bowl turning

[david]

hello all
can anyone tell me where i am going wrong.
i am new to woodturning and made my first bowl last week
albeit a little rough around the base
the problem being is that when i have finished the bowl and remove it from the chuck i am left with indentations from the chuck
can anyone tell me how to alleviate this problem
i am using a standard chuck supplied with my clarke lathe
very beat regards to you all
david.

 

[TEP]

Mornin' David. In my experience all scroll chucks will mark the timber, even when the holding point is cut to fit the jaws when they form a perfect circle, if they are tightened too hard.

One way to alleviate this is to turn the base of the bowl then cover the holding point with tissue before fitting into the chuck, then don't grip the work too tightly. But I don't advise that for a beginner as you can lose the work. You don't want a part turned bowl orbiting your work place. :shock:

The best way is to mount the work is on a sacrificial part of the timber, be it a spigot or rebate. Then when finished reverse chuck the work and remove the holding point. It is not as difficult as some say, but you do need to work slowly and carefully. As with all things in this hobby, once told or shown how and you do it a couple of times it becomes quite easy.

DO NOT try this until you have gained some reasonable degree of control of your tools, the death of a lot of this work is folks trying to run before they learn to walk.

 

[Russell]

What chuck are you using and what jaw size would be my first question.

To minimise the problem you chucking point should be as near to the optimum size of the jaws that is when you open the jaws to a perfect circle that is usually about 3/16" from fully closed but will differ. Gripping at this point helps to stop the "corners" of the jaws digging in. I don't recommend tissue because I think to make it work it needs to be too think or to hold the work to tightly.

You need to learn how to reverse your work with some bowl reversing jaws or a jam chuck so that you can clean up or remove your chucking point. I now as a matter or routine completely remove all trace or my chucking points to finish the bowls properly.

 

[Bodrighy]

The other alternative is to turn a recess in the bottom of the bowl and use the chuck in expansion. You can make a feature of this and rarely (in my experience) have chuck marks as long as you keep the chuck in a reasonably small expansion. This method doesn't have as strong a grip but I find it better with spalted wood or end grain which can (and does) snap sometimes.

Pete

 

[david]

thanks very much for your replies regarding my chuck holding problems
i normally do make a recess in the bottom of the bowl aboutone and a half inches in diameter and then use the jaws in expansion mode.
but like i say when i remove the piece from the jaws ,,,i have these awful indentations in the recess and then there is no way i can re-hold the bowl to remove them(i hope this makes sense).
suppose i will have to invest a model makers sanding gizmo.
best regards to you all.
david.

 

[Blister]

How about :-

Using a thick elastic band on the outside of the chuck jaws before you expand out into the spigot :wink:

WORKS 4 me :wink: :wink:

 

[Russell]

David, You can reverse the bowl by making a jam chuck to fit the out side use a disc of MDF or similar and then support the work with the tail stock to do work on the recess. The expensive option is cole jaws but there are other things such as the longworth chuck that you could make. Look up jam chucking bowls in some books or online and see how its done. It is a very easy process that is worth a little effort.

 

[CHJ]

......i normally do make a recess in the bottom of the bowl aboutone and a half inches in diameter and then use the jaws in expansion mode.
but like i say when i remove the piece from the jaws ,,,i have these awful indentations in the recess and then there is no way i can re-hold the bowl to remove them..

David it sounds like possibly two factors are contributing to your problem.
1. you are not preparing the recess to the optimum size and shape for your jaws. See the first paragraph here
2. you may be gripping the piece too firmly, this rarely increases the 'hold' just crushes the wood.

Regarding finishing the base then in addition to Russells pointers have a look at the Doughnut Chuck principal A google will find many more versions.

 

[david]

once again thanks to all of you for your excellent suggestions
i am gripping the recess of the bowl too tightly as i was frightened of it flying from the lathe
i realise now that i was going about things in the wrong manner.
if the truth be known i am trying once again to run before i can walk and shall do a lot more reading and research before i get angry with myself.
i must say though that the links you have posted regarding methods of holding the workpieces are fantastic,
first thing tomorrow i shall try and make a doughnut chuck,,,her indoors will be bringing my dinner into the shed again..
thankyou all.
regards
david.