Inadequate grip

[Graham]

I am having some problems holding bigger pieces with the 'normal' C jaws on my Axi Evolution chuck.
As an example I am trying to make a large chalice out of a piece of Yew 13 inches long by 4 inches wide. I rounded it off with no problem but when trying to hollow the end it keeps coming out of the chuck ) and is impossible to get back in and run true again )
I am thinking of getting a set of these
http://www.axminster.co.uk/piranha-114mm-gripper-jaws
Anyone familiar with them ..... or know what I am doing wrong ?

[seventhdevil]

what tool are you using to hollow out the end?

[Graham]

I am not getting that far. Just a light cut to start removing the spigot I put there for something else pulls it off

[davidbrac]

any chance of a photo so we can see what is going on?

[woodndesign]

Graham, At the length and size you're working at you may need a steady ... http://www.axminster.co.uk/axminster-heavy-duty-fixed-steady  ..... http://www.axminster.co.uk/axminster-fixed-steady ...

You may come to be more dependent in using a steady as you go large with form or with hollow forms in the future, maybe more so than the jaw set, not being dismissive of the piranha jaws, the standard large or medium gripper jaws maybe better suited overall as you consider the amount of waste timber there will be with the piranha tenon.

http://www.axminster.co.uk/piranha-114mm-gripper-jaws ... http://www.axminster.co.uk/type-g-large-gripper-jaws ... http://www.axminster.co.uk/type-h-medium-gripper-jaws ...

And you've the cost consideration as well with the piranha, I now you're looking at the 114mm to suit the chuck.

Cheers  David

[seventhdevil]

you may need to give the work some support with your fingers as the chisel starts it's cut.

you could just bring the tail stock in to play whilst flattening the end.

where are you? i'm in maidenhead so if you want some help you are welcome to come round.

[bodrighywood]

Make sure that the tenon is the right shape for the chuck and tight up against the main section of the wood. When I do bigger goblets, largest so far was 18" long and 5" across the bowl, I drill the centre first and basically scrape the guts out of it either with a scraper or shear scraping with a spindle gouge.

Pete

[Graham]

Many thanks for all your answers and the thought that has gone into them.
I sort of have two problems now.
1... I cannot get it to go back into the jaws and run true again so a forester bit to drill it out isn't working very well.
2... If I retrue it, and lose some width, whats to stop it happening again.

I looked at the other gripper jaws before seeing the piranha but am not sure if the extra grip they give will be enough.
My thoughts with the piranha is that they may not waste as much wood as it seems. With 'c' jaws you make the spigot short enough that it cannot reach the 'face' of the jaws. Presumably you do the same with these so with a big chunky workpiece you might make a spigot up to about 38mm ( max depth is 40mm ) but for smaller pieces you would only need the standard 5 or 6mm ?
Does that make sense ?

[Bryan Milham]

Re-Truing the blank is not hard but you may need to read through this a couple of times to get the idea.

Put the blank in the chuck and tighten it almost all the way up, it does need to move slightly later on.

Set the tool-rest beside the blank but at a slight angle - the end nearest the headstock the furthest from the blank.

The other end needs to be less than the diameter of whatever you are going to use - your Knock-out bar or a bowl gouge or whatever.

Turn the lathe on and put your Knock-out bar (or whatever) into the widest gap and then move it slowly towards the other end. It will push the blank back into true.

Be careful until you get the hang of it and hold tight to your (whatever) as if you go too far, it can be grabbed and snatched.

[bodrighywood]

Re-Truing the blank is not hard but you may need to read through this a couple of times to get the idea.

Put the blank in the chuck and tighten it almost all the way up, it does need to move slightly later on.

Set the tool-rest beside the blank but at a slight angle - the end nearest the headstock the furthest from the blank.

The other end needs to be less than the diameter of whatever you are going to use - your Knock-out bar or a bowl gouge or whatever.

Turn the lathe on and put your Knock-out bar (or whatever) into the widest gap and then move it slowly towards the other end. It will push the blank back into true.

Be careful until you get the hang of it and hold tight to your (whatever) as if you go too far, it can be grabbed and snatched.

I thought it was just me that dis things like this LOL. If you do it, go gently and keep the speed down, too fast and the piece can spin out of the chuck. DAMHIK

Pete

[Richard Findley]

C jaws are my main jaws for this kind of work. I've made a 20" x 5" deep burr oak bowl on them, and some 20" long x 4" diam 'Olympic' type torches with them, hollowing about 6" deep into the end. The jaws grip perfectly well. I did need a steady with the torches but not to stop the wood coming out of the chuck, just to reduce vibration to achieve a good cut.

Make sure you cut a perfect tenon. C jaws need a 56mm diam spigot, slightly dovetailed, no more than 8mm long. This will hold anything. Make sure the shoulder sits felt against the face of the jaw to prevent the work rocking. Jaws work in 2 ways. They grip to. Stop work coming away, and they have contact at the shoulder to prevent vibration and the work twisting out of the grip.

Hope this helps

Richard

[edbanger]

that's a great tip for relining work 

I don't know the C jaws but if they are similar to the patriot  you get a spigot size range but the maximum grip is always the minimum size range. If your spigot is on the large size remount between centres and adjust the spigot size.

Ed   

[Graham]

Spigot is definately not to big, I tend to work to a single size that will be the minimum. ( 56mm with these jaws ) I will go and re measure it though before  try DFs methoud.

Nobody uses the gripper type jaws then ?

[julcle]

I use the gripper jaws on the Evolution and they are rock steady. As Richard has said it is so important to have the spigot at the correct diameter and sitting firmly against the face of the jaws, this also means that you have to true up the face after cutting the spigot so that it is perfectly flat also put a pencil mark against jaw 1 so that it goes back in the same way if you have to remount it.    Julian

[John]

I use the "H" gripper jaws and the mega jaws, I don't have any problems when using these, I seldom use "c" jaws on long hollow forms as I find they are not the best for me.
John