Cutting Even Bevels

johnnyjump

johnnyjump

Well-Known Member
After ruining another blade at the end stages of grinding, this is one of those days I'm ready to throw in the towel and concede defeat. But I'm not a quitter, and I will figure this out one way or another! But any suggestions would be greatly appreciated!

I've been making knives for a number of years now, and have always had trouble getting clean plunge lines and even bevels. It doesn't matter if I'm using a bevel jig, or free-hand, I just can't get a decent bevel grinding from my right to left. Left to right is no problem, but right to left is next to impossible. I try to concentrate on locking my elbows and moving my hips with a nice, even pressure, bit I still end up with that smily face on the grind line taunting me as if to say, "loser!" :):( I've decided to go back to square one and practice on some cheap bar stock, which has shown some improvement, but I still can't pinpoint what I'm doing wrong when I grind right to left.

My question is two-fold: how do I avoid the smily face, and what to I do to correct the problem if I get one? It seems once I try to correct the problem by easing up or reapplying pressure, it makes matters worse.

Help! :oops: Thank you in advance.
 
I can't picture what you mean by "smily face". With plunge cuts, you ALWAYS start forward of where you want them to end up. How far forward depend on how good/lucky you are when getting them into a final location. I generally leave them 3/32" to 1/8" forward of where I want them to end up..... then, when the rest of the blade is finished on the grinder, I put on a worn 220 grit, run it over the edge of the platen (or wheel if using it) and GENTLY cut the plunge in with a "straight in" move....and then slight pressure into the plunge. I get them very close with the 220, then do the same thing with 400 and 600 on the machine.....from there it's hand finishing to blend. My grind are mostly flat, with convex edges, done on a flat platen.

Even after 30+ years of doing it, plunges remain a variable in every knife I build..... and it is CONSTANT practice...... because if you don't do it for a while....it is a perishable skill.
 
johnnyjump said:
After ruining another blade at the end stages of grinding, this is one of those days I'm ready to throw in the towel and concede defeat. But I'm not a quitter, and I will figure this out one way or another! But any suggestions would be greatly appreciated!

I've been making knives for a number of years now, and have always had trouble getting clean plunge lines and even bevels. It doesn't matter if I'm using a bevel jig, or free-hand, I just can't get a decent bevel grinding from my right to left. Left to right is no problem, but right to left is next to impossible. I try to concentrate on locking my elbows and moving my hips with a nice, even pressure, bit I still end up with that smily face on the grind line taunting me as if to say, "loser!" :):( I've decided to go back to square one and practice on some cheap bar stock, which has shown some improvement, but I still can't pinpoint what I'm doing wrong when I grind right to left.

My question is two-fold: how do I avoid the smily face, and what to I do to correct the problem if I get one? It seems once I try to correct the problem by easing up or reapplying pressure, it makes matters worse.

Help! :oops: Thank you in advance.
Click to expand...

Couple things you can check.

Is your platen flat?

Does the right side edge look like the left side, or is one side more radiused?

**Is the platen pushed out far enough so that there is no gap between the belt and the platen? The platen is not always square to the rollers, meaning one side of the belt can give slightly while the belt is firm against the platen on the other side.

Are you using the same grip for both directions? Same amount of support or pressure with the support hand?
 
This is something I have trouble with as well. Ed's method works well. I've started using a slight variation on his method with decent success. For me I seem to do better on thicker stock also. I also use a Bubble jig almost all the time. That little bubble helps me tremendously.
 
JJ, if I understand your problem correctly, one bevel has a straight line from your plunge cut to the upper part of the blade where you end the grind. On the other side of the knife, your bevel has a curve (smiley face) from the plunge cut to where you end the grind toward the front end of the knife. I fight that very same problem every time I grind a blade if I don't concentrate. Bob Dozier has watched me and has critiqued my grinds and has advised me that I have a "lazy hand" on the side with the curve. Meaning I allow my hand to dip a bit and not stay straight or level as I bring the grind across. By dipping I mean I let the hand holding or steering the back end dip just a wee bit and it causes the curve in the grind line. Try to keep the rear hand holding the handle end level or straight through your grind sequence and see if that helps any.
 
