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How I find the "Sweet Spot" (4 Parts)

This topic contains 23 replies, has 10 voices, and was last updated by  MarcH 09/24/2018 at 8:05 am.

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  • #45204

    MarcH
    Moderator
    • Topics: 53
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    Richard, I would select your answer #1.  For me the sweet spot is the balanced placement where the knife is clamped in a position that the stone will reach the knife edge all along the entire bevel length as close to an equal amount of contact as possible.  When clamped in the sweet spot the amount of metal removed at a given set angle should be as close to equal along the entire blade.  With a good sweet spot the variation, of metal removed along the blade, will be very minor.  If the amount of metal removed at one portion of the blade is a great difference from another portion of the blade the knife can be clamped in a more appropriate position.

    After the first time the knife is sharpened, clamped at that selected sweet spot position, with each repeated sharpening,  in that same clamped position, the sweet spot will match right-on because all the minor variations have been profiled to line up with the stone.  That is to say all the uneven metal has been removed to shape by that first selected sweet spot clamped position.

    Some knives are hand ground and free hand sharpened.  Their custom shapes may be difficult to match the fixed angle WE sharpening system.  It may be near impossible to find a sweet spot for these knives.  That is a single clamping position that allows you to reach the entire bevel similarly.  These knives may be sharpened easier by doing them in sections then moving and reclamping the knife again.  Then these portions are blended together at the end.

    Just to be clear, if you have chosen to profile your knife to a blade or bevel shape of your own liking or design then the knife should be clamped in a position to best allow removal of steel from the areas you want to remove the metal from.  Then with subsequent sharpenings this same clamped position will also then be the clamping sweet spot.

     

    Marc
    (MarcH's Rack-It)

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    #47311

    MarcH
    Moderator
    • Topics: 53
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    Here’s a more recent WE Forum post on this same subject matter; finding the “sweet spot” and “matching the original bevel”.  It’s well worth your time to read this:  https://knife.wickededgeusa.com/forums/topic/starting-point-for-zero-tolerance-0801/#post-47304

    Marc
    (MarcH's Rack-It)

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    #47313

    Bob
    Participant
    • Topics: 3
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    Hi MarcH,  can you help me with 2 areas I’ve ran into unsuccessful progress?  In your process when you are setting up the knife  and you can tell the Sharpie ink at the tip has been left on below the bevel,  you “loosened the vice and rotated the tip down while keeping the knife heel resting on the one forward key pin” how  much do you (let’s use the back of the blade reference) lift the blade off the rear key pin to start?  Do you start with very small increments such as an 1/8 of an inch or do you do even less?  Like a 1/4 of an inch or more. As you realize the tip needs to be “rotated” down even more, again, what kind of incremental measurements do we use!? Fractions of an inch?

    A late attempt last night on a French (chefs)  knife,  I had no success trying to find the sweet spot as I kept rotating the tip down until I ran out of spine to clamp. I thought maybe the knife was either set in the jaws to far forward (or backward) so I brought the knife back in the clamp (closer to my chest)  and started over. After I rotated as much as I could, again running out of spine to clamp,  I called it a night and would wait till today to ask.

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    #47317

    MarcH
    Moderator
    • Topics: 53
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    Bob , You didn’t specify the pin position, if the pin was placed in the upper holes I would try moving the pin down to the lower holes, first.  If I got the majority of the knife to line up in the upper holes It should still do the same, now resting on the pins in the lower key holes.  Then I’d see if that affect the tip any.  You may find you have to go back to the upper pin holes.  It’s a lot of “trial and error”

    I have to say up front that it’s a give and take situation.  As I wrote in the post, you may have to sacrifice a small amount of steel in the initial profiling of a knife the very first time you sharpen it on your WEPS.  That being said, all my movements are small incremental movements.  I reapply the sharpie and reuse the stone across the bevel then re-inspect.  Move, reapply, reinspect.  It may get a little better then nothing else makes an improvement.  Sometimes I find I can just slide it backwards, or forward to get it right.  Sometimes you have to “quit while you’re ahead.”

    You may get the knife so the heel, the belly and all but the very small portion of the tip is good.  That’s the best you can do.  Remember it’s a compromise.

