Goblet attempt but having wobble problems

[edmund]

Hello All,
Thought I'd show my first effort at turning a goblet.
http://www.filehigh.com/serve/3221/157756.jpg
It was slightly less painless than I'd anticipated, but I still have some tearout problems during the process. Had a slight problem with this on the base (hidden by the stem in the picture). More practice methinks.

As to the wobble, the problem I'm having is that once I've turned a blank cylindrical between ends, I put the piece in the chuck and cylinder doesn't rotate in a straight line on its axis. Even after I've tried to true it up it still wobbles on its axis. I'm using a Record RP4000 on a CL1 lathe. Any guidance gratefully received. Thanks, E

 

[DaveL]

edmund,

I am not a wood turner, I have turned metal in the past.

The wobble you had may be caused I think, buy the centres not being in line.
Check by sliding the tail stock up to the head stock, do the centres meet?
Offsetting the tail stock on a metal turning lathe is one way of turning a taper. However I think with a hand held tool when wood turning you could still get a cylinder that is out of square.

Having reread that, I am now not sure if I have made sense. 8-[

 

[PowerTool]

I agree with Dave - the most likely cause is being slightly out of line when between centres (or the chuck being ever so slightlyout)

Otherwise,it is a very elegant and nicely-proportioned piece

And in which order did you turn it ? It is best to leave as much thickness as possible for as long as you can,to increase stability.
Tearout might be made worse by the chisel becoming blunt,and sometimes it is easier to use a scraper rather than a gouge/skew.
And can also be affected by the timber (some species are distictly worse for it than others) as well as lathe speed.

It's all practice,but you have still produced a very nice goblet.

Andrew (still very much at the practicing stage :wink: )

 

[edmund]

Thanks Dave. However, the problem I'm having is when I'm not turning between centres, i.e. one end of the blank is held in a chuck and the other end is unsupported to allow hollowing. Hopefully someone else will be able to help.

 

[Colin C]

Hi edmund
I do a bit of turning and to me it seems like something is lose, it might be you chuck or are your bearings ok.
As said before it should be ok after you have started to re-turn the piece :? .
Try to see if your head stock has to much side to side movement, that might help, also how old is your lathe?

 

[PowerTool]

I have also had balance problems caused by differences in density of parts of the timber e.g location of knots or bark,or location of heartwood/sapwood.
Last thing I turned was an eggcup for my grand-daughter (and forgot to take any pictures ),roughed it out between centres,trued one face up,mounted it on the chuck,and still had to turn it to round again as it was running slightly eccentric.

Andrew

 

[Anonymous]

Edmund/Power tool

Instead of turning between centres and then mounting in a chuck, mount directly into the chuck. If it's too big to fit in the chuck simply turn a spigot (between centres) and then mount in the chuck.

This should eliminate eccentricity problems... unless you have a catch in which case it all goes to hell :lol:

 

[CHJ]

...snip...
As to the wobble, the problem I'm having is that once I've turned a blank cylindrical between ends, I put the piece in the chuck and cylinder doesn't rotate in a straight line on its axis. Even after I've tried to true it up it still wobbles on its axis. I'm using a Record RP4000 on a CL1 lathe. Any guidance gratefully received. Thanks, E

edmund :
How are you locating it on the chuck? I presume in compression on a spigot or expansion in a recess. Either way it is likely that some areas of the wood are compressing more than others due to grain orientation and causing a slight offset. Make sure that your blank is seating correctly on a flat face register on the chuck, if seated correctly you should not have an option to change its alignment. If you have or do then it is almost certain that it will move again during cutting loads.

I assume your chuck is locating correctly on its spigot and the jaws are running true. Some chucks are fussy as to which jaws their accessory jaws are mounted (they are machined as matched assemblies) but I would have expected a record chuck to be fine regardless of location.

