[Welder2022]

It is normal practice to use a box fitting chucked in a lathe to hold taper threaded parts which have a pin on them.
Has anyone tried to thread the actual chuck soft jaws to hold a pin directly?
I would open the chuck then bore and thread the jaws so the pin would thread in.
Then close the chuck to tightly grip the part.
Open the chuck to release the part easily.
No setscrews or chain wrenches required.

[deadlykitten]

hy i just saw this, and is a briliant idea

yes, like you said, do it with chuck opened, and target a minimal play, only to allow to screw in your part ... the lower the play, the smaller the hidraulic travel when you close the chuck; but how your thread is tapered, you can actually control the play, by how much you screw in the part, thus this is a less worry, as in comparison to a normal straight thread

also, consider lower than usual chuck pressure ... 0.5 mpa ? just to have the cilinder moving, ohterwise, a big pressure, may damage the thread, because griping is not uniform, as the jaws tilt

also, when you machine your part, not the jaws, be sure to cut in a direction that has the tendecy to screw in your part, towards the chuck, otherwise, it may fly out; thus all tools to require same spindle sense

i think you can make this work, especially for big threads, as smaller, fine pithces, are more sensible / kindly

[deadlykitten]

thus all tools to require same spindle sense

if not possible, then consider machinig with doors open, dry, slow, and carefiul for vibratins, any sign that is losing grip

Open the chuck to release the part easily.

if i get it right what you need, you simply unscrew it, should not be possible to pull it by hand

it may also be a chalenge, if jaws will deform a bit, so consider a flat on your part or something, to use a wrench ?

and one more thing : if chuck is not in good condition, then crafting soft jaws with chuck opened may lead to too much tir

i think it will work

[deadlykitten]

hello again

few more tips :
... modify thread taper for soft jaws, in respect to jaw tilting, at least to ensure that contact is near jaw face, not near chuck
... to ensure contact only on flancs :
...... decrease tool nose radius, when crafting the jaws; as sharp as possible
...... increase inner diameter before threading; you may go larger than standard tolerance

if you find it hard to measure the inner diameter ( setter mismatch, or tool break, or the dial caliper can not find a place, or not big inner micrometer, etc ), you can check dimension in comparison to chuck outside diameter, with 0.1 accuracy, as long as chuck od tir is small