Thread: Expansion Mode for your Chuck

Clear concise easy to follow. Well done as usual. Jay

Thanks Brendan

Nothing like an Aussie tutorial

Your video leads me to a design 'flaw'.

Perhaps dovetail jaws should be cut smaller (the 1/4 sections) so that when compressed inner and outer are diameter is smaller then what the radius of the arc should be. This way they can be expanded (allowing for the slack taken up due to the dovetail) to 'truley round'

Jaws could be supplied with the actual grip range, inner and outer. Instead of 8 or 4 point contact we could get closer to complete contact

regards

Dave

ps - I used to live in Horsham, shame I did not get into turning in those days

Good YouTube video Brendan. I am sure it will evoke some discussion.
BTW Carl Jacobson gave you a good mention in his latest video.

A good video on the pros and cons.Brendan
I hardly ever use expansion mode because of the risk of cracking the dovetail.I never thought about the 4 vs 8 contact points.
On the few occasions I have used it, I would still tidy up the dovetail when the bowl is finished but I am not trying to make a living from woodturning and time is not important to me.
Using a tennon also makes it easier to apply the finish.I know you like to spray your bowls, but I like to use DO as a finish and apply it while the bowl is on the lathe. With a tennon, you can grab hold of it and don't end up leaving fingerprints on the wet DO or having to leave the bowl in the chuck overnight.
After finishing the outside of a bowl,I will often hotmelt glue another tennon on top of the original tennon. This gives me even more to grab hold of when applying the finish.
If I am using my bowl saver, I will often cut a 100mmx10mm tennon on my blank then after coreing, glue on a smaller diameter tennon and then I can incorparate the original tennon into the foot of my bowl.
Just a few thoughts.
Ted

I rarely use expansion and go with contraction most of the time. I use a lot of brittle hard woods and find contraction even though I waste more timber, works well for me. I also turn some fairly chunky pieces up 250mm deep through smallish holes. So I can at time have 250+ hanging out of the chuck which is a bit of leverage and on occasion I lose them.

But never the less a good video and we all must work as safe as we can and that can mean different things depending our current level of experience.

For those who are just starting out this video should be a must as it raises very good points on jaw contact.

Brendan,

thanks for another great video. I am very grateful for your videos. It is so much easier to learn from watching than reading. Personally I prefer the look of the bowl with expansion mode so I use it when I can.

My questions to all you experienced (and you too Brendan , as you mentioned it) is the depth of the recess. My schoolboy physics would seem to think that the deeper the recess, the more contact and less chance of breaking the wood, but even the instructions for the Teknatool scroll chuck say a maximum of 6mm while there could be a maximum depth of around 12mm before the wood hit the 'bottom' of the chuck. I'd love someone to tell me if I have this correct or why I don't understand. I understand for cosmetic reasons why you want a smaller recess but if you need strength why not go for deeper?

cheers

Mick

Originally Posted by mick59wests

Brendan,

thanks for another great video. I am very grateful for your videos. It is so much easier to learn from watching than reading. Personally I prefer the look of the bowl with expansion mode so I use it when I can.

My questions to all you experienced (and you too Brendan , as you mentioned it) is the depth of the recess. My schoolboy physics would seem to think that the deeper the recess, the more contact and less chance of breaking the wood, but even the instructions for the Teknatool scroll chuck say a maximum of 6mm while there could be a maximum depth of around 12mm before the wood hit the 'bottom' of the chuck. I'd love someone to tell me if I have this correct or why I don't understand. I understand for cosmetic reasons why you want a smaller recess but if you need strength why not go for deeper?

cheers

Mick

You're absolutely right Mick. The deeper the better for strength but I go for shallower recesses because of the aesthetics, as you mentioned. Also, the deeper it is the more the jaws will scroll out.

Great video Brendon.
I had never really thought about the 4/8 points.

An additional point to me is wood area. Nova suggests 1” of wood surrounding a recess and I do this on green wood. A 2” spigot has 3.14 sq inch of wood surface to break away. A 2” recess surrounded by 1” of wood has 12.56 sq inches; minus the interior 3.14 (which is holding nothing) you still have three times the area of wood holding the item on.

I usually go at least 3/8” deep with green wood but with dry maybe only 1/8” depending on size and wood strength. If it is too deep I just trim a little off while cleaning up the foot; sometimes I trim it all off and just leave a little concave.

I do the same cutting the recess diameter. According to Nova the kerf made by cutting the jaws apart is 2mm so I cut the recess so the jaws will just slide in when fully closed. When expanded in the dovetail it is as close to a perfect circle as you can get.
Sketch is how I do it.

NCPaladin - thx for the info on the jaws. Answered my concern

Originally Posted by mick59wests

Brendan,

thanks for another great video. I am very grateful for your videos. It is so much easier to learn from watching than reading. Personally I prefer the look of the bowl with expansion mode so I use it when I can.

My questions to all you experienced (and you too Brendan , as you mentioned it) is the depth of the recess. My schoolboy physics would seem to think that the deeper the recess, the more contact and less chance of breaking the wood, but even the instructions for the Teknatool scroll chuck say a maximum of 6mm while there could be a maximum depth of around 12mm before the wood hit the 'bottom' of the chuck. I'd love someone to tell me if I have this correct or why I don't understand. I understand for cosmetic reasons why you want a smaller recess but if you need strength why not go for deeper?

cheers

Mick

Mick I often go for a full 10mm and trim the base later. Quite often I dont even bother with a spigot, just simply glue a block on the bottom. The depth is generally the same as my power grip jaws. It really depends on the timber and what I am planning, ie If its a small bowl I will completely finish the outside with a bead for a foot and give its primary coating of finish. Then flip it around and hollow it out, my foot beads are around 6mm.

Originally Posted by hughie

I rarely use expansion and go with contraction most of the time. ...

I use shark jaws expanded into a hole cut with a bit forstner bit to hold my bowl blanks for roughing the outside & turning a foot with a bevel for then gripping in contraction.

Another excellent video, Brendan.

Like you, I use expansion mode in the same way for the same reasons.

Because I use a wax finish, I do that on the lathe, so the piece is finished when it comes off the lathe after only being flipped once.

A double layer of Gladwrap (food wrap film) between the jaws and dovetail protects the wax finish while turning and polishing the inside.

Another downside of expansion mode, and matching the dovetail diameter to the jaw size, is the number of jaw sizes you need to have to keep the foot size in proportion to the bowl diameter. At last count I had 13 different jaw sizes, which gets a tad expensive when you hate changing jaws and like to have a chuck for each set of jaws...

A chart of previously worked out Blank sizes: to Foot diameters: to Jaw sizes saves a lot of unnecessary splinters under the fingernails...

The exception to using expansion mode is when I'm coring, which involves a lot more torque, in which case I use contraction to clamp on hard. But I do turn a dovetail on the inside of the cored bowl with which to grip it when I come back to turn the outside of the bowl when dry, at which stage I revert back to expansion mode.

Originally Posted by NeilS

A double layer of Gladwrap (food wrap film) between the jaws and dovetail protects the wax finish while turning and polishing the inside.

Neil - another good tip

Thank you

Excellent video Brendan. Thanks for the tips. Quite a few things there that I hadn't thought about.