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TheBigBJ
10th August 2003, 07:47 PM
Hi guys,
It occurred to me the other day after a long time spent in reflection that I am an idiot!
I have been turning for a couple of years now and I am constantly having trouble with my bowls when I try to re-chuck them.
The method I use when I am turning bowls is as follows:
I mount the blank on a screw chuck where the profile is turned , anded and finished.
Then I remount the bowl by the foot (I size the foot so the chuck jaws leave no discernable mark) in my scroll chuck. ( I use a Vl200sm lathe and VM 120)
This seems straight forward but I must be missing something as I am yet to turn a bowl with an even thickness around the rim.
I am pretty sure that it is not the method that is wrong because according to Bert Marsh's book it is pretty much the same method he uses to turn bowls that are only 2mm in thickness. Now, I am not comparing myself to Bert but you would think I would have managed to something right by now.
I have a suspicion the problem is over sanding as the thick points are always located near the end grain but I can not be certain.
Has any one had this problem? If so what was your solution?
As I believe I am in need of some proper instrucion I was wondering if there was any one in the Geelong (Victoria) area that would be able to come and give me some lessons at my place. Naturally I will pay (money or beer your choice).
I am also interested in any one elses techniques for bowl turning and re-chucking ( If you'll divulge your secrets)
Hope you can help with my problems.
Thanks From BJ

q9
10th August 2003, 10:48 PM
At a guess, one of the chucks is off centre slightly. I'd suggest using one or the other, or alternatively rough down using the screw (even just turn a bit so you can get the jaws something to hold onto, I use a drive dog for this) then use the scroll chuck for everything else. Where you don't want to waste good wood, you can glue a bit of sacrificial piece of pine (or similar) to the ends of the piece, and turn that to a size that fits in the scroll chuck.

BrianR
11th August 2003, 09:44 AM
The strength of the wood changes as you remove more, allowing the shape to change.

When you turn the outside the circular shape is held by the wood on the inside but when you remove the inside wood, the strength is now all in the thin wall and and the base. There will be different stiffness from base to rim and the walls are different on the sides parallel to the grain and at 90 degrees across the grain.

The result is that the spinning forces expand the rim at points parallel to the grain more than those across the grain so you'll make an elliptical cut on the inside and finish up with an uneven wall thickness.

The only solution I can think of if you want thin walls is to reduce the turning speed.

;)

TheBigBJ
17th August 2003, 08:17 PM
Thank both for your replies.
I think I figured out what the problem was. I was not giving the chuck jaws a smooth and flat surface to but against. then I was over sanding the piece. Now that I have figured out the problem I just need to practice cutting in a way that reduces sanding.
Thanks again
BJ
BTW. Has any-one tried turning a timber called Goldenwood?

Jeff
23rd August 2003, 04:29 PM
...learn to turn in a way that reduces sanding.... Well, spend the time you have been using sanding and learn to sharpen your tools. If your tools are sharp, the wood properly chucked, and you use good technique, sanding becomes a very minimal task. Really. Good woodturning skills will virtually eliminate all the sanding. Sharp tools, sharp tools, sharp tools!! Good luck!