Help please - tail end wobble

[Lightweeder]

Has this ever happened to you? You do something for months on end, then all of a sudden it doesn't work ?

I've been making these for a while and have an order to fill, but I can't get the thing to run true. The tip and the 'whorl' appear to be fine, and it feels right all the way up the stem, but there's a nasty wobble in the last two inches. I'm taking a lot of care to keep my speed down, tools sharp etc, and it should be OK, but I'm wasting too much time binning this and starting over. Can anyone suggest what I'm doing wrong.

PS I've bought a centre support for my lathe, which is currently being milled down to fit, but I can't wait any longer.

 

[CHJ]

Is it you producing the wobble, or failing to turn it out: or is it your stock moving with internal stress relief ?

 

[Lightweeder]

Is it you producing the wobble, or failing to turn it out: or is it your stock moving with internal stress relief ?

To be honest Chas, I drilled the first attempt out and took the greatest of care with the second. It felt OK, though when I started to sand it down, it seemed to bounce so much in the middle - apparently from the heat. As it was just about finished, I let it cool then took it off. When I roll it along a flat surface, the tip's not right. I'm finding the skew hitting a bumpy road, so I actually sanded this tip down. Still wobbles though. It's for the bin anyway, but I don't how to get it right next time. I'm having difficulty thinking of the thing as three separate bits - head, middle and tail and all behaving differently. I can only turn the whole thing.

 

[CHJ]

Are you turning the whole thing out of one piece of stock ?

 

[Lightweeder]

Are you turning the whole thing out of one piece of stock ?

Yes, the shaft is one piece. No problems all the way up - you can feel no vibration through your fingers when it spins, but the tip (thin end tip) is all over the place. I can't understand it.

 

[Bemused]

As an engineer and only a novice turner my engineers head says find what has changed and that's probably the cause.
Seems nothing has changed except the wood :- stress being relived once turned.

 

[CHJ]

PM sent.

 

[nev]

excuse the ignorance, but what is the item in question?

 

[LancsRick]

excuse the ignorance, but what is the item in question?

Looks like one of those spinning weights for spinning flax? I could be completely wrong...

 

[Lightweeder]

excuse the ignorance, but what is the item in question?

This is a 'Tibetan' spindle. In preference to a spinning wheel, this is one of the many ways spindlers turn their fleece into wool.

 

[Lightweeder]

First of all, many thanks for your help Chas.

I've found a way 'round the problem, though it feels like cheating. I turned down about six inches at the headstock end, to the required diameter, then I cut off the mounting section, added some masking tape and slid five of those inches down through the chuck. It was easy enough after that to turn the remainder without any vibration to speak of. It's not the way I would choose to be doing it, but it actually seems fine.

 

[CHJ]

If these are a regular requirement then I would suggest that you make yourself a split collet out of Beech or similar to fit in your chuck jaws, method of mounting in jaws is dependant upon which accessory jaws you normally have fitted.

Turn it spindle fashion with grain in-line with bed of lathe.

Just turn up a blank to suit so that it can be relocated reasonably accurately each time and protrudes 25mm or so forward of the chuck.

Mount turned blank in jaws as intended for use, drill/bore, a hole down the centre to match your work piece spindle size.

If the grip range required for spindle size is small then you may get away with a single fine saw cut along its length through to the central hole, so that when the chuck is tigtened the collet grips your spindle.

If this method does not run true enough then take drilled collet blank off lathe, make two fine saw slits at right angles in protruding end, use a jubilee clip to compress 'jaws' onto spindle.


PS: there is nothing wrong with relocating the work as you did to gain true running or better machine control, it's done regularly in engineering.

Here's a sketch of something similar:

 

[dickm]

PS: there is nothing wrong with relocating the work as you did to gain true running or better machine control, it's done regularly in engineering.

Interesting comment; in my experience relocating work is a sure way to lose true running, unless you are using a clock gauge and an engineering chuck with four independent jaws. Or am I missing something?

 

[Lightweeder]

If these are a regular requirement then I would suggest that you make yourself a split collet out of Beech or similar to fit in your chuck jaws, method of mounting in jaws is dependant upon which accessory jaws you normally have fitted.

