Actually, they are not so peripheral
It should now be obvious that in my view mass is less important when chopping mortises, especially for the cabinet maker and lighter weight joinery most woodworkers find themselves employed in. When you see the next video series on making the workbench on Youtube you will see how effective a 1/2″ bevel edged chisel is on chopping through 3 1/2″ legs; knots and all.
A convex camber eliminates unnecessary secondary bevels
On chopping the mortises in the video we posted a couple of days ago, looking through the glass, you could see clearly that there is considerably more resistance to the huge surface of the bevel of the chisel. Leverage points, the fulcrum of the bevel, is a long way from where you need it and so by the time leverage is exerted, it has only minimal effect and when leverage is applied it tends to push the whole chisel from the hole and not lever our the waste. With the ultra small bevel-edged chisel this is not the case and every time any leverage is exerted the fibres offer only momentary resistance before yielding to even the slightest bevel. Even the mid-weight chisels are twice the weight and three the bevel length of the bevel edged chisel and this reflects in speed and efficiency, but as I said where carelessness is anticipated, or morticing is the everyday work, a stronger chisel helps.
One of my favourite chisel hammers
We should not dismiss the important elements of equal and opposite forces. If you use a heavyweight chisel then you must use greater weight in the hammer or mallet. That’s fine for the start, but when many mortises are to be cut, the hammer will get heavier and heavier. Mallets in wood tend to be large, but not weighty. I have several wonderful mallets in different woods. The very best by far is made from a native Texas wood called cedar elm. This has nothing to do with cedar, it is extremely heavy and dense-grained deciduous hardwood that holds up where beech and maple would dish and hollow in the face. The same is true of my Bois d’arc mallet I made from an old fence post two decades ago. My Thorex hammer delivers the goods in precise measure and unfalteringly. The COP (centre of percussion) is perfect, but it takes a little time to master the accuracy. On regular wooden mallets there is a sweet spot, not in the middle of the mallet head, but near to the handle. That’s where most of us aim for and even after 4 decades of using one, I still found myself either searching for it or missing it more times than hitting it. That doesn’t mean the mallet didn’t hit the chisel handle, simply that the blow was less productive. With a panel- beating hammer like the Thorex, there are many other good makes too, I hit the sweet spot (COP) dead centre almost without fail every time. That matters.
Back to Newton’s law:
For every action, there is an equal and opposite reaction
Literally it means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. It takes much more weight to drive the heavy weights and this is what makes the difference. Add to that the massive bevel in the wood being over 1′ instead of less than 3/8″ and you better see the criteria.
All of that said, I believe there is a place in woodworking for the larger heavy-weight chisels, otherwise those men of old would not have developed them to such a level of perfection that they did.They are quite beautiful. I do enjoy my heavy weights and have a set made by Ray Iles that are second to none in craftsmanship and quality. Old mortise chisels are hard to find but Tools for Working Wood carries the very best new-mades from Ray Iles and is the sole distributor in the US. I used to meet Ashley Iles, Ray Iles’ dad at tool auctions and such back in the 70′s and 80′s. When it comes to the art and craft of tool making, the Isles family have it down.
With regards to secondary bevels.
Manufacturers bevel at 30-degrees
I do not advocate second bevels as such. I do change the bevel angle on my diamond stones if I am chopping mortises with my bevel-edged chisel. This simple task is a matter of lifting up the chisel on the coarse stone to add five degrees to my general 30-degree angle. As all of my chisels are generally sharpened at 30-degrees, and then immediately cut back in a macro camber rather than using micro-bevel secondary-bevel sharpening, I must increase the bevel to strengthen the edge for the higher exertion of pressure on the edge by the chopping and the use of hammer blows. After the mortises are cut I simple restore the 30-degree bevel in subsequent sharpenings. Fact is, there is almost no difference felt between 30- and 35-degree bevels anyway.
A convex camber works well on all chisels and eliminates the need for secondary bevels but gives the same keen edge in short order.
Obviously, on my mortise chisels I keep the start of my macro-camber at 35 degrees (see top pic) and then drop off to around 20-degrees on the close of my sharpening and honing strokes by the natural process of honing. I never grind the bevels of my chisels on a mechanical grinder except to remove damage by edge fracture, hitting something foreign in the wood or dropping on concrete.