get the same edge thickness.

like this

oXRDw93.jpg
 
Yep on a hollow grind you gently move the grind up and blend in down to the edge. If you get good it will match on both sides, if not you will chase that grind all the way to the spine.
 
If the goal is to produce a grind line that is parallel with the spine I will make that the priority using the angle that gives me the result I'm looking for. I can always work the tip farther on in the grinding process. Using a BJ allows you to control the desired angle so you can grind from the tip to the rear of the blade if that is what's needed. There is no need to start at the ricasso and then grind forward unless that is what's called for.
You are correct in that a 1 x 36 belt not being the most desirable to grind blades on.
Fred
 
I'd be tickled to get that quality of grind on my 2x72!! Looks fantastic for a 1x30 (I have both!)
 
Remember that trapper I built with the "fixed" blade? This is why you just throw one that isn't great into the bucket and not away. The main takeaway here is you did it and you learned. As your skills grow you can come back to it and "fix" it. That too will help your skills grow. Keep it up man, your doing great!
 
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