Sunday, May 31, 2015

Making a Barrel Band for my QB77

Got back on track with the QB77 project.  The original barrel band was a brittle plastic and finally gave up.  

Found a chunk of aluminum in my scrap bin.   Dusted the edges on the mill to make them somewhat parallel and easier to clamp.  If I ever make another, I'd seriously consider using black colored acetal.   Strong enough, even easier to work and permanently colored.  Anyway, aluminum it is for now.  Marked the center line.

Centered up on the milling machine. Need two holes.  The gas tube is 0.875" in diameter and my barrel measures 0.555"--just over the 14mm nominal size.  

Spotted then just through drilled the 0.875" hole (7/8").  No drill chuck.  Clamped the shank in a collet.


I didn't have a custom sized 0.555" drill bit, so after spotting the hole it was first drilled with a 0.500".

Thought about taking it to the lathe and boring the hole to size, but then I remembered I had this small boring head.  Pump and Products Co. Tool Division, Cleveland, Ohio.  Patent probably still pending.   Got it from a co-worker a year ago.  Guess it's at least 30--OK, probably at least 50 years old. Anybody know anything about the company?   The setscrew clamps a 0.375" boring bar.

The two screws on the back allow you to change the angle of the boring bar relative to centerline. 

Well, I've never used this tool before, but after looking at it for a minute, I realized that this is probably wrong.  The cutting edge of the boring bar likely needs to be in the same plane as the adjustment angle.  Here, it's at approx 90 degrees.

Lined up.  Adjusting the two upper screws makes the cutting edge move in or out.  Set it just slightly larger than the hole diameter and plunge.  Downside?  There's no micrometer reference on the tool like there is on a modern boring head.  It's bore, measure, adjust, bore, measure, adjust...  After a couple adjustments, the hole was done.

So now, I've got this incredibly cool block with two holes in it.

With the front sight, and the gas tube cap removed, it was a successful test fit.

Back to the mill to clean up the faces.  Gotta get them now while it's still rectangular and easy to clamp.

After it was faced, I penciled in some lines and started milling edges.  Eyeballed all the set ups--just made the line look parallel to the top of the vise jaws, then milled to the line.  It's not like this is a precision part.

Starting to look like something.  Eventually, I did nine edges.

Did some more magic marker layout and drilled for a setscrew to clamp to the gas tube.  

Tapped M4 x 0.7mm.  

It's done for now.  May need some additional shaping/fitting in the near future.  No set screw for the barrel as yet.  Not sure if it'll need one.

Hope to start the stock next.

Sunday, May 24, 2015

Quick Rear Sight for a Crosman 1377

This should probably be titled, "How to drill and tap straight holes in a drill press or mill."

I was distracted from the QB project this morning.  Noticed the lack of a rear sight on my Crosman 1377.  It must have been wearing a red dot that was appropriated to another gun.  Fortuitously, the 1377 was wearing a Crosman steel breech. 

Rummaged through the pieces parts and came up with a rear pistol sight of unknown pedigree.  At least it's all steel and looks to be well-made.  It was an eBay find that cost all of four or five dollars.  It was rebuilt and re-blued then put aside a couple months ago.

It's a dead simple install--two threaded holes.  Removed the breech from the 1377, set the sight on top and eyeballed the front to back location.  After figuring out where it best fit, I found, then marked the centerline on top of the breech.

Then marked how far the holes are apart from each other.  Rummaged through the hardware and found that 3mm flat heads were the best fit to the sight's mounting plate.

Set the breech on top of a parallel in the milling machine.  This would also be an easy set up in a drill press.

Used a wiggler with a needle point to center up on the hole locations.

Spotted with a center drill.  Spotting hints:  When spotting a hole on a scribed line, it's good practice  to just lightly touch the workpiece (barely leaving a mark), then stop and double check that it's exactly on location before drilling any deeper.  It's also a time saver to drill deep enough with the spotting drill so the hole is countersunk for the final threaded hole diameter.  This takes a bit of practice to get the counter sink diameter correct, though the tap or screw thread can be used for comparison.  Saves from having to countersink after threading--which ususally necessitates cleaning up the thread a second time.

Through drilled with a 2.5mm drill bit.

I believe my grandfather made these low profile points.  Probably back in the 1950's. 

Helpful as a tap center when you don't quite have enough vertical space for the vise, parallel, workpiece, tap, tap handle, chuck...

Good tap handles have 60 degree centers at the end for alignment.  This is a M3 x 0.5mm tap, btw.

Light downward pressure on the quill holds it all vertical as the tap is started.  Here, the thread is being cut in the second hole.

Cleaned up for the pic, but there was plenty of thread cutting oil for the actual tapping.

Deburred the inside of the breech's bolt channel with a small half-round file and test fit.

Don't like the vertical end at the front of the sight.  Not a good blend to the chamfered loading trough.  Scratched a line on the side of the sight that carried the angle.

And back to the milling machine with a four-flute endmill.  Set the sight at an angle that made the scratched line parallel to the vise jaws. 

No measurements necessary. Cut until I reached that scratched line.

Deburred the razor sharp edges with a file and blued the milled surface.

Test fit number two.

Looked OK.

Reinstalled the breech.

Back to the QB77 next time.