how to cut perfect insert from a template?

[hayaku]

hi all,

i have an mft template that has a series of 37.3mm circles every 96mm on center.  the manufacturer's instructions are to use a 30mm router bushing with a 1/2" bit inside this 37.3mm hole template to cut the desired 20mm holes.  problem is too much human error is introduced running the router around following the bushing on the template. (slight angle tipping, not getting perfect circles)

i want to cut a 37.3mm plug to fit exactly inside these holes in the template.  from that plug, i'll drill a 30mm hole in the center with a forstner bit creating a ring (37.3mm OD and 30mm ID) and then i can use this new bushing ring around the factory bushing with a 20mm boring bit to keep everything perfectly centered.

i have pattern bits to make a copy of the hole, but i don't know how to go about making the opposite plug.  any tips would be greatly appreciated!!!

thanks

 

[hayaku]

i think i figured out my own problem...

to make a circle insert that fits my circle template perfect, i'm planning on this:

copy the circle template to a new piece of wood.
then use a 1/2" rabbet bit to expand the template circle and then a flush trim bit to fully expand the circle by 1/2" outside diameter all around.

now i have a larger template by 1" diameter or 1/2" radius.
using this new template, i can use a 5/8" bushing with a 3/8" cutter that gives me a cut of 1/2" from outside bushing to max edge of the cutter. theoretically giving me a circle the exact size of the originally template.

since festool doesn't make a 5/8" bushing, i'm going to have to get a porter cable bushing set to try this out.