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thumb trimmer
29th Jun 2010, 11:57 PM
I've just (about 30-odd mins ago) finished the bottom of a camphor bowl.
I knew there was a split in the blank so I tried to cut most of it away. I wasn't able to get rid of the split entirely, and was pretty happy with the result, until ...

... I turned the bowl off the worm screw, flipped it over to grab in the chuck (expand within a groove cut in the base) and the sod cracked ... grrrrrr :~ ...

With the exception of buying a bigger set of jaws for my G3, has anybody got a suggestion for 'gripping' the work.

I should also note that I have a set of the 'soft' red jaws for the G3.

regards
TT

Manuka Jock
30th Jun 2010, 12:33 AM
My thoughts.

If the wood has splits in it don't use the worm screw , and don't use the chuck in expansion mode .
Use a faceplate or a glue on spigot , and then use the chuck in compression mode.

Split or cracked wood doesn't need to be helped along to do what it does best , it needs to be hinderd :wink:

John Lucas
30th Jun 2010, 03:16 AM
YOu have two potential problems. If you have a split you may not have cut all of it out. The other problem is how much wood did you leave around the jaws in expansion mode. Expansion into a rebate can be done successfully but you have to leave a fair amount of wood around the jaws. If I'm going to use expansion mode I turn the bowl without a foot. The jaws then expand into the bowl so there is a lot of wood surrounding it.
Normally I start a bowl between centers. This allows me the option of changing it several times if necessary to get rid of or include things like bark inclusions, cracks, etc. Once I get the outside shaped I turn a tenon for either a faceplate or chuck. This tenon is going to be turned away in the final step so I can make it quite large to hole the screws from a faceplate or fairly small for a chuck if necessary.
I place the bowl in the chuck and then true up the outside. Then turn the inside. Then I reverse it using the most convenient way and turn the foot. To reverse it the simplest way I simply put a rubber sink stopper over the chuck. Then I bring the tailstock up put the center in the hole left from the very first step (when you mounted the bowl between centers). Now you can turn away all but a tiny cone that can easily be carved away.
that's how I do my bowls. others will offer a different opinion.

thumb trimmer
30th Jun 2010, 10:27 AM
Thanks John.
Yeah I didn't cut all of the crack out of the timber. I was hoping that it'd be 'alright'. And yes, I know, I probably should have left more 'meat' around the groove, but ... :shrug: ... oh well ... lesson learnt on that one.

In the meantime this is the bowl in question ...
http://www.woodworkforums.com/members/30814-thumb-trimmer/albums/other-stuff/4624-6th-bowl-camphor-laurel-but-foot-has-split-so-not-sure-how-im-going-turn-inside.jpg

... any ideas on how I can re-jaw the bowl to turn the inside?
If possible I'd like to save the foot, as I kinda like the form/shape I've created.

regards
TT

John Lucas
30th Jun 2010, 10:44 AM
Looking at your bowl you had two problems. The foot you were expanding into was definitely too thin. If you had tapered the bowl up toward the lip from the very bottom you might have succeeded but by making the foot straight you took away thickness where it was needed most.
Here's what I would try. Cut a hole in a wasteblock the same size as the base of your bowl. Then jam it in and glue it. Centering it could be tough. Fit it in the jam chuck without glue. rotate it by hand and find the high side. Bump this to align it. Do this until it's running true. Then move the tailstock up to put a center point in it. If you have trouble getting it to align use the tailstock to hold it. Put a small washer on the point of your tailstock to keep it from penetrating very far. Then when you get everything aligned remove the washer and jam the tailcenter in pretty hard. Then you can use the tailstock to keep it aligned while the glue dries.

joe greiner
30th Jun 2010, 10:18 PM
At the first indication of a crack or split, STOP working on it. With the piece still mounted on the lathe, or not, repair the crack. I do this by routing deeper with a small bit in a Dremel, usually a miniature dovetail bit or a dental burr to create an undercut, and if possible beyond the future far side of the wall. Then I pack the hole with a "mortar" of epoxy and filler material. The filler material is usually ground coffee or key-cutting shavings. I pack the mortar proud of the final surface, so that proceeding cuts and sanding intersect the material.

If turning the inside reveals the same weak spot or another, repeat the routing and packing as with the outside.

The final surface(s) can imitate miniature terrazzo inlays. Here's a close-up (last picture): http://www.woodworkforums.com/f8/cedar-bowl-77115/

Cheers,
Joe