We have all seen many jigs to put in a dado for shelft(s) in a book case or cabinets.
Most have two boards that hold the router in place,from moving from side to side, like the one Norm made on his show most will jam when you push the router up the tack .
This one will Not jam because in runs on the brass guide that is true unlike most base plates on the router base.
They stamp out the base plate and it's not a true machined part.
This jig will take that error out and you will get a true slot,right on the button every time.
You can make a quick guide to use with this jig with 1/2" MDF and a dado slot and 3/4" plywood cut off stock to hold the spacer guide from one slot to the other.
In that way you will get a slot every 12" or what every you want it to be.
We all know that plywood is not a true size that's to say that 3/4" plywood is 23/32" and we need to use the right bit size to get it to fit right,same with 1/2" and 1/4" plywood.
I try and make most of the book cases or cabinets 11 3/4" wide so I can put the slot in both at the same time and then split the 24" plywood and end up with both sides that are dead on.
Then use a face frame to cover the plywood ends and to hold the shelf sq. and add support to the shelf ,with a T & G bits you can put a slot in the shelf and the face frame.
T & G bits ,set it to cut 1/4" deep on all slots.
You can also use the T & G bits to make a 1/4" spline that's 7/16" wide and it's dead on 1/4" thick and it will work great to hold the shelf and face frame as one.
I have put a link or two for the bits you need to use and the bits you need to make the jig and the brass guide, It true that Harbor Freight has a better price on the brass guide set, but it will not come with the 1" O.D. one you need to use for 3/4" plywood and this jig.
Grizzly.com® -- Home
for the bits and brass guide kit.
Plywood bits H5559 and H5558 at a good price
1" bit 1/2" shank C1017 also a good price
Brass Guide Set H3134 it's bit high in price BUT has the 1" guide you need.
If you need more info please ask
Plus some other snapshots of jigs, see below ▼
NOTE*** drawing below/plans
Router Forums - View Single Post - Dado Jig
Snapshots are out of order sorry about that, out of my control.