Question

[hawkeyefxr]

I have a chuck with 'std' jaws that cover a range from about 42mm to 60mm. My lathe swings 6 inches making a 12 diameter bowl in theory. My question is are my jaws man enough to hand on to a bowl that size. I have one on the go at the moment and it's around 10 inches diameter and about 4 1/2 inches deep when finished, I am turning it with a faceplate at the moment in my chuck and it is steady enough but when i come to hollowing it out i will have either 42mm tenon or a 55mm recess for the jaws. My bowl is made of parts glued together. I prefer to use a recess as i think it looks better but i am wondering if i should go up a set of jaw sizes.
Hope that all makes sense.

 

[Walter]

The standard jaws will be more than man enough for a 12" bowl so lomg as the spigot or tenon is a good fit for the jaws at their optimum opening. (I.e. when they are at their nearest to an exact circle)

 

[Louie_Powell]

Agree with Walter - make sure that your tenon or recess is properly sized for the jaws so that the jaws grip uniformly around the tenon/mortise. If the tenon/mortise is too large, the jaws will only grip at one or two points and the hold will be much weaker. Also, make sure that the nose of the jaws fit tightly against the bottom of the bowl. If you are using a tenon, it must not 'bottom out' in the jaws. Finally, make sure that the wood is as firm as possible at the tenon/mortise - soft/punky wood will reduce the effectiveness of the hold.

Oh, and try to avoid catches. If you get a good catch, the size of the jaws is no longer an issue - the bowl will come off the mount. DAMHIKT.

Not a hard rule, but with a segmented piece, a tenon is often preferable. Expanding jaws into a mortise made up of pieces glued together puts a separating force on the glue joints.

 

[Walter]

Not a hard rule, but with a segmented piece, a tenon is often preferable. Expanding jaws into a mortise made up of pieces glued together puts a separating force on the glue joints.

I prefer a tenon on large pieces anyway. Wood is stronger in compression than in tension.

 

[Dalboy]

As Walter stated. There is a video somewhere but for the life of me can't find it which explains in great detail the optimum holding of jaws.

 

[Bill Mooney]

All good advice.

 

[Penpal]

Absolutely shown that chuck useage is vital in compression.

Peter.

 

[wm460]

Page 18 & 19 give you the Expansion and compression of vicky chucks might give you an idea.

https://vicmarc.com/files/4-Jaw-Chuck-Manual-Aug-10.pdf

 

[Graham_C]

All good advice - as always

 

[hawkeyefxr]

Thanks for all the replies, they pretty much confirmed what my sawdust told me. Segmented hold in compression bigger bowls also. Keep the tenon/mortise as neat as possible to the optimum gripping area.
I have finished the bowl now and don't like it, looks like a piddle pot or bowler hat with the top flattened off, oh well. I was just using up wood that i had had for years hanging around indoors so it was good and dry.

Next one tomorrow