Longworth Chuck

[rhwoodcraft]

Hello everyone,

I have been woodturning since June 2011 but this is my first visit to a forum. Having had no formal tuition I am feeling slightly out of my depth. I have had a lot of help from books and you tube videos but feel I have been running before I can walk!

When I turn a bowl I screw a faceplate ring to the green blank, turn the outside of the bowl and turn a chuck hole in the bottom, I then hold the bowl on the chuck and turn the inside of the bowl. I leave the bowl slightly larger then finished size to allow for movement when drying.

With the help of my brother I managed to make a longworth chuck. Once the bowl has dried I second turn it using the longworth chuck to finish the base and re do the hole on the bottom of the bowl for the chuck. I then finish the rest of the bowl holding it on the chuck.

Is this a sensible way to do it? I'm struggling to get on with the longworth chuck but if it's a good way to do it I will persevere.

Thank you in advance,
Bec

 

[CHJ]

Nothing wrong with your basic procedure for green turning.

However a Longworth chuck is not the most secure method of trying to clamp an out of round distorted blank.
The inability to get a decent clamping force renders them more suitable for just centring a finished item with tail stock support whilst you remove the bulk of the chucking details.

If you can't run to the purchase of a set of Cole Jaws with the ability to add additional clamping if necessary for mis-shaped items you might find it beneficial to investigate making a Donut Chuck, possibly use your longworth as a base for one?

 

[henton49er]

My only comment on the Donut Chuck in Chas's link would be the depth of the block mounted in the chuck jaws. This puts the work piece a considerable distance from the chuck, with the potential for loss of accuracy. I would have thought a dedicated faceplate ring to suit the chuck jaws would be more effective, and true up the base plate before drilling holes etc.

I too have thought about making a Longworth Chuck but have never quite got round to it and have managed quite well with a series of jam chucks. I might now change my mind and make a Donut Chuck instead; you do need however to make a variety of rings to suit different bowl sizes. Bolts with rounded tops which site as flush to the ring plate as possible would also be a good safety measure!!

 

[chipmunk]

Hi Bec,
Just a suggestion based upon what I do...

Have you thought of leaving a spigot inside the bottom of your rough turned bowl as well as on the bottom? Like the conventional one, it will distort and shrink so like that one make it close to the largest that your jaws will accept so that it will still fit when it dries and it won't be too small.

...but for re-turning the chucking point on the bottom of a bowl it's quite handly especially since the rim often distorts a lot so even laying it flat inside a donut chuck is tricky.

HTH
Jon

 

[rhwoodcraft]

Thank you for the replies.

After doing some research earlier I did think about a donut chuck but like chipmunk says I wasn't sure how you would ensure the piece was centred with it being distorted.

However, leaving a spigot inside the bottom is a good idea as that is as safe, if not safer than holding a distorted bowl in a longworth chuck. I will certainly give it a go.

Thanks again.
Bec

 

[KimG]

Thank you for the replies.

After doing some research earlier I did think about a donut chuck but like chipmunk says I wasn't sure how you would ensure the piece was centred with it being distorted.

However, leaving a spigot inside the bottom is a good idea as that is as safe, if not safer than holding a distorted bowl in a longworth chuck. I will certainly give it a go.

Thanks again.
Bec

That's the method I am using, I have the long nose jaws for the Sorby chuck and they give a very extended reach into deeper bowls, the nova chucks have a very similar set of jaws too. So far it has worked very well.

 

[CHJ]

One thing to be aware of with green turning, dependant upon the orientation of the grain, pith etc. in stock, is that increased thickness of the base in rough turned form intended for drying can lead to increased risk of splitting.

Best practise is to avoid the pith and keep wall thickness as even as possible, the latter is hard to achieve when leaving complimentary fixing options.

 

[chipmunk]

Chas,
That's a good point.

For green bowls I usually orient my bowls for maximum utilization with the rim close to but not including the pith and this means that the chucking points are effectively near the edge of the log.

I also don't use great big thick chucking spigots (1/4" each is plenty).

HTH
Jon

 

[CHJ]

Splits have a tendency to propagate from sharp edges in some configurations, a little rounding of corners adding tension strength does not come amiss in rough turned items.

 

[paulm]

Not sure what a Longworth chuck is ?

I use the chuck jaws as a surface for the inside base of the rough turned bowl to rest again, held in position with the tailstock, to true up the external spigot, or alternatively use a protruding stem of timber with foam pad on the end and held in the chuck jaws and against the inside base of the bowl as before. These two methods work very well for me with the shapes and sizes of open bowls that I tend to do, from 6" diameter up to 16".

Tend to use the cole jaws on finished work rather than rough turned due to the rim distortion on rough work, but do chop and change and use the above for finished work too sometimes, or an mdf circular board held in the chuck jaws and bowl held in place by the tailstock again if I can't be bothered faffing about with the cole jaws !

Lots of different methods depending on the situation and what I think will work best at the time.

Cheers, Paul