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boydy=number1
29th May 2007, 10:18 PM
Hey guys im new to woodturning and when im tuning a bowl i turn the complete outside first gripping with a faceplate or screwchuck. I sand the outside completely and turn a spiggot or a dovetail to suit my nova 50mm chuck jaws, both the dovetail and spiggot i turn are paralell but when i reverse chuck the bowl to turn the inside out i have trouble getting the bowl to run true i then have to re-turn the base to try and true up the bowl can anyone help me with this problem?:-

Cheers

Cliff Rogers
29th May 2007, 11:03 PM
When you say "both the dovetail and spiggot i turn are paralell" what are they parallel with?

Do you mean that the sides of the foot match the sides of the dovetail on the jaws?

After you cut your dovetail or spiggot, you aren't trying to sand them are you?

When you cut them, do you make it so part of the foot of the spiggot or outside of the bowl around the dovetail can sit on the shoulder or floor of the dovetail on the jaws?
If you do that & make it true too, (not rough or sanded back) then you stand a much better chance of getter it to grip square on the jaws.

Hope all that made sense.

thefixer
30th May 2007, 12:49 AM
When you say "both the dovetail and spiggot i turn are paralell" what are they parallel with?

Do you mean that the sides of the foot match the sides of the dovetail on the jaws?

After you cut your dovetail or spiggot, you aren't trying to sand them are you?

When you cut them, do you make it so part of the foot of the spiggot or outside of the bowl around the dovetail can sit on the shoulder or floor of the dovetail on the jaws?
If you do that & make it true too, (not rough or sanded back) then you stand a much better chance of getter it to grip square on the jaws.

Hope all that made sense.


Geez Cliff, if I didn't know what you meant then I wouldn't have known what you meant:D

Cheers
Shorty

TTIT
30th May 2007, 09:21 AM
What Cliff said but also go easy with soft timber when you're tightening the jaws as it will crush slightly, but rarely evenly, which skews the bowl slightly.:U



Hmmmm - Cliff - I thought you weren't supposed to sit the piece against the foot of the dovetail, only the shoulder - or do I have my appendages around the wrong way????:doh:

Cliff Rogers
30th May 2007, 09:35 AM
Nar, I know what you mean & it is just me trying to explain something without 27 8 x 10 glossy photgraphs with the circles & the arrows & a parragraph on the back of each one.

You are right, for a spiggot, you make a shoulder on the base of the bowl at the base of the spiggot that sits on the top of the dovetail on the jaws.

Rookie
30th May 2007, 09:57 AM
Hey guys im new to woodturning and when im tuning a bowl i turn the complete outside first gripping with a faceplate or screwchuck. I sand the outside completely and turn a spiggot or a dovetail to suit my nova 50mm chuck jaws, both the dovetail and spiggot i turn are paralell but when i reverse chuck the bowl to turn the inside out i have trouble getting the bowl to run true i then have to re-turn the base to try and true up the bowl can anyone help me with this problem?:-

Cheers

I may be missing your point but don't assume that the face that has the faceplate or screwchuck is going to be parrallel to anything when you turn the piece around to mount the spigot in the chuck. It will still need scraping to get it true.

And also what Cliff said. Make sure your spigot is not too long for the jaws and therefore sitting on the base instead of the shoulders.

joe greiner
30th May 2007, 12:48 PM
Ditto what TTIT said about crushing soft timber. On spalted timber especially, I've reduced crushing by dribbling some CA (super glue) on the spigot/tenon, letting it soak in, before re-mounting the piece. Learned that one the hard way.

Joe

rsser
30th May 2007, 02:14 PM
Yep, they never run perfectly true when you reverse them. Not only because the grain compresses (and you can play with where the jaws bite into end vs side grain to try for a marginal improvement here) but also because shaping the outside will always relieve some stresses in the lump of timber and it will move.

boydy=number1
30th May 2007, 08:17 PM
thanks very much for giving me some advice! much appreciated. do you suggest when I turn the outside of the bowl, I don't completely finish it before I reverse it in the Jaws? Thus enabling me to true up the outside of the bowl if it is not running true.

Cliff Rogers
31st May 2007, 12:42 AM
If the problem continues, yeap.

I tend it finish the bottom around the foot & leave the part up around the lip only rough sanded & then finish that bit when I do the inside.

reeves
31st May 2007, 01:20 AM
thanks very much for giving me some advice! much appreciated. do you suggest when I turn the outside of the bowl, I don't completely finish it before I reverse it in the Jaws? Thus enabling me to true up the outside of the bowl if it is not running true.

er yep, unless yr wood is pitch perfect dry and yr original tenon is pitch perfect on the sides and foot u will still have to 'finish ' off the bowl.

I find it best to just get the tenon right and rough the outside and then do both inside and outside from the front. Then you just gotta deal with the base after the bowl is done. If u go with your original tenon I find the expanded chuck hold the best and the larger jaws better than the standard dovetail jaws for fit and pressure.

Grab a copy of Raffans bowl book, endless examples of how to do it 'properly' but in the end its whatever works for you. Also i'd say it impossible to underestimate the capricous power of wood to move and change.