These days there seem to be two kinds of mortise chisel – the relatively inexpensive that are quite traditional and the very expensive that tend to have not just high quality materials and finishing but one or more design innovations.
The former include chisels such as those from Narex, Sorby and the older makers. The latter include mortise chisels from Lie-Nielsen, Veritas and, now, Blue Spruce.
Some innovative (or are they) design features are:
* Veritas chisels with the bevel to top transition rounded rather than a sharp transition, supposedly to improve the leverage of chips out of the mortise channel.
* Lie Nielsen with parallel sides and cryo-treated A2 blades of high hardness, respectively to keep the mortise chisel square in the channel and to need less frequent sharpening.
* Blue spruce, also with the parallel sides but also a through two-piece blade-to-striking cap metal core, to save the wooden handle from mallet blow damage.
Personally I use the Narex, after first trying Two Cherries, which were hopeless because not well made, with blades that often had a twist or skewed trapezoid end profile, as well as coming with dubbed edges from being over-polished to look shiny.
I’m puzzled by one or two of the design differences in the more expensive mortise chisels, particularly the parallel sides of the blades. My understanding was that the tapered sides of the blades in traditional designs was to help prevent the chisel jamming when leverering out chips, with the edge touching the mortise sides acting also as a scraper to smooth those sides as the levering of chips was done.
I also thought that, rather than keeping the chisel straight in the mortise channel, even the slightest not-square first blow would make it impossible to then cut the mortise straight, as the parallel chisel sides would force the initial skew to be carried to the next dig of the chisel …. ?
And isn’t a metal ferule around the wooden end of the handle at the striking end enough to preserve the handle from being broken by the mallet blows? Do hand mortisers constantly break their chisel handles?
I’d be interested in he observations and thoughts of others about mortise chisel design, particularly from those who use them a lot. (I use them myself regularly but not often, generally relying on a Domino).
Replies
The mortise chisel as a parallelogram is a nice thought. If the manufacturers achieved identical grinds on both sides then in theory they might work. However, they rarely do achieve such uniformity and as a result this type twists in the cut. As Ian Kirby proclaimed "nothing can stop it." He was right. Grind them back (by hand) into a rectangle and you'll be much happier. They won't get "stuck in the cut" if you know how to use them. Lie-Nielsen used to make ones that were rectangular in section but they haven't been available since the pandemic. It seems they may never come back. What a pity.
Lie-Nielsen's web site has them for sale: https://www.lie-nielsen.com/nodes/4174/mortise-chisels . I dare not click the 'Add to Cart' button to see if there's a subsequent note that they are not currently available, lest I inadvertently buy one. Or all 5. But they seem to still be offering them.
I share lat_axe's puzzlement at how some mortise chisels are made. I have one L-N and several Sorby's. I find all of them will cut oversize -- the corners of them, particularly when you get towards 1/2", are sharp and cut sideways too easily. I've taken to using one size under. I use a paring chisel to cut to final size on the sides and use the mortise chisel as a paring chisel to cut the final lengths. Or use the Domino:-)
I also wonder why they are not tapered. I do find them useful because of the ability to lever out wood as you get deeper. I also don't know why you'd need steel on the top. I use a wooden mallet to hit chisels, works fine, one of those with a tapered cylinder business end, up to an integral handle (not a hammer-like mallet). Easy enough to make one on the lathe.
Parallel sides are not limited to the newer ‘innovative makers’. Sorby offers both “sash mortice” and “registered firmer” chisels. The former are listed as having a 2 degree side relief angle. I have the latter in 3 sizes and true to their registered name, they have a truly rectangular cross section with parallel sides. In my experience they do tend to jamb in mortises. I have never had an issue with their double hooped ash handles — they can (and do) take a beating.
Since I mostly use them for squaring up ends of routed mortises and adding haunches to same, I have carefully disk-sanded my 6mm/1/4” and 10mm/3/8” chisels narrower to better match with the imperial sized router bits I use (their original dimensions favored the metric designations). I maintained the rectangular profiles to aid in clearing chips and aligning haunches. That said, if I was mostly hand cutting my mortises rather than squaring up machine cut ones, I would certainly experiment with the 2 degree (or perhaps a bit more) side relief of Sorby’s “sash mortice” chisels. BTW, Veritas lists theirs as “chisel sides are slightly relieved to reduce sidewall friction and allow for minor cut corrections”, but I don’t know what this actually amounts to in practice.
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Above comment deleted by accident. I wonder what those old Federal and English craftsmen used for chisels? What were their shapes? What did the mortises look like? Did it matter??
See the lat axe post below. The Ray Iles chisels made today are what were available for a few hundred years. They are exceptional tools.
The great majority of mortises in period furniture were 5/16. That's pretty much all I use.
I found this interesting webpage about Ray Iles pigsticker mortise chisels.
https://toolsforworkingwood.com/store/item/MS-MORT.XX/English_Mortise_Chisels_by_Ray_Iles
The article contains this paragraph:
"The sides of the chisel form a slight trapezoid, so that if your chisel isn't perfectly aligned with the cut you won't damage the sides of the mortise, and more importantly, there is a lot less of a chance for the chisel to get stuck. You just push the chisel in the mortise a little and it loosens up. Lighter sash mortise chisels are ground parallel but that's because they are designed for shallower mortises in window sashes which are usually in soft wood. Some manufacturers say that that parallel sides make it easier to guide and align the chisel with the mortise but in fact the alignment of the mortise is determined by the first stroke of the blade into the wood, long before the sides of the chisel can have any effect."
That makes sense to me. A trapezoid shape allows the user to make a not-quite lined up first cut with the chisel which can then be corrected as the trapezoid shape allows some wiggle in the cut to get the next one straight. A parallel sided chisel is going to force the blows that are subsequent to the first one to repeat any skew.
So, if you get that first blow exactly right, all well and good (although your chisel might tend to jam when you lever out chips). But if you get the first cut skewed .....
I'll stick with me Narex trapezoids, then. They do work very well. It seems that nearly all European and British mortise chisels have included the trapezoid shape, for decades or even centuries, but so have the latest Veritas items. So far I can only find Lie-Nielsen and Blue Spruce with parallel sides although there's no doubt others.
I’m now convinced to refine my Sorbys to a trapezoid—as Lat_axe points out, jamming is a risk unless you get that first strike perfectly square.
I use Veritas and Japanese mortice chisels. They have trapezoid sides - these are very slightly done, so-much-so that you may not notice. By contrast, LN mortice chisels are square. The reason for the relief angles is to prevent the deep blade of a mortice chisel becoming stuck in the mortice.
Regardless whether a mortice chisel is trapezoid or square, the lands need to be sharp - not rounded as with worn, vintage chisels. If rehabbing vintage chisels, lap the lands for cleaner cutting of mortice walls.
There are instances where a square/parallel-sided chisel is useful. This is when squaring up the ends of a machine-made mortice. What I prefer to use in this case - using a router or the Domino as a morticing machine - is a hollow chisel. This works very well.
Regards from Perth
Derek
That hollow mortise chisel use is a very good tip.
I have squared up Domino-cut mortises for through rectangular tenons - using a standard bench or mortise chisel is not ideal as it can easily go out-of-square.
The hollow mortise chisel, I presume, auto-aligns the end cuts at 90 degrees with the mortise side walls in a way that a bench or trapezoid mortise chisel might not.
The great majority of mortises in period furniture were 5/16. That's pretty much all I use.