Results 1 to 7 of 7

Thread: How to Determine Blade Angle

  1. #1
    Spyderco Forum Registered User Bolster's Avatar
    Join Date
    Mar 2007
    Location
    Mexifornia
    Posts
    1,434

    How to Determine Blade Angle

    I've forgotten my geometry from high school. Is there a relativley simple way to determine the angle of a blade? I mean, the angle to which a blade is ground, from spine to edge? (I'm not asking about sharpened edge angles, but the whole blade.) For instance, my full size Manix ... at thickest part of spine, about 4mm. Depth of blade, about 34mm. Another way to ask the question: How does one calculate the most acute angle (vertex) on an isosceles triangle?
    Congratulations—your brainwashing is complete!
    Perform ongoing maintenance by daily consumption of mainstream media.

  2. #2
    Spyderco Forum Registered User bh49's Avatar
    Join Date
    Feb 2006
    Location
    former Constitution state
    Posts
    8,043
    IIRC 3.4 degrees or 6.8 inclusive.
    To calculate this angle you need divide half of the thickness on width and to use arctg function on your calculator. In this case your angle is arctg( 2/34) =3.4 deg
    Somebody younger may be will correct me, I studed trigonometry about 35 years ago.
    "People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf"
    George Orwell
    Any knife without Spyderhole is defective.
    My top choices Native5, G10/VG10 Caly 3.5/3 & C83 Persian Black micarta/bolsters

  3. #3
    Spyderco Forum Registered User Bolster's Avatar
    Join Date
    Mar 2007
    Location
    Mexifornia
    Posts
    1,434
    Thanks BH. That makes sense, an isosceles is merely two right triangles, thus the half thickness calculation. Does "arctg" mean arc tangent, aka inverse tangent?

    Regarding your comment about the younger guys answering the question...I dunno, the average math & science scores from the current crop of students is widely reported as less than stellar. If I were to ask a question about 'sensitivity training' or 'social diversity,' I would throw it to the younger crowd, for certain. But a useful geometry question involving numbers? That's old school. Maybe some young bucks will step up and defend the geometrical honor of their generation.

    So, knowing the grind angle of my Manix blade will help me determine what angle I'm actually using to sharpen, with my Edge Pro. With an Edge Pro, sharpening a full flat grind, you have to subtract half the grind angle to determine what angle you're actually getting on the edge. So, thanks!
    Congratulations—your brainwashing is complete!
    Perform ongoing maintenance by daily consumption of mainstream media.

  4. #4
    Spyderco Forum Registered User bh49's Avatar
    Join Date
    Feb 2006
    Location
    former Constitution state
    Posts
    8,043
    Quote Originally Posted by Bolstermanic View Post
    Thanks BH. That makes sense, an isosceles is merely two right triangles, thus the half thickness calculation. Does "arctg" mean arc tangent, aka inverse tangent?
    You welcome.
    Yes, arctg is arc tangent or inverse tangent.
    Also, for such small angles, value of an angle (in radians) are equal to the tg. So in this case, math can be simplified. Your angle equal to 2/34 (tg) times 180/3.14 (conversion of radians to degrees).
    Math can be fun, I always felt this way.
    "People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf"
    George Orwell
    Any knife without Spyderhole is defective.
    My top choices Native5, G10/VG10 Caly 3.5/3 & C83 Persian Black micarta/bolsters

  5. #5
    Spyderco Forum Registered User Bolster's Avatar
    Join Date
    Mar 2007
    Location
    Mexifornia
    Posts
    1,434

    Some Angles Calculated

    So here are the grind angles calculated for several Spydercos, using a dial caliper and calculating grind angle geometrically. Thickest part of the blade was used for the spine thickness measurement, generally occurring around the hole. The leaf-style blades hang in the 6-degree range. The even .1 progression below is simply an odd coincidence of how the numbers fell out.

    Grind angles likely predict "raw" slicing ability to some degree (for comparable depth blades, right?). Notice how the hollow grind has a considerably steeper angle, due to the fuller, but the number is an average, as if it were a saber flat ground. You'd have to calculate for particular points on the hollow grind if you wanted more accuracy for a hollow grind.

    CalyIII ZDP = 6.1
    CalyIII VG-10 = 6.2
    Caly Jr ZDP = 6.3
    Yojimbo = 6.4
    Manix = 6.5
    Mini Manix = 6.6 (A little steeper b/c the blade thickness is the same but the blade depth is a little shorter)
    Mini Persian = 9.8 (Measured from edge to where the hollow grind terminated at its fullest, well into the belly of the blade)

    For fun, I also calculated my retro Queen D2 teardrop slippie, which I thought had a thin acute blade, and was shocked to find it calculated a comparatively obtuse 8.2 angle. But then, the blade depth is minimal on it (14mm), so you don't really notice the steeper angle causing much drag.
    Congratulations—your brainwashing is complete!
    Perform ongoing maintenance by daily consumption of mainstream media.

  6. #6
    Spyderco Forum Registered User Bolster's Avatar
    Join Date
    Mar 2007
    Location
    Mexifornia
    Posts
    1,434

    OT comment on math skills

    Off topic to be sure, but previously in this thread I took a shot at today's students' math skills. A few days after my mean-spirited comment, the WSJ ran an article showing that the class of 2007 has recently logged the worst drop in math scores on the SAT in 3 decades!

    For the record, the class of 2007 also logged a drop in critical reading/verbal skills, too--the lowest scores since 1994.

    Writing scores also slipped. Taken together, the class of 2007 has the distinction of producing the lowest test scores of the decade.

    These are tomorrow's metallurgists. I think we should question our unbounded faith in ever-better knife steels being produced.

    Anyway, sorry for the OT post. Back to the important stuff...
    Congratulations—your brainwashing is complete!
    Perform ongoing maintenance by daily consumption of mainstream media.

  7. #7
    Spyderco Forum Registered User The Deacon's Avatar
    Join Date
    Sep 2004
    Location
    Upstate SC, USA
    Posts
    20,998
    Quote Originally Posted by Bolstermanic View Post
    These are tomorrow's metallurgists. I think we should question our unbounded faith in ever-better knife steels being produced.
    Or at least pondering what parts of the globe those steels will be coming from. In the game of life, when someone drops the ball, there's almost always someone else ready to pick it up and run with it.
    Paul
    My Personal Website ---- Beginners Guide to Spyderco Collecting ---- Kiwimania ---- Spydiewiki
    Dead horses beaten, sacred cows tipped, chimeras hunted when time permits.
    WTC # 1458 - 1504 - 1508 - Never Forget, Never Forgive!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •