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self catering v independent

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Eric Cox03/08/2021 09:42:19
537 forum posts
37 photos

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.

Martin Kyte03/08/2021 09:45:31
2558 forum posts
45 photos

Basically yes. More likely the square was slightly rectangular.

regards Martin

Michael Gilligan03/08/2021 10:05:15
18923 forum posts
941 photos

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


But, yes … I agree with Martin.


HOWARDT03/08/2021 12:46:30
778 forum posts
28 photos

Agree. The continuous cyclic knock causes the scroll to loosen, had something similar recently.

Oldiron03/08/2021 13:12:33
850 forum posts
23 photos
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.


Andrew Johnston03/08/2021 13:30:47
6264 forum posts
677 photos

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:

square head bolts.jpg

And the resultant swarf:

square swarf.jpg

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


not done it yet03/08/2021 14:02:42
6321 forum posts
20 photos

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.

Andrew Johnston03/08/2021 14:39:10
6264 forum posts
677 photos
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.


not done it yet03/08/2021 18:42:30
6321 forum posts
20 photos

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.

old mart03/08/2021 20:19:05
3345 forum posts
208 photos

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.

roy entwistle03/08/2021 21:18:50
1407 forum posts

I always thought that a 4 jaw self centring chuck was for woodwork

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