Thanks for the thoughts, David. I am not sure I agree with your analysis re: One Time spackle. I have done a ton of painting houses in summers and as a contractor for the 15 years after teaching. I have found that spackle remains pretty durable especially with a coat of epoxy on it. I realize your concern is the reaction between spackle and foam.
I know when I was removing some excess spackle from the foam it was holding very well. As for time, I can not comment. But realizing my flying skills, the shelf life of many of my planes is rather short. But, the areas where there is spackle, those can be sanded and can remove most of the One Time. I have to work on my foam wing cutting. I have been using laminate for my templates and when I pull the wire across the template, I often feel some resistance. Wouldn't plywood be even more troublesome? Or do you wax the top of the template? Grabbing at straws here!
One neat technique I just used to cut out a wheel well for the retracts: I made up a small U shaped piece of wire and attatched it to a piece of lite ply with some 4-40 screws and washers (much like you would make a lot of small foam cutters). I then cut a balsa template a bit undersized from the U piece of wire, turned on the cutter and scribed the wire around the balsa. That gave me a circular trough about 1/4" wide. I then used another wire tool but wider and cut out the remaining foam core. Actually worked pretty good. I suspect there is an easier way, but this one kind of evolved. I then cut a 1/32" lite ply and lined the bottom of the well. Tomorrow I will soak a piece of 1/16" balsa in water with a bit of ammonia and wrap it around a similar size cup as the well and then epoxy it in. Paint it black. The retract has been fitted with the wheel and everything seems lined up.
Got the chin block glued in place and will do some shaping tomorrow. So, how was your day?
Tim