Wednesday, April 27, 2011

An Aperture for the IZH Diopter Part 1

Needed an aperture for the sight purchased at Findlay. Blog reader Duskwight correctly ID'd it as an Izhmesh biathlon rifle sight.

The silver adjustment knobs are plated steel. The diopter has some heft to it--surprising to me for a biathlon sight. I would have expected it to be lighter.

The hole size for the aperture has a (non-standard?) M9 x 1.0mm thread. Is there a standard? I think some of the Chinese rifles use M8 x 1.0mm.

Here's an aperture from a different target sight. It's essentially the piece I need to make.

Pretty straightforward. But this one has an M9.5 x 1mm thread and fits sights like Anschutz, Feinwerkbau, Walther, etc. so it doesn't fit this IZH sight.

Found a 1" diameter 6061 aluminum rod and cut about 2" off the end.

Faced both ends.

Cut a couple shoulders.

Taking one end down to my threading diameter of approximately 8.95mm.

Added a few steps to make the transition more aesthetic.

The first step from what will be the M9 thread is 12.5mm in diameter. I took some care to get the face flat as this will bottom against the block in the diopter.

Chamfered some of the corners.

Only had a hex die in the M9 x 1.0mm thread, so I used the milling vise as a holder. Was able to cut the thread to full depth by rotating the headstock manually. The carriage wasn't locked so the entire carriage advanced into the workpiece as the thread was cut. Worked perfectly.

Made a relief cut at the base of the thread. It's darn near impossible to cut full depth threads right to the end, so this allows that 12.5mm shoulder to index and seat flat and tight to the sight.

Just a couple more views.

It's good practice to cut threads on a solid rod if possible. Bore it out after the threads are cut or there's risk of collapsing the tube while threading.

The aperture will be used with a rubber eye shade. Usually, the eye shade snaps over the front lip of the aperture for attachment. Works just fine, but I had left some extra material--mostly so the 3-jaw had something to grip while cutting the thread. Decided to leave the extra material on the rim and cut a groove for the flange on the eye shade to fit into.

Getting there.

Used a boring bar to cut a relief.

Done except for the through hole.

I flipped the piece again and drilled out the threaded end. I think I used a 13/64" bit. Wanted to leave just a thin wall of aluminum to drill the sighting hole through. The problem was, I didn't leave it thin enough. No pic of the problem, but I attempted through drilling the hole with a 1mm bit. Of course, the microscopic drill bit snapped off flush in the hole... I had a few choice words when that happened.

More later.

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