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.

Tuesday, May 12, 2015

Making a Bulk Gas Tube for a QB Rifle -- Part 3 Final

With all the holes and slots in the tube finished, I wanted to add a couple more screws to better anchor the valve.

Installed the valve, spotted, and drilled right through the gas tube into the valve body. 

Tapped M5 x 0.8mm.

Used a center cutting endmill to counterbore the screw heads into both the tube and part of the valve.   The idea is to get the larger diameter head of the fastener to bear the load rather than the smaller diameter thread.

Yeah, the extra valve screws are tiny.  Here's one I made from a turned down M5 button head.

And installed.  They barely stand proud of the tube.

Another view.

I took the tube into work, and with the owner's OK, polished it at lunchtime on our Rand-Bright BH-50.  This is an industrial polisher used to finish shafts and hydraulic tubes (among other things).

It's a great machine but I don't get to run it as often as I'd like.  A large sanding belt rotates while a feed wheel spins and draws the part under and across the belt.  You can vary the pressure of the belt on the part, as well as the speed of the feed wheel.   Of course, there are a large assortment of various sanding grits available. 

Took longer to install and adjust the feed guide platens than to do the actual polishing.

Started with a 240 grit and did about three passes.  Then a 400 and about the same. 

I think this pic is after the very first pass.  The smudged looking spots  are non clean up areas.

Final passes were done on a diamond coated belt.  I could've done a few more passes, but I didn't want the gas tube to look substantially better than the QB's barrel and breech. 

Four coats of Van's Instant Gun Blue had it looking pretty good. 

Overall, I'm pretty happy with the Van's bluing.  The only drawback, like all the cold blues I've tried, is lack of durability.  Handling the steel seems to wear the bluing off pretty quickly.  If it becomes an annoyance, I'll either epoxy coat the tube, send it out for hard chrome or have it hot blued. 

Here's the QB reassembled with the extended gas tube.  The action now has strong overtones of a Benjamin Discovery.

I see that I still need to figure out a replacement barrel band--the original plastic band cracked in several places due to age.  The walnut DQ stock is probably up next, though I do have a piece of aluminum on the workbench for that barrel band.  We'll see which feels more inspiring next.

Man, almost forgot.  The entire purpose in making this tube was to increase the on-bard CO2 capacity.  I haven't had nearly enough time to do the shooting, but this more than doubles the original gas tube's volume.  So, I guess I'm hoping for at least 100--110 good shots.

Check back soon.

Monday, May 4, 2015

Making a Bulk Gas Tube for a QB Rifle -- Part 2

Picking up where I left off....With the tube threaded for the bulk fill cap and cut to length, I wanted an easy way to add the holes and slots for the breech, striker and trigger components.

A square collet block will provide for easy 180 degree indexing to align holes top and bottom.

Not shown--I painted the tube in layout fluid then using a caliper, transferred all the hole and slot locations to the new tube.

If I had to do this again, I'd set the collet block to the left of the vise and clamp the tube directly rather than use jacks for support.  This did work, it just wasn't as rigid as I'd have preferred.

Edge finding.  Once I found center, I started spotting holes, drilling and milling using the original tube as a guide.


Had to make a tap run.  Didn't have the oddball M5 x 0.5mm tap on hand for the forward trigger mounting position.

Tube finished.  Pretty straightforward for once.  Not shown:  As expected, I had to dust 0.003 to 0.004" off the valve body and striker to fit into the ever so slightly smaller bore of the  new tube.

The only problem was the extended tube length meant my old valve tool was far too short to reach the valve face.  I did a test assembly anyway without tightening the valve.

Everything fit together and functioned correctly. 

Now for that valve tool.  My old valve tool consisted of a flat strip of steel.  Wanted a better tool this time around.  Used a slitting saw to slot the end of a 22" length of 5/8" drill rod.

Flipped and through drilled the opposite end 5/16".

Cut the end off my old valve tool, squared it up then press fit it into the new extension.

Cut and finished the ends of a piece of 5/16" drill rod.  Even did a quick coat of cold blue.

A bit nicer than what I was using before.  I stripped the action back down, tightened the valve and added a bit of CO2.  It held pressure for 24 hours, so I'm calling it good.  Need to anchor the valve into the tube a bit more securely, make or source a new barrel band then begin working on the stock.

More in a few days.