Heat-resistant tubing is supplied with your cutter bit to keep the bearing from riding up the shank. You can also use the tubing below the bit to raise the bearing to a height that will ride against your template should this become necessary, but always take up the gap between the bearing and collet with more tubing. Be sure to cut the ends squarely. Keep at least 1/2" of shank in the collet at all times. It may also be necessary to raise the entire template with shims to make contact with the bearing for shallow passes. It is always better to make several shallow passes as opposed to fewer deep passes.
Once the cavity is deep enough to allow the bearing to ride against the wall of the cavity, the template can be removed for additional depth if necessary.
We recommend that you use the 1/2" bit for the bulk of the work, and the 3/8" for touching up the corners only. The bearing on the 3/8" bit is very delicate, and will not hold up to the work necessary for the entire cavity.
Do not use the ball bearing cutters without wearing eye protection!