The way I reasoned through that design aspect, you're correct from the sense there's a risk of weakness due to having too thin a tenon wall--possibly a result of limiting tenon size to commonly available ferrule diameters. OTOH, we also don't ordinarily leave that end of our tool handles at the full diameter of the blank. So somewhere in between is a point where there's enough wood to offer the necessary strength--with low potential to break. Add a well bonded insert to the tenon and you achieve equal or better strength in that area than wood alone, as long as you maintain the integrity of the combination. That's where the ferrule adds value, IMO.
Granted I may be overthinking the design of these tool handles, but I tend to tilt toward doing things at least a little beyond whatever is "just enough". If a ferrule
- distributes force
- reduces the likelihood of splitting
- is typical on commercially produced tools
then as long as I can utilize a ferrule sized to allow a tenon wall thickness similar to what I measure on high grade commercially produced tools, I'm inclined to incorporate that into my overall handle design.
And in going "a little beyond", like Clark mentioned, I was also planning to drill a deep enough hole (similar to tool tang diameter, beyond the larger one for the insert) to accommodate the longest tang or part of a tool I could potentially encounter. From my research, that'd be a Mastercut double-ended bowl gouge, unless there's an alternative I've overlooked.
Now that I've ordered some material for making custom sized ferrules, with quality hardwood for the handle stock, I'm presently not too concerned about weakening the handle at the tenon or by drilling some extra hole depth.
The feedback has been good, so as I await the rest of the materials for my project, I remain open to others' thoughts. . .
