Sharpening a leather punch that's off-center

[Kemrot]

Hi- I'm trying to sharpen a leather punch and have had some luck doing it without a jig. However, I'd sure like to have more accuracy and was wondering if anyone had any ideas on how to 'mount' a center punch that has a square shanked upper part that isn't precisely centered with the cutting hole on the bottom.

I'd probably need some sort of attachment that could hold the punch and that was adjustable so that the cutting end of the punch could be centered along its longitudinal axis. I have sharpened this in the past using my lathe with a four jaw chuck but was hoping to speed up the process.

In the future, I need to be sure to only buy punches that are entirely barrel shaped and can be simply rotated around their center axis once place on the tool rest.

[RickKrung]

Nice that you have a lathe and a 4-jaw chuck.  Very handy tools.  Using them is what I first thought of, but of course, not feasible for use on a Tormek.  Is it a wood or metal lathe? 

Very interesting challenge.  I don't have any ideas, yet, but my thinking cap is on.   

Wait.  Do you have any tubing the handle will fit inside of?  If so, can you jamb the handle in there, offset, like you would in a 4-jaw.  If you can get it centered that way - might have to use a larger dia. tube to do so - then you might be able to rotate the tubing on a rest - free handing the grinding.  If you could rig up a "V" shaped rest, to cradle the tubing in a consistent location/orientation to the grindstone, you could probably get a better grind result.  That way, you would only have to regulate the depth or grind pressure, and not have to try to maintain lateral or angular position.  I think it would facilitate smoother rotational motion, which should also improve bevel result. 

Was it Jan that made the free hand drill grinding platform, using a piece of angle aluminum?  Similar to that, but I would try to tilt it so the tubing would rest in the "V" of the angle. 

If your lathe is metal cutting, perhaps you could bore the ID of the punch to true it up.  Depends on its size and how far off-center the hole is and how much latitude you have for the size of the hole, plus meat on the OD of the punch for re-establishing the bevel. 

Rick

[RichColvin]

Mike,

I would consider two options.  The first is to make a holder that grips the tapered part of the shaft.  If the holder is round like Rick noted, it could be rolled on an SVD-110 Platform.

Alternatively, consider taking the sharpening to the tool.  By that, I mean make a jig that fits into the tool's bore (where the cut pieces are pushed thru), and has an "umbrella" shape mid way up.  The umbrella would need to be the shape of the area to be sharpened.  That umbrella area would be used to hold a piece of sandpaper for the sharpening.  Finally, the umbrella area would need a projection of some sort to put into a drill for spinning it.  Think of putting a mushroom into the tool, and the underside of the mushroom's cap would do the sharpening.

Then you would change the grit of the sandpaper to achieve the surface you want. The shaft part that goes into the tool would be the reference surface, so it would need to be pretty close to the internal diameter of the tool. 

This would be easy to make on a metal lathe.

Kind regards,
Rich

[Kemrot]

Thanks to both of you for your comments. I hadn't thought about inserting something into the inside of the bottom opening in order to secure the punch. That seems like the best idea.

And Rick, your idea of putting it inside of some sort of tube was also my first thought. I thought of making a plastic casting from a mold that fits around the tool, then turning the outside on my lathe to make it round. That would work, but the amount of labor required would be just too much for this one tool considering how inexpensive a new one with a circular shaft would cost.

The casting for this punch is rather coarse, and even the initial ground angle on the cutting surface wasn't too accurate to begin with.

It's kind of ironic to have a precise sharpening system, only to own a tool that needs sharpening that has no precise reference surfaces

[Ken S]

There is a little used, frequently overlooked technique I have found useful. Instead of trying to use the platform, slide the support bar close (almost touching) to the grinding wheel. Use the support bar as your platform. With your leather punch, you might try using either the edge or the side of the grinding wheel. I would start with the edge. Grade the wheel very fine and use a light touch. This will slow the operation but give you more control.

Ken

[Kemrot]

I just had excellent luck using a drill bit inserted into the open end of the punch. I clamped down a piece of aluminum onto the tool rest and sharpened the punch on the side of the wheel. By having the drill bit inside the end, I didn't even have a burr to get rid of on the punch.

So sharp that I actually now have a circular cut on my thumb!

[Ken S]

Well done, Kemrot. Your question and solution are good examples of how we push bach the frontiers of knowledge on this forum.

Ken