Sharpening a Rasp

[Tom Stenzel]

When I go to rust hunting instead of trying to bargain the price down, I try to get other things added. I wanted (and got) a ID caliper that I needed plus two rasps thrown in. One of the rasps was a large flat Continental. The tips of the teeth were flat, it looked like someone had tried to rasp down a steel plate.

I got the idea to sharpen it from someone who (sorry, don't remember who) wrote in about sharpening a bandsaw blade by nicking the backside of the tooth with a Dremel. So, armed with a Dremal I had at it.

There were a few mishaps testing different wheels, obliterating a few teeth by accident, sometime destroying teeth that were adjacent to the one I was working on. Found the best approach was to use a fiber type cut-off wheel, I could reach in and grind down the back of the stitch until the flat spot was gone and there was a sharp edge. Plus without obliterating the other teeth. Once I got the hang of it a tooth took a few seconds. After practicing on one side the second side took about 20 minutes.

The result? Tested it on a scrap piece of apple and it really took the material off!

The finish it left behind? Well it... er, ... um, .. it sure slaws the material off fast! The teeth are now no longer rounded on the tip, they’re flat across so it doesn’t cut like a rasp normally does. If you want a nice finish forget about it. Still, having all of three rasps including this one it’s a welcome addition to my arsenal.

If anyone else wants to have at an otherwise ruined rasp the one recommendation I have is to use a magnifier between you and the Dremel. It both protects the eyes and allows you to see what you’re doing.

-Tom

[Derek Cohen]

Hi Tom

I sharpen my bandsaw blades by grinding the back of the teeth flat.

However, I sharpen files (not tried rasps yet) by soaking them in citric acid.

Regards from Perth

Derek

[Tom M King]

If you have enough to meet the minimum number, there are a couple of file sharpening services that sharpen rasps. Boggs , and Save Edge.

The only oddball things I sharpen any differently than what you normally see, are hole saws. I sharpen them with a 4-1/2" side grinder with a thin, metal cutting blade-you can't file the teeth that are set towards the outside. I use the thin disk like a regular grinding wheel. It only takes a minute, and they cut better than new. Just lightly touch each tooth.

[Tom Stenzel]

Hi Tom

I sharpen my bandsaw blades by grinding the back of the teeth flat.

However, I sharpen files (not tried rasps yet) by soaking them in citric acid.

Regards from Perth

Derek

Hi Derek,

If I got the idea from a posting of yours, well, thanks! I've got a couple of bandsaw blades to try it out on.

The rasp had probably lost 1/3 to 1/2 of the tooth's height leaving a fairly large flat spot. A bit of cloth and an ant family could have a picnic at one. I don't think that an acid bath would salvage this particular wreck, too far gone.

Thanks,

Tom

[Tom Stenzel]

If you have enough to meet the minimum number, there are a couple of file sharpening services that sharpen rasps. Boggs , and Save Edge.

The only oddball things I sharpen any differently than what you normally see, are hole saws. I sharpen them with a 4-1/2" side grinder with a thin, metal cutting blade-you can't file the teeth that are set towards the outside. I use the thin disk like a regular grinding wheel. It only takes a minute, and they cut better than new. Just lightly touch each tooth.

Tom, any sane person would have looked this rasp, grunted, and walked away. And so should you. I wouldn't think that buying junk rasps to send out for sharpening would be worthwhile. But with the current state of new rasps for sale that thought might have to go out the window.

I bought it thinking I could use the piece of steel somewhere. The idea of sharpening it came two years or more later.

Nice tip on sharpening hole saws, have to file that one away.

Wait a minute, that's a power tool! (Looks one way, then the other) Hope we don't get into trouble!

-Tom

[Tom M King]

That one might be toast, but I've sent some junkers in to get up to the minimum number, and was surprised how sharp they were when returned. We can get three or four sharpenings out of horse hoof trimming rasps, and they get pretty dull before they go in the tobesharpened bin.

[Peter Evans]

Hi Derek,

If I got the idea from a posting of yours, well, thanks! I've got a couple of bandsaw blades to try it out on.

The rasp had probably lost 1/3 to 1/2 of the tooth's height leaving a fairly large flat spot. A bit of cloth and an ant family could have a picnic at one. I don't think that an acid bath would salvage this particular wreck, too far gone.
Thanks, Tom

Actually, worn down rasps sharpen quite well in acid (if teeth are still there). Because the teeth are flatter in profile, the rasp becomes smoother than when new, and fairly sharp on the leading edge. Having said that, American Pattern rasps are not in the class of the hand stitiched rasps that I now use (FTWW, Liogier), nor the (older) Nicholson Patternmakers' rasps. But for rough removal, work ok.

cheers
Peter