Router bit question

I recently used a 1/2" shafted flush trim bit with bearings and 2" of carbide spiral cutting blades to trim some roofing substrate (T&G and 1/2" ply) flush with the underlying 2x8" stringers while making a cut-out for skylights. The result turned out beautiful.

What would you think would be the amount of material a 1/2" bit should reasonably take safely and without ruining the bit? Obviously, the smaller the bite the better but would taking a 1" bite be too much for the router and the life of the bit?

As a hard and fast rule, your depth of cut should not exceed HALF the diameter of the cutter bit.

1" Cutter=½" cut depth
½ Cutter=¼ cut depth
¼ Cutter=1/8 cutting depth etc

You did not ask for this, but this might help you out as well...


Bit Diameter and Maximum Speed

Up to 1 inch
24,000 rpm

Up to 2 inches
18,000 rpm

Up to 2-1/2 inches
16,000 rpm

Up to 3-1/2 inches
12,000 rpm

For what you did you had no way to take small bites because you were using what was underneath as you guide. It is the same method used in manufactured housing around window and door holes for years. And used to cut the opening after an undermount sink has been installed in a solid surface counter top. You already know you are exceeding what the bit manufacturer considers safe. I would say if you are going to do this thick template operation you be very aware of the feel of you router and stop when it starts to labor so you don't bend or snap the bit as it dull or gets loaded up with gunk that causes over heating.

I remember reading someone's idea of a rule of thumb; the area removed should be no more than 3/8" x 3/8" or something around there. This would mean your 1" tall cut should be a bit less than 1/4" deep per pass. The bearing doesn't have to rest against your guide right away. Work away the material in a few passes ending up with a final pass with the bearing in contact. HTH.