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 -

388727

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 (https://www.cpooutlets.com/makita-98202-blade-sharpener/mktn98202,default,pd.html?ref=pla&zmam=31282435&zmas=47&zmac=722&zmap=mktn98202&gclid=Cj0KCQjw1NzZBRCoARIsAIaMwusRdzH0ZcNU3XujUqGC BXG11QN9qcWiVRRy7qh-poKP-rC-ep3G6wAaAnUpEALw_wcB). 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 (https://www.cpooutlets.com/makita-98202-blade-sharpener/mktn98202,default,pd.html?ref=pla&zmam=31282435&zmas=47&zmac=722&zmap=mktn98202&gclid=Cj0KCQjw1NzZBRCoARIsAIaMwusRdzH0ZcNU3XujUqGC BXG11QN9qcWiVRRy7qh-poKP-rC-ep3G6wAaAnUpEALw_wcB). 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?

[Warren Mickley]

You have to look at how the chisel behaves when you sharpen and use it. In sharpening we usually just work the last inch or two of the back. If abrading on the back on your fine stone does not touch the burr or even polish the area near the burr, there is a problem.

If you really use the chisel, and abrade the back near the edge, after five or ten thousand sharpenings the whole back is no longer flat. This is of no consequence as long as the area near the edge can register flat on the stone. And if you are really going to use the chisel, time spent in preparation will not be wasted.

[Frederick Skelly]

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

I was assuming they meant something like these Doug. LINK (https://www.amazon.com/Flyshop-Granite-Diamond-coated-Grinding/dp/B07DBYYXSJ/ref=sr_1_16?ie=UTF8&qid=1530397428&sr=8-16&keywords=5"+lapidary+disc) Don't know if I'm right. But I've used a similar brand on my Worksharp and flattened my Narex Paring set with them. One of the guys here introduced me to them.

[bridger berdel]

I was assuming they meant something like these Doug. LINK (https://www.amazon.com/Flyshop-Granite-Diamond-coated-Grinding/dp/B07DBYYXSJ/ref=sr_1_16?ie=UTF8&qid=1530397428&sr=8-16&keywords=5"+lapidary+disc) Don't know if I'm right. But I've used a similar brand on my Worksharp and flattened my Narex Paring set with them. One of the guys here introduced me to them.

Yep, that's the makita, and the diamond plates are like those but bigger. I made a backer disk for them from i think 1-1/2" thick acrylic. I run the machine in a deep laundry sink.

[John C Cox]

I will pile on with many others.

Just sharpen up the bevels good (ignore the backs for now) and see how they do... You can get them really sharp just honing the bevel and then when you do final stropping - run the back over uncharged leather strop to wipe off any feather edge.... If they work well in your hands and you don't have trouble with them pulling up out of a cut or cutting crooked - then let them be.

If they don't - then it will be time to sort out the backs.

Chisels humped like that take me an hour to an hour and a half to sort out. I finally sorted out a method that works well enough after taking the plunge into vintage chisels again... And 100.00% of the ones I have came in with a hump in the back...

Perhaps we need to work up a tutorial for sorting out vintage chisels.

[Mark Gibney]

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

No, the lands are sloped, it just doesn't show in the photo.

As to what I will use them for - ask me again in a year!

[Andrew Pitonyak]

There are two reasons (off hand that I can think of) for flattening the back. First, because the edge on the back and on the face of the chisel must meet in a nice line. For that, you can flatten a very small portion of the back. Second, if the back of the chisel registers against something. So, if that large warp on the chisel is not registering against something, then it really does not matter to take that bow out of the back. I would be afraid of over-heating the chisel.

[lowell holmes]

I hone the back 1/2" of my bevel edge chisels on a diamond hone and put a micro back bevel on them. They will pare translucent shavings.

Try it, it works.:)

[James Pallas]

When tools are old you don't have any idea of how they were used. I have read on this forum even that one of the good things about patern maker chisels is flexibility. That being said maybe those chisels were flexed often and steeply and took a bit of a set that way. Tools do do that.
Jim