Saturday, July 28, 2012

Custom Crosman Breech--Part 2 Starting the Shroud

Picking up where I left off... 

Chucked a Crosman 22XX barrel in the lathe jaws and pushed it into the counterbore in the breech.

Just using the barrel for alignment.  Used several setup blocks as well as some shim stock underneath the breech until the through hole was centered up on the lathe's headstock.  I need to paint that window frame in the background...

Then I clamped the breech down to the crosslide.   Aluminum sheet was used between the setup blocks as well as the clamps to prevent marring the breech.

Removed the barrel and mounted a 5/8" center cutting endmill in the lathe chuck.

Very slowly shaved metal to produce a stepped hole at the front of the breech.

No measurement as the depth isn't critical.  About 1/4"+ will do.

The plan is to sleeve the skinny 7/16" OD Crosman barrel for additional muzzle weight and stability.

The step will accept the end of a 5/8" OD barrel sleeve.  The sleeve will be made from the piece of DOM tubing on the right.

The DOM tube is both too long and too small in the ID for the Crosman barrel to fit into.

With a parting tool, I cut about 3" off the end of the tube.

Then through drilled with a long 7/16" bit in the tailstock.  Had to flip the workpiece around and drill from both ends to the center.

Cleaned up the ends of the tube.  Not shown:  After drilling, a 7/16" reamer was run through the tube for clean up.

Couldn't take the humidity outside any longer.  Brought the tube indoors and wrapped the Taig bed with foil protection and polished the tube to 400 grit.

Test fitting.

Barrel slip fits into the breech.  It'll get set screws later.

Sleeve installed over the barrel.  Could've just butted the tube against the end of the breech, but recessing the end is cleaner.

More soon.  The next step is make or break.

Sunday, July 22, 2012

Custom Crosman Breech--Part 1 Drilling

Thought I'd give the breech project another go.  I'm still trying this the hard way as I still haven't sourced a 4-jaw chuck for the new-to-me lathe.  If it all goes south again, I'll have to move the 4-jaw a bit higher on the list of priorities.

Chucked a chunk-o-steel.

Gonna try this on a larger drill press.  This is a 3/4 hp and about the largest "bench top" press that will still fit on the bench.  I need a step stool to change the belts (since it's awkward to work in high heels).  Not shown:  Adjusted the table to get it perpendicular to the bit then locked down all the table adjustments. 

A pile of milling clamps secured the vise to the table.   Going to through drill the block up to 0.250", as that's the diameter of the pellet loading bolt. 

If you've never tried to put a 0.250" hole through a piece of steel 6" long,  you really don't know what you're missing.   This is where the 4-jaw independent lathe chuck would've come in handy.  Could've held the bit steady in the lathe tailstock and spun the work.  Anybody got a 5" diameter plain back?   I could've just started with a large enough piece of round or hex stock and use the 3-jaw and be done with it.  More milling time afterwards, but the drilling would be more straightforward.

A brand new 7/16 "aircraft" drill bit.  It's waaaaay too long for this job--around 14".   Most of it is shank as they're used to drill holes in odd, tight locations with poor access--like wings and fuselages.  The blue tape is to protect the flutes...

...while I shorten the shank.

Looks about right.  

Progressively drilled with larger sizes until finishing with the 7/16"--the OD of a Crosman 22XX barrel.  Didn't have to through drill with the 7/16"--only had to go about 3.250" deep.

Success?  Well, maybe just, "so far, so good".  Test fit a Crosman barrel and there's very, very little runout.  The barrel is exceedingly close to parallel to a straight edge set against the sides of the breech.  Yeah, my technical drawing there leaves quite a bit to the imagination.

Still a multitude of ways I can screw this up for the recycle bin.  More in a couple days.