Straight vs. Angled Sides on a Mortise Chisel

[Mark Leifer]

I've seen threads discussing the pros and cons of straight-sided versus bevel-sided mortise chisels. The big takeaways seem to be
1. Straight sides encourage a straight mortise with less chance of side-to-side wander
2. Chisels with angled sides are easier to extract after a chop and aren't so prone to splintering wood where the sides of the mortise meet the top
There are many examples of each, including those from modern premium makers (beveled: Lie-Nielsen, Veritas, Narex; straight: Blue Spruce, Sorby) and there are defenders of each on the forums. One thought is to combine the best features of each!

Some years ago, I bought my first mortise chisel--it was from Ray Isles. The business end was a sloppy mess, like someone had been on a bender all weekend and couldn't see straight when he (she?) fashioned this chisel on Monday morning. I sent it back and received a replacement that was worse. The indentation from Rockwell hardness testing went all the way through the metal, twisting and distorting the edge. It went back, too.

Exasperated, I bought a vintage Sargent VBM mortise chisel for $22 and was pleased to find out that it held a good edge and performed well.
IMG_1769.jpg
This chisel was made between 1908 and approximately 1918. Interestingly, one edge is straight and the other is angled, as you can see in the following photos.
IMG_1774.jpg IMG_1765.jpg
(The bevel is to the left in each case.) These are original to the chisel, so far as I can tell. I only own two mortise chisels and don't chop enough mortises to tell if design this tracks better than a chisel with two angled sides and is simultaneously easier to extract than one with two straight sides, but I can say that it's an interesting design that works well.

EDIT: changed Ashley Isles to Ray Isles

[Rafael Herrera]

I believe it's the Ray Isles company that makes the oval bolstered (aka pig stickers) mortise chisels. Ashley Iles is a different company and they don't make that style.

On deep mortises square sided mortise chisels are likely to get stuck. That's the reason for the slight angle on the sides.

[stephen thomas]

I've surface ground mortise chisels to get a very specific size, or to straighten & clean up flea market finds.
If i bias the angle, it is very slight. Like a piece of paper or .003 under the sine roll in the magnetic chuck. Then double that to do the other side.
The sine rolls in that chuck are 5" apart => .069 deg. (7 one hundredths of a degree total).

A mortise chisel without essentially parallel sides that are perpendicular to the register face & sharp, is a beast to steer and use rapidly.
But you don't want the angle to be negative.

[Jimmy Harris]

An interesting design idea.

Though I don't know if that is the "proper" way to angle the side of a mortise chisel. At least on mine, they're still square in cross section, it's just the square gets smaller the further you go up. Angled the way that one is, it doesn't really allow you to tilt the chisel, side to side. But rather just twist it a hair in one direction.

But if it works, then it works. And that's all that really matters.

[Warren Mickley]

I've surface ground mortise chisels to get a very specific size, or to straighten & clean up flea market finds.
If i bias the angle, it is very slight. Like a piece of paper or .003 under the sine roll in the magnetic chuck. Then double that to do the other side.
The sine rolls in that chuck are 5" apart => .069 deg. (7 one hundredths of a degree total).

A mortise chisel without essentially parallel sides that are perpendicular to the register face & sharp, is a beast to steer and use rapidly.
But you don't want the angle to be negative.

In 1979 Frank Klausz wrote in Fine Woodworking that a mortise chisel needed to be tapered front to back so you could "steer" it. It was obvious from his other remarks that he had little experience making mortises by hand.

What you don't want is a chisel that is wider on the side away from the cutting edge. You also don't want a chisel that is wider anywhere up the shaft than it is at the cutting edge. So if there is a tiny amount of taper in a helpful direction, it helps insure against irregularities that would cause the chisel to get stuck in the cut. Otherwise the four corners of the shaft should be sharp and square to help clean the sidewalls of the mortise.

[Rafael Herrera]

Someone on a reddit thread posted this picture. A Blue Spruce mortise chisel.

It is presumably square in cross section, since that's the current trend in 'improved' mortise chisel making nowadays.

It seems that their improvements also included a threaded tang.

The chisel seems to be stuck in the mortise it was being used to cut. The poster reported that he had used it for about 20 hours before it snapped.

w9e39vzqzz2d1.jpeg

[Edward Weber]

Otherwise the four corners of the shaft should be sharp and square to help clean the sidewalls of the mortise.

You make it sound as if you want to "square" the corner by cleaning the sidewall and endwall at the same time, that's the job of a corner chisel.
There is no cutting edge on the side of a mortise chisel other than a 90 degree corner.
When cutting the endgrain;
A square mortise chisel just pushes the cut fibers on the sidewall in one stroke.
A mortise chisel with tapered sides, cutting the end grain slices through and terminates the fibers on the side wall, where they can easily be pared off. This takes a second stroke but IMO leaves a better result with less tear out.
To each his own, I have both styles, they all have their place

[Mark Leifer]

Oh right, Ray Isles. Thanks for the correction.

[Cameron Wood]

In 1979 Frank Klausz wrote in Fine Woodworking that a mortise chisel needed to be tapered front to back so you could "steer" it. It was obvious from his other remarks that he had little experience making mortises by hand.

What you don't want is a chisel that is wider on the side away from the cutting edge. You also don't want a chisel that is wider anywhere up the shaft than it is at the cutting edge. So if there is a tiny amount of taper in a helpful direction, it helps insure against irregularities that would cause the chisel to get stuck in the cut. Otherwise the four corners of the shaft should be sharp and square to help clean the sidewalls of the mortise.

You embarrass yourself with this statement, IMO.

[Eric Brown]

One consideration is that you don't want a tight piston fit. A little bit of slop will allow glue to squeeze out.

[Kent A Bathurst]

........beveled: Lie-Nielsen..............

Just an FYI - this is not correct. At least, the ones in my drawer are "straight" cross-section - they are maybe 20 years old, so could be they've changed the design.

I like this feature. I chop my mortises by starting at the DP, then a moderately-wide bench chisel to quickly pare down protruding ridges, then the mortise chisel. The cross-section makes quick work of squaring up the mortise sides.

[Tom M King]

This has quickly turned into one of the strangest threads ever. I like a little bit of clearance on those 1/2" and bigger, and parallel for narrower. This Ulmia 1/2" has some taper both ways.

[steven c newman]

Been using Narex brand Mortise chisels...a lot...They are a tad wider at the business end...
Cheap Mortise Chisels, side view .JPG
But...even my sash Mortise chisels have a slight "tumblehome"

And..I have yet to get any of these stuck inside a mortise....

YMMV, of course..

[Edward Weber]

Just an FYI - this is not correct. At least, the ones in my drawer are "straight" cross-section - they are maybe 20 years old, so could be they've changed the design.

I like this feature. I chop my mortises by starting at the DP, then a moderately-wide bench chisel to quickly pare down protruding ridges, then the mortise chisel. The cross-section makes quick work of squaring up the mortise sides.

Very much the same way I go about it.
Scrore the perimeter, drill (hog out) the waste and then pare the corners and sides.
IMO, chopping the entire mortise by mallet and chisel is a pointless endeavor if you have access to a drill of some kind, that includes brace & bit.

[Tom M King]

I haven't found that drilling holes saves any time. I drill them for big timber framing mortises in dry wood, but otherwise don't. I start in the middle and work towards both ends in different directions.