Hearnshaw 5/32 sash mortise chisel ?

[Downwindtracker2]

At the fleamarket I picked a couple of what I thought were 1/8" mortise chisels, the Hearnshaw instead was 5/32". Any reason for that size?

 

[AndyT]

Old chisels were made and ground freehand, without measurement. The sizes were nominal and some variation from a catalogue size is normal. This doesn't matter to the end user, who would select a chisel by looking at its actual size, then use it to cut mortices, then cut tenons to fit the mortices, all without any measurements expressed as numerical values.

 

[Downwindtracker2]

I don't think that size was mistake, rather it was deliberate. I worked as a millwright (maintenance fitter) and we did some welding, from a distance you could see the difference between 5/32 (4mm) and 1/8(3.2mm) rods. So the toolmaker was likely aiming for that size.

 

[AndyT]

The 1871 Sheffield List has 1/16" 1/8" and 3/16" as the smallest sizes of chisels. I've not seen any catalogue with a size in 32nds.

 

[Downwindtracker2]

Thanks for the checking out the old catalogue . I was just wondering if there had been a special purpose. Half the fun of finding old tools is learning who made it and their history. It's tang chisel with the flair being 8 sided. The beech handle is what I would call classic English with 14 lines. It and a 1" E.A.Berg bench chisel only cost $5.00 Canadian (about 3 pounds) .When it comes to old chisels, I find a lot more English then American .thx

 

[Argus]

I agree with Andy.... amongst the very old mortise chisels I have, there are subtle variations from the usual 'nominal' sizes.

It's not unknown for variations in the shape of the shank, too. Modern mortise chisels that I've seen tend to be machined as a rectangle in cross section all the way up the shank, but some of my older ones are marginally wider at the cutting tip than the measurement at the bolster end and some are trapezoidal in cross setion.
Allowed some some lee-way in the sides of deep mortises, I suppose, to stop the chisel jamming in the hole.

At the end of the day, cut by hand, users trimmed their tenons to suit the mortise hole.

P.S....... I automatically presumed that we were talking about so-called 'pig-sticker' type chisels, but sash and firmers tend to be parallel as far as I can see in my stash and most of the nominal sizes are not bang-on exact, so I can say there's a bit of variance in my tool box.