Well, T, that depends on a lot of things... the sizes of router bits you have, the size of template guides you have, etc. There are a couple of things you can do.
First, you could start by trying to find a bit with the same radius as your plate. Then you could simply run some straight sticks in a rectangle the same dimension as your baseplate adding the difference in the offset between the bit and the outside edge of the template. Then cut into your tabletop the depth of your baseplate thickness. I would recommend cutting a piece of the same material that you use for your template and placing it in the field of your cut out so the router will not tip away from your template, undercutting your rabbet and possibly making your hole oversize. After this is done, you could use your jigsaw to cut the rest of the hole out, leaving the rabbet, or make another smaller template and cut all the way thru your top with several passes.
I have made a cut out once using the router base for a guide, I just added 3 inches in each direction (the difference between the edge of the router and the cutter. It worked pretty well, but router bases themselves are not as accurate as a properly centered guide bushing.
If you want to make an inlay type pattern, I think it would be more work than you really need to do.
First, you could start by trying to find a bit with the same radius as your plate. Then you could simply run some straight sticks in a rectangle the same dimension as your baseplate adding the difference in the offset between the bit and the outside edge of the template. Then cut into your tabletop the depth of your baseplate thickness. I would recommend cutting a piece of the same material that you use for your template and placing it in the field of your cut out so the router will not tip away from your template, undercutting your rabbet and possibly making your hole oversize. After this is done, you could use your jigsaw to cut the rest of the hole out, leaving the rabbet, or make another smaller template and cut all the way thru your top with several passes.
I have made a cut out once using the router base for a guide, I just added 3 inches in each direction (the difference between the edge of the router and the cutter. It worked pretty well, but router bases themselves are not as accurate as a properly centered guide bushing.
If you want to make an inlay type pattern, I think it would be more work than you really need to do.
