While building a large sanding block I needed to glue together pairs of triangles. Came up with this jig for insuring that the parts stay aligned. The base is just a single piece of foam board. The edge, or fence on two sides, is a double piece of foam board with a little overlap. That is glued to the base. So, put glue on one triangle then put the other triangle on top of the first. Slide them around a bit to spread the glue out. Temporarily push the triangles into the fence until alignment takes place. Then remove the parts to avoid gluing them to the jig permanently. Hold them together until you are certain that the glue is set, maybe 30-45 seconds.