Tuesday, April 2, 2013

Crosman MK2 Modifications -- Part 4

Since the plug base for the hammer spring is part of the Crosman MK2 factory shroud, I'm on my own for a replacement.  Initially, I had visions of silver brazing the plug to the new shroud, but my actual solution was pretty mundane.

Found a scrap of 0.750" steel rod.  Dunno what it's from, but it looks like a slice of a low carbon steel.  Based on how it cut, it's probably a "free-machining" steel like 12L14.

Cut it to shorter length and took a couple passes to get the small diameter to slip fit into the hammer spring tube.

Thinned the outer face.

Milled some clearance for the radius of the shroud. 

The only "difficult" part was deciding to drill a hole in the MK2 frame to add a cross pin for the plug.  I've got the gun clamped by the shroud--the shroud is seated against the bed of the milling vise.  Used a surface gauge to indicate several spots on the flat of the grip frame.  This sets the grip frame parallel to the surface of the mill table and perpendicular to the spindle.  While I know it's not going to be perfect, it's much better than just eyeballing it.  Also added a jack screw under the grip frame to prevent deflection from the drilling.

Lined up with the slot for the cocking knob and spotted the hole with a center drill.  The plug, by the way, is installed in the gun along with the spring sleeve--minus the hammer and hammer spring for the drilling. 

(Very slowly) Through drilled with a 0.125" bit.

Vaccumed the chips and was careful to keep them out of the gun's action.

0.125" pin made from O-1 installed.  Heat blued the ends of the pin with a small torch.

Doesn't look out of place.

Removed everything for deburring. Here's some of the parts.

Going back together.

The hammer spring pressure alone against the plug wasn't enough force to hold the cross pin in place.  Removed the cap and spotted...

Drilled into the cross pin hole...

and tapped #8-32 for a set screw.

Blued the plug and installed.  Filed a flat on the cross pin for the setscrew to bear against.

A new front sight and some color on the shroud should finish this one up.

Check back soon.