The hand holding the tang steers the blade across platen. 3 basic movements. You can twist the tang which adjusts if you're applying more pressure to the spine or the edge. You can push or pull the tang toward you or away from you which mostly adjusts pressure from the left or right side of the contact area being ground as it moved across the platen. You can move the tang up or down from parallel which will mostly amplify one of the other movements.

I'm no pro, but when I get stuck in a loop not getting a grind straightened out, those are the terms I think in. Isolate and adjust one at a time, and go to a higher grit belt to so changes aren't too drastic and can't be undone.
 
I'm still learning and haven't ground that many blades. The way I learned I use the tool rest and a push stick similar to you I have a stronger side. I don't know if you're taking full passes every time, but when I run into you're problem(I hope I understand smile is on the spine) I concentrate on the problem areas move my push stick to remove more material were needed. Sometimes I'll use a marker on the opposite side as a guide . It doesn't sound like you use a push stick but the principal should be the same apply more pressure to problem areas remove material slowly , check a lot ,when refining lower grit.I feel funny giving advice hopefully it helps.
 
I am always a bit confused on how the cut happens. For example if I have a two length of bar steel and press it against a two inch platen , if I don’t move and just hit and pull back, the bevel line should be level.
So when I press an 8 inch blade against the platen and start moving left to right at a consistent speed did the first two inches of the blade get more , less or the same amount of cutting time? Am I overthinking this?
 
Retroguy said:
I am always a bit confused on how the cut happens. For example if I have a two length of bar steel and press it against a two inch platen , if I don’t move and just hit and pull back, the bevel line should be level.
So when I press an 8 inch blade against the platen and start moving left to right at a consistent speed did the first two inches of the blade get more , less or the same amount of cutting time? Am I overthinking this?
Click to expand...
Yes, no, and maybe.
It should be the same cutting time, but if you present the blade at angle on any plane, and everybody does, whatever spot hits first will grind more quickly. So if you lead in with the edge, the spine, the plunge, or the middle of the blade, that first point of contact will grind faster. This effect is pretty apparent at low grits.
 
Retroguy said:
I am always a bit confused on how the cut happens. For example if I have a two length of bar steel and press it against a two inch platen , if I don’t move and just hit and pull back, the bevel line should be level.
So when I press an 8 inch blade against the platen and start moving left to right at a consistent speed did the first two inches of the blade get more , less or the same amount of cutting time? Am I overthinking this?
Click to expand...

That is a great question, and the answer is yes until you develop a very soft touch. That’s why so many people will recommend that you don’t start your grind in the same place every time. And especially don’t dwell on the plunges.

But you can also use this to your advantage. On kitchen knives where you want a lot of distal taper to get very thin at the tip, it helps to spend some time starting the grind near the tip, travel to mid blade, then back to the tip end again. That way the tip end spends twice as much time on the belt. Average time on the belt at the same pressure is much easier to control than using pressure to try to grind deeper. It makes for very even, very blended grinds, whereas varying your pressure can cause dips and waves.

You do need to learn how to adjust pressure, how to twist, etc. to control your grind line. But pressure isn’t the only tool in your arsenal.
 
EdCaffreyMS said:
I can't picture what you mean by "smily face". With plunge cuts, you ALWAYS start forward of where you want them to end up. How far forward depend on how good/lucky you are when getting them into a final location. I generally leave them 3/32" to 1/8" forward of where I want them to end up..... then, when the rest of the blade is finished on the grinder, I put on a worn 220 grit, run it over the edge of the platen (or wheel if using it) and GENTLY cut the plunge in with a "straight in" move....and then slight pressure into the plunge. I get them very close with the 220, then do the same thing with 400 and 600 on the machine.....from there it's hand finishing to blend. My grind are mostly flat, with convex edges, done on a flat platen.

