I put the punch from
this grommet kit in my drill press, spun it, and hit it with the angle grinder at a 45 degree angle while spinning to sharpen it, made punching the holes much cleaner
if you know of an industrial, half inch hole punch, similar to those that punch paper, let me know, it would make life much easier (and quieter)
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Try sharpening the angle to 60*, use a sanding disk (if you only have a 36 Grit, make sure it's well used), and gently touch the the side of the punch with the rotation of the wheel directed downward from the top of the body of the punch down toward the cutting edge (
BE VERY, VERY, VERY GENTLE WHILE DOING THIS STEP;) since we don't know what grade of steel the punch is made of.
A loose rule of thumb from heavy industry; when sharpening anything where you are unsure of what type of steel it is, keep it cool enough that you can touch it with your bare fingers.
If you get it hot enough that the cutting edge starts to change color, you are in the zone where you could be pulling the temper out of the steel, which will ruin the cutting edge.
Now, if you have a knife sharpening stone in the house, use it the same way you used the grinder; as low an RPM for the punch as possible, hold the stone at the same angle and keep the stone lubricated.
When you start, you are going to have the stone grab a lot; that's normal. Until you have some experience sharpening anything like this, take it slow. The focus of the exercise is to refine the cutting edge. When the vertical grind marks start to go away, that's when you really need to lighten up on the pressure you are putting on the stone; the goal is to be able to wipe the wire edge burr off the cutting edge of the punch with just your finger, without harming your finger in any way (should just fall off as dust)
Did I mention that you have to keep the stone well lubricated???
It serves 2 purposes;
1] It controls the temperature of the operation.
2] It removes/ flushes the metallic particles abraded away by the stone.
These tips used in a typical tool and die shop will allow a stamping die to go as far as 10,000 parts without sharpening; actual results may vary.......
Pat