I cut with a 3-wing bits.
Less than .100 kerf.
Your mileage might vary.
My taper machine works on gravity.
The spindle is parallel to the taper groove. No springs.
On that note, if you are still using a router , you might wanna consider VFD and air cooled spindle .
They are so cheap now on Ebay, you are suffering for saving a few dollars .
Routers are so much noisier have so much run-out.
Reserve them for roughing and coning .
https://www.ebay.com/itm/1-5KW-110V...h=item41f0f13ef6:g:2QsAAOSwr~tbxxlq:rk:6:pf:0
110V vfd with a speed knob . That is ridiculously cheap.
Air cooled spindles can be had for $150 or less.