old chisel blade length

[Yorkshire Sam]

I have lots of old chisels of varying lengths. I understand that after they have been ground down by numerous sharpening they can become too short to be of any real practicable use, but how much of the blades length is treated to be able to take and hold an edge?

 

[Biliphuster]

This depends entirely on the chisel.

A old laminated chisel will obviously be hardened upto only the end of the lamination.

More modern chisels (such as Ashley Iles) they heat, quench and temper most of the blade, though the very end may be a bit softer. See here for a video of AI heat treating chisels.

Run a small file along the underside edge of the blade up near the shank, this should tell you if it is hard enough to be workable.

 

[Cheshirechappie]

One old Marples marketing slogan for their chisels was, "Hard to the last inch". I think most makers followed the same basic method, though. Blade hardened and tempered; shoulder, bolster and tang left soft.

I've never had a chisel that short, but I'd imagine the hardness doesn't suddenly give out, but diminishes over a distance of about 1/4" to 1/2". If you do have a very short chisel that won't hold an edge, maybe it's time to buy a new one!

 

[sdjp]

I've never had a chisel that short, but I'd imagine the hardness doesn't suddenly give out,

It might - if the tool is not totally immersed, but instead mostly dipped in, then there can be a line of hardened steel in the tank, and the part outside (usually the tang) not have any martensite formed. This is a common approach, as total immersion brings it's own complications.

The common way of tempering is to bake the whole tool in the oven, so that part not dunked in the hardening will exhibit quite a sharp step in hardness.

In some cases, the tang is deliberately tempered softer, via a torch. If that's done, then it's likely that this will leave a gradient in the hardness. In most of the files I buy [0], I can see evidence of this. However, files are generally left harder, thus the point tempering of the tang is more important. I can't relate that to socketed chisels through.

That said:

If you do have a very short chisel that won't hold an edge, maybe it's time to buy a new one!

full agreement there - empiricism over theory on that one any day.


[0] I did a count, and appear to have 14 files (not including diamond and needle files … is this the early signs of a problem developing?)

 

[Vann]

I've noticed, when de-rusting blades in citric acid, that the hardened portion come out darker than the non-hardened steel - almost a black vrs grey. Usually on plane irons the dark portion stops at the bulbous part of the slot.

So I guess you could try dipping your chisel into citric acid for a few hours to see where the darkened portion finishes.

Cheers, Vann.

 

[Yorkshire Sam]

Thanks for the information guys very helpful. I don't suppose that I would run out of hardened blade then as I find that a chisel blade much shorter than about 2" becomes impractical to use although one can occasionally find use for some of these stubbies.