Dimensional section view of the LM-4 Lap Mold
The success of our previous LM-1, LM-2, and LM-3 models led us to develop the latest in our family of lap molds, the LM-4. This "Perfect Pitch" lap mold allows you to quickly make picture-perfect pitch laps for mirrors from 4" to 40" and above, with a single lap mold. The LM-4 is molded using a premium, platinum cure silicone, which is completely inert, allowing it to work with any pitch, including synthetics, with no interaction between the lap mold and the pitch. It combines the smaller facets of our LM-2, the larger mold dimensions of our LM-1, and the pyramid facet angles of the LM-3. These pyramidal facets improve the separation of the mold from the lap, and also extend the pitch lap service life. As the pitch squares begin to close in during use, the facet walls slowly steepen to 90 degrees, requiring trimming only after they have moved well beyond 90 degrees and threaten to contact each other. The 10 degree pyramid angle is also present in the outer edges of the lap mold; when used to make laps for large mirrors in "tiling" mode, this butts precisely against a previously poured pitch square column, assuring a perfect, seamless transition between lap sections.
Note that this lap mold is unlike older open-mesh "doormat" molds such as the one Edmund's used to sell. The "Perfect Pitch" lap mold has a continuous floor, which lets you lay it directly upon your mirror without risk of pitch sticking to the mirror. It also conforms directly to the radius of the primary mirror, reducing hot pressing to a minimum. A dimensional drawing of the LM-4 lap mold is shown below, together with the relative positions of the mirror, tool, and pitch.