Inadequate grip

[Graham]

Thanks John, the 'H' type is one that I am looking at.

Jucie are you using the 100mm 'H' type on your evo chuck or the 114mm Piranha gripper ?

[woodndesign]

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.

Link to a past thread on just this: http://www.awgb.co.uk/awgbforum/index.php/topic,1348.0.html ...

[Graham]

That looked easy.

[julcle]

Graham, Mine are the 100mm H Gripper Jaws, to be honest I have never had a need to go bigger than this as they have held everything I have tried. The last time I used them was when trying out the
Big Brother on a piece of Ash about 10" long and 10" wide and it didn't even want to move. It's a pity you are not closer or you have borrowed them to try.  --  Julian

[Graham]

Thanks Julian, the reason I asked is that the 100mm 'H' gripper is serrated  whereas the 114mm Piranha is multi dovetail. I think I will get a set of the 100mm H, they sound hood  ( and are much cheaper )

I will also give the 'knock out bar nudge' a go but have my doubts about it working on a 4 inch plus spindle.... though I suppose the bit in the chuck is the same .

[TWiG]

I bought some gripper jaws years ago and felt pretty disappointed to be honest  I think dovetail jaws of the same dia offer a much better grip , and can be used for bowls etc and very rarely change jaws at all ... my gripper jaws are dusty & rusty somewhere as I never use them now .

[Richard Findley]

I'm pretty sure that 'Gripper' jaws are designed primarily for wet wood.

Richard

[Paul Hannaby]

I use the gripper jaws primarily on spindles such as hollow forms, goblets, vases etc. but also for bowls sometimes. I use them on both wet and dry wood because they offer much better grip than dovetail jaws.

[TWiG]

I use the gripper jaws primarily on spindles such as hollow forms, goblets, vases etc. but also for bowls sometimes. I use them on both wet and dry wood because they offer much better grip than dovetail jaws.
[   /quote]                                                                                                                       I am utterly perplexed by this as I find the complete opposite !   A dovetail of the same dia has a better ( more overhang/ undercut ) purchase on the wood  than gripper jaws of the same dia and relocate more accurately if work is unchucked / rechucked .It must be quite confusing for some one thinking of getting a set to read 2 completely differing accounts .. lol !!             

[edbanger]

I've only ever used dovetail type jaws and have to agree with TWiG they have never caused me any problems and I've mounted some big stuff. Even the old Multi chuck with its 4mm deep dovetails holds a lot of things, it's just down to how well the spigot is cut.

[Graham]

It must be quite confusing for some one thinking of getting a set to read 2 completely differing accounts .. lol !!             

It is, it is, but forums are ever thus.
I suspect that Edbanger is right and the quality of my spigots is suspect...... but I may well get a set of grippers anyway 

[The Bowler Hatted Turner]

I'm meant to be having a bit of time away from all this for a few days but thought that I had to comment on this post. I am sure experienced turners (like Pete and Bryan) may get away with altering the centre whilst the lathe is in operation but this is not something I could condone, I think it is a dangerous practice.
  Graham forgive me for asking, and I do not wish to be rude, but how long have you been turning? I wonder if you have not been turning very long if you have not yet mastered the tooling skills needed to turn a 13" goblet. You say the wood was previously worked, should you not consider cutting the end off with a saw to make the whole process easier. Have you turned an 8(?) inch goblet to practice the techniques you require to turn a longer one? As I said I do not wish to offend but walking comes before running and if you are relatively new to turning ie. have been turning for less than a year, you may want to gain experience before turning something that will vibrate because of the overhang from the chuck and also will be liable to come off centre very easily. At the very least you should consider using the tailstock for support for as long as you can before removing it.
John BHT

[Graham]

No offence taken John, you are quite right in that I have only had a lathe since March and only had time to make about 4 things on it, none of which was a goblet/chalice..... However.... I want/need to make one 12 inches long 4 inches wide.

When I said the wood had been previously worked, what I meant was that I had roughed it down to round, put a spigot on each end and then bored down the centre of what will be the stem ( I want to do an open spiral for the stem ). I then turned it around, made some rough cuts on the outside to define the outline of the bowl ( tailstock in place ) then removed the tailstock and tried to GENTLY clean up the end/remove the spigot. this is when it ALMOST left the chuck, I managed to stop the lathe with the wood wobbling badly but still attached.

So..... I am thinking about the grip of the C jaws I have, making a steady rest, and practicing on a smaller goblet ( which still needs the steady to hollow the bowl ) while I think about it. I think I may be being a bit slapdash when making the spigots.

Running before I can walk ?  Yeah, I guess so, but it makes learning more interesting to try and achieve something specific and every failure is a learning experience. Nobody thought I would be able to do it anyway  

[Bryan Milham]

Graham,

sorry it never dawned on me that you had not been turning for very long. John is right the technique I described is not hard to do but does need a fair degree of confidance.

You have grasped the bull by the horns jumping into a goblet 12" x 4" as a first one. As said a very well cut tennon for C Jaws will do it, Gripper jaws will be better but even then a heavy 'dig-in' will move the wood out of true.

About the best advice I can offer for that is drill the goblet cup to almost full depth with as big a drill or better yet forstner bit as you have. Then hollow out carefully, if the hole is big enough use a French Curve scraper.

Once the inside is cut and sanded, make a jam chuck that will fit inside the goblet cup and the back of it, to fit onto your rotating tail centre. This will provide support and also keep it centrerd while you are cutting the stem. Don't over tighten it or it will force the stem to flex/bend - somthing you don't want at all.

As ever work from the cup back in stages (1½” to 2” at a time) towards the headstock. If you try to cut it down to size all in one go it will vibrate and bounce something awful.

[bodrighywood]

John is right about the method of re-centring whilst the lathe is running being potentially dangerous. I do it at a slow speed not flat out so if it does come out of the chuck it isn't going to do any damage as such. . When I do goblets I seem to do them in the reverse order to others as well as i shape the outside first leaving plenty of wood at the base of the bowl part then drill and excavate the inside. When the inside is finished I stuff it with tissue and bring the tailstock up holding the piece between centres whilst I finish the outside of the bowl, do the stem and foot. As I said before I find that shear scraping with a ring tool or one of these type of tools is both quicker and safer as trying to do it as with a bowl in what is a comparatively small space is much more likely to get a catch. I probably make about 30 or 40 goblets a year and have tried various methods and found that this is both the quickest and most efficient. I echo John regarding making smaller goblets with a smaller stem first until yo get the hang of the excavation part.

Pete