Total noob: jigs, bushings, calculations ...
Ok, this is something I have never bothered with before ... my router came with what I assume you 'd call a bushing,
attaches to the router base, pokes out of the bottom for a router bit to stick through and provide guidance along
the edge of a jig.
I want to cut a rebate around the holes in the top of my assembly bench so I can get a friend to do some 3d printed
plugs for it, to stop things from falling into the holes.
I am completely baffled by how to calculate anything here.
So I decided to resort to empirical data:
I have a bushing with an outside diameter of 18mm.
I am using a 1/2" router bit.
I cut a 32mm hole into a scrap of plywood to use as jig for an experiment.
The hole I ended up cutting below the jig turns out to have a diameter of 28mm.
Which happens to be more or less exactly what I needed. But: I have no idea
how that number came to pass.
12.7mm inside 18mm inside 32mm gives a result of 28.
Would the size of the router bit change this ? One would intuit it should, but ...
If anyone has a link to a website that explains this, or a youtube video, I'd be grateful.
Or .. explain it here ;-)