    Sometimes due to the shape of the tip on some knives, (e.g. those with a curved tip),  I have to roll or rotate the stone around the tip curve to maintain contact with the steel and this reaches the very last strip of steel.  For these knives with the stone rotated at the tip, I work just the tip area separately and blend it to the rest of the knife. I want to follow the curl or roll of the tip still working the stone flat and off the tip, but avoid rolling over the bevel.

    For a straighter tipped knife I just may have to work with what I have.  Either way you choose to do it, it’s “give and take”, and you may sacrifice a portion of a mm or so of the knife’s total length off the tip the first profiling.  If you record the positioning well in your log, with as many points of reference as you can, you’ll be able to get it right in this same place for future touch-ups. This is where the Advanced Alignment Guide works well.  Remember the guide need not reach beyond the knife’s tip to give you points of reference to save in your “sharpening log”.  As long as the blade crosses the grid a some points you can record,  multiple “X” and “Y” positions.  This could be the heel or the spine, or a part of the blade of the knife.  As long as it’s recreatable.

    Remember the knife was not ground in a fixed angle jig so it may not match up perfectly across the entire length of the blade.  All you can do is the best you can do.  After the first profiling with good positioning and minimal steel loss you’ll never notice the difference.

    Marc
    (MarcH's Rack-It)

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    #47321

    Organic
    Participant
    • Topics: 16
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    French style chef knives are pretty flat in overall blade profile aside until the curve at the tip. I have an 8 inch chef knife like this and I clamp the blade with about 75% of the blade behind the clamp and 25% in front of the clamp. My settings are bottom holes F 3 on the advanced alignment guide. Try that as a starting point and see where that gets you.

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    #47333

    Bob
    Participant
    • Topics: 3
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    Ok, thank you. It makes sense and is much clearer now at this time of day, rather after a 12 hour work day and into the 16 th hour of my day. It was the 1st time this knife was in in my WE and I seemed to have become afixated on perfection. I know exactly what your saying here and probably read your post over 3 times ignoring the obvious last night. I think I became convinced there was a problem. We’ll thank you. Oh,  I was in the lower set of key holes. No work today and can give my sharpening a couple dedicated hours.

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    #47334

    Bob
    Participant
    • Topics: 3
    • Replies: 9

    Thank you Organic. That is a valuable piece of info and exactly where I will start today. Not having a  starting point and literally just guessing on the 1st clamp kind of effects my confidence right out of the gate. I will now have a starting point. As I think about your 75% reference to the rear of the clamp I already know that will eliminate the play or deflection in the steel. I ran into this numerous times last night. I knew that couldn’t give me any consistent accuracy when I can see the blade give a little as I made my pass toward the knifes tip.

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    #47335

    Organic
    Participant
    • Topics: 16
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    Bob, I compensate for the blade’s side to side movement caused by the blade flex by either working one side at a time (which takes a long time) or by pressing the handle up against my torso a bit to stabilize it.

    I just want to make sure you know that I’m saying to clamp the knife close to the tip with the majority of the blade behind the clamp. Either way, you will need to continue using the sharpie to verify that the clamp position you have is a good compromise.

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    #47719

    MarcH
    Moderator
    • Topics: 53
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    Here’s a copied and pasted email correspondence I sent to a Wicked Edge user and Forum member in an attempt to answer his question.  It is right in place in this forum thread so I thought it’d be appropriate to include it here:

    There is something like you described you’re wanting, drawings showing how the knife clamping position affects the “sweet spot” and how to determine the initial bevel angle, in the Knowledge Base on the WE website. Click the blue link.

