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.