Collet closing

[Dave HalfordParticipant @davehalford22513]

Does anyone know the number of turns required to close up a 4C collet please?

[bernard towersParticipant @bernardtowers37738]

Surely depends on the material tolerances.

[JasonBModerator @jasonb]

If anything like 5C than as Bernard says it will depend on the stock. Bit of silver steel and it’s Hardly anything but BMS would need a bit more as its a few thou under. Either case nowhere near a full turn.

[DC31kParticipant @dc31k]

In principle, you could calculate the number.

You know the pitch of the thread on the collet.

You know the included angle of the collet nose.

[Dave HalfordParticipant @davehalford22513]

Thanks Jason,

That’s good news, a lot less than I thought it would be.

 

[SillyOldDufferModerator @sillyoldduffer]

Or does Dave mean “How many turns to grip tight”?

If so, done with a torque wrench, not by counting turns.   There’s plenty of torque info on the web for tightening ER collets, but I couldn’t find same for 4C.  Possibly Machinery’s Handbook.

In practice though, I don’t tighten my ER collets to spec with a torque wrench.  Rather I’ve learned to tighten them by feel – enough to avoid slipping.  Maybe a full turn or so after the collet has made good contact with the job, which is probably significantly less than recommended.    Acceptable for the lightish hobby cutting I do, and keeps me happy because the literature says the worst sin is over-tightening.  Doing so bends the collet and holder, increasing run-out and possibly damaging both permanently.

Dave

 

[Michael GilliganParticipant @michaelgilligan61133]

Maybe worth noting that 4C collets (et al) fall into the same design concept as watchmaker’s collets … and therefore are intended specifically to hold nominal size.

Obviously the realities of life demand some tolerance … but this very small and the quality of holding falls dramatically if liberties are taken.

MichaelG

[Michael GilliganParticipant @michaelgilligan61133]

A short extract from:

The Watchmaker’s Lathe

It’s Use and Abuse

Goodrich : 1903

.

.

Scale as you see fit, but the principle is inescapable.

MichaelG.

[SillyOldDuffer]

On SillyOldDuffer Said:

Or does Dave mean “How many turns to grip tight”?

 

 

I do,

I’m making the drawbar, the closer is part of the spindle and would like to use as much of the available 20 tpi thread on the collet as possible.

[bernard towersParticipant @bernardtowers37738]

I would imagine that the drawbar that you make will be inferior in strength to the collet so using anything over half the collets threads should be strong enough. Not saying that your drawbar would be in anyway inferior.

[Dave Halford]

On Dave Halford Said:

would like to use as much of the available 20 tpi thread on the collet as possible.

There is some logic to making the drawbar threads such that they bottom out on the collet before you overtighten the collet and damage it.

 

Edit:

20tpi and 20 degree included angle. That means one turn of the draw tube gives 0.018″ diameter reduction, which is about six times the generally-noted closing range (0.003″) for this style of collet.

Hence, the answer to your question is roughly 1/6 of a turn.

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