help: bowl and goblet mouths uneven

[trojan62]

hi all
ive been practising the last few weeks and havent done too bad, learning all the time, but i still seem to be getting the problem on the mouth radius of a goblet or bowl, uneven. thicker around some of the circumference and thinner around another area.
why is this, is it the way i have it in the chuck or the wood is not exactly round.

thanks for your help....

cheers,

chris.....

 

[CHJ]

What species of wood are you using.

Is the wood you are using fully dry or Green.

Are your tools kept very sharp.

Are you pressing too hard against the rubbing bevel.

Are you forming the inner and outer as you go,
or,
Doing one and then the other.

Are you attempting to go back over the goblet bowl some time, 1/2 hr -hrs-days later.

 

[trojan62]

hi
im using leylandi at the moment and the tools are sharp as much as i can tell.
to do a bowl, ill screw it to the faceplate and form the bottom and outside and cut a tenon and then mount it in the chcuk and hollow it out.
i cant seem to see what i could be doing wrong, i realise it could be many factors causing the trouble.

cheers

chris.....

 

[duncanh]

Although I don't make goblets, I can imagine 2 reasons why this might happen.

1) you're turning the outer shape between centres, transferring to a chuck and then turning the inner. When transferring to the chuck ensure that the outer is running true.

or 2) you're turning the outer in the chuck including the thin stem, then turning the inner. If you turn the stem thin the wood can move and the top no longer runs true. Consider turning the outside of the top and then the inner before moving on to the stem to make sure the wood does not move.

 

[CHJ]

... ill screw it to the faceplate and form the bottom and outside and cut a tenon and then mount it in the chcuk and hollow it out.
...

There's your problem, you must only rough the outer before you mount on the tenon.
It will not run perfectly true on the tenon because the wood will compress unevenly across the grain.

Finish truing up the outer when mounted for hollowing the bore.

Be careful you do not get tool bounce on the uneven outer, make sure that you are holding it securely on the rest and not pressing hard against the bowl outer.

Within sensible limits the faster it is spinning the easier it is to avoid tool bounce as it cuts down on the time for you to react and push the tool into the unsupported area.

 

[CHJ]

hi
im using leylandi at the moment and the tools are sharp as much as i can tell.
to do a bowl, ill screw it to the faceplate and form the bottom and outside and cut a tenon and then mount it in the chcuk and hollow it out.
i cant seem to see what i could be doing wrong, i realise it could be many factors causing the trouble.

cheers

chris.....

Two or three things immediately spring to mind.

1. The wood is not dry enough and as soon as you turn the outer the piece starts going oval before you get it re-mounted and start on the inner, can be minutes not hours.
2. leylandi is a soft textured wood and can compress unevenly when gripped in chuck jaws and easily run out of true.
3. Basically the same reason as 1. if the wood is not dry then it will distort as you are turning it and the stresses are released and moisture loss occurs.

Best advice I can give is to get yourself a piece of decent commercially dried wood such as beech and turn that and compare the results with what you are getting with your leylandi.
And if you have not already got it get a copy of Keith Rowley'sBook, A Foundation Course either purchase or get your local library to get it for you.

There are a couple of Bowl turning examples in the Help Sticky, albeit without using a chuck, but the principles are the same and one of them solves any remounting run out by using a jam chuck to hold the item true.

 

[Tazmaniandevil]

I concur with all of the above.
My approach is to turn the blank to round, then turn the tenon for the chuck. I then mount in the chuck and true the blank up before hollowing.
I hollow the cup of the vessel, and sand/apply finish.
Next I use a tennis ball between the hollowed out section and the tailstock to support the work. and start shaping the outside.
Once shaped, I remove the tailstock to sand/apply finish.
Finally, I reverse onto a waste block with a piece of router mat to carefully remove the tenon.

Bowls are pretty much the same. I tend to mount the blank and rough it between centres wherever possible. Turn the outside and form the spigot/tenon/recess sand and apply finish to the lower outside and bottom before flipping it and working on the inside.

HTH