So you epoxy it, but lo and behold, the stress of your gun firing breaks the joint. Your epoxy is not too weak, but your
Case 1: Longshot bolt to barrel. This longshot has an AR-15 spring added to the stock spring, and shoots 90+ feet. The bolt is epoxied to the brass barrel, and has held for over two months with no loosening.
Case 2: Crossbow coupler. This crossbow has a Defender T3 Arrow-shooter spring in its plunger, and is shown with its bungees. There is a coupler identical to the one on the end epoxied directly to the plunger tube, with a short length of CPVC extending to the visible coupler. At least 3 months now, and no loosening or coming off.
Case 3: Big bad bow coupler. This coupler, when glued incorrectly, WAS, in fact, shot off by the force of the gun. It was an "experiment" of sorts; now, glued correctly, it is rock-solid. (Looks ugly because red FBR got on it while it was still sticky)
Case 4, no picture: Nitefinder barrels. Same problem as BBB - they get shot off if glued incorrectly or weakly. The ones I've glued correctly have no such troubles.
Let's take a nitefinder air restrictor as our example (because it's what I had on hand).
You've cut out the middle, and are ready to attach a barrel of some sort, be it brass, PVC, CPVC, PETG, crayola, or a coupler. If you were to put some epoxy on there, and stick the barrel in place, you would be WRONG.
Epoxy is strong, but it has to have something to hold onto. Smooth plastic and a smooth barrel give it nothing to hold onto, so the epoxy is going to loose its grip on one or both pieces when put under stress. You need to give it something to hold onto. So grab some sandpaper, and sand every surface that will have glue on it (including whatever barrel or coupler you'll be using), until it looks more like this:
In some cases, this may not be enough. Case #3 (BBB) was one of those cases. I needed MORE, LARGER grooves and cuts for the epoxy to sink into and hold onto. So I took a dremel and cut little grooves into the area that was going to have epoxy on it. In the BBB's, case, this was 8 grooves around the outside of the front orange piece at different angles, and 8 grooves around the raised inner ring.
Here, for the Nitefinder air restrictor, I've just cut four on the raised inner ring. It is hard to see, but they are at approximately the 1, 4, 7, and 10 o'clock positions around the ring.
Sandpaper must be applied to ALL surfaces the glue will touch, if possible. The cutting of grooves should only be done in areas where it will not seriously change the overall "geography" of the surface - I cut several small grooves in the large, flat, orange area of the BBB's front orange piece, such that the coupler could still sit on there and be aligned straight. Small grooves, not large gouges.
Now, when your epoxy hardens, it will have lots of little footholds on both surfaces that were glued, and will be much less likely to detach under pressure.
Also, the more surface area that is covered in epoxy, the stronger your bonds will be. Take a look at Case #3 (BBB). There is epoxy not just where the coupler meets the gun, but along the outside of the coupler, spilling over the entire surface of the orange piece - more area for the epoxy to hold onto.
In case #1, the bottom of the bolt and the top of the brass barrel were sanded.
In case #2, the front of the crossbow plunger tube and the base and sides of the coupler were sanded. Grooves were cut into the front of the crossbow plunger tube.
In case #3, the sides of the coupler, base of the coupler, and entire orange surface were sanded, and 16 total grooves cut into the orange piece.
For my nitefinders, I sand the back and sides of the barrel/coupler, the entire front surface of the air restrictor piece, and cut 8 grooves (4 on inner ring, 4 on flat side of AR).
NO gun that I've glued this way has EVER had a problem with epoxy weakening. The plastic holding one of my nitefinders' plunger tubes in place weakened and broke before the barrel came off.
Hope this helps.
Edit: I use Loctite 1-minute epoxy for most of my gluing needs.
That image will probably break sometime in the future.
Edited by Gengar003, 22 June 2007 - 10:31 PM.