I want to make a mini router table. The base material is a type of birch plywood with 15 layers or so, 21mm thick. Well if the dictionary serves me right, it's actually called "textured coated board" in English, (Siebdruckplatte in German), i.e. birch plywood with phenol resin coating or something like that - rough on one side, very smooth on the other.

Then I have an 8mm thick, 20cm x 10m, or so, cast aluminium plate, pre-drilled to fit one of those cheap Katsu 101750 hand routers. alu plate

Now, that aluminium plate has rounded corners. I first want to route out a rectangular region (with rounded corners) to only 8mm depth, to maybe a finger's width or two of the outer circumference of the alu plate towards its centre - leaving a rim for it to rest on at 8mm depth, making it flush with the upper plywood surface. And then completely cut out the inner rectangle, so the hand router can be mounted to the plate from the underside.

How do I do this to match the rounded corners of the aluminium plate perfectly? Do I need a straight router bit with exactly the same radius as the corner, or can this be done with smaller bits?

I guess it could be done with a guide bushing (correct English name for "Kopierhülse"?) and some sort of frame with rounded corners - which has to be larger than the alu plate by exactly the same amount... no idea of how to efficiently produce such a thing.

Side note for the worried: I did also buy a quality safety switch which ensures it will stay off after the end of a power outage. (and a momentarily-on foot switch, eh... to boot!)

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    This is pretty standard template routing. It can be done with or without a guide bushing or bearing-guided bit. Ideally you'd want to use a plunge router for the job, do you have one? To get the depth right test on scrap until the base plate is exactly flush with the surface, do not just go by measurement. – Graphus Nov 15 '19 at 8:28
  • Yes I have a plunge router, but not a great one... when plunging, there is perpendicular (to plunge direction) play, I'm not sure how much but I could clearly feel it. The play is not there when the plunge depth is fixed with the screw/depth-"staircase"-wheel-thingy. It's Black+Decker 1200 something (1200Watt). I wonder what would be used as template, to get the curve radius of the alu plate perfectly matching? – user1847129 Nov 16 '19 at 2:20
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    There are many u tube tutorials here is one I suggest that you look at several youtu.be/W4utHdZO3iA here is just one – Monte Glover Nov 16 '19 at 3:57
  • Nice, thanks! And my alu plate had an installable guide bushing coming with it, and I had a suspicion that it has the same inner curve radius as the plate corners... so I layed the plate no a piece of paper, drew around the corner with a pencil, then but the bushing on the paper and eye-balled it to be aligned, drew the inner circle, and what do you know, it looks like a perfect match - 1/2" diameter router bit should fit, it looks like one of the most commonly available even on German amazon (although we are doing metric here), interesting. – user1847129 Nov 16 '19 at 13:00
  • Wanted to say something to you about the type of info you're looking for and a better way to get it. I know you're a longtime SE user but this is really not the ideal venue for you. Even if Woodworking were as busy as it was ~3-4 years ago it would still be dominated by North American posters, and quite a bit of their input and recommendations would be of limited use to Europeans (as is the case with the existing content). If you are starting from the ground up you'd be much better served joining an active forum, ideally one based in Europe if not your home country. – Graphus Nov 17 '19 at 18:54

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