Templates for Cutting Round Corners
From contributor D:
Wouldn't 2 or 3 passes with a template and a router produce a better result?
From contributor P:
Each of the above replies has a piece of the process. For nuts-on accurate yet square-edged radius, do the following:
1) Choose your radius, for instance the coffee can mentioned above.
2) Trace the radius on one corner of a 12" X 12" square piece of 1/2" MDF.
3) Rough cut the radius with a jigsaw to about 1/16" outside the line.
4) Finish to the line. Easiest is a stationary edge sander. My second choice would not be a belt sander; I would clamp the piece vertically in a vise and fair out the curve with a sanding belt – cut - holding each end in one hand and sanding directly down on the cut with a sawing motion until the cutline is fair and transitions smoothly to the straight edges of the square piece. Making this template is the most important part of the process. Spend some time and make it nice! (Actually smooth is more important here than exactly round...)
4) Hold the template on the ply corner with the two adjacent straight edges flush with the plywood edges and draw the radius on all the corners that you want to shape.
5) Again, rough-cut the radii close to the line.
6) Place the template as mentioned above with the straight edges again exactly flush with the plywood edges.
7) Clamp on the two opposite corners of the template away from the radius. Make sure the template is clamped firmly and hasn't moved.
8) Rout to the template with a straight, top mount bearing bit. For 3/4" ply, I would use a 1/2" shank spiral upcut bit. Make sure the bearing lines up properly with the template and the cutters will engage the entire piece of ply. Start the router on one of the straight edges away from the radius and cut firmly around the corner until you hear (and feel) the router stop cutting the plywood on the adjacent straight edge. If you cut close enough to the line in step 5, one pass should be sufficient.
9) If necessary (but it shouldn't be), dress with a sanding block before you remove the template.
Here's another tip. I generally stick a piece of 150 grit sandpaper to the bottoms of my routing jigs with spray adhesive - a little more insurance that they won't move.
From contributor J:
Same as contributor P, but I also laminate the pattern face of the template. Bridges any minor inconsistencies (fill any gaps between back of laminate and face of template with wood filler) and prevents the template from wearing out.
From contributor B:
I just dropped off a job for 11 countertops, all with radii. It breaks my heart to hear they'll be using coffee cans!
From contributor O:
Woodworkers Supply sells some little cheap plastic templates for concave and convex corners. I used to use assorted cans, sockets, or whatever that was round until I bought these jigs. For a couple bucks a piece, I think I'm ahead by not scrounging around my shop looking for something with the right radius.
From contributor A:
Making a template for router finishing of the radius is the right idea. If you have access to a band saw, you can cut almost any diameter radius almost perfectly using a circle cutter attachment or simply drilling a hole through the template at the desired radius and driving a nail through this hole into a holding block. Snug the assembly to the blade at the start of the cut, and swing the template through the blade to produce a just about perfect radius.
Figure out your most commonly-used radii, and reproduce four of them on a 12"x12" template. 1/4" or 1/2" MDF work well as templates. Apply laminate to one side and the edge all around, 120 grit sandpaper to the other side, mark the radii on the template, and you'll have a useful template for years of use (until somebody else decides they need it more than you do). If your band saw has a relatively fine tooth blade, laminate the side first, then cut the radii. No band saw? (What?!) You can get the same result by rough cutting the radii with a jig saw, and a fixed disc sander or a disc sander plate installed on your table saw. Use the same method as above using a hole and nail to a mounting plate clamped to the sander or saw table at the proper radius.
In use, place the desired radius on the material to be cut, draw the radius, rough cut outside the line with a jig saw, clamp the template in place, and finish the edge with a top bearing 1/2" pattern bit.
From contributor R:
When I fabricated Corian, I used this interlocking phenolic straight edge system made by the guy in the building next to mine. They are like 4" wide pieces of 9mm phenolic that dovetail together to provide straight edges the lock into perfect radius corners. Just jig saw off the extra wood, leaving 1/16" or so as mentioned earlier. A flush trim bit and a collet and you're good to go. They used to have a web site, but was able to find them in Google Local: A.M.P.S. STRAIGHTEDGE SYSTEM, Hudson, MA
From contributor O:
I was also going to mention that the templates I use are just for marking. They won't work for flush trimming. One thing I like about them is that they are colored, so you can kind of visualize what radius will look best.
From contributor T:
First off, plywood is alright for some small sink tops, but 3/4" PB bought in 25x120 pieces is a much better substrate. If you are going to build up the top to 1 1/2", use the plywood there (DW steam). Having done probably 100 miles of p-lam tops through the years, most of the guys have the right idea. But why fool with jigs? Make the radius on the build up - 6"x6" scrap and a $2 compass for the 1st one, cut on bandsaw, finish shape on 6x48/disk sander, make dozens all radii for stock, nail on as buildup, rout with top mnt bearing. (You build the tops upside down first, edge trim B/S, file, flip over.) Don't use H20-based contact! Even with a pinch roller, I have not had good luck. Stick to solvent base. Get a HD (rigid) trimmer with the base mnt bearing guide for the best final trimming.
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