You could start here: M4 Router Be Gone (installed the spindle) - Hardware / Sled - Maslow CNC Forums
In short, instead of using a router, buy an actual spindle and use that instead.
There is some more effort required, probably including doing your own mains voltage wiring up, which requires obvious caution … 
But the rewards are significant.
There are some awesome alternatives from my approach that really facilitate rapid swaps of whatever the M4 is pushing around.