Bowed Bellied Chisels

[Nikolaj33]

I have got three of my old Marples Bevel Edged chisels with significant bellies, rather a bow on the full length, 1/4", 5/8" and 3/4". It seems quite impossible to flatten these. I have been trying to flatten them with sand paper on glass, but I don't think I made any progress with them after hours of lapping. It seems to me that since the bow runs along the full length it is not possible to find an anchoring point so to speak and the bow remains.
I read somewhere that it could be possible to heat them and bend them the other way, although this is not without risk of them braking. In any case, I have no furnace that is able to develop that sort of temperature. I might have to wait till winter to try it at my mother's fire oven.
Is there anything else I could try? Please give me some suggestion, perhaps there is some lapping technique that can work in this case. Did you have any good experience with flattening bowed chisels?

 

[AndyT]

Is there any particular job that you have tried to use these chisels on, where the lack of flatness made it impossible?

 

[D_W]

Use them as they are. I promise that unless either:
* you're using paring jigs
* the belly is severe right at the tip

you won't notice any significant issue in use. Your brain is a great compensating tool and will point you to how to use them to get the results you want.

 

[Bod]

A photograph of the problem will help.

Bod

 

[custard]

If you're making furniture to the very highest standards then it's useful to have a couple of dead flat chisels, but you only need a couple. Most times you can get away with something that's not absolutely flat so I wouldn't sweat this too much.

 

[Nikolaj33]

Thank you for replies. I haven't yet tried them to be honest. I will maybe try to apply pressure at the tip only and see if I can polish it.
I have some experience with other chisels whose backs I couldn't polish due to bellies, which just never seemed sharp enough for sculpting sort of work. Maybe ok for chopping.

 

[woodbloke66]

If it's a really significant convex 'bellie' it's almost impossible (IMO) to remove because as you rightly mention, you have no points of reference and the tool will just tend to rock on the high spot. If it's quite bad I would find it frustrating and personally wouldn't use them. Conversely, a small concave bow in the back of a chisel is a desirable feature - Rob

 

[Ttrees]

I would be careful that you don't abrade through the hardened steel on the vintage chisels.
See how far the hard steel goes up looking at the bevels when ground, if you can't see them already.
I have one vintage chisel that aint flat, and would become flimsy for paring if I did flatten it.

What method are you using to flatten the other ones?
I suggest cutting some abrasive roll in half, stretching one piece across a plate and clamped either end of the lap for a narrower area that will be in minimal contact with the end of the chisel until you get the belly out of the middle.

Skew the chisel in both directions whilst lapping them.

Tom

 

[AndyT]

One other question - when you say 'old Marples chisels' that could mean many different things. From the boom years of the 1870s, through expansion and consolidation in the twentieth century until about 1998 when the brand became the property of successive American owners and production in Sheffield ceased.
During this long period, Marples made hundreds of types and sizes of chisels, with different methods of production and degrees of automation.

What's old to you could be relatively new to someone here trying to help you.

 

[Nikolaj33]

Here ithe picture of the chisels in question. I also tried to capture where the main problem is, you will see that there is convex banana tuning along the full length of the chisel

 

[thetyreman]

can it not be grinded out on a bench grinder? I'd be tempted myself, and quench it in water in between until it's slightly hollow.

 

[woodbloke66]

can it not be grinded out on a bench grinder? I'd be tempted myself, and quench it in water in between until it's slightly hollow.

That could be done, but not easily. Might be easier say, on a water cooled Tormek wheel with a larger dia stone - Rob

 

[AndyT]

Try them. As already said, unless you are doing something uncommon like this

they'll be fine.

 

[MikeG.]

They only need to be flat within, say, 10 or 20mm of the business end. You'll be an unusual person if you sharpen more than that away in your lifetime, so flatten that bit and forget the rest. Andy has shown you the one circumstance I can think of where it would be an issue, but that aside, it's utterly irrelevant what goes on more than an inch above the edge.

Don't take any notice of the nonsense about lapping it away. Hand lapping with a single point making contact with the lapping medium at any one time.....that's a recipe for making things worse, not better. Leave well alone, sort out the last half inch or inch, and get on with doing some woodwork. If it disturbs you that much, sell it on.

 

[Nikolaj33]

How can I lap last half an inch if not using single point of pressure on the very top?

 

[MikeG.]

You can't get half an inch flat? Really?

 

[Nikolaj33]

No, I mean, the way I was to try to do that was to press hard down close to the tip. Would this not work?

 

[Max Power]

They're forged not cast' so unlikely to incur any damage if you put a piece of wood at either end and gave them a careful tap in the centre to remove the bend

 

[worn thumbs]

If it's a really significant convex 'bellie' it's almost impossible (IMO) to remove because as you rightly mention, you have no points of reference and the tool will just tend to rock on the high spot. If it's quite bad I would find it frustrating and personally wouldn't use them. Conversely, a small concave bow in the back of a chisel is a desirable feature - Rob

I have to disagree about a bit of concavity being desirable.It makes it more likely that the chisel will dig in.I don't see too much to get bothered about with the chisels in question,its something you get used to and each chisel has a different feel in your hand in any case.Probably best to put in a few hours to get the feel established in your hand/mind .

 

[richarddownunder]

Does it look bent (the front has a curve as well - it kind of looks like this in the picture) or poorly ground? If it is poorly ground maybe it can be re-ground. I'm no expert on older chisels (especially if its laminated, so may be spouting rubbish) but if it was bugging me then I'd take to it (gently) with a linisher to remove the belly. But I like grinding knives and have a linisher and can do it without ruining the temper. Alternatively, how about calling someone who does like grinding chisels such as Asley Iles - I'm sure it'd take someone with experience a couple of minutes to get it flat, as long as is not removing too much metal. If it is significantly bent, that may be a different story. Can chisels be bent along their whole length like that?

Cheers
Richard