Need advice to repair polycarbonate scope body

guninhand

guninhand

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Wind blew over my Kowa scope on a tripod and it got a crack in the body that goes about 50% around the eyepiece. I clamped the crack shut and applied Lepage Marine epoxy, thinking the stuff was tough and bullet proof. The scope was working just fine until it took a small bump and the epoxy snapped along the same crack line. I'm going to grind the Lepage epoxy off and am looking for advice on better material to secure a permanent fix. I'll want something with material that will span the crack such as wire mesh, fiberglass cloth or some type of fiber as well as give a strong bond. Near as I can find, the body of the scope is polycarbonate (purchased 2002). I see the new scopes have a magnesium body. All advice welcome.

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You sure it's polycarbonate?

It takes a lot to crack that, unless there was already a defect.

Fiberglass resin sticks to polycarbonate a bit but not a super strong hold.

Have you tried looking for specific polycarbonate bonding agents?
 
I'm not sure it's polycarbonate, but that is what Kowa is using now for the scopes that don't have the magnesium bodies. With the paint removed the color of the underlying body is black.
 
I've had good luck using this stuff on projects before

http://www.loctiteproducts.com/p/13/7/epxy_plstc_s/overview/Loctite-Epoxy-Plastic-Bonder.htm

3M also has some crazy advanced, high strength tape out there...I don't know enough about that stuff to give advice, but I got the sale pitch from an engineer over lunch at work, it sounded pretty damn amazing, maybe try googling for it

are you not worried the crack has allowed the gas to escape, and will cause fogging issues?
 
Solvent is used for bonding polycarbonate. Most recommend is methylene chloride. The solvent evaporates and leaves the pieces fused together. Syringe for application, not a plastic one as it will dissolve.
 
Without a scrap piece to test on I would be leery of using the methyl chloride. I'll probably try the plastic bonder loctite with wire mesh. I don't know if the scope ever had nitrogen inside to begin with, the inside seems to be wide open when the eyepiece is removed. Used it at a match last weekend in a 50 mm all day downpour (it got bumped the next day) and got no fogging, leaks or any problems.
 
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