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Holding wet wood

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OldWood

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I've a 250mm dia. vaquely bowl shaped lump of wet elm on the lathe. I cut a large diameter foot on it and did an internal dovetail - mistake as I then launched a 4lb rapidly rotating projectile when the dovetail wall broke for no apparent reason - ie I didn't get a catch that I noticed !! No further damage fortunately.

Now the dovetail was perhaps not as deep as it could have been, but having remounted on the face and reformed the foot I realise that a foot in the order of 60 to 70mm diameter for an outside dovetail is too small for the bowl size - it currently is 90mm dia and looks about right.

Will a deeper internal dovetail - full jaw depth - solve the problem with obvious careful turning, or do I go for the external dovetail and reform that area when the bowl is dry ?

Rob
 

Paul.J

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Rob,i always prefer a spigot/tenon to hold,especially if it's a large or out of balance piece.
When i do do an internal i leave plenty of wood on the outer part.
It's also best to make it as small a dia as you can else you will be left with a wide base that might not look right.
Also when using wet wood check the tension on the chuck at regular intervals and tighten if neccessary.
You will alos need to finish off the bottom when the top is done else it will move too much to refinish.
 

CHJ

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You are always safer clamping on a dovetail spigot with green wood that is subject to greater compression, also check jaw tightness during turning.

Take good note of grain orientation on spigot though, and how near to the sapwood it is, it's not unknown for green wood to let go across a growth boundary.

Having said the above I regularly get away with socket support but leave plenty of material on to be removed during final reverse turning.

Whether you are using a socket or a spigot you need to make sure you dimension it to give maximum support against the widest part of your chuck jaw.

I.E. jaws should not bottom out in a socket and spigot must not bottom out in the jaws, that ensures the taper pulls the piece hard up on the outer flanges of the jaws.
jaws.JPG



And as Paul says unless you are just turning green oversize to remount once dried you must work both inner and outer as you proceed to remove wood from the front face, rarely can you safely go back with the tools because it will move out of round as soon as it starts to dry, we are talking minutes here not hours.
 

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jumps

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I would just add to the above -

1. gripper jaws are significanlty better in both modes
2. the grain orientation you are turning will influence choice of mode
3. always start with the tailstock in supporting mode - if you find yourself having to make significant adjustments to the chuck jaws as you turn in the early stages seriously consider whether to proceed further without it's support or let the wood dry for a little. Even a few days will allow the fibres to firm up in the chucking area.
 

Bodrighy

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If you are turning over the bed bring the tailstock up and turn away as much as possible with it in place as green wood is deceptively heavy and can shift its weigh. as well as it spins. Keep your spigot or recess if you do decide to use one as near the lower dimension of the chuck as possible to maximise the contact grip.

Pete
 

cambournepete

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I agree with the advice given so far except:
Paul.J":eslekzst said:
It's also best to make it as small a dia as you can else you will be left with a wide base that might not look right.
You can make the spigot completely sacrificial, and turn the bowl shape completely outside the chuck. That way the shape of the bowl is not at all compromised by how you've held it on the chuck.
 

Paul.J

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cambournepete":guh556ju said:
I agree with the advice given so far except:
Paul.J":guh556ju said:
It's also best to make it as small a dia as you can else you will be left with a wide base that might not look right.
You can make the spigot completely sacrificial, and turn the bowl shape completely outside the chuck. That way the shape of the bowl is not at all compromised by how you've held it on the chuck.
Pete i was referring to using an internal hold/grip which Rob was asking about.??
 
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