Another Breech for a Crosman. Part 3

Finishing the breech today. 















With the bolt handle slot cut, there were just a couple more procedures to attend.

Centered on the rear breech screw hole and counterbored for the head of a #8-32 socket head cap screw.  The counterbore was done when I could drop in the #8-32 fastener and the head was just below flush.

Dovetails!  Before cutting dovetails, I took a couple passes on each side to leave a center rib just shy of 12mm wide.

Followed by a small 60 degree cutter.  The work was only cut from one side, then turned around in the vise with the Y-axis locked.  This puts the dovetails in the center of the workpiece.  There's quite a bit of variance on what is known as a 3/8"--or 11mm--or .22 dovetail.  I cut until a Leapers medium scope ring would tighten with minimal gap on the clamping plate. 

At this point, the breech is done.  Boring, but done.  Those plain slab sides needed something to add some visual interest.  Set the milling table stops and used a Woodruff key seat cutter to add horizontal slots along the sides and break up the smooth surfaces.

Before clean up.  Click any pic to make it larger.

Wet sanded (WD40) to 500 grit on a surface plate.  Slots left in the raw.

Wanted a tad more sprucing up.  Used a maroon, then gray Scotchbrite pad to polish the breech.  Various riffler files were used in the slots to remove the cutter marks.  Did minimal clean up of the dovetails as I was concerned about the accuracy of the angles.

Breech is done and I'm satisfied with how it looks.  Still need to make all the incidentals--the loading bolt, bolt handle, cocking pin, transfer port, barrel sleeve...

Thanks for reading.  We'll have more in a few days.

Another Breech for a Crosman. Part 2

Right where I left off...

























Picked up the edge of the breech then cranked the table to center.

With a 7/8" ball mill, I cut the radius to fit against the gas tube.

It was a pretty slow cut and produced a lot of chips.

The last pass was done at high speed taking off about a thousandth.  Gave an acceptable finish.

Back to the mill (after some chip clean up) and spotted the hole for the rear breech screw.

Through drilled.

Drilled for the forward breech screw.

0.250" hole for the transfer port.

Set the X-stops.





 













Milled the slot for the hammer cocking pin.

Not shown:  Drilled three #29 holes for barrel set screws.  Went through the small taps and found a #8-32 plug tap.

Tapped.

Flipped the breech--this is the top--and countersunk the rear breech screw hole.

Left turn(side), Clyde.  Set the table stops for the bolt handle slot.  That's a 3/16" end mill.

A few passes later.  Yep, cleaned up the chips before taking the picture.

This contraption is a tilting table.  Allows the work to be angled relative to the spindle.  I set it at about 12 degrees fahrenheit.




 













This is a train wreck.  The breech is in an insert vise that's been bolted and step-clamped to the top of the table.

All for this little cut.

Should let the bolt handle angle downward when locked in the forward position.

Marked out the location for the loading slot.

0.750" end mill looked about right.

Just breaking through the 0.250" through hole for the loading bolt.




 













Luckily (OK, I did actually measure first) I didn't break through at the front into the 0.4375" hole for the barrel.   Would've still worked though.

Lined up on the front breech bolt through hole...

and counterbored for the head of the fastener.



More in a couple days.

Yep, I Need Another Breech for a Crosman. Part 1

There's a pile of projects on my to-do list, but this appealed to me the most.  I'd like to make another breech for a Crosman 22XX-type gun.  Something simple this time.  There's no plan to make it a repeater like the last time around. 















Starting with a piece of 6061 aluminum. 

I finally got around to purchasing a 4-jaw independent chuck for the lathe.

Put off getting a 4-jaw because I couldn't figure out which chuck to order.  (and there wasn't a pressing need)  Eventually, I broke down and just picked out a 6" diameter "plain back" chuck then made an adapter plate-- a "back plate" in machinisty terminology.  The "back plate" adapts the chuck to the spindle of the machine. 





















Scribed a center line on the face of the aluminum and adjusted the chuck until the line centered up with a pointed indicator held in the tail stock.

Notice the offset.






















Spotted the hole and all looks good.  The offset is easier to see here.  this is part of the advantage of a 4-jaw chuck.  Offsetting work as well as the ability to hold work that isn't round, triangular or hex shaped.

This piece of aluminum is 6" long and I'm drilling a 0.250" hole all the way through.  The flutes need constant clearing as well as lubrication with a cutting fluid to prevent the aluminum from welding to the cutting edges.   It's a very laborious process to drill a hole this deep.  And the smaller the diameter of the drill bit, the harder the job becomes as the bit wants to flex and walk the hole out of alignment by the time it breaks through on the far side.  Slow going, can't force the bit. 

Finally through.  There's 6.25" of drill bit through the aluminum here.  If I make another breech, I'll use a 0.375" drill bit for the through-hole.  The bump-up in drill size make for a more rigid set up. 

It gets easier now.  The .250" hole is partially drilled out with a .4375"  bit--the same diameter as a Crosman 22XX barrel.    I drilled this hole for the barrel just shy of 3.175" deep.  The painter's tape on the bit gave me a quick and dirty depth measurement.

Followed with a 0.4375" reamer.  A spot of dykem on the shank and a scribed line made it easy to hit the exact depth.

As I'm not a fan of the way the "soda straw" Crosman barrel looks, I'm going to add a barrel shroud to bring the barrel up in diameter.   To do this, I drilled a counterbore about 0.600" deep with 0.625" bit.
 

Not shown:  Finished the bottom of the counterbore with a 0.625" endmill to achieve a clean, flat bottom.

With the holes finished, I faced the piece.

The counterbore for the barrel cover is easy to see here.

Moved to the milling machine and fly cut what will be the right and left sides of the breech.  The fly cutting was used to remove just a couple thousandths and produce a nice surface finish.

A multi-anvil micrometer was used to measure the wall thickness at each side of the counterbore.  One of the sides was thicker than the other by  0.003"--hardly enough to worry about, but I recut the high side until it matched. 

Next is the radius cut along the base of the breech to fit against the gas tube.

Caliper set at 0.3675" to scribe the center line.  I'll use it as a secondary reference and use an edge finder to find true center for the milling.



More soon.