Re: collets

Marcus & Fred,

You've made good points regarding collet making. I still stand by my
initial statement, I'm pessimistic about "home-made" collets.

You've both mentioned the use of a spindle as a holder in final
sizing the collet's ID. That's "cheating", since the collet then
becomes spindle-dependent and not general purpose. IMHO, a collet
should be concentric and accurate by itself, making it
interchangeable between machine spindles. That's the part where I
see the major problems.

Fred, it's not my experience that the typical CNC shop is about to go
out of business. Where are you located that you see this?

thanks to you both for sharing your knowledge,

Doug

--- In CAD_CAM_EDM_DRO@y..., "Fred Smith" <imserv@v...> wrote:
> --- In CAD_CAM_EDM_DRO@y..., "Marcus & Eva" <implmex@a...> wrote:
> > Hi Doug:
> > My strategy is to use prehardened steel, most often P20
because
> I use it
> > a lot for moldmaking,
>
> In the US 4140/4150PHT (Pre-Heat Treated) is more readily available
> than P20 and has nearly the same chemistry and physical
properties.
> It is about 30-32 Rc hardness and machines very nicely with carbide
> tooling. You can file corners made with it, but it will make you
> much more tired than brass. ;-)
>
>
> >so I've got lots kicking around.
> > I turn all the outside bits in one setup, and rough drill the
bore.
> > Then I cut the slots, but not all the way to the free end. I
leave
> a stub
> > that is unslotted.
> > I can then drop the collet into its seat and bore the hole in
> position on
> > the spindle on which it will be used if at all possible.
> > Sometimes this is the hardest step, because the spindle might not
> be easily
> > set up for the boring operation.
>
> Also if the spindle socket is worn, you may find that you want to
> mark the orientation of the collet so that when you remove it and
> place it back, the contact is at the same angle as when you bored
it.
>
> Use a die grinder NOT a dry marker and just put a small notch on
the
> collet face that lines up with a feature or similar mark on the
> collet holder face.
>
> > Last thing to do is lap the hole if needed (rarely) and lop off
the
> stub.
> >
> > For hardened collets:
> > Best steel I've found is H13; it is tough, goes to about RC52-54
> and turns
> > and grinds well.
> > The secret to success for me with hardened collets, is not to cut
> the slots
> > all the way through into the bore before heat treat.
>
> The slots can then be finished all the way through with a .030
> or .040 thick surface grinder wheel.
>
> > But most people don't need "Tenths" accuracy for most tasks
anyway.
> > I have made a few hardened collets for threaded production parts
> that needed
>
> The commercial tolerance on collets is usually stated as TIR at a
> given distance from the spindle nose. Typically .0005-.001 for
> standard collets and .0005-.0003 for precision lines. The distance
> that the measurement is taken varies by manufacturer and collet
style.
> The cheap imports often run out .001 or more.
>
> > -----Original Message-----
> > From: dougrasmussen@c... <dougrasmussen@c...>
>
> > >closed position. With the exception of the rough machining all
of
> > >the operations would present a challenge to the typical machine
> shop,
> > >not to mention the home shop.
>
> Unfortunately, the typical machine shop today is a CNC production
> shop, about to go out of business, without a doubt they would
seldom
> have a toolmaker on the payroll. However the typical tool or gage
> making shop has all the needed equipment and skilled toolmakers to
> make something as simple as a collet. If you want to make
something
> hard, try an HSK tool holder(rated for about 20-30,000 RPM). Shank
> angles are ground with precise location to a ground shoulder and
> tolerances inside of about .000050, as opposed to standard CAT40 or
> CAT50 tapered holders with tolerances of only .000200 on the angle
> and about "Who Cares?" on the location with respect to the flange.
>
> Best Regards,
>
> Fred Smith
> IMService