Training for Compression

I've got a project that involves endlessly slapping a perfect edge/arete with one hand and am curious how to best train my shoulders for something like that?  It would be ideal to build a compression simulator/plywood box out of plywood and just endlessly slap up and down it with both hands, but I'd rather figure out exactly what exercises to do so that I can save on the plywood and don't have to store it.  Any suggestions?

Cable machine flys at a gym - try various heights and angles (relative to your own shoulder) and various grips. If you get lucky, your gym's cables will have carabiners on the ends and you can trade grips out to something squared off (chunk of 2"x4" w/sling around it?) or even a squareish piece of rock with a bolt drilled into it. 

Chest flys on the rings are the way to go in my opinion. Perfect for building strength and stability in wide positions. Personally, I like doing them completely horizontal from a pushup position with a pause at the bottom of each rep. If they get too easy you can up the difficulty with a weight vest.

-Will

The plywood box is fine but I think the other two's suggestions to do flys is the way to go. I also prefer the rings but do both. With cables or rings you can control the movement and the resistance better. This equates to more training on the muscles and less stress on the joints, which will be important later in your climbing career. Don't forget to do some training on your hamstrings and flexibility work, leg power and flexibility is equally if not more important in those types of problems I've found. Also, its been a month since you posted, did you send? What worked what didn't?

Thanks for all the beta!  I almost sent on TR (it's a bit of a headpoint) before the summer closed out the climbing season there.  I'll for sure be back for it in the Fall.  I didn't actually start any specific training for it as conditions weren't great and I knew I wasn't going to be leading it this spring.  I'll probably be doing a bunch of flys this summer and can post up in the fall when I get back to it to see if it helped or not.