Knife bevel grinding help

T

Trevor51

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Jun 24, 2015
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I'm a beginner knife maker and all I have is a 1x30 belt sander. I am currently trying to figure out how to grind a bevel on a knife. I have a simple piece of angle iron with a bolt to tilt the bevel on the jig. (One of those really simple grinding jig) I am really confused on how high the set screw should go to have the correct bevel on my knife. My knife is one inch wide and I want the bevel running 3/4 of the width. I am 14 so I'm not sure if this is really simple math that I will learn later in school. Also this might be a really dumb question but I'm having a hard time figuring it out. Sorry for the confusing post but I hope someone will understand it and help. That's for your time
 
I have always just done what feels right. Like Tump said, Start at a steep angle and as you get close to the middle of the steel, start decreasing the angle of the bevel until you are near the center of the blade thickness and where you want your grind lines to be. Really, it's just feel, but if you want to go all mathematical on this project, the equation you are thinking of is Pythagorean's Theorem; A2+B2=C2. To be honest though, nothing beats good old practice and good hand eye coordination :)
 
but if I started steep and moved to less of a angle when I get down the center of the material wouldn't it give me a convex bevel?
 
Also, on a lot of the 1x30s, the back plate for the belt flexes quite a bit. Make sure yours doesn't, or beef it up if needed.
 
Trevor51 said:
but if I started steep and moved to less of a angle when I get down the center of the material wouldn't it give me a convex bevel?
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This is really hard for me to explain so bear with me...
Hypothetically speaking, yes it will if you don't spend enough time grinding at each shallower and shallower angle. As you approach the desired edge thickness (usually between .005" and .015"), you stop changing the angle . You continue using that shallow angle until everything is flat and your grind lines and edge thickness is where you want them to be. I hope this makes sense?

Also, ctaylorjr is right, your 1x30's platen will have a considerable amount of play in it and will probably yield a slightly convexed/uneven bevel due to the movement of the platen. Try to support it with something to give it some rigidity to keep it from flexing.
 
Just to add what others have said, make sure you support the platen on the 1x30, it is too soft to give good support for knife grinding. I started out on a 1x30 and ended up making a new platen but you can use a block of wood wedged in that "triangular" space to give it some backing.

You may also want to put a piece of sheet metal on top of the 1x30 table... that table has groves in it that will make it difficult for you to push your jig and knife blade into the belt; you'll be able to slide it left to right but you'll have a hard time pushing it forward and pulling back with the screw sticking out of the bottom of the jig.

As for the angle, you will learn all you need to know when you take geometry and the math isn't terribly difficult to learn. The easiest way to figure out what works without math is like BackardCrafter said: start with the blade at 30-45 degrees to the belt to start your bevel, get the "edge" to be about 0.03-0.04" thick (you should leave it a little thick at the edge before heat treating) and then make the angle more and more narrow until you get the bevel up to 3/4 of the blade width. I think you were looking at it the other way where you start with the blade almost flat against the belt and roll it forward as you pull the knife back, which would give you a convex grind. Think of grinding your bevel edge-to-spine and it might make a little more sense.

It might also help you out if you get a steel protractor from a hardware store, like the Empire stainless steel protractor and you can find the angle between the face of your jig and the table on the grinder. Once you work on the bevel until you get it where you want you can measure the angle and have a good idea where to set the jig for future knives.

In my opinion it would also be a good idea to learn how to hand sand/file as well. Nick Wheeler has some great videos on hand sanding blades and it is pretty easy to shape a hand sanding tool from some hard wood using your grinder. It is difficult to get a good, flat, final grind with the 1x30 in my experience and hand sanding will allow you to go slow and really polish out the bevel. The 1x30 is a fantastic tool for getting 90% of the grinding done so you aren't stuck using a file to shape the entire bevel... but it is challenging to really get the bevel even and clean with it.
 
get a digital angle finder $30 at harbor freight. start at 10 degrees for the first knife. After you get the idea you can experiment to see what you prefer. under 10 degrees for higher grind lines (bevels) over 10 for shorter.
 
Matthew R.L. Malone said:
Get the "edge" to be about 0.03-0.04" thick (you should leave it a little thick at the edge before heat treating)
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I completely forgot to account for heat treat. My bad. Make sure to leave the edge a a bit thick prior to heat treat as Mr. Malone stated. If you take the edge down too far, it will essentially turn to bacon ( it will warp).
Thank you for correcting me :o
 
Ok thanks every one I'll work on my knife today using your guys suggesting thanks for your help. Just a quick question when making a larger knife for chopping is it nessasary to have the spine of the knife heat treated differnt then the bevel to have it flex at the spine. And should I go a convex grind on that? A little off topic but I didn't want to make a new thread.
 
Trevor51 said:
Just a quick question when making a larger knife for chopping is it nessasary to have the spine of the knife heat treated differnt then the bevel to have it flex at the spine. And should I go a convex grind on that? A little off topic but I didn't want to make a new thread.
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Although softer spines can be beneficial for preserving toughness for chopping, differential heat treatments can be very tricky and definitely aren't necessary for having a good chopping knife. Convex grinds are popular with chopping knives but again, not necessary. Flat V-grinds are often viewed as good once-size-fits-all kind of grind, you can think of it as halfway between a hollow grind and a convex grind in terms of trade-offs. But hey go for it, experimenting will let you learn what works :thumbup:
 
This^^^ look how much he will learn! 14 and looking for a mathematical answer! That's great, but I don't think math is the answer to this one. Keep trying, you'll mess a bunch up, but you will learn from each one. Pretty soon you will have a good looking knife, and lots of life lessons you never even realized you learned.
 
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