The wing tube centerline is drawn on the bench, I laid down a strip of marking tape and drawn the centerline on it so I can easily see it. Templates are made from 1/8 plywood, both hole are the same height above the work bench. I use a hole saw to cut the templates and sand the id for smooth surface, there's also a saw cut from the top of the template down to the hole for wire to past. I don't waste to much time on templates since the hole surface isn't a big deal, maybe sand with 220 grit. Templates are aligned and screwed down to the working surface, the straight edge is clamped down to the bench that aligns the foam cores. The holes will be cut in both cores simultaneously so the everything lines up. Notice the filler pieces sticking out of the foam blocks, these will be installed in the blocks while cutting the airfoil shape, I will be vacuum bagging the wing so all holes must be filled. The small section will be glued in after the outer wing socket plates and sockets are installed.
The blocks are positioned and weighted down to ensure a straight wing. Please be sure to use 1 pound virgin Expanded Bead Polystyrene for your cores. Typical insulation grade foam may contain regound beads which is difficult to cut with the hotwire and achieve acceptable results. I order my foam from the local foam manufacturer, it's blown to order.
I make a small bow that fits on the outside of the templates, heat the bow, cut through the saw cuts down to the bottom of the template, work the bow around the template using caution when it's near the saw cut. I find it easier to remove the first half moon pieces before cutting the other side, once it's loose, it just gets in the way. Be careful not to move the blocks at this point.