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OMG, help me with this math

This topic contains 12 replies, has 4 voices, and was last updated by  tcmeyer 04/18/2019 at 3:51 am.

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  • #50163

    phillyjudge
    Participant
    • Topics: 19
    • Replies: 55

    I just spent oodles of time checking my 360s angle cube against angle blocks on a surface plate that was zeroed out. I’m pretty comfortable with the cube, it is maybe twitchy by .01 to .02. Here is the thing, and I noticed  it while sharpening, but attributed it to an off-ground blade and kept having to adjust the arms for it…..If I zero the cube on the right side of the angle bar ( the square bar parallel to the mounting plate), I am .25* up on the left side! I checked by zeroing on each side and checking the other.

    So, do I zero on each side now before setting my angles, or subtract the .25 from the high side and set my angle that way?

    • This topic was modified 8 months ago by  phillyjudge.
    #50165

    MarcH
    Moderator
    • Topics: 58
    • Replies: 1917

    Phillyjudge, one zero, one time, for everything.  This allows you to set all angle settings relative to that one zeroed position. Then all the angles are all relative to the zeroed cube and to each other.  Use the zeroed cube to set both your guide rod angles to profile and sharpen both knife side bevels to that relative angle, with each other.  We’re looking for the consistency between angles and sharpening technique.

    If you keep re-zeroing the cube, again and again, relative to a different position adjacent to the W.E. sharpener.  Then each angle settings has no relationship with the rest of the angles.  I check my cubes zero only once in a while.  I have determined that my DXL360S  stays zeroed relative to the same zeroed position for months on end.  I really only re-zero the cube when I move the position of the sharpener and it’s base after cleaning or something.

     

    Marc
    (MarcH's Rack-It)

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    #50166

    airscapes
    Participant
    • Topics: 11
    • Replies: 198

    When you zero the gauge it is taking into account any off level of the surface it is on.   So put it on the blue foot of the sharpener if you can, or directly in front of the vise centered with the knife.  Zero it there and you are done unless you move the setup, the table is moved, or you accidentally hit the zero button.

     

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    #50167

    phillyjudge
    Participant
    • Topics: 19
    • Replies: 55

    But if the angle bar is off, and the rod assembly slides on it, then one side is plus .25 to the other side’s zero….like the bar is bent on one side vs. the other, so don’t I need to account for that?

     

    I men , the zero side will be at 20* and the “wrong” side will be at 20.25*, if i ignore the error.

    #50168

    MarcH
    Moderator
    • Topics: 58
    • Replies: 1917

    Have you disassembled and removed the square angle bar and put a straight edge across it’s full length to verify that it is bent?  Maybe use a level or carpenter’s square.  Or, are you just assuming the angle cube readings are showing you it’s bent?  Without verifying the square bar for straightness, you are just guessing.  If you determine the square angle bar is indeed bent.  Give W. E. Customer Service a call.

    Marc
    (MarcH's Rack-It)

    #50173

    tcmeyer
    Participant
    • Topics: 34
    • Replies: 1866

    Phillyjudge:  The accuracy of the zero is completely unimportant.  It is only required to put you in the same plane as the blade.  If it happened to be off by a full degree, there are only minor consequences: your apex would be pointed 1 degree off of dead center and one bevel would be slightly wider than the other.  If the difference in width is enough to draw your eye to it, (and it won’t, since we’re talking a real error of 0.25 degrees, not 1.0) it’s a simple matter to take a few more strokes on one side with your starting grit.  With the 0.25 degree error and assuming an angle of 20 dps, one bevel will be at 19.75 degrees and the other will be at 20.25 degrees.  The difference in width would be on the order of 0.3%, or less than one or two thousandths of an inch for a typical bevels.

    Who was it that said “Don’t sweat the small stuff”?  This is small stuff.

