I've been using a router plane primarily to trim tenons. It makes fitting tenons easy and fast -- without it, fitting tenons would take me much longer. I'm sure there are members here who are much more skilled at making tenons with a saw and chisel, but this is what works for me.
I don't have a shoulder plane or rabbet block plane or any other plane that would work for tenons. With the router plane, it's easy to ensure that the tenon is centered, and parallel to the faces -- things that are not guaranteed if you use a shoulder plane or rabbet plane. Keep in mind, though, that if your tenon is angled, the router plane will be useless on the angled sides.
Using a router plane to trim a tenon really doesn't require much skill, and that's fine with me, given the time I have available for woodworking.
I debated for a long while whether a large router plane was worth it, but then I decided to just make one. Derek Cohen has a great article about making one here:
https://www.inthewoodshop.com/ShopMa...uterPlane.html
His is very nice, but you can go much simpler, and make one in a couple of hours.
Hardware needed: an eye bolt, washer, wing nut, and a Veritas 1/2" router plane blade. Total cost: about $20. I used a piece of scrap walnut for the body, cut off a strip and put it on top rear.
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Dimensions are about 8x3.5 inches, and the strip on top is about 1 inch wide. The hole is 1.5 inches in diameter. As router planes go, it is very wide, so that I never have to worry about it hanging out too far off the edge of a workpiece and losing parallel.
This is a closer look at the parts cut out for the blade and eye bolt. I cut out the mortise for the eye bolt with a narrow chisel.
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Fine adjustment can be done this way: loosen the nut, then move the router so the edge of the blade is slightly beyond the edge of the workpiece, then tighten the nut. The bottom of the blade is angled, so the farther you move the blade past the edge of the tenon, the lower the blade will go. Here it is with the blade resting slightly past the edge of a tenon.
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Another way to do fine adjustment is to rest the blade on the tenon, loosen the nut, push down on the blade a bit, then tighten the nut. This may not make much sense until you've actually done it, this will move the blade down ever so slightly, due to play in the parts and compression in the wood workpiece.