I'm on Sketchup 2017. I've chosen not to upgrade past that because I have some plugins that I was told (actually, by you, I think) that they wouldn't work in newer versions. I'll try the cross section and follow me. Thanks.

I tried drawing a cylinder the right size and then using Follow Me to put in the groove, but apparently I "cant extrude on a curved face."
Stumped.

Forgot to put the second / in- now all is good.

Is it correct that one takes the Pro trial and then after 30 days can licence Make?

Thanks I'll try that

Dave-
I seem to have it working, appreciate your assistance.
We talked about the change from SU Make to SU Free- if I heard you correctly, you said that Make would be continued on offer, but not updated after 2017- did I hear you correctly? Because when I go onto SU.com, I don't see any reference to Make anywhere. Could you clarify? thanx

No, it's not a component.
I deleted the cutter after copying it so I could open the side for editing and then paste the cutter back in place.
Was that the wrong way?

Argh!!!
Made the box. Cut the dovetails.
Marked the curve and made the cutter oversize.
Copy to clipboard. Delete the cutter.
Hide the ends (didn't bother to rotate but I've done it.)
Open a side for editing. Edit-> Paste in Place. Everything now within Edit box.
Edit-> Intersect faces with Selection
"No intersections found between selection set
and the rest of the model"

Tried again- same thing

Probably a simple answer- usually is

Well, I'm trying it without much success-
Drew the boards (just 2 adjacent with dovetails at this point) and made the cutter- seems ok
Think I got the cutter copied ok to the clipboard- paste in place seems to work
But if I select the cutter I lose that selection when I open the component for editing.
And if I have the component open I get an error that there are no intersections in the model.
Guess maybe I wasn't paying as good attention as I thought I was....

Dave-
Thanks again for your help.
In looking at my notes, it's unclear if I make the cutter a component.