That is true and it's a good question. I picked up the practice from David Ellsworth's book, and the primary purpose to me is that it gives you some extra breathing room and makes it so you aren't "locked in" to the final foot size being either the diameter of the tenon, or the diameter of a flat above the tenon. Instead, this setup gives you the room to make more decisions about the final foot size and shape, and it helps you visualize the bottom of the bowl while you are hollowing compared to not having it. David calls it the "base cut" and there is more detail in his book on page 120.
Good video, thanks. I note that Crown Tools, in advertising their dovetail scraper, states that "Tests have shown that as much as 50% of a collet chuck's gripping power is lost if the dovetail angle is out by as little as 5°." This might just be an effort to sell their scraper, but even if the point is true, I think that it is not difficult to eyeball the angle within 5º, so it is likely to be accurate enough to do it without any special tools or measurements.
I use One Way chucks and whatever diameter I have for the tenon works fine, I make it my way and it works fine. You and all the others that waste their time trying to figure out the correct diameter, buy a good set of jaws and you won't have to worry about this minor thing.
First time I've heard about the jaw size issue. Might explain why I've had so many things flying around the shop lately.
I’m a total newbie. Very helpful video. Thanks.
What does that second tier do vs not having it? You could still have a flat surface for the surface of the Chuck to grip.
That is true and it's a good question. I picked up the practice from David Ellsworth's book, and the primary purpose to me is that it gives you some extra breathing room and makes it so you aren't "locked in" to the final foot size being either the diameter of the tenon, or the diameter of a flat above the tenon. Instead, this setup gives you the room to make more decisions about the final foot size and shape, and it helps you visualize the bottom of the bowl while you are hollowing compared to not having it. David calls it the "base cut" and there is more detail in his book on page 120.
Good video, thanks. I note that Crown Tools, in advertising their dovetail scraper, states that "Tests have shown that as much as 50% of a collet chuck's gripping power is lost if the dovetail angle is out by as little as 5°." This might just be an effort to sell their scraper, but even if the point is true, I think that it is not difficult to eyeball the angle within 5º, so it is likely to be accurate enough to do it without any special tools or measurements.
Well I thought there was some best practice in doing this but was always secret squirrel stuff
I use One Way chucks and whatever diameter I have for the tenon works fine, I make it my way and it works fine. You and all the others that waste their time trying to figure out the correct diameter, buy a good set of jaws and you won't have to worry about this minor thing.
LOL, imagine thinking that Oneway chucks are better than Vicmarc. 🙄