Even after 30+ years of doing it, plunges remain a variable in every knife I build..... and it is CONSTANT practice...... because if you don't do it for a while....it is a perishable skill.
Click to expand...
 
What I mean by smily face is the line of the bevel slopes upward as it moves toward the tip of the blade. I’m sure what it means is there’s more meat on the blade as it moves toward the tip. If true, I must be applying more pressure toward the Ricasso and somehow easing up as I finish each pass. Try as I may, I can’t seem to get even pressure moving right to left as I apparently am left to right. Make sense?
 
John Wilson said:
Couple things you can check.

Is your platen flat?

Does the right side edge look like the left side, or is one side more radiused?

**Is the platen pushed out far enough so that there is no gap between the belt and the platen? The platen is not always square to the rollers, meaning one side of the belt can give slightly while the belt is firm against the platen on the other side.

Are you using the same grip for both directions? Same amount of support or pressure with the support hand?
Click to expand...
 
I just installed a glass platen, so I’m sure it’s flat. The platen also seems to be properly squared and out slightly ahead of the rollers. I’m thinking it has to do with the difference between my right and left handedness, meaning I must be applying inconsistent pressure on my right hand.
 
Rick Weaver said:
JJ, if I understand your problem correctly, one bevel has a straight line from your plunge cut to the upper part of the blade where you end the grind. On the other side of the knife, your bevel has a curve (smiley face) from the plunge cut to where you end the grind toward the front end of the knife. I fight that very same problem every time I grind a blade if I don't concentrate. Bob Dozier has watched me and has critiqued my grinds and has advised me that I have a "lazy hand" on the side with the curve. Meaning I allow my hand to dip a bit and not stay straight or level as I bring the grind across. By dipping I mean I let the hand holding or steering the back end dip just a wee bit and it causes the curve in the grind line. Try to keep the rear hand holding the handle end level or straight through your grind sequence and see if that helps any.
Click to expand...
 
I think your experience seems to mirror my problem perfectly. I just wish I had someone available like you to look over my shoulder. It’s probably time for me to register for a class if I could find one close to me in NW Arkansas.
 
On a related subject, I’ve also run into problems if I finish the flat AFTER I’ve finished my bevels. By that I mean I’ll finish the flats at 300-400 grit, which reveals all the high and low spots on the bevel grind lines. The only solution I see is to finish the flats BEFORE I finish the bevels. Does anyone else have any experience with this? Thanks!
 
Do you mean the plunges?

If so then yes. You can finish the plunges as the last thing you do. Ed’s response has great tips on doing just that.
 
johnnyjump said:
After ruining another blade at the end stages of grinding, this is one of those days I'm ready to throw in the towel and concede defeat. But I'm not a quitter, and I will figure this out one way or another! But any suggestions would be greatly appreciated!

I've been making knives for a number of years now, and have always had trouble getting clean plunge lines and even bevels. It doesn't matter if I'm using a bevel jig, or free-hand, I just can't get a decent bevel grinding from my right to left. Left to right is no problem, but right to left is next to impossible. I try to concentrate on locking my elbows and moving my hips with a nice, even pressure, bit I still end up with that smily face on the grind line taunting me as if to say, "loser!" :):( I've decided to go back to square one and practice on some cheap bar stock, which has shown some improvement, but I still can't pinpoint what I'm doing wrong when I grind right to left.

My question is two-fold: how do I avoid the smily face, and what to I do to correct the problem if I get one? It seems once I try to correct the problem by easing up or reapplying pressure, it makes matters worse.

Help! :oops: Thank you in advance.
Click to expand...
I know EXACTLY what you mean by the smiley face. Grind line is higher at the plunge line and towards the tip and bellies downward in the middle, ive been fighting it too, I’ve just been working that middle section on the platen to bring it back in line with the rest of my grind
 
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