holding an octagonal shank
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  1. #1
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    Default holding an octagonal shank

    i finally got around to regrinding a collection of dull center punches. i had no idea they would give me so much trouble. they all have octagonal shanks, i have four sizes, 3-5 of each. how to hold them on the tool grinder? i need either square deckel collets (6mm, 8mm etc.) or er collets in 13 (for 12.75), 11 (for 10.75) and 8.5 mm. i have neither of those. so just for fun i made a split bushing, 12,75/16mm for the deckel collet and the second problem occured: runout of around 0.5mm. i ground one punch and it was ugly to look at. i ended up shimming the bushing with tape in two places and got a punch down to 0.04mm. the next one of course was different so i got tired of it. id either have to make 4 excentric bushings, buy collets worth more than the punches or get some independent four jaw for grinding (morse or deckel u29). does such a critter exist? and how do they grind the punches when they are made anyway?

    so any ideas how to do this seemingly simple job without to much effort?

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    I allways regrind centre punches by hand up on their end, wheel direction down from point to shaft.

    A V notch in the rest on the bench grinder and hold the punch taper in this V notch.

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    Octagonal can be held in a 3 or 4 jaw...It is very handy to mount a small 3 or 4 jaw chuck to be used in a tool grinder. Having a 12 index ground into the chuck holding flange is also very handy..an adjust true in the chuck holder can make very close work..
    Last edited by michiganbuck; 03-11-2019 at 04:26 PM.

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    Let me get this straight, the OP is talking ordinary ( as in place on mark and hit with a hammer) centre punches?

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    A Vee block on a magnetic chuck would be my go to on this on a cylindrical grinder although I would just do centre punches "off hand".

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    Stick the center punch in a cordless drill and grind it . Bill

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    Quote Originally Posted by SVE Performance View Post
    Stick the center punch in a cordless drill and grind it . Bill
    I doubt the 3 jaws of the cordless drill would hold an 8-sided shank very well.

    If it were my problem I'd find a way to make or broach a tight hex hole in a piece of larger rod, then hold the tools in with set screws and grab onto the round rod.

    metalmagpie

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    Quote Originally Posted by Limy Sami View Post
    Let me get this straight, the OP is talking ordinary ( as in place on mark and hit with a hammer) centre punches?
    If you're a perfectionist, yeah, it's got to be perfect, or it's no good

    Good subject for the brand spankin' new Impractical Machinist forums

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    I like my punches to be (near) perfect..angle can be off some, but smooth/round and near center is the drill.
    but I have TC grinders so that is done as quick as on a bench grinder.

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    Quote Originally Posted by HuFlungDung View Post
    Good subject for the brand spankin' new Impractical Machinist forums
    This is genius, since they seem to insist on coming here rather than one of the hobby forums.

    I say this as a hobbyist. I like this forum because I can see how professionals get things done.

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    Quote Originally Posted by dian View Post
    how do they grind the punches when they are made anyway?
    When mass produced, as a hand punch I guess they were never ground on centre in the first place?

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    Quote Originally Posted by SVE Performance View Post
    Stick the center punch in a cordless drill and grind it . Bill
    ok.....i was thinking wtf...go to pedestal grinder or belt sander and hold it at approximate angle and...brrrrr. done.
    I dont particularly care about center punches.....but WTF....how have i over looked this equation...
    Pedestal grinder + cordless drill + something round in chuck = nice way to rotate part for grinding a point to it.


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    Quote Originally Posted by toolsteel View Post
    ok.....i was thinking wtf...go to pedestal grinder or belt sander and hold it at approximate angle and...brrrrr. done.
    I dont particularly care about center punches.....but WTF....how have i over looked this equation...
    Pedestal grinder + cordless drill + something round in chuck = nice way to rotate part for grinding a point to it.

    First shop I worked in this is how we modified endmills to have a reduced shank. Worked okay for 1/2 endmills, was downright stupid for 1/16 endmills with a 1/8 shank. I still sharpen short TIG tungstens this way, but any eccentricity in the drill chuck shows up readily.

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    Carbide pencil sharpener. All the other good complex ideas are used up.
    I like the drill
    Last edited by mllud22; 03-12-2019 at 07:15 PM.

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    well, this was more about workholding than the (hand) punches. can anybody point me to a small, around 80mm 4-yaw (independent)?

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    3.1416 makes a better yaw.
    80mm or 3.1496 yaw would make your diameter a little off size
    Im thinking about .2 1/2% big


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