Re: collets

--- 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