I personally never bother with between centres turning for something as short as a goblet blank, just mount it on a worm screw in the chuck and turn a spigot or recess in the other end and rough true it before turning it around to hollow the bowl. Just occasionally the blank end grain won't give an adequate hold for the worm screw then I resort to centres in the chuck and tailstock to form a spigot rather than a recess if I have enough spare length, if not, I glue the blank to a sacrificial piece of hard wood such as beech that have been pre-recessed to fit chuck jaws.

I would never expect a piece of timber to run absolutely true when re-gripped in a chuck, unless it is something hard like boxwood.

By the way, you did not pick the easiest bit of wood to do your first goblet, well done.

 

[edmund]

How are you locating it on the chuck?...
I assume your chuck is locating correctly on its spigot and the jaws are running true...
...just mount it on a worm screw in the chuck and turn a spigot or recess in the other end...
By the way, you did not pick the easiest bit of wood to do your first goblet, well done.

Thanks for this guidance Chas. I think the chuck is locating correctly - it seems to run cleanly when there is no wood in the jaws. I think the points you make about imbalance caused by the differing hardness in the wood (the Eucalyptus was quite soft) are good. BTW what's a "worm screw"? Is that the chunky screw which came with the chuck (and sits in recess in the middle of the chuck??). Is this something you would use in addition to the jaws of the chuck? Also, would shark jaws (the ribbed ones) be better? And while I'm in question mode, what are the merits/demerits of compression v. expansion if you have the choice?

Thanks for the feedback on the goblet. The wood was a bit tricky, but I thought it has such nice figuring that I'd give it a go - fun to experiment, and I'm enjoying practising with the tools. I had a go at an eggcup with the remainder of the blank, but I made the stem too thin and it snapped! One more for my collection of nearly but not quites
Thanks, E

 

[CHJ]

...snip... BTW what's a "worm screw"? Is that the chunky screw which came with the chuck (and sits in recess in the middle of the chuck??).
...Is this something you would use in addition to the jaws of the chuck? ...

Yes it is, it is not used in addition to the jaws as such, the securing of the workpiece is down to the thread alone, although the jaws do secure it and will act as a register for the blank when the wood is screwed onto the worm.

I use a Nova Chuck System, the worm screw on that just needs an 8mm hole about 20mm deep for fixing, you will need to check your Record item for drill size.

Also, would shark jaws (the ribbed ones) be better?

I have not needed to acquire and use any "shark jaws" for any of the turning I have attempted, but is is really a matter of preference as to how you wish to work, and in some instances they may give you more secure fixing if the wood is soft, does not have a flat surface to register against the chuck or is projecting some distance and you cannot use the tailstock.

...snip...And while I'm in question mode, what are the merits/demerits of compression v. expansion if you have the choice?

For sound wood very little, an expansion recess if finished and polished as part of the base before it is turned round can mean that when inner hollowing is completed the item is finished when taken off the chuck.

A spigot usually means the the project has to be remounted and/or finished by hand to remove it as a final operation even if you are parting off at the chuck end.

One area that a spigot can help on the safety front is with suspect wood such as Yew which is very prone to cracks, some which will not be seen. In compression mode the wood is clamped solid, in expansion mode if a crack propagates then there is nothing to stop it flying off the chuck.

 

[treefella83]

well the goblet is very good i love it .
i also have a cl1 and i had the same problems that you have mentioned.
place a spirit level across the two bed bars at each end of the lathe and you might see a difference.
there could be a very slight twist even if your lathe bench is level.
also there could be a problem if the head stock is not centered properly.
if you rotate the head stock to turn a large bowl and then rotate it back to turn between centres you could find that the head stock is not true to the tail stock.
i always line up the live centre with the tail stock centre so that when every thing is lock off and tight the drive centre will touch and rotate the tail stock centre and should be true along the full length of the bed bars.
i hope this helps happy turning

 

[edmund]

Thanks for all the tips and info. Lots of things for me to investigate and practice. Thanks, E