I am fairly new at routing and making a router table. Which is better for cutting a 3/4" dado slot x 3/8" deep in a 3/4" laminated plywood top - using a 3/4" dado stack on my table saw - or 3/4" straight router bit?
I'd do it with a router with a 3/4 bit that will make a flat cut on the bottom. Clamp the straight edge in place so it doesn't move between passes. With a full sized router, I would make three passes, each an eighth inch deeper. Mark the top of the router base with an arrow and keep that running against the straight edge to make sure the router doesn't rotate and possibly make a slightly curved cut. If the slot is just too tight, you can use some sandpaper wrapped around a stick to widen it just a bit. Probably a good idea to make a test cut in some scrap and see if your track fits. My own preference would be to use a mortising bit that makes a nice smooth and flat bottom.
Follow @Rebelwork & @DesertRatTom's advice and you will be very happy with the results, although I prefer a very careful repositioning of the fence and an additional pass, if the bit doesn't cut quite wide enough for your desired result.
Always make a test cut in scrap to be certain that it will work for you and several light passes at increasing depths is always better. Also make sure that the bit is pulling the router toward the fence by moving the router in the correct direction. With one direction of feed the router will pull away from the fence and in the other direction the router will pull toward the fence. Looking down at the bit rotation when it's cutting, the blade of the bit should be cutting against the feed direction and then curving out away from the side that the fence it on. Again, a test cut will assure that you do this correctly.
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