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Old 09-09-2017, 03:53 PM
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How-To:Tech Sights Windage Knob Upgrade



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I say "upgrade" because I think such a practical sight system should be finger-adjustable. I haven't posted any projects in a while, but I recently got such good results from some experimentation that I thought others might like to see, so here's my technique for adding an A2 windage knob to Tech Sights. Rapidex knobs seem to be hard to find, these days.

You will need to get these parts. One is an A2 sight knob. The other is a weird black thing from your hardware store. It's got a ID of 7/32", and a thickness of about 1/32" or a bit less. Pretty much any washer with those dimensions will work, also, but I liked this thingy because it hides well


Next, you'll need some little tiny files. I found that a triangular diamond file and a tapered round file worked well. The pictured 1/8" round file was barely used, and probably not needed.


Put the knob in a vise, backside up as shown. Here I show how a cruddy, old, rusty clamp-on vice is good enough. This is kitchen table level work. Make sure to pad the vice jaws to avoid damaging the fragile finish on the knob. Cut a line down the center of the back of the knob as shown using an edge of the triangular file. I just use hand and eye, but if you want to make some kind of fancy jig, that's cool, too. Oh, and take care not to breathe or ingest aluminum dust - it's bad, m'kay? Clean things up afterwards.


The triangular file bites into the metal nicely and helps establish a nice, straight cut, but then, the tapered round file is used to deepen the grooves. Be careful not to cut too deeply, and try to use the thinner tip of the round file - 1/8" diameter round file is too big, and makes too wide a channel. You can always remove more material if needed, much harder to put it back


Repeat to create a radial pattern, resetting the knob in the vice as you go. Pictured cuts should be considered an example of maximum.


Next, use a 1/16" punch to drift out the roll pin holding the A1 windage drum on you rear sight. Don't lose the pin, and once it's removed, hold the sight drum down carefully as you slide your punch out - the drum is under pressure from the detent and spring, and while mine didn't seem to want to launch, better safe than sorry


This it what's underneath: A detent pin and curved spring washer. In the bottom of the detent hole is also a spring. Might as well remove all three parts, since they'll likely fall out anyway when you flip the sight over later.


Chuck the detent pin in a hand drill and polish the tip that contacts the sight drum. I used 600, then 1000 grit. Don't go crazy here, it doesn't take much, you're just trying to break the sharp contours of the tip's profile and make it round.


Next, you'll need to remove the windage crossbolt from the sight by unscrewing it, add the little black thingy underneath the head, and reinstall. Yes, the peep assembly will come loose in this process, so be mindful of how it sits in the assembly before taking things apart. When you're done, it should look like this:


Reassemble the whole sight using your modified A2 drum in place of the A1 piece. Don't forget to put the little spring washer under the drum, and of course, the detent spring and newly rounded detent pin go in their proper spot. Getting the knob on while resisting the pressure of the detent pin and also lining up the holes in the shaft and knob can be tricky. Line them up visually before pressing the knob on, and then slide a 1/16" rod or punch in to hold things together while you tap in the roll pin. Make sure the threaded windage cross-bolt is fully seated and the head is not sticking out the other side even a tiny bit, or the holes for the roll pin won't be able to line up. Be patient, you can do it


This is what it should look like when done. The reason for the little washer thingy we added is to take up some of the gap between the A2 knob and the sight base - the clearance is different than the A1 drum, and it's a bit much for the little spring washer to handle on it's own. You might be thinking that the detent has enough force to take up that slop, and you'd be mostly right, but that uneven pressure causes the knob to sit crooked and feel sloppy. Shimming under the head of the windage crossbolt by about 1/32" seems to be a nice solution, and leaves enough play on the other side that the knob doesn't drag, and the spring washer compresses nice and tight. The spring washer and detent combined put plenty of pressure to keep the windage setting stable under centerfire recoil. Oh, and on that note, I have had the roll pin work loose on certain Tech Sights assemblies, namely the AK, wherein the sight base itself is part of the recoil system and takes quite a pounding. In fact, I devised this whole hack because an A1 drum flew right off an unmodified Tech Sight rear assembly on an AK Tempted to loctite :/


So, if you haven't already figured it out, the radial cuts we made with the file serve as the receptacles for the detent pin, giving us positive click adjustments: eight settings per rotation. I suppose you could do less or more, if you want And no, the detent hole in the A2 drum doesn't seem to be a problem; the tip of the detent pin should skate right past without finding it Adjustment may be stiff as first, as the channels we cut have sharp edges, so I like to oil everything up well and work the peep back and forth across the entire windage range 3-4 times, letting the detent pin wear a little track into and out of the radial grooves. This will create some aluminum crud to be flushed out, but then the track stabilizes, and the rounding of the detent pin not only helps it feel smoother, it doesn't cut into the aluminum excessively.

I experimented with unmodified detent pins and radial grooves cut with a triangular file, but it locked far too tightly. The same can happen if you cut the grooves too deeply with your file and the pin goes into them too far. In turn, if the grooves are cut too wide (wider than the rounded tip of the detent pin), the pin doesn't lock into place firmly enough, and you get some slop as the tip of the pin moves in the channel. Less is more. Note that even if you do everything perfectly, there can be a tiny bit of slop at each "click position", because the detent pin itself can move a little in its hole...but it's pretty darn tight if you file the grooves correctly. Use my pics as an indication of maximum depth, and consider putting everything together for a test before you file too far. Yes, it can be a pain to take it all apart and reassemble it more than once, but if you go too far, all your effort will be wasted.

An interesting alternative I tried is to remove the spring washer entirely, shim the head of the crossbolt enough that there is almost virtually gap on the detent side (1/32"+a hair, YMMV), and replace the A1 detent pin with an A2 detent ball bearing. Holy heck, is that some easy-turning smoothness, perfect for little fingers or low-recoil rimfire applications. Ultimately, I decided that I wanted the firmer hold on the detent points created by the friction of the original A1 detent pin, but the feel of the ball bearing clicks sure made me smile

Questions welcome
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  #2  
Old 09-09-2017, 05:03 PM
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I put a Rapidex knob on mine several years back. It already had ten ball detents. I had to file down the boss in the center because the Tech is not made the same as Mil-Spec sights like the Nodak, which accepted the Rapidex without modifications. On the both the Tech and Nodak, I flipped the plunger over and contoured the pin to resemble a ball shape, using the bottom side so I could reverse it and restore the original adjuster wheel if so desired. It's a great improvement over original.
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Old 09-09-2017, 07:53 PM
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Nice! I probably would have gone that route as well, if I could ever find any rapidex drums in stock anywhere This mod was borne of that lack (and the A1 drum disappearing from the rifle during a shooting session), and I figured I might not be the only one, so I thought I would share in case anyone else wants to try I thought about flipping the detent pin as well, might be a good experiment to try. A larger bearing area might be nice.
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  #4  
Old 09-10-2017, 03:15 PM
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You did a good job with the photos and describing the procedure, a worthy effort. Keep it up.
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