Replies

1. 
   Andrew | Aug 03, 2004 12:27am | #1

   How thick are you leaving the walls after rough turning? You should leave them about 1" thick depending on the bowl size, or you can just turn to final dimensions while green and let it warp into a cool shape.

   There's more to this but I'm sure some more experience turners can explain it better than I can.

   Andrew

2. 
   KeithNewton | Aug 03, 2004 02:10am | #2

   Hi Greg, Could you tell us a little more so we can help you home on the problem.

   Some things I would want to know are. What kind of lathe. What kind of wood, how big, how thin, final desired shape. Are you new to turning, or is this a new problem that could be related to bad bearings. About what RPM are you turning etc.?

1. 
   GregW | Aug 03, 2004 06:42pm | #4

   Rootburl,

   I am using a homebuilt lathe, fashioned after the BH&G Shop Tools book. The kind of wood  varies from maple, cherry, pear, apricot, walnut, etc. Most of my bowls are 8" in dia or less and 3 to 5" thick. I have been turning bowls a couple of years and its not a new problem. I don't get much time to turn and a recent try at finishing a couple of bowls I rouged out a while ago prompted my post.  The speed is 1000 to 1500 rpm.

   I tend to like a thin walled bowl (1/4 or less) so I 'm thinking maybe this might be a cause. Recently I have taken to turning start to finish with green wood and just hoping it doesn't crack.

   Thanks,

   Greg

3. 
   Alan | Aug 03, 2004 02:52am | #3

   Greg,

   My wild guess would be that as your wood dries it is contracting across the grain, which distorts it from a circle to an oval.  This distortion can easily be enough that bowls will no longer be balanced as they turn.

   Alan

4. 
   Napie | Aug 05, 2004 07:45pm | #5

   Greg,

   Are you keeping the bevel rubbing during the cut?  Some chatter is going to happen as the wall gets thinner and that just requires backing off on the pressure and bracing the work. Also I agree that it could be a bearing problem in the headstock.  I turn a couple hundred bowls a year and some just behave bad, just like people I guess......

5. 
   adamws | Aug 06, 2004 05:16pm | #6

   I've had this problem on segmented bowls.  I figured out that my problem had to do with the thickness of the wall.  When I roughed the segments down to at least smooth I have to start at the top of the bowl, it is chucked at the bottom, and take it down to close the to the final dimension, which for me is also pretty thin (sometimes 1/8").  I normally will take each layer of segments down to the final dimension, one at a time until I'm to the bottom of the bowl and then I sand.

   What I found was happening is that if I took the whole wall down to its thin dimension all at once the top of the bowl would not have a lot of stability and one touch with a scraper and it would knock it into small oscillations which would cause the chatter and the ugly grooves that result.

   So, my suggestion would be to, as another poster said, leave a good inch thickness in your bowl the first time around then start at the top of the bowl and go in sections until you're at the bottom.  By the time you've taken the stable base away from the top of the bowl you don't need to touch it with a tool anymore.  With that said, sometimes it is nessecary to touch up the higher layers once the final dimension is reached.  I use very, very light cuts and sometimes just use sandpaper.

   Another suggestion: I have not tried this, but I think a bowl steady device may help.  It is the device that looks like it has roller blade wheels on it that rest against the outside of the bowl.

   Good Luck,

   Adam