I wanted to knurl the front of the tube before I reduced the wall thickness too much. Figured I'd better do it now before doing any more drilling--knurling thin tubes is fraught with crushable danger. I impressed a diamond-pattern knurl into the end.
Next up was getting a taper in front of the thread. The taper will act as clearance from the sight base.
Set up the compound on the crosslide and cut at 60 degrees.
With light cuts, aluminum cutting fluid and a sharp knife, I got a halfway decent finish on the taper.
Quick test fit to check those clearances.
Passes, but I noticed that the sight is almost completely out of right windage adjustment and the tube won't install if the sight is buried to the right--there is a small block inside the sight body with a too-small window. The alignment problem is caused by the narrow dovetail on the IZH. Fixing both problems will require disassembly of the sight--I'll get to it in the next blog post.
Back to the tube, it's helpful to remove as much from the center as possible. This prevents the interior from getting into your sight picture. Opened up the base end.
Gave the body a light pass just to clean everything up and get a defined border at the knurl.
Turned it around once again and progressively drilled it to 3/8". Took care to not drill into the taper or I would have drilled it in half.
A small boring bar finishes the hole. Didn't measure, just removed metal until it was thinned out as much as deemed practical.
Another quick test fit.
I'll paint it to match the front anti-glare tube. They don't quite match, so it looks like I'll have to knurl the front tube after all.
Sight tear down and some milling is up next.
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