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Sharpening involute cutter

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  • Sharpening involute cutter

    Is there any particular angle for grinding the top of the teeth of an involute cutter? I have been looking for a particular cutter for a year or two and now I've found one which is in dire need of sharpening. It's blunted on one side with the cutter teeth rounded off and needs a couple of mm at least ground off each tooth to bring the profile back right, but it's already been sharpened somewhat and if I sharpen it more at the same angle I'm going to increase the rake on the top of the teeth. That's fine for what I need it for (cutting acetal) but will it affect the tooth profile significantly?
    Peter - novice home machinist, modern motorcycle enthusiast.

    Denford Viceroy 280 Synchro (11 x 24)
    Herbert 0V adapted to R8 by 'Sir John'.
    Monarch 10EE 1942

  • #2
    It must be flat and radial (ie along a centre-line) and no side or back rake.

    Take it easy as its too easy to "burn" the cutter.

    http://www.google.com.au/#hl=en&rlz=...47e94720a76d26
    Last edited by oldtiffie; 04-22-2012, 06:51 AM.

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    • #3
      Thanks Tiffie.

      This one has been sharpened by moving it axially, not rotating it. I guess I'll have to dead-reckon the first tooth then index it to repeat for the others.
      Peter - novice home machinist, modern motorcycle enthusiast.

      Denford Viceroy 280 Synchro (11 x 24)
      Herbert 0V adapted to R8 by 'Sir John'.
      Monarch 10EE 1942

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      • #4
        You need to maintain the ORIGINAL rake of the teeth, otherwise the tooth profile that you cut will be incorrect.. The rake is with respect to a radial line drawn through the centre of the cutter and the face is probably itself radial i.e. zero rake. However, you say that the cutter has already been sharpened somewhat so a lot depends on how well that sharpening has been done. If it has not been correctly re-ground you have more of a problem. [Just noticed that you have replied to say that it was incorrectly reground]

        You can use a tooth rest to index the cutter in a T&C grinder. Sometimes a small flat is ground on the opposite side of the tooth using the main face to index against. This flat can then be used to index against and grind the face of the cutter. You need to keep going around until all the cutter faces clean up. To maintain the correct rake, the cutter needs to be rotated to increase the cut. The grinding wheel should not be moved linearly to add cut since this will change the rake angle and hence the tooth profile.

        As you regrind, the cutter OD will get smaller and the thickness of the teeth smaller, but you can get several regrinds before this is a problem.
        Bill

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        • #5
          You only sharpen the face of the tooth . The straight face down in to the gullet . Look up cutter sharpening .On involute cutters it will show you how and were to grind.
          Every Mans Work Is A Portrait of Him Self
          http://sites.google.com/site/machinistsite/TWO-BUDDIES
          http://s178.photobucket.com/user/lan...?sort=3&page=1

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          • #6
            Originally posted by Peter.
            Thanks Tiffie.

            This one has been sharpened by moving it axially, not rotating it. I guess I'll have to dead-reckon the first tooth then index it to repeat for the others.
            I don't know how many teeth there are on the cutter, but its pretty sure to be divisible into 36 (3, 4, 6, 9, 12, 18) and if it is you can use a Spindexer on a magnetic chuck on a surface grinder fitted with a "saucer" wheel.

            You are going to have to make a 1" mandrel/arbor to fit the cutter bore and a spigot to suit the 5C collet you have in the Spindexer.

            A say 3/4" thread will be needed on the end of the 1" mandrel/arbor - and a nut and washer to suit.

            Set the grinding wheel cutting face (the "lip" on the "saucer") over/above and to the Spindexer centre so that it is cutting a radial face.

            Index the cutter by either loosenting the nut and moving the cutter angularly and re-tighten the nut or loosen the 5C collet and rotate the mandrel/arbor and re-tighten the collet.

            It will be slow going but at least the cutter will be correctly sharpened and all you need is a/your surface grinder and a Spindexer - both of which are in many HSM shops.

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            • #7
              Cutter Grinding

              If you're set up on a Spindex why not use the shot pin to index the cutter instead of all that loosening and tightening? After the initial setup (presumably at 0 degrees) you would just pull the pin, rotate X degrees and stick the pin back in. That would make it quick and easy.

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