Do I need to lap these chisel backs flat?

[Mark Gibney]

I bought a set of four older Pexto "paring" chisels (they are long, but not flexible) off craigslist this week.

The blades are all bowed, the backs are convex. Here's a photo of one -

IMG_7247.jpg

I swore to myself my days and nights of endless lapping of old chisels and plane irons were over, so do I need to lap these flat?
Or should I straighten them a bit in the vise first?
Or polish the first inch or so of the backs and use them?

What would you do?

thanks, Mark

[Jim Koepke]

Straightening them in a vise may end with a snapped blade.

Get the back close to the edge flat and that should be good.

There is some debate that some chisels were made this way to help elevate the handle in use.

Others say timber framing chisels are extra heavy to avoid this kind of 'use warping.'

jtk

[James Pallas]

For my own use I would sharpen and see how they work. It is far better to have them that way than the opposite. I would guess that in use you won't notice it. Much advice is given about having flexible paring chisels so you can bend them that way. Yours are just "pre-set" for use.
Jim

[Doug Dawson]

I bought a set of four older Pexto "paring" chisels (they are long, but not flexible) off craigslist this week.

The blades are all bowed, the backs are convex.
I swore to myself my days and nights of endless lapping of old chisels and plane irons were over, so do I need to lap these flat?
What would you do?

I might lap something like that only if somebody was holding a gun to my head, otherwise I'd stash them next to the paint cans.

It might be fun to experiment with very carefully eroding away the convex back material with a grinder, being careful not to overheat it. (Japanese chisels do something like this, only less crudely.) You could gauge your progress with bluing on a flat plate.

But no chisel is so rare that I would spend the time and effort to do that for it, starting from that condition. It would have to be out of morbid curiosity.

[bridger berdel]

I might lap something like that only if somebody was holding a gun to my head, otherwise I'd stash them next to the paint cans.

It might be fun to experiment with very carefully eroding away the convex back material with a grinder, being careful not to overheat it. (Japanese chisels do something like this, only less crudely.) You could gauge your progress with bluing on a flat plate.

But no chisel is so rare that I would spend the time and effort to do that for it, starting from that condition. It would have to be out of morbid curiosity.

There are a number of ways to do the heavy grinding should you wish them flat. Upside down belt sander is a popular one. I have a flat top makita grinder converted to diamond disks with which i can progress from 50 grit or so to 3000 grit with a large surface area and some horsepower behind it. It works well for that kind of heavy flattening.

[Doug Dawson]

I have a flat top makita grinder converted to diamond disks with which i can progress from 50 grit or so to 3000 grit with a large surface area and some horsepower behind it. It works well for that kind of heavy flattening.

Hmmm, tell me more about that Makita grinder and those diamond disks. Model numbers, current availability? That could be useful for some things.

[les winter]

I just bought some new Robert Sorby paring chisels with the same issue. I could have returned them. Seller checked his remaining stock and they were no better. I used 45 micron diamond powder and oil on a mild flat steel plate. It helped but not much. Ultimately I decided to grind back the first 1/2" or so. That did it. It's the first thing I should have done. Your chisels may be shorter to begin with and my solution may not be acceptable to you.

[steven c newman]

About the only thing missing in the above posts.....someone saying how much they LOVE their Brand X chisels. Sharpen them up, put them to work..AS IS. Each time you re-sharpen them over the years, you can flatten a bit more of the back..IF needed.

IF they had been bent the other direction...yes, THEN I would grind the "offending" part off. The way these are "bent" right now, merely saves your knuckles from being hurt.

[Frederick Skelly]

About the only thing missing in the above posts.....someone saying how much they LOVE their Brand X chisels.

I just LOVE my Aldi chisels! I have them sharpened at 20* and use them exclusively for paring.
(Sorry. I just couldn't help myself. And I really do have some Aldi's set up for paring.)

Mark, I'd use them as is and see how it goes.
Fred

[Mark Gibney]

Well, before someone tries to convince me to flatten the backs I'm going with the wisdom of the crowd here - sharpen as is, and use.

Thanks everyone for your advice.

And like Doug Dawson I'd also like to know more about the Makita grinder Bridger Berdel uses.

[Mike Henderson]

And like Doug Dawson I'd also like to know more about the Makita grinder Bridger Berdel uses.

This is probably it. You can also go with a WorkSharp, which is a bit less expensive. Lee Valley has one also, bit expensive.

Mike

[Doug Dawson]

This is probably it. You can also go with a WorkSharp, which is a bit less expensive. Lee Valley has one also, bit expensive.

I looked at that Makita (I'd forgotten all about it,) I thought he was referring to something more akin to a surface grinder, not water stones.

Anyway, messy as all get-out. You'd probably want to mount it inside a high-sided cardboard box or something and wear a sacrificial apron.

I wouldn't flatten the OP's chisel backs on a WorkSharp (which I have,) due to overheating issues. You might also have wound up spending more money on the abrasives than the chisels are worth.

Still not clear on the "conversion to diamond plates" thing for the Makita, I didn't find anything about that.

[Jim Koepke]

My suggestion is to give it a sharp edge on your stones, work the back near the edge to your preferred degree of polish, then put the chisel to use.

Most likely you will have no problems with a slight belly on the back of your chisel.

In other words, wait until you can identify a problem before trying to fix it.

jtk

[Doug Dawson]

My suggestion is to give it a sharp edge on your stones, work the back near the edge to your preferred degree of polish, then put the chisel to use.

Most likely you will have no problems with a slight belly on the back of your chisel.

In other words, wait until you can identify a problem before trying to fix it.

I don't mean to get all biblical on you, but if thine chisel offends thee, pluck it out. Some people can find uses for a chisel that's bent like a pretzel, and that's okay.

[Mike Brady]

Isn't that a firmer chisel; and if so, to what use would you put it?