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TOPIC: Why are my blades tilted in the clamp?

Re:Re: Re:Re: Why are my blades tilted in the clamp? 4 weeks 2 days ago #18562

  • tcmeyer
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My comment was directed at the situation where the left side of the blade is flat against the stationary jaw. The right side jaw is "kicked" out at the bottom to match the right side face of the blade.

In a situation where the left side of a FFG blade is at -1.2 and the right is at +3.2, then the total primary grind included angle is 4.4 degrees. The centerline of the blade is assumed to be centered at 2.2 degrees. If the left face reads 1.2 degrees, then the blade is leaning 1.0 degrees to the left. For a 20/20 bevel, you'd set for 19 deg. left and 21 deg. right. Just think in terms of the blade's centerline.
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Re:Re: Re:Re: Why are my blades tilted in the clamp? 4 weeks 1 day ago #18576

  • razoredgeknives
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tcmeyer wrote:
My comment was directed at the situation where the left side of the blade is flat against the stationary jaw. The right side jaw is "kicked" out at the bottom to match the right side face of the blade.

In a situation where the left side of a FFG blade is at -1.2 and the right is at +3.2, then the total primary grind included angle is 4.4 degrees. The centerline of the blade is assumed to be centered at 2.2 degrees. If the left face reads 1.2 degrees, then the blade is leaning 1.0 degrees to the left. For a 20/20 bevel, you'd set for 19 deg. left and 21 deg. right. Just think in terms of the blade's centerline.

Wow, this totally makes perfect sense, thanks Tom! I don't know why I couldn't think clearly about this before but I understand now. Thanks!
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Re:Re: Re:Re: Why are my blades tilted in the clamp? 4 weeks 1 day ago #18577

  • uofaengr
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I did this quickly in CAD so bear with me, and I'll try to explain as not to confuse anyone. I used CAD to create perfect lines and angles plus CAD has a measure utility where the angles of two lines can be measured. Everything I have written by hand was measured with CAD.

The first picture represents a FFG blade mounted in the vise, and shows a common scenario that happens to me almost every time in that one side of the blade is not at a perfect zero degrees (usually the LH side) and is canted towards the right. In all of these illustrations, towards the left is the negative direction and towards the right is the positive direction relative to the centerline of the blade. Our goal is to sharpen the centerline of the apex as not to create uneven bevels that are different sizes and not in line with the centerline of the blade. The blade in this example is ground at 10 degrees inclusive for a nice, round number. The dashed line running through the center of the middle triangle is the centerline of the blade, and the two right triangles on either side of the "blade" represent the vise jaws.

In this scenario, when we tighten the blade and place the angle cube on the LH side, we get a reading of 1.0 degrees. Placing the cube on the RH side, we get a reading of 9.0 degrees. Common sense tells you which direction these angles are relative to (9 degrees leaning left or right) but the angle cube has two tiny arrows that will tell you whether it's leaning clockwise or counterclockwise relative to zero which in this case is equal to the vertical inner surface of the vise jaws. Knowing our positive and negative directions, the formula below shows positive 1.0 degrees plus a negative 9.0 degrees which equals negative 8.0 degrees or the blade in total is leaning 8.0 degrees toward the LH side...or does it? What we're interested in is the centerline of the blade so dividing 8 in half gives us 4.0 degrees. As proved by CAD, the centerline of the blade is in fact exactly 4 degrees toward the negative direction relative to a vertical zero degrees. If we're seeking to sharpen the centerline of the apex at a true 20 degrees per side, we would place the LH stone at 16 degrees and the RH stone at 24 degrees to have a true 40 degree inclusive cutting edge.



The second image shows what happens when the blade is tilted and we set our stones at 20 degrees to sharpen. Relative to the centerline of the apex, the LH stone set at 20 degrees is actually 24 degrees, and the RH stone set at 20 degrees is actually sharpening the apex at 16 degrees resulting in widely uneven bevels and an off-center apex.



The final image shows what happens when we use the math from the first image to make sure we are properly sharpening the centerline of the apex. Setting the LH stone at 16 degrees and the RH stone at 24 degrees puts our stones both a perfect 20 degrees relative to the centerline of the blade. I forgot to mention that the bolder lines on the outside represent the stones placed against the edge.



I hope this helps anyone that has trouble getting even edges on FFG blades or that has difficulty with the math. Now back to work. ;)
Last Edit: 4 weeks 1 day ago by uofaengr.
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Re:Re: Re:Re: Why are my blades tilted in the clamp? 4 weeks 1 day ago #18583

  • razoredgeknives
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Man... this should be in the wiki!! is it ok to include these images in a video Jordan? I think it would help ppl visualize as well... I will try to do one soon.
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Re:Re: Re:Re: Why are my blades tilted in the clamp? 4 weeks 1 day ago #18584

  • uofaengr
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Not a problem, bud. They're to help everyone so use as you wish! :)
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Re:Re: Why are my blades tilted in the clamp? 4 weeks 1 day ago #18585

  • GibCurry
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GEEKMEDIC wrote:
Thank you Sir. Your post on the knife sharpening class you took inspired me to find a class at the Phoenix Knife Shop, which I am going to take next month. I have never been able to get anything resembling a sharp edge by hand, but the knowledge I am gaining here is starting to make me think I might be able to get closer with some instruction. I also appreciate you saying you fumble with the math. Perhaps you might clear something up for me. In the picture above it shows a cant to the left of 3.2 degree. If I am figuring it right, and that is a big if, it seems to me that in order to address a 20 degree edge correctly I should have the left stone at 16.8 and the right at 23.2. Is that correct or am I off my rocker?

