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rhunnell 09-12-2011 02:03 PM

bowl turning problems
 
Hey everyone,
I new to turning and have been trying to learn how to turn bowls. The problem I am having is after roughing out the bowl. I have found that the walls have a different thickness. Also the height of the walls are sometimes different.
I have been preparing my blanks from fresh cut logs. I cut them down the center, then trace a circle on them. Then cut off the excess with a chainsaw. I then attach a screw chuck in the center of the blank (pith side) and a live center on the bark side. After roughing out the outside of the bowl, I then cut a tendon on the bottom of the bowl . Next I reverse the bowl and mount the screw chuck to the tendon and begin hollowing out the inside of the bowl.
I am not sure what I am doing wrong. Maybe the blank is off center?. But even with having problems it is still fun. Any advice would be appreciated.
Thanks
Robert

Glidden 09-12-2011 03:08 PM

The mistake I've made is not having a flat bottom on the tennon, or not having the tennon long enough to bottom out in the chuck. Make sure the chuck is nice and tight, and if you get a catch, you may be making the bowl just slightly off center which would need to be corrected before you start turning again. Instead of a wormscrew to turn the outside, have you thought about using a faceplate? It will give you a more solid platform to work with when rounding a blank and cutting the outside to shape.

Manuka Jock 09-12-2011 03:10 PM

Quote:

Originally Posted by rhunnell (Post 244865)
I am not sure what I am doing wrong. Maybe the blank is off center?. But even with having problems it is still fun. Any advice would be appreciated.
Thanks
Robert

Yep , could be it . Usually is if after the bowl has been reversed on the chuck the newly turned outside has a wobble on .
In your case it could be the how screw chuck is mounted onto the tenon .
Do you have some photos of this . Can you remount the bowl and take some . Get one of the screw chuck on its own too .

sawdustfactory 09-12-2011 03:12 PM

First, get yourself a chuck so you don't have to screw into the tenon. If you're turning green wood (sounds like you are) then if your walls aren't close to uniform thickness then the bowl is probably going to warp. Once it dries, remount and turn to final thickness.

Glidden, your tenon should not be bottoming out in your chuck. The face of the jaws need a flat spot to register against and your tenon should be shy of the bottom of the chuck.

NCPaladin 09-12-2011 05:40 PM

1 Attachment(s)
Hi,
From what you said I assume you have a four-jaw scroll chuck since you talk about turning a tenon.
There are screw chucks (flat plate with a screw which threads onto the spindle) however, a scroll chuck with a worm screw is typically also called a screw chuck because it serves the same purpose.
After turning the tenon remove the screw from the jaws. Below is a graphic of what sawdustfactory described.
If dry, the tenon diameter should be maybe a 1/8 larger than the jaws at optimum gripping strength. If green wood which you will allow to dry I normally go 1/4- 3/8 larger than the optimum in order to re-true the tenon after the wood warps (the tenon typically goes oval).

RyanLincoln 09-13-2011 04:50 AM

I'd go with the guess of turning with the tool in the wrong orientation. I see this a lot when I teach. When turning the inside of a bowl, you need to be turning from the rim to the center with the flute held in the direction of travel. I prefer to have the beginners also hold the gouge with the flute at 45 degrees or midway between the flute being up and parallel to the ground. This is a good starting point!

rhunnell 09-13-2011 10:28 AM

Thanks for the advice. A couple of thing that were mention could be my problem. The bottom of the tendon that I mounted the screw chuck to is not completly flat. The screw chuck that I have is a screw mounted to a small face plate. Also when hollowing out I didnt always work from rim to center.

Any suggestions on what, would be a good jaw chuck to turn bowls with.

Thanks again for the advice.
Robert

TomC 09-13-2011 11:16 AM

Quote:

Originally Posted by rhunnell
Hey everyone,
I new to turning and have been trying to learn how to turn bowls. The problem I am having is after roughing out the bowl. I have found that the walls have a different thickness. Also the height of the walls are sometimes different.
I have been preparing my blanks from fresh cut logs. I cut them down the center, then trace a circle on them. Then cut off the excess with a chainsaw. I then attach a screw chuck in the center of the blank (pith side) and a live center on the bark side. After roughing out the outside of the bowl, I then cut a tendon on the bottom of the bowl . Next I reverse the bowl and mount the screw chuck to the tendon and begin hollowing out the inside of the bowl.
I am not sure what I am doing wrong. Maybe the blank is off center?. But even with having problems it is still fun. Any advice would be appreciated.
Thanks
Robert

From your post I take it you don't have a chuck. If this is the case it will be difficult to center the bowl on the screw chuck when reversing the bowl. You might want to first reshape the outside of the bowl when you reverse it and then start the hollowing. This should have everything on the same center.
Tom


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