How do I mount this on a lathe

[Arron]

Hi. Occasional woodturner here.

I’m trying to turn a parallel sided bowl out of this rather large blank.

I’ve turned the outside and the base. My intention was to leave a shallow tenon on the bottom for grip when I flipped it over to do the inside.

Of course when I started I promptly forgot about the tenon.

So now I need a method to fix the piece in the lathe to do the inside.

A complication is that it weighs just short of 3kg.

A further complication is that I’m doing it at a Men’s shed, so at the end of the session I had to demount it from the lathe and remove the faceplate to leave the lathe free for any other user. I marked the orientation of the faceplate carefully, so I’m sort of confident that if needed I can get the faceplate back on and spinning true, but not 100% confident.

My current thinking is to glue a roughly-round piece of timber to the base (to replace the tenon that should have been there). Fix the faceplate back to the base in the original holes and remount. Then turn the newly glued-on timber down to make a tenon. Then demount, remove faceplate and remount with tenon in a chuck. I’ll move the tailstock in and work around it till I have most of the weight off the piece. Then move the tailstock out of the way and finish the inside in the normal way.

That sounds feasible but where I can see it going wrong is 1. Not getting it centered properly again and 2. Removing the tenon will mess up the bottom.

If I had one of those fittings which held the bowl face inward (I think they’re called remounting jaws) so I could clean up the base, then point 2 wouldn’t be a problem. Unfortunately I don’t.

So are there any other ideas out there please?

Cheers
Arron

460511

[Skew ChiDAMN!!]

I'd either go as you suggest and glue on a scrap piece as a temp spigot, or turn a shallow recess for use with the jaws in expansion mode. Probably the first, as expansion mode isn't the best choice when it comes to hollowing out large amounts. (But at least with exp mode you don't have to wait for glue to dry or a tenon to remove when all is falmost inished... :rolleyes:)

When it comes to re-centering, well... you do the best you can and generally accept that you will have to do another pass or two over the outside to true things up again.

Still, sometimes you get it right and everything lines up nicely. It's generally worthwhile dismounting and remounting a few times if you're not happy with how it's mounted, just to see if you get lucky. But I wouldn't be be overly fussy, you should be able to get it close enough that it's only a few moments work to fix.

FWIW, learning to accurately remount should be part of every turner's skill-set, as there will always be oops moments when you need to dis-/re-mount unexpectedly and contrary to plans.

In the past, in similar situations, I have mounted with Cole Jaws for hollowing (I think that's what you mean by 'remounting jaws') but I really don't recommend it... they don't have much holding force and are designed for cleaning up a piece, not doing heavy work. ie. The chance of UFOs is greatly increased with them. ;)

Another option, of course, is to simply re-turn the bottom the way you want it. The bowl'd be a tad shallower, but c'est la vie. Re-centering would still be an issue, of course

[clear out]

Why not just glue a suitable disc on the back with a paper joint using pva.
You can Then true this up after remounting on your original set up.
If the face plates on the lathe are true you could turn a rebate to ensure your register.
Just screw in onto the faceplate into your new glued on bit.
When you’ve finished hollowing etc just use a wide chisel or plane blade to split the paper joint.
H.

[Arron]

Why not just glue a suitable disc on the back with a paper joint using pva.
You can Then true this up after remounting on your original set up.
If the face plates on the lathe are true you could turn a rebate to ensure your register.
Just screw in onto the faceplate into your new glued on bit.
When you’ve finished hollowing etc just use a wide chisel or plane blade to split the paper joint.
H.

Yep, I’m liking your suggestion of just turning a rebate in the glued-on piece to center a faceplate.

The paper joint thing is something I’ve seen but never done. Two questions:
1. Is it robust and reliable enough for a 3kg blank?
2. Do you need special paper - or is reflex copy paper good enough

I presume that if I don’t use a waterproof pva I’ll be able to just soak and scrub the residual paper off - so no need to ruin my nice clean finish on the bottom surface of the bowl.

[Paul39]

I think grocery bag brown paper is generally used fro gluing between work piece and scrap.

My method would be to glue on a scrap directly, make your spigot and leave a good deep mark from the tail center, remount in chuck and completely finish the inside and around the outside as much as you can reach, remove from chuck and make a round piece in the chuck about 1/2 diameter of the bowl, pad that with some stiff foam and cloth, place inside of bowl on padded round and bring up tail center into hole left in made spigot - tight!, check that bowl is running true, turn down spigot leaving nub under tail center, finish bottom, remove from lathe, lay on padded surface and using razor sharp bench chisel break / slice off nub, sand and finish area of nub, done.