Let us know how the sharpening class goes. I was pleasantly surprised how much it helped me WE sharpening. And it is also true that the WE sharpening gave me something that helped me better myself free hand.

I can't tell you how happy the other guys jumped in to explain the angle conundrum with FFG blades.

Your question is, obviously, very timely for all of us. Thanks for speaking up.

~~~~

Great information everyone...Thanks a bunch.


For Now,

Gib

-- Sent via HTC One using Tapatalk.
~~~~

For Now,

Gib

Φ

"Things work out best for those who make the best out of the way things work out."

"My goal is to be a good, practical knife sharpener. My dream is to polish molecules."
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Re:Re: Why are my blades tilted in the clamp? 4 weeks 1 day ago #18586

  • 5string
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One thing that I notice on my WE, and I assume all do, that can cause the blade to cant left is the clamping action itself. As the bottom screw is tightened it creates incredible bending (and clamping) force, moving the uppermost part of the clamp jaws to the left. That movement is amplified if the top screw is not sufficiently tightened. Clamp and watch the blade closely as the bottom screw is tightened and you will see the blade rotate to the left as the clamp jaws flex to the left. I don't see this as a problem. Rather, the point is that the lower screw exerts incredible bending and clamping force and as it does it also torques the clamp jaws to the left. This makes sense - as the bottom of the right jaw moves to the right, the top must move to the left. To limit that rotation, the top screw must be tightened completely, and securely.

I think. Or am I missing something?
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Re:Re: Why are my blades tilted in the clamp? 4 weeks 1 day ago #18587

  • GEEKMEDIC
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5string wrote:
One thing that I notice on my WE, and I assume all do, that can cause the blade to cant left is the clamping action itself. As the bottom screw is tightened it creates incredible bending (and clamping) force, moving the uppermost part of the clamp jaws to the left. That movement is amplified if the top screw is not sufficiently tightened. Clamp and watch the blade closely as the bottom screw is tightened and you will see the blade rotate to the left as the clamp jaws flex to the left. I don't see this as a problem. Rather, the point is that the lower screw exerts incredible bending and clamping force and as it does it also torques the clamp jaws to the left. This makes sense - as the bottom of the right jaw moves to the right, the top must move to the left. To limit that rotation, the top screw must be tightened completely, and securely.

I think. Or am I missing something?

Incredible information! And thanks so much everyone for taking the time to respond. I agree that as the bottom screw is tightened it moves the blade even farther. I did some checking with the angle cube attached as I tightened the bottom screw and it definitely moves the blade as it is tightened. I am not worried about the fact that it moves, only how to adjust the stones. Now that I understand that a little better life is moving along nicely :)
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Re:Re: Why are my blades tilted in the clamp? 4 weeks 1 day ago #18588

  • razoredgeknives
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I have not noticed the blade moving before! I will have to keep an eye on that next time to verify.

One thing that may be the issue is that people are clamping incorrectly... Before you clamp you should make sure that your bottom screw is protruding about the same width as the spine of your knife. then you clamp the top screw as tight as you can. At this point you will notice that the bottom screw is holding the jaw out so that the gap in the middle of the vise is almost parallel the whole way down (it will be slightly smaller at the bottom, but not much). this is when you tighten the bottom screw until the gap is perfectly parallel all the way from top to bottom.

give this a whirl and see what you think...
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Re:Re: Why are my blades tilted in the clamp? 4 weeks 1 day ago #18589

  • tcmeyer
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Having a blade move on you during the clamping process says in big, bold letters that it ain't being clamped right!

With FFG blades, I always hold the left flat of the blade flat against the left jaw of the vise. This is a positive fixed position that you'll be able to repeat. Shims and pads and such are not repeatable without a lot of care and measuring.

With the blade held flat against the left jaw, I loosen the top screw and then pinch the top edges of both jaws together, holding them both flat against the blade. I then take up the slack in the top screw, taking care not to move the right jaw. With the top screw very lightly tightened, I run the bottom screw in until it makes contact, then make one-quarter to one-half more turns to tighten the vise. This works with most FFG blades, but thick blades may be beyond the range of the screws.

The following drawing shows the general idea. It shows an FFG blade with a 5.3 degree grind, but that might also be beyond the range of the vise. I have done knives up to 4.4 degrees.

And the blade does not move!

FFGviseset-up.jpg
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