I've got a collection of blunt centre punches and its some time since I had a go at resharpening one. I've never been told the "proper" way to do it.
Could someone please tell me how I should go about it?
Thanks.
You'll need a bench grinder, with built-in tool rest.
I've no idea whether this is the recommended "text book" method - but it will work! Hold the punch on the rest in such a way that it is horizonal, but at the correct angle to create a cone at the sharp end. As you grind, slowly rotate the punch about its own axis. You should then get a sharp point, which is exactly on the centreline of the punch.
Roger
If the pointy end is removeable you can put it in an electric drill, and spin it whilst grinding. Gets a nicely centred point.
According to some machining books, the center punch should be held so that the grinding marks run from the sharp point toward the back of the centerpunch. In line with the axis of the centerpunch. Reasoning behind this is that grinding "around" the point creates the possibility of the centerpunch "mushrooming" slightly behind the sharp point during use whereas grinding in line with the axis transfers the force of use in line with the axis of the centerpunch. But what do I know??? I typically grind mine in line with the axis and have no problem. (you really don't need a "long" point on them - look at the angle before you grind, and try to maintain the relationship). Ken.
i've been taught the same thing, grind from the tip to the back so all the grind marks are radial.
i use a belt sander, its just as easy. be careful the point doesnt catch.. or point it the other way. :)
i'm guessing the mushrooming would only be a problem if you're using your punchmarks for delicate layouts.. where, for example, a steel rule could get hung up when sliding it around.
in the end, as long as its 'pointy' it should be ok. unless we're talking about transfer punches. i sharpen those in a lathe.
-tony
If I'm not mistaken, anytime you use a centerpunch in a material that is softer than the punch, the metal will displace.
That hole you made, was once metal.
Where did you think the metal went?
Hey Tony,
Good centre punches should last a loooooonnngg time without sharpening too. Do you start with a prickpunch and work up to a heavier size. Prick punches a real "sharp" and use only a light tap to mark, but centre punches are pretty dull becasue of the flatish angle they are ground to. A 3/8" taper tap makes a good punch, and are "chuckable".
Take care.
Brian Laws>I've got a collection of blunt centre punches and its some time since I had
If any are Craftsman, they'll replace them under warranty.
Erik
Good point, Brian. I find that prickpunches work even better if twirled between the fingers with very light downward pressure. Then work up to the more blunt centre punch. All this easier to do if one is using a headband magnifier and layout blue.
The only way I can get my starret to work.
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