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    #50174

    tcmeyer
    Participant
    • Topics: 34
    • Replies: 1866

    On a slightly related topic, I wanted to mention that I’ve noticed some slight variation in angle readings when comparing one side of a stone/handle/stone assembly to the other.  I usually don’t take readings after I’ve done the initial set-up, but on a few occasions I’ve caught myself using a different grit than usual and on checking it, found it was well out of whack from my initial angle setting.   In trying to analyze the problem, I found that the two sides  gave me different readings, but I also found that the readings changed when I inverted the block.

    If we insist on pursuing the perfect angles, I think it behooves us to check our blocks for parallelism.  A platen that is not seated correctly in its pocket will likely not be parallel to its mate.  The angular error will be reversed if you invert the block.  I haven’t counted the number of handles I’ve bought in the last eight years but not counting blank handles, I would guess it’s about thirty or so.  Three of the blocks had platens which were not properly seated.

    I tried to negate the error by using the rod itself to take readings – (the DXL-360 and 360S have V-grooves on each of the perimeter sides to allow for measurement of rods and pipes and corners) – and found that this too was skewed, as the rod is not parallel to the platen face except when the user applies pressure to the rod (not the back of the block) while the platen is vertically centered on the bevel.  This angular error (different from the platen parallelism problem) is caused by bore tolerances and was the reason I had gone down the bronze bushing path some years ago.

    Having spent more time, money and effort on the issues of angular accuracy than is reasonable, my advice is to itemize the problems as you perceive them, fix the major ones (if you can) and then go to bed and try not to think about the other issues.  If you must, perfect your technique to the extent it can help you live with the other issues and pretty soon you’ll learn that everything is just fine.

    • This reply was modified 8 months ago by  tcmeyer.
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    #50179

    phillyjudge
    Participant
    • Topics: 19
    • Replies: 55

    Thanks, fellas. I cancelled my therapy appointment.

     

    MarcH, I am going to do that, I can’t understand why the left side would be off compared to the right.

     

    TC, thanks, but I am so concerned about precision, (or is it accuracy), that I am trying to reduce as much error as I can, and I lost my way. Maybe.

    #50180

    airscapes
    Participant
    • Topics: 11
    • Replies: 198

    Also take a look at the specs for your cube.. accuracy too XXX repeatably xxx .. 🙂  It is easy for us to become sucked into the black hole of perfection .. but when using consumer grade measuring devices there is only so much you can do..

    Which setup do you have as that will determine if a slightly bent bar would matter..

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    #50181

    MarcH
    Moderator
    • Topics: 58
    • Replies: 1917

    I am trying to reduce as much error as I can, and I lost my way. Maybe.

    You’re attempting to remove the finest, almost unnoticeable, equipment and mechanical errors.  I think you’re loosing site of the human errors we are contributing that are far greater, IMO.  These human error contributions are something we can reduce with proper care, better technique and more attention to detail.  Remember this is a hand operated hand tool with a strong human influence by the operator.

     

    Marc
    (MarcH's Rack-It)

    1 user thanked author for this post.
    #50196

    phillyjudge
    Participant
    • Topics: 19
    • Replies: 55

    Who says I’m human?

    muhwahhaaaaaaaahaha

    #50197

    phillyjudge
    Participant
    • Topics: 19
    • Replies: 55
    1. Reply to airscapes, I have the newest vise, ball joint arms and just got the new micro adjusts.
    #50234

    tcmeyer
    Participant
    • Topics: 34
    • Replies: 1866

    I just watched a Youtube video on mil dots vs MOA and it prompted me to do a simple calculation, trying to put our obsession with precision in some perspective.

    One tenth of one degree amounts to only 6.28 inches at 100 yds.

    Yes, the 6.28 is actually two times π (3.14) and works here because there are 3600 tenths of degrees (360° X 10) in a circle and 3600 inches in 100 yards.  There are two times π radii in the circumference of a circle.  Here, our radius is 3600 inches (100 X 36″) and 1/3600th (360  X 10) of the circumference is 6.28″.

    Completely unrelated (but included here if you’re curious) is that a minute of angle (MOA) is 6.28 / 6, or about 1.047 inches  A minute of angle is 1/60th of a degree, as opposed to 1/10th of a degree in our explanation above.

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