Motise Chisel Bevel Angles

[horseleft]

Just got a new 5/8" Crown mortise chisel with a manufactures bevel ground on of 35degs. What Primary and secondary bevel angles do i need to hone on :?: .
Thanks for your help :? :? :?

 

[matthewwh]

35 is about right for a morticer, hone a couple of degrees steeper so that you are just working on the edge and don't forget to hone the first inch or so of the sides, a mortice chisel has three cutting edges.

 

[Derek Cohen (Perth Oz)]

I suppose that the answer really depends on the thickness of the blade. I use oval bolstered types which are deep. Still ....

The 35 degrees is fine for the secondary bevel, but 20 degrees would be better for the primary for ease of entry.

Regards from Perth

Derek

 

[matthewwh]

I just had a quick google of Crown's mortice chisels, and strictly speaking they are registered firmers, which is a different animal entirely.

You can still cut mortices with RFs using the drill and chisel technique, but a true mortice chisel (as shown in Derek's photo) is at least as deep as it is wide, slightly trapezoidal in section, and designed to 'stitch' mortices from scratch. The back of the blade is used to lever out the chips and the sharp sides of the blade clean the sides of the mortice as they go.

A firmer is a general purpose heavy duty chisel, to cut mortices with it you would mark out both sides of the mortice and a centreline, drill most of the waste out with a brace or a drill press and then clean up the ends and sides.

Firmers are usually used for chunky, coarse tolerance joinery like house framing and boatbuilding. I'm surprised that Crown, who should know better, are describing them as mortice chisels.

 

[horseleft]

Thanks for your replies guys,
The chisel is described in the Axminster catalogue as a Crown Registed Mortice Chisel. Thanks again for your advice , its cutting well.
Ian