Adhesives for aluminum to carbon fiber attachment?

AR/M4 AR General Discussion
1

I am revisiting a problem I encountered a few months ago: I have only a tiny amount of clearance between a rail section (for a BUIS front sight) Mlok nut and a gas block. The handguard is carbon fiber, and I have only one spot for the BUIS to go. After basic assembly, there was contact between the Mlok screw and the block. Even after shortening the screw, there is less than the thickness of a 3x5 card between the gas block and the nut, and barrel whip/flux/flex/vibration/whatever continues to cause contact. Go ahead and laugh at me, but it’s a situation I would rather not have.

Currently, I am using only the front Mlok screw and nut. I can solve the problem by leaving off the rear screw and nut, but I would rather have another point of attachment. Swapping out gas blocks would probably not solve the problem. (The difference between a relatively tall block, like the Geissele, and a short one, like the BCM, is only about 0.012".) I could grind off a chunk of the gas block, buy a different barrel (with a shorter gas system), or buy a longer handguard.

Or, because I am strange and stubborn, I could try an adhesive to make the front sight base a “bomb proof” installation. I consider a front sight base to be a fairly permanent addition, so that doesn’t bother me. After scouring the web for ideas, at websites used by bicyclists, hobbyists, archers, etc., I have collected (and offer for your amusement) only a few suggestions. Evidently, aluminum and carbon fiber to not work well together with most glues. In this case, the front sight base is a specialty low profile item, so a Magpul plastic base will not work. They are:

Specialty adhesives: used by the aerospace industry; obscure, expensive, and difficult to find.

Fiberglass strips as a bridge: both aluminum and carbon fiber would rather attach to fiberglass via epoxies than to each other.

High temp epoxies: even if you get a good bond with a fiberglass strip or a specialty epoxy, most glues start to fail at about 350 degrees F; assembly would be sitting right over the gas block, so maybe a crappy hold for a high temp epoxy is better than a good hold that will fail at high heat.

Chewing gum: No kidding; it came from a Brit archery guy who had to attach aluminum points to carbon fiber shafts; easy to apply and replace as necessary.

Any other more specific suggestions?

2

HYSOL 9340

3

JB Weld, FAQ does NOT list either material in their list of what their product does not work with.

https://www.jbweld.com/faqs[IMG]https://uploads.tapatalk-cdn.com/20220725/36497182e32e59090aac91ba56c5002c.jpg[/IMG]

4

Why can’t you get a longer rail section with three attachment screws and use two of them?

5

.45fan:

Yeah, JB Weld is pretty special stuff. It’s worked well for me a bunch of times, but has not ALWAYS worked as expected. I have a tube of high temp (450 deg. F sustained, 500 deg. F intermittent) JB Weld epoxy putty on my bench (which I have never used before). If I can’t find anything better, or run out of chewing gum, that’s going to be my first choice. :cool:

6

I’ve used JB Weld on a lot of shit not on the package.

If this isn’t a ringing endorsement, I don’t know what is:
“I have used J-B Weld for more than five years on my farm equipment and I have decided that it is even better than bailing wire.” -A Kansas farmer said,

7

Not laughing, the struggle is real. Sometimes I hate M-Lok and considering ditching it and going back to Pic.

8

Todd.K:

Thanks, but, been there, tried that, I am ordering the t-shirt. The problem is when using the three bolt Mlok version, both the rearward nuts come in contact with the gas block. It’s a pretty unfortunate spacing circumstance that I did not anticipate when ordering this group of parts. I have also tried placing the Mlok rail (both two and three bolt versions) behind the gas block (i.e., closer to the receiver than the gas block), but the clearance with the gas tube is not very good, and I would rather have the block smacking into the nut than the gas tube. Also, it’s just not where I want the rail section to go.

9

Titsonritz:

You can’t really say that a Kansas farmer doesn’t know what he is talking about when it comes to repairs. I have actually given some thought to the misapplication of the word " fix" for “repair”. When you fix something, you are making it rigid in a particular place; it only moves it it is part of another mechanism that moves. In the days when most machines were mechanical, a repair was replacing the handle, or reattaching the harrow blade, or reinstalling the exhaust hose. That was “fixing”, which eventually morphed into “repair”.

10

Maybe you can find some of these.

https://www.midwayusa.com/product/1003260586

11

titsonritz:

Just try finding a Centurion C4 pic rail these days.

12

Todd.K:

I think I remember these, and wondering what they were good for. Now I know. It would be a bit of trouble, but I might make some of these for future projects. Thanks for the idea.

13

They were for the old Troy handguards with Vtac slots

14

Still available with a sling stud and plastic washer.

https://www.midwayusa.com/product/1003261228

15

I would try a local body shop that deals in high end cars…there are adhesives out there that would bond to both materials…Lord Fusor and 3M are two of them…

16

Centurion currently has a 9" and 12" in stock.

17

Never heard of Fusor. I am going to have to check them out.

18

Thanks for that info. I am just coming off a bunch of builds and I have yet to shoot any of them. (One of them did not pass a no go check; the manufacturer said to shoot it anyway. We shall see.) I usually get the 10" anyway, but I have to plan for a new project before I get to looking for handguards.

19

Why don’t you put put a proper tube on it. Sounds like you are chasseing you tail trying to make incompatible parts play together with glue.

20

GH41:

That’s a fair question. Here’s an answer:

This project was based on an idea that a “utility carbine” could be put together that would have about 90% of the capabilities of the overloaded duty carbines I’ve seen around, including some NV lasers and/or illuminators, but weigh as little as you could reasonably expect. The list of stuff that some people think is required on a duty carbine is pretty daunting. It used to be sufficient to say you have an optic, a light, and a sling and you were good. I ran into one guy doing military sales who had a carbine with a LPVO, a MAWL, a PEQ, offset RDS, another light … damn near busted a gut trying to pick it up. I started to plan a carbine that shaved off ounces where I could, and use fixed power optics instead of a LPVO, but be made from off the shelf parts. This is not “Project Featherweight”.

At any rate, I was not aware that Wilson Combat’s new proprietary gas system for their (lighter, but not lightweight Ranger) barrel would cause my plans to go awry. And, until the last few weeks, a Streamline carbon fiber handguard that would work (the 15" version) was made of unobtainium. It is usable, but longer than I want, and another $350 on the budget. If I continue down this road, I see these choices:

  1. Buy the 15" handguard
  2. Bombproof the problem front sight rail on the 13" handguard (using one Mlok attachment and glue)
  3. Not use a BUIS
  4. Change the barrel to a midlength (if I can find the right profile)
  5. Change the handguard (probably something heavier)
  6. Start from scratch

This is one of four uppers that might work for this project. It was also the first I put together, and I have learned from my mistakes. Any suggestions are welcome.