I took the 9 day course in New York under Mr. Sellers instruction.
The class was also presented with a formica covered guide that was clamped in the vise
with the legs to be mortised. This made for a consistent offset and helped keep the chisels square.
The guide is clamped with the open side away from the user, and the same edge is kept tight
against the guide.
The bevel edged chisel will certainly twist, and try to follow a path that is least resistant.
The essential point of the demonstration is that you can get started with just bevel edged chisels.
I believe Mr. Sellers prefers to work this way, but as mentioned above, he does have years of experience.
I will use my basic Marples chisels to cut shallow mortises, but if the material is tough or I've got lots of mortises to cut,
a Jessem zipslot jig is a welcome appliance. Mortising absolutely wrecks my elbow in ways that chopping dovetails does not.
You can certainly do mortise with a bevel edge chisel, but they've got to be very sharp and a guide jig might be necessary.
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