Re: [CAD_CAM_EDM_DRO] collets

Hi Lew:
You want to use a prehardened steel like P20 or 4140 HT.
These are typically supplied at about RC 35, soft enough to machine with HSS
tooling, but hard enough to be a bit springy, and to resist dinging and
wear.
The turning is straightforward, and the slotting is done with a slitting saw
in the mill.
Sometimes, I have had best success with the slitting operation if the collet
is left a bit long at the front end, and the slots are not carried all the
way to the end.
This tends to keep the slotted segments from vibrating as they are cut, and
allows you to support the end of the collet with a tailstock and a bullnose
center.
The excess stub is lopped off as a last operation, with the collet seated in
its socket, and a bar of the correct diameter chucked in the collet.
The bar prevents the collet jaws from being caught by the parting tool and
getting bent out of shape.
I've made dozens of special collets this way, all the way from 5C size down
to weeny little collets 0.075" long with a bore of 0.020".

Cheers

Marcus

-----Original Message-----
From: LEW BEST <bcl@...>
To: Southbend List <southbendlathe@yahoogroups.com>; Milling Mach List
<millingmachines@yahoogroups.com>; Logan Lathe List
<lathe-list@yahoogroups.com>; Home_Machinist group
<home_machinist@yahoogroups.com>; CAD_CAM_EDM_DRO
<CAD_CAM_EDM_DRO@yahoogroups.com>
Date: Wednesday, November 07, 2001 7:13 PM
Subject: [CAD_CAM_EDM_DRO] collets

>Hi All
>
>Sorry to post this to so many lists, I know some of you are on multiple
>lists and this will get repetitious.
>
>I need to try to make a collet. The design is like a 5C with external
>threads but much smaller. An R8 is only slightly larger in outside

diameter

>(I thought I might be able to turn down and externally thread an R8, would
>also need to slightly flatten the nose taper. However after reading the
>specs in the Mcmaster catalog I feel they are probably too hard steel to
>turn.
>
>The collet I need is for a Black Diamond 31 drill grinder, is the large
>collet that holds the larger bushings and the 3/4" bit for sharpening. BD
>wants $120 some-odd for the one collet so I'd like to try to turn one
>myself.
>
>All it does is hold the bit in place for sharpening it, no high torque as

in

>milling, drilling, etc. I'd appreciate any suggestions as to material to
>use, how to cut the 3 thin slots on the face that allow it to tighten, etc.
>BTW my eq is all manual, even though the CAD CAM group is included in the
>list. I get good info from all the lists!
>
>Thanks
>
>Lew
>
>
>
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