This is a special 3/4" diameter router bit with a pin inserted in the center which makes it very easy to route gains for tracks using 1/4" braid. Note the center pin is designed to ride in a slot cut using another router bit (i.e. the center pin on this bit will NOT route/cut the slot). The router bit has a 1/4" diameter shaft.
We start with a high-quality, Freud (brand) double-fluted carbide router bit. Next, our machine shop permanently inserts a 1/8" steel pin in the exact center of the bit. The center pin rides in the track's slot which keeps the router bit perfectly centered at all times. The result is both "gains" are the same width around the entire layout - even in the corners (refer to Figure 1 below).
In contrast, using a router base with a 2 pin (leading/trailing) setup and a standard router bit will result in gains with varying widths in the corners. One gain will be a little too narrow, the other gain a little too wide - the greater the distance between the pins and the tighter the corner radius, the more pronounced the differences will be (refer to Figure 2 below). This will be further exagerated if the pins are undersized.
IMPORTANT: These router bits require a slot which is at least 1/4" (6.35mm) deep to work properly. The center pin in the special router bit is NOT designed to be bottomed out in the slot to set your gain depth (doing so will typically result in gains that are MUCH too deep). The center pin's SOLE purpose is to guide the bit. The gain depth should be set using a scrap piece of MDF and a short piece of the actual braid you plan to install. Make some test cuts (slot and gains) using the scrap MDF to achieve the correct gain depth BEFORE routing the actual gains in your track. For more information about setting the bit cutting depth for the track gains, please see the how-to article entitled, "Track Braiding Overview".
IMPORTANT: When routing gains for a banked turn, route the gains when the track section is still flat (i.e. BEFORE pulling the track section together to form the banked turn). If this is not possible, you will need to use a compact router with the smallest base possible (you may need to custom fabricate one) to minimize variations of gain depth when the router base passes over the banking.