[yunk]

Hi all!
I would like to make an AMF/IMAO machinable collet for my workshop.
Does anyone understand how the pulling mechanism inside the case is arranged?

[deadlykitten]

hy yunk please take a look at attached image

inside the base is a nut, capable of up/down movement

od clamping :
... is used normal screw, maybe with bigger than usual head
... this screw makes contact, with the collet, towards the base (z-), and this creates the effect of rotation at the higher surface of the collet
... because of rotation, there is also an effect of pull-down

id clamping :
... is used a tapered screw
... contact with collet is towards the collet surface (z+), and this creates an effect of contrary rotation, so the coolet expands at top
... 2nd effect is that collet rotates reverse at (z-), or at least has the tencendy to do so, but this is less important

please notice, as explained in the bottom zone, that surface contact is only among a ring, not full face

i did not draw them, but pins are used to prevent collet rotation among z axis

pulling mechanism inside the case

is a simple rota to linear mechanism; it may have a drive pin, a lobe ... it is designed to lock at blocking angle, thus the cutting forces to not be able to rotate it back

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a cheaper alternative for a regular shop, is to take a 3 4 6 normal chuck, and use pie jaws

even cheaper, if your parts are simple, is a vice with custom jaws;by cheap i don't reffer only material cost, but also the time needed to craft it / kindly