Ring (cup) centres to fit in a chuck?

[wilfy100]

Hi everyone,
 I am very new to wood turning. So much so that my first and only bowl made from green Oak decided to split virtually all the way through. I have quite a large amount of green Oak, could anyone suggest the best way to prepare this for turning, is leaving it for a long time the only way to dry it. I suspect Oak might be very prone to cracking, I have some Ash and Mulberry wood that seems to be noticeably more stable than Oak.
I would like to turn some chisel handles from the Ash wood, I would like to use a ring (cup) centre in the chuck to provide the drive. I am somewhat limited in that my lathe has a 1" x 8 tpi mandrel so morse taper centres cannot be used. I was hoping to get a ring centre with a parallel shank that I could hold in a chuck but I have not found one of a suitable size. I have seen a suitable ring centre used for this in an American youtube video, it was pointed out that if you got a catch with this the wood would just slip round on the ring  and so was better from a safety point of view. Any help with this would be much appreciated.
                                                                                                                                                                       Cheers Ian

[Lazurus]

Green oak can be turned to near final thickness and left to dry, I aim for 1" thickness and have good results with that, then finish turn. Or depending on the item turn to final thickness and let nature do what it will, if the wall edge is reasonably thin it will dry fairly quickly and can give interesting results.
As for the ring drive, I have only used standard prong drives and not had an issue, perhaps if you are a little unsure visit your local club, they will support and encourage your development in a safe and educational environment.

Enjoy.

S.

[malcy]

The drive centre you are talking about is a Steb centre. Robert Sorby do one to fit a four jaw woodturning chuck. They are not cheap, about £45, and they tell me that is because they have to pay patent fees to the originator. Hope this helps. Malcolm.

[Derwent Woodturning club]

Hi Ian,

Welcome to the world of woodturning. I will answer your question about your bowl splitting with another question but please don't take it the wrong way if you already knew this.

Many people assume that because trees are round and bowls are round, that a bowl is turned from a slice through the trunk. Was that how you created your bowl blank?

Unfortunately the wood cut that way ends up with all the growth rings concentric and this is the worst case for splitting, as wood shrinks most circumferentially.
A bowl is much better turned from a section of the wood cut lengthwise from the log, so the grain is across the bowl. This is hard to describe but I hope that makes sense.

Regarding drive centres to fit in a chuck, I agree with Malcy that steb centres are very good but they ARE expensive, and they aren't a cone centre.  If they slip the multiple teeth will tear the wood and you need to put more pressure on them to maintain drive. By the way, other manufacturers are producing very similar but less expensive, products.

You can get four prong drive centres that will fit in a chuck, (Nova do one for around £15 - often on sale on auction sites) but again this isn't a cone centre.

But I wonder if your reason for wanting a cone centre is wrong. Their key benefits are they will not try to split the timber, as may happen with the centre of a basic drive centre, and, second, they don't go far into the timber, good if you have expensive timber and are looking to reduce waste at the ends. I agree cone centres will slip if you are too heavy with the tool but that should not be the reason for wanting a cone centre. They don't make turning any safer, in fact I will put forward an argument that they are LESS safe as it is easier for the wood to come off the lathe, since there is very little metal in the end of the wood. And I totally agree with Lazurus's comments on this topic

Sorry for going on a bit, but hope that helps.

[crazylegs]

what about getting one from here www.chronos.ltd.uk/acatalog/SCT-Drive-Centres-etc.html and see if a local engineering company can cut the shaft to the desired length . turning it straight to be held in a chuck should be easy for a metal worker.
Just a thought.

[fuzzyturns]

If you have a local engineering company that will do this, then fine. Model engineering clubs are another possible resource. However, I have to point out that all the above comments still apply. I don't have such a centre and I've never needed it, either (and I do have quite a bit of kit otherwise).

[Paul Hannaby]

Have you considered a morse taper adapter that can be held in the chuck? Axminster do one and there may be others out there.

[crazylegs]

there are some on ebay, Sorby ones new at around £45.

[wilfy100]

HI,
     Thanks everyone for the replies, the bowl was turned from a short length of log , i.e I mounted the log, turned it fully cylindrical and then rough shaped the bowl. The central axis of the bowl was the central axis of the log. I believe I should have proceeded to rough turn the bowl as soon as possible after I had cut it from the branch.  I do have a large section of log that I cut down the length either side of the central pith to produce in effect two short thick "planks". One has cracked badly but the other up to now is OK. These are big enough to turn a small/medium sized bowl at 90 degrees to the logs original axis. Due to poor planning I have put to much time into wood collecting rather than working properly with what I had got. In fairness I only have a cheap basic lathe (an old Sealy one) and have been making a substantial base platform to strengthen it up as the bottom square section rails are missing. It is usable as is but I have to take light cuts and keep the tool rest in close. I am fairly sure that when the lathe is firmly bolted down to the heavy solid platform then it should be OK.  I may well move on to a better lathe at some point but this will suffice for me to gain some experience. I will be putting some industrial castors onto the platform frame to make it portable enough to roll it out of the garage to work outside when the weather permits. Its far easier to clean up the shavings that way.
I have much to learn but that is what appeals to me, I will report back when I have turned a bowl on the strengthened up lathe. I will look into the drive centre suggestions.
Cheers Ian

[fuzzyturns]

So essentially you have turned an end grain bowl. To be honest, the result is not entirely surprising.
You have to consider the nature of wood: each fibre is like a little straw. It's filled with water and acts as a small pipe to carry water up and down the tree. When the wood dries out, the water us removed, first the "loose" water in the pipe, then the "bound" water in the cells making up the pipe. And therein lies your problem: the pipes don't get shorter, but the space their cross section takes up is now only a fraction of what it was before. If the pipes were completely free to move, they'd just rearrange into a tighter, smaller pack. But they are not free to move, they are joined to other pipes around them (or otherwise trees would have no strength at all). So when the pipes shrink, something's gotta give. and that's where your cracks and splits come from.
It's more pronounced in some woods than others, but the principle stays the same. It can be avoided to some degree by producing vessels with thin(nish) walls of (and this is the important bit) even thickness. And even then you have no guarantee. Some pieces will warp and others will crack. Tata ma chance.