Double Rabbet

Had a quick try of the twin rebate bit (in this case the one for the thin glass (3mm))

Picture Framing Bit

Took it in a couple of passes, but the bit didn’t have any problem anyway, and the finish was good.  Particularly given this is meant for the back of the picture anyway.

Twin Rebate

The principle behind the bit is to cut two rebates at once.  The first (narrower) one is for the glass, the second is for the backing.  You could certainly do this with two bits, or two fence positions, or two different sized bearings, but if the intention is to make a few frames, getting to do it all at once saves a lot of effort, and ensures consistency from job to job