Tuesday, March 26, 2013

Crosman MK2 Modifications -- Part 3

Next up on the MK2 is end cap for the shroud.   Essentially, it's a glorified nut.  It will thread to the muzzle end of the barrel and support the front of the shroud.

Dug though my metal stock looking for a piece of 7/8" OD rod to match the OD of the shroud.  No luck, but I did find a piece of 1" stock.

Faced the end.

Turned the OD down to 7/8" then cut a step to slip fit into the shroud's bore.

 Center drilled.

 Through drilled 21/64".


Started the 3/8"-24 thread with the tap held in the tailstock for alignment, then finished by hand. 

Parted off the endcap.

Needs some clean up.

In a fit of insanity, I decided to make a fancy interface and special wrench for the cap.

The cap was held in a 5C collet and the collet went into a six-sided (hex) collet block.

This was then set in the milling vise and a hole was drilled, then the block was rotated 1/6 of a turn (60 degrees) re-clamped and another hole drilled...  A work stop was used to get the block clamped in the same location in the vise each time.

Eventually, I had six evenly spaced holes.  Removed the collet block--being mindful to not move the X or Y position of the mill table.

For the wrench, I faced a thin slice  of 1.125" round stock. 

Rebated to fit over the end cap.

And it went into the same hex block using a larger collet.

Back to the mill and the work stop where it was drilled six times.  In theory, the holes in each of the two pieces line up.  

Turned down some thin brass rod and made six pins.

Found center and through drilled the wrench with a 3/16" bit.


The (freshly blued) wrench, brass rod cut into small pins, and the end cap.

The brass pins were pressed into the body of the wrench.  Used some Loctite 680 bushing retaining compound to help keep them in place (probably forever).  Chucked the wrench and faced the pins down to the same height.  Not shown:  Cut a handle from a piece of 3/16" drill rod.

Along the way, I added a groove to the cap for an o-ring and used a boring bar to remove about four or five of the 3/8"-24 threads from the muzzle end.  Also chamfered the pin holes and generally cleaned things up.

Wrench and end cap. 

 They practically press fit together.

The end cap threaded into place.  Nice, clean fit with the OD of the shroud.

Here's the new business end of the MK2.  By removing those forward end cap threads, it looks like a deeply recessed crown.

Still need a new plug for the hammer spring tube.  Oh, and probably a front sight.

More soon.