    The Knowledge Base explains how the stripe of exposed steel, the stripe where the marker was removed during the stone contact, moves relative to the position of “the collar”, (i.e., the micro-adjustable “L” brackets).  With wide “L” bracket positions the stripe is high up the edge closer to the apex and with narrower “L” bracket positions it is lower down on the edge closer to the shoulder.  I’ll add to it, if you can picture in your mind, conceptualize, the position in space the actual knife edge sits in relation to the position where stripe of exposed steel is, that is, where the marker was removed with the stone’s edge swipe(s).  Then you can affect the stripe placement on the knife edge by physically moving the knife and repositioning it so that the edge will align with the where the stone had previously exposed the steel with the stone sweep.  In your mind, separate the two things,  Visualize the stones sweep and imagine where it will contact the knife steel as the knife edge raise or lowers relative to the stone sweep.  Some people apply blue tape with a line mark across the stone perpendicular to it’s length and rotate or arch the stone across the knife edge while watching how the line mark moves relative to the knife edge.  This helps them to know which direction to move, raise or lower or rotate the knife, tip up or down, to better meet or align to the arching that was mark drawn on the stone.
    You physically and actually raise the knife edge to position it higher up relative to the stones contact position.  This can be accomplished by either rotating the tip up, (and the handle down, as it sits on the depth key) or sliding the knife forward under the stone so a wider taller portion of the knife is aligned with the place the stone had contacted the edge and removed the stripe of marker, then the stone will now meet and contact the knife edge lower down on the bevel.  Remember when you have a desired bevel angle setting the “L” brackets are fixed at their angular position relative to the bevel to accomplish this angle setting.  Then the only way to contact the knife edge efficiently is by choosing the best knife clamping position to facilitate this, “the sweet spot”.  Since the angle is set it can only be accomplished with knife movement and positioning relative to the stone’s contact swipe.
    The opposite holds true, by lowering or rotating the tip down and the handle up or sliding the knife backwards the tip will be lower now relative to where the stone previously contacted the knife edge, now the stone will be contacting the knife edge higher up and closer to the apex.  All of the movements are made incrementally, little by little, and rechecked while reapplying and removing the marker.  It can be tedious but through time, repetition and patience you’ll put together a method that works for you.
    This is where the depth key position is also important.  We primarily consider the depth key position to elevate the edge.  Through experience we’ll learn we can use the depth key position and the knifes contact point(s) with the depth key to our advantage when choosing and finding the best clamping position.  Sometimes I find I have to clamp some knives just by the tips of the jaws with no depth contact at all.  This is when the Advanced Alignment Guide is worth having and using.
    For me the common sense, neutral starting place, for clamping any knife would be to position the depth key such that the knife edge was high enough above the jaw line to avoid the stone from contacting the jaws while sharpening the knife.  Then I balance the length of the knife equally forward and behind the jaws imagined vertical centerline.  Usually we select the depth key position to help accomplish this first task, the neutral starting position.  This may be accomplished while the depth key is in either the lower or upper positions. In that case we use the depth key position to better help us accomplish finding the sweet spot and then finding and matching the original bevel angle.  As long as the knife is in physical contact with at least one of the depth key pins the knife can be rotated tip up/handle down or tip down/handle up, and/or slid forward and backward while positioning it for clamping in a repeatable, recordable position using the alignment or advanced alignment guides.
    You may find that the shape and/or the flexibility of the knife requires you to change or move this neutral starting position to better and more securely clamp the knife to eliminate blade flex.   That is clamp the knife with more length forward of the jaws centerline or the opposite, more length behind the centerline.  You have to make the judgment call by physically feeling how the knife flexes while clamped securely and also see how it flexes during stone contact.  Sometimes we may have to sharpen a flexible knife while supporting the opposite side with hand pressure to keep it from flexing, while working one side at a time, alternatingly.
    I also try to position a knife so the majority of the flat area of the knife blade is parallel to the horizontal top of the jaw line.  For larger kitchen/chef knifes with a gentle curved arc tip section.  I imagine a line from the tip to the heel portion of the knife edge and clamp the knife so this imaginary line is parallel to the horizontal jaw line, as a starting point.  Then with the marker removal I’ll fine tune the position moving the knife forward or backward or rotating tip up or tip down, as needed to best position the knife for the most efficiency edge contact, i.e., in the sweet spot.
    When this is all said and done, every first time a knife is sharpened with a Wicked Edge System, (any WEPS model), the knife edge no matter how perfectly the knife clamping position was chosen, will still see some profiling.  That is some removal of steel resulting in minor shape change(s) of the knife edge as the stone contacts and removes steel during the first, initial, sharpening.  The next and every time after the first, if the knife is clamped repeatedly in that same clamping position no further profiling will be made, only sharpening and polishing of the existing bevel if the position and rod guide angles remain the same.
    I wish I had software or the knowledge to utilize the software I have to give you the drawings you request.  All I have is my ability to write, hopefully choosing the appropriate words to help you to more clearly understand how to do what you need to do.
    I hope this is helpful.

    Marc
    (MarcH's Rack-It)

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