self catering v independent

This topic has 11 replies, 9 voices, and was last updated 3 August 2021 at 21:18 by roy entwistle.

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3 August 2021 at 09:42 #556810
Eric Cox
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@ericcox50497
I've been turning (conquest super) some 1/2" square MS. down to 7/16" Dia. Each cut was 0.010 over a length of 2", supported by a centre in the tail stock and held in a 4 jaw self entering chuck. The intermittent cutting caused the chuck to open slightly and the job to come loose. Would I have been better using a 4 jaw independent chuck.
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3 August 2021 at 09:42 #28287
Eric Cox
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@ericcox50497
3 August 2021 at 09:45 #556813
Martin Kyte
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@martinkyte99762
Basically yes. More likely the square was slightly rectangular.

regards Martin
3 August 2021 at 10:05 #556824
Michael Gilligan
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@michaelgilligan61133
I nominate your thread title for the Typo of the week, Eric

But, yes … I agree with Martin.

MichaelG.
3 August 2021 at 12:46 #556836
HOWARDT
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@howardt
Agree. The continuous cyclic knock causes the scroll to loosen, had something similar recently.
3 August 2021 at 13:12 #556842
Oldiron
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@oldiron
Posted by Michael Gilligan on 03/08/2021 10:05:15:

I nominate your thread title for the Typo of the week, Eric

Oh the joys of predictive text.

regards
3 August 2021 at 13:30 #556843
Anonymous
It would be better to take one cut rather than lots of small cuts. The 2" bolts at the bottom of this photo were turned from 1/2" square steel down to 1/4" diameter in one pass with no tailstock support:

And the resultant swarf:

To be fair the work was held in a 1/2" square collet which doesn't work loose, but still no support needed.

Andrew
3 August 2021 at 14:02 #556845
not done it yet
Participant
@notdoneityet
How fast were you turning and how thick were those ‘curly band saw blades’, Andrew?

Between 230 thou. and 125thou deep, so an average cut of about 175 thou.

Apart from the catering aspect, using a ‘self entering’ chuck must save some time and effort? Does it tighten itself as well?

I don’t particularly like self centring 4 jaw chucks for that very reason – they can only work 100% on perfectly round or square work pieces.
3 August 2021 at 14:39 #556855
Anonymous
Posted by not done it yet on 03/08/2021 14:02:42:

How fast were you turning and how thick were those ‘curly band saw blades’……….

Probably running at 1000rpm. I don't have any swarf left (that I can find) but thickess is likely around 8-10 thou. Without measuring I don't know the exact feedrate, as the lathe in question only has an uncalibrated hydraulic feed – you adjust it to give the required finish.

Andrew
3 August 2021 at 18:42 #556900
not done it yet
Participant
@notdoneityet
Thanks Andrew. A bit more than a 1/2HP myford could hope to cope with🙂

Too much for my lathe, too, but I might be able to avoid the intermittent cut with a bit of adjustment with feeds and speed – but possibly not without tailstock support.
3 August 2021 at 20:19 #556916
old mart
Participant
@oldmart
The main shortcoming of a 4 jaw scroll chuck is that it requires perfect material to hold, and even if the material is perfect, there is always a large chance that all of the the jaws are not always the same distance from the spindle axis. A three jaw scroll always clamps on the workpiece even if not accurately. The 4 jaw independent takes more time and effort but can hold the work in any position you would desire.
3 August 2021 at 21:18 #556925
roy entwistle
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@royentwistle24699
I always thought that a 4 jaw self centring chuck was for woodwork
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