Your drawing illustrates my point. As the clamp is tightened the blade leans to the left off vertical as shown in your illustrations. I don’t think it has anything to do with right or wrong, just physics. And it’s not just the blade, the jaws themselves flex to the left. You can clamp a quarter in it and it flexes or leans left.
Hey Jordan, can you explain this a little bit more? Wouldn’t +1 and a -9 be a spread of 10 degrees? not 8? I just caught this as I did a video on this… maybe you can explain it better lol. Thanks!
As I was thinking about this more, I think you can do it either way…
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either you can take the higher number and subtract the lower number, then divide that number in half to figure the cant, or
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you can add the two numbers (1+9 = 10) and divide in half (5) which will give you the target of what each side should actually be at. So the difference between ‘5’ and what it truly is ‘1’ or ‘9’ is a spread of 4 degrees. And you adjust accordingly…
what do you think?
I strongly believe that Jordan’s math is correct. One angle clockwise and second is counterclockwise, so it is positive 1 and negative 9. the sum is negative 8, adjustment is half, meaning 4 per side.
But your method is much more simple. I will try it next time.
Thank you to both of you.
[quote quote=“razoredgeknives” post=18650]As I was thinking about this more, I think you can do it either way…
-
either you can take the higher number and subtract the lower number, then divide that number in half to figure the cant, or
-
you can add the two numbers (1+9 = 10) and divide in half (5) which will give you the target of what each side should actually be at. So the difference between ‘5’ and what it truly is ‘1’ or ‘9’ is a spread of 4 degrees. And you adjust accordingly…
what do you think?[/quote]
Yeah basically you’re just subtracting the lower number from the higher number every time and dividing in half, then adjust your angles accordingly. I put the positive and negative signs there to give a visual of what you’re seeing when you put the cube on the blade. The result should actually read -8/2 = -4 which technically means that the centerline of the blade is leaning 4 degrees towards the negative direction (left). -8 is just the sum of +1 and -9.
Aargh! The AngleCube gives you the angles relative to a zero, but you can’t treat them as positive and negative numbers! You are reading values which are simply above or below the zero reference. Consider this: If you zero the AngleCube when it’s lying on its side, it will read 91 degrees on the left side and 81 degrees on the right, for an included primary grind angle of 10 degrees. The centerline of the blade is therefor displaced five degrees from the faces. Since the left face says it’s at one degree, that means the blade is leaned 4 degrees toward the left side.
Set your angles at 4 degrees lower than nominal on the left and 4 degrees above nominal on the right.
So, I have two questions.
- Would this also apply to other grinds like hollow grounds? As long as the clamps are on the flats?
2)What if the blade cants to the right, instead of to the left? Same math and everything, just for the right side?
I ask because I can’t for the life of me get this ZT 0560CBCF centered or even near centered in the clamp. It’s canted off to the right and you can visually see it. Maybe I’m doing something wrong?
I’m not treating the angles themselves as positive and negative numbers but in the sense of a number line where for example 0 is in the middle and everything to the left of zero is negative and everything to the right is positive. No matter how the angle cube is zeroed, measuring this way you’d still get a sum of -8. This method works and the cad backs it up. Everyone may understand it in a different way or have their own way of doing it. As long as the results are the same, then that’s fine. If it’s too complicated then butt the left side flat against the jaws every time and you know that side is always zero. Measure the right side and divide by two. Common sense will tell you to move the left arm inward X number of degrees and the right arm outward or further away.
[quote quote=“KnottyEagle” post=18655]So, I have two questions.
- Would this also apply to other grinds like hollow grounds? As long as the clamps are on the flats?
2)What if the blade cants to the right, instead of to the left? Same math and everything, just for the right side?
I ask because I can’t for the life of me get this ZT 0560CBCF centered or even near centered in the clamp. It’s canted off to the right and you can visually see it. Maybe I’m doing something wrong?[/quote]
My answers: (1) If the flats are parallel to each other, the blade should clamp vertically. If not, then yes, but I don’t think you’d be able to get a valid reading to base it on.
(2) Because the left vise jaw is always vertical, no symmetrically ground blade should ever cant to the right. If it does, it’s not clamped correctly. An asymmetrical grind wouldn’t apply either.
If you add +1 and -9 and get 8, you must be adding them as positive & negative numbers. They simply tell you how far on either side of a particular point they fall. One degree to the right and nine degrees to the left. Ten degrees apart.
I’m going to jump back in and show this vid i just did a day or two ago… don’t know if it is the exact correct way to calculate but it gets the right answer =) see what you think.
Wow, that solved so many things that have been making me crazy…
Thanks!
Good idea. Thank you.
The method described by uofaengr and Josh at RazorEdgeknives gets you to where you need to go.
I prefer a slightly different scheme for FFG blades. I calculate the angular displacement between your knife’s two faces ahead of time. This gives me the centerline of the blade, which I record for all future sharpenings. Then, when I mount the blade in the jaws of the vise, I am looking for a zero-degree angle for the left face. This is very easy to attains, as the blade wants to settle there anyway. I kick the bottom of the right-hand vise jaw out by at least the total grind angle to ensure a positive clamp. Since I know the blade’s centerline angle, say 1.75 degrees, I know the blade is canted 1.75 degrees to the left and that value is exactly how much to deduct from the left angle and how much to add to the right angle.
The easiest way to measure the angle for your blade? Mount the knife in a vise (not necessarily your WE vise) with the blade entirely exposed. Place your AngleCube against one face. When you are satisfied that the reading is valid, zero the readout. Now move the AngleCube to the other face. The reading you get is the total displacement between the two faces - the primary grind angle. One half of that will be the angle of the centerline. No confusion, no arithmetic formulas. Straightforward and repeatable.