Mortice chisels which size

[TRITON]

Since buying the Ax morticer, I've yet to get a small selection of chisels for it. It's not really needed right at the mo, so kind of putting it off.

I was intending to buy 2(possibly 3) and was thinking of 6mm and 8mm.
Really down to timber sizes and the 1/3 you know. 6mm being for 18mm, 8mm being for 24mm timber. But I wondered if you should go bigger, say 12mm too.

So if you only were getting a few chisels, what size would you pick ?

 

[Jacob]

The usual collection is 1/2" 3/8" 1/4" plus 5/8" if you do any bigger stuff. 1/2" is probably the most commonly used.
The 1/3 idea is just a rule of thumb. A mortice doesn't want to be much more than 1/3 of width of component but may be a lot less. The opposite for the tenon - doesn't want to be much less than 1/3 of the component width.

 

[Yojevol]

You can always do multi-passes for the odd occasion when something bigger is required.
Brian

 

[niall Y]

I would have to agree with Jacob on this. as I have all the sizes that he lists.
I am often reluctant to change the chisel if I don't have to, so I often make do with the chisel that is in there. 1/2" is handy for ex 2" doors, it allows for thinner 1/2" panels, rather than 5/8" which would be the 'rule of thumb' size.
I also found it handy to have additional inserts made to accommodate the varying diameters on some of the makes of chisel that are available.

 

[eribaMotters]

I must admit that my 3/8" stays in the machine for 95% of the time. If I need a wider mortice I tend to set the chisel up off centre and rotate the timber so I've done a run with the face side towards me and away from me.
When cutting my tenon cheeks on the bandsaw I then only need to worry once about setting up the bandsaw fence accurately once.

Colin