Turn it spindle fashion with grain in-line with bed of lathe.

Just turn up a blank to suit so that it can be relocated reasonably accurately each time and protrudes 25mm or so forward of the chuck.

Mount turned blank in jaws as intended for use, drill/bore, a hole down the centre to match your work piece spindle size.

If the grip range required for spindle size is small then you may get away with a single fine saw cut along its length through to the central hole, so that when the chuck is tigtened the collet grips your spindle.

If this method does not run true enough then take drilled collet blank off lathe, make two fine saw slits at right angles in protruding end, use a jubilee clip to compress 'jaws' onto spindle.


PS: there is nothing wrong with relocating the work as you did to gain true running or better machine control, it's done regularly in engineering.

Here's a sketch of something similar:

Great! I'm so relieved at finding a way 'round this, and more so if it's not frowned upon.

dickm - I'm assuming a lot has to do with how you relocate it. If I tried to put it back in my pin jaws, it would be all over the place, but in my (dare I say it) old Charnwood chuck with all the teeth removed (who does this remind you of :shock: ), it works a treat, and got me out of a BIG hole today. Cheers all.

 

[CHJ]

PS: there is nothing wrong with relocating the work as you did to gain true running or better machine control, it's done regularly in engineering.

Interesting comment; in my experience relocating work is a sure way to lose true running, unless you are using a clock gauge and an engineering chuck with four independent jaws. Or am I missing something?

Talking general terms, using collets and reducing overhang whilst machining.

This is a woodworking forum after all and not a site for precision engineering, I'm afraid I tend to make statements and offer guidance relative to the precision needed.
Don't think there is any need to venture down the line of applying zone tolerances and getting out the Renishaw probes.

 

[jumps]

I think I finally understand the process being used here ie the spindle is being turned in a chuck (of some sort) rather than between centres?

As such the only obvious variable is the chucking, and chuck tension/tightness outwith the actual material stresses etc

I would certainly look to turn the 'far end' first, on as full a stock as possible, then locate to a live centre of some sort before completing the rest. Despite being finished 'thin' it's short enough that between centres would firm it up for consistent finishing.

 

[Lightweeder]

I think I finally understand the process being used here ie the spindle is being turned in a chuck (of some sort) rather than between centres?

As such the only obvious variable is the chucking, and chuck tension/tightness outwith the actual material stresses etc

I would certainly look to turn the 'far end' first, on as full a stock as possible, then locate to a live centre of some sort before completing the rest. Despite being finished 'thin' it's short enough that between centres would firm it up for consistent finishing.

Thanks jumps

 

[duncanh]

Just wondering - what turning method are you using? You posted recently about starting at the tailstock end and turning a short length to final diameter before moving closer to the headstock to do another short length. Once the tailstock end is to final diameter it can then be supported.
Also, what tool are you using? I find than on small diameter lengths I get better success with the skew. I tend to feel that the force of the tool acts along the length of the piece rather than with a gouge where the force feels as though it's into the wood, which causes flex.
Another thought - carefully support the back of the spindle with your fingers to minimise flex. If they have to press so much (to counter force of the tool) that they get hot then you're applying too much force with the tool

Duncan

 

[Lightweeder]

Just wondering - what turning method are you using? You posted recently about starting at the tailstock end and turning a short length to final diameter before moving closer to the headstock to do another short length. Once the tailstock end is to final diameter it can then be supported.
Also, what tool are you using? I find than on small diameter lengths I get better success with the skew. I tend to feel that the force of the tool acts along the length of the piece rather than with a gouge where the force feels as though it's into the wood, which causes flex.
Another thought - carefully support the back of the spindle with your fingers to minimise flex. If they have to press so much (to counter force of the tool) that they get hot then you're applying too much force with the tool

Duncan

Hi Duncan - Happy New Year :deer

PM sent.

 

[Lightweeder]

I'm still struggling with this. There must be some reason why I'm getting an actual bend in a spindle. It shouldn't be possible!