Assembling the feet are probably the single most time consuming parts of building R2-D2, however they are not difficult to do, just require some patience.
1.
The first step is to clean up the resin around the small lip on the top of the foot base to have a place to glue the shell to. Then you will need to trim the styrene shell so that it fits nicely on the resin base.
When the parts are cleaned up, you will want to place them as best as possible, tape them in place and with a couple of daps of super glue, you will want to secure it in place. I don't use the super glue for permanancy, but it works great for holding it down.
Once the glue has set, take some Liquid Nail, and fill in the gap on the inside of the foot. THis is a cheap and easy filler, not to mention a extrodinarily tough glue. Let it sit over night.
2.
Next you will need to cut out the trench section in the foot. Make sure the trench will be wide enough when you are done to accomodate the ankle.
You should be able to see a faint line in the styrene giving you an idea where to cut the trench. Once the trench holes are, I take a scrap of styrene, place it in the trench and trace a pattern onto it, cut it out, repeat for both sides, the glue a bottom on it.
3. and 4.
All thats left is adding the detail and the clean up. Once you attach the detail pieces you will want to go to through, bondo up the seams and clean it all up.
It's a bit of work, but well worth it in the end.
Tip......
When you are done, you can flip the foot over and lay a couple of layers of fiberglass into the foot shell for support. I have done that with my feet and they hold at least 100 pounds each foot.