Usually with a 20A circuit it will work out OK. Miter saw and vacuum current will all be on one circuit with most of those switches. You can roll your own with a current sense relay if you really need to, but it's usually not necessary.I’m want to build myself a router table and/or mitre saw bench, may combine them in one, still planning. But what I would like to do is use my shop vac as a dust collector (probably with a separator). I see some ready-to -buy current sensing switches , some actually called vacuum switches I think. Am I better off just buying one of those or components to build one in the cabinet. Any gotchas or things to watch out for (total load of course… what else)?
At the miter saw the vacuum starts the second I start the saw.An intermittent vacuum on a miter saw won't do much. By the time the vac comes alive and the air is flowing you will be done with your cut. Better off to start the vac, then make the cut. Leave the vac on for another few seconds. Many of the switches have that off delay feature.
On the router since you start the router before entering the cut, there will be enough time for the vac to ramp up.
And there are blast gates that will let you switch between hoses w/o having to disconnect.
Maybe a foot switch or an oversized push-on/push-off switch for the vac at the edge of the table. One that you can bump with your hip would be nice if your hands are ******* holding the work and machine. I could see the use of a paddle switch working opposite of how they normally do. But I have never seen one.