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.

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