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Old 12-07-2009, 10:28 AM
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Reducing Outside Diameter of Slimline Insert

Originally Posted by MonkTx View Post
... I got a couple of the old CM-2's from CDNN ....

Has a consensus been reached on what diameter Slimline inserts fit the CM-2 rifles' front sights...?
The Stickies:
The 17mm diameter inserts are the KRAG. - 17mm Slimline Inserts work in CM-2
CM-2 Front Sight Inserts - CM-2 ... insert size of 16.85mm
refer to new contemporary CM-2's being currently manufactured and sold.
This information may not apply to vintage/surplussed VOSTOK CM-2's.

Originally Posted by Charlotte View Post
Although this makes those with machinist backgrounds reel and gnash their teeth
the 18mm plastic inserts are oversized by 1mm which means that you only have to
remove half that much in a swipe around the circumference with a nail file....
If you're more of a pragmatist than machinist ... Charlotte has advanced a solution that works in the field.
Her method involves a simple tool and finesse - a fingernail file and hobbyist skills.

For the machinist types (that be me ), I'm proposing a more mechanized method.
Using a jewelers file, an electric drill (poor man's lathe) and machine screw with nut.
Rig a a simple mandrel using a machine screw and nut.
The screw diameter should be slightly smaller than the aperture size of the insert.

Sandwich the insert between the screw head and nut.
Synthetic washers maybe placed on both sides of the insert to prevent marring.
The complete assembly should vaguely reassemble a cut-off wheel apparatus.

Then mount the assembly in the chuck of an electric hand drill.
This is done in preparation to uniformly file the circumference of the insert.
A vise would be a handy way of mounting the drill in a steady position for this procedure.

Power the drill to rotate at high rpm.
Then very, very lightly touch the file to the outside diameter (OD) of the insert while it is spinning in the drill.
Stop the drill and measure the OD of the insert to guage the amount of material that has been removed.
Use a micrometer or caliper to measure the outside diameter frequently until the proper diameter is reached.

Originally Posted by Charlotte View Post
... the 18mm plastic inserts are oversized by 1mm which means
that you only have to remove half that much in a swipe around the circumference ....
I'd stop at an indicated 17mm to check the fit of the insert (still mounted on the mandrel) within the globe.
If the fit is too tight, re-chuck the mandrel and further remove a minute amount of stock from the OD.
Then, check the fit again and again until you are satisfied.
Remember: "measure twice" ... "before cutting once."

This is a semi-precision process that may yield acceptable results.
(I'm cringing a little as I write.
But, my teeth are not gnashing.
However, I am wringing my hands.)
W. Edwards Deming ... Quality: It is not enough to do-your-best;
you must know what-to-do, and ... then ... do-your-best.
Ever-Onward ... Through the Fog ---- Fort Stockton TX 79735
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