Another Hare-Brained Idea...

[Tensaw]

Shit just pops in my head, so I figured I'd share. I'm sure there are reasons why this is not a good idea. Let me have it.

I find it hard to believe that straight-walled posts/bosses are actually doing much work in preventing optic movement on a pistol slide/plate. It seems like any straight-walled boss/post-hole combo that is able to be set in place by hand is, by necessity, going to have some play or slop in the fit - and the threaded fasteners end up doing all the work to secure the optic anyway.

It seems like a *tapered* boss/post for securing an optic to a slide or plate would be superior to a non-tapered boss. The taper would make up for any tolerance stacking that would be present and provide solid, positive boss-to-optic contact when tightened down.

I thought of a tapered boss interfacing with a tapered hole on the optic - but that seems like threading the needle a little too close - getting the tapers to match up and allowing the optic to fully seat on the attachment. So I'm thinking straight hole sized to match the fattest part of the taper. (Although I can see where if the hole was too small for that, you would end up with a problem.)

Is there a place for tapered bosses/posts in mounting red dots on pistols?

The other option that seems pretty viable is to size up the diameter of the threaded fasteners as large as possible (perhaps in combination with some E9000 adhesive) and just dispense with the charade of posts/bosses (like Walther tried to do).

What say ye?

[Sig_Fiend]

That's a good idea. I like where your head is at with this. I do think consistency in size/shape of the bosses would be the big difficulty.

One design I think offers some interesting possibilities is FN's 509 optic plate system. The bosses are on a separate little front plate. I think the bosses being separate and replaceable is key. Something like this would also open up the aftermarket to create plates with better fitting bosses.

One thing I wondered, which I hadn't seen discussed elsewhere, is why not use shims fore and aft? For example, some strips of tin and shears to shim the front and back of the optic if the optic cut is as loose fitting as some are. I can't see it hurting, provided it doesn't interfere with fully seating the optic. Seems like it would better distribute force so everything isn't relying solely on those little bosses and/or screws.

To your last point, I'm curious how important diameter of the screws is as opposed to amount of thread engagement? I would think thread engagement would be the more important factor.

[mmc45414]

Great idea (IMO), but would be significantly more complex to manufacture.

[Archer1440]

H&K optics plates use a combination of conventional round and diamond-shaped lugs to achieve some of this. I've always had a perfect re-zero with RMR battery changes on all my HK pistols so equipped.

[Tensaw]

That's a good idea. I like where your head is at with this. I do think consistency in size/shape of the bosses would be the big difficulty.

One thing I wondered, which I hadn't seen discussed elsewhere, is why not use shims fore and aft? For example, some strips of tin and shears to shim the front and back of the optic if the optic cut is as loose fitting as some are. I can't see it hurting, provided it doesn't interfere with fully seating the optic. Seems like it would better distribute force so everything isn't relying solely on those little bosses and/or screws.

To your last point, I'm curious how important diameter of the screws is as opposed to amount of thread engagement? I would think thread engagement would be the more important factor.

Shimming sounds kind of ghetto, but I bet a pretty elegant and standardized system could be developed. Anything that takes slack out of the system, and is stable, should increase mounting reliability. And shims enable the user to tailor the fit to the specific slide/optic combo. Given the right pack of various sized shims, you could probably find either one or two (front and back) that would do the trick - and that would be pretty sweet.

So, in my pea-brain, the screws act as de facto posts, so the bigger, the better. The thread engagement provides clamping force and threads are capable of exerting force that is very out of proportion to their "size". In other words, even small diameter threaded fasteners can generate a *lot* of clamping force. And it seems like you only really need enough clamping force to keep the relatively lightweight optic from parting ways with the slide. Adding additional clamping force via thread engagement likely becomes irrelevant after a certain point. That said, still, the more thread engagement the better, if for no other reason than more threads with some sort of Loc-tite are less likely to loosen. I could definitely be wrong in my thinking on diameter versus engagement.

[Tensaw]

Great idea (IMO), but would be significantly more complex to manufacture.

I'm sure you are correct. Maybe take a regular cylindrical post that has been machined to a taper and press fit the cylindrical part into a hole in the slide that leaves the tapered part exposed? Not ideal but should hold up?

[Tensaw]

H&K optics plates use a combination of conventional round and diamond-shaped lugs to achieve some of this. I've always had a perfect re-zero with RMR battery changes on all my HK pistols so equipped.

Interesting. So probably the diamond shape is easier/quicker and so less expensive to machine. But it still sort of locates the optic front-to-back and side-to-side. Less surface area mating up as opposed to a true taper, but yeah, I get it...

[mmc45414]

I'm sure you are correct. Maybe take a regular cylindrical post that has been machined to a taper and press fit the cylindrical part into a hole in the slide that leaves the tapered part exposed? Not ideal but should hold up?

Might be a great approach, because you could use harder pins. For a while a buddy and I were eyeballing our slides wondering if you could just mill with a conventional machine and press dowel pins into holes, but the more we thought about it the better it looked to just send it off to a company all setup to chuck it in a CNC machine and push a button.

[OlongJohnson]

That's not how it's done. A taper fit adds a requirement to control z-axis tolerance to the requirement to control x and y. Dowel pins are a thing and work very well when needed.

[Drogo Bunce]

I'll raise your hare-brained idea: How about skim bedding the RDS fore-and-aft? Just like skim bedding a rifle action: Generously apply release agent to the slide, especially the threaded holes, apply a thin layer of epoxy/bedding compound to the front and rear vertical surfaces of the optics cut, install the RDS, and clean up any excess. Since optics cuts are generally pretty close to the optics, you'll end up with a very thin layer of bedding affixed to the optic, but enough that it will relieve the mounting screws of handling recoil stresses. I'd probably try it with JB Paste to ensure that nothing flows where it shouldn't. If you want to move the optic to another slide, a little sanding/filing to remove the bedding compound and you are ready to go.