epoxy bonding to acrylic
Bonding anything to acrylic is difficult. It is not very receptive. Polyester should be avoided. Fuel sealants such as proseal are not menat to be used as an adhesive. They are sticky and will seal. And they do stay in place. But a strong bond from epoxy adhesives works best.
IF you choose to use the Sika adhesive, a urethane, you must read and follow the instructions exactly. I recently took a windscreen off that had been bonded using this technique. The builder was very precise and still there were significant areas where the bond was very weak and ealily pealed away.
Bonding epoxy to aluminum or acrylic requires some specific techniques as well. Everything must be very clean. I avoid strong solvents as they may interfear with the bond if not completely evaporated. I use an alcohol and water cleaner as the last wipe. Sand the acrylic with 80 to 180 grit paper, after cleaning. Sand the aluminum at the last moment. Exposed aluminum starts to oxydize in seconds, so I sand it one last time after I mix the epoxy. Then brush on a coat of resin to seal it from oxygen.
Your technique of making the part over a tape then bonding it after sanding a nice edge works well, if the part is formed well. You should dry fit it and tape the edge so your bonding adhesive that squeezes out can be easily wiped off. Then mix epoxy, and for this West is a good choice because it has a rather high flexibility and will easily absorb the minor expansion differences in materials. Use flox as a filler to make a past sort of like peanut butter or just a little thinner. Paint a coat of pure epoxy on all surfaces, spread the flox mixture and squeeze it all together. Wipe off the excess that came out. If you didn't squeeze some out, check if you used enough. Have tape ready to hold it all down while curing. I use a lot of stretch wrap for this as well. Just wrap the whole front of the plane.
Hope this helps.
Charles
