I need to find a router bit the will cut a "groove" with a 2.5 to 3 inch diameter. I only need the groove to be about 1/4" deep.
I saw one that was a panel cutter, with a 1.5 inch radius, but the bottom was flat and the edges curved up. I'd like an arc, not a "profile".
Anybody know where I can find this, or how I can achieve it with a router?
You have two (2) choices.
My choice would be a lathe; however, if you must use a router, find and old Craftsman Router/Crafter like the one I still have someplace.
HTH
Lew
Hmmm....that's interesting. Might work. Given I have a 10" blade on my table saw, what angle would I need to do to emulate a 3" diameter.
Not sure the finish on this would be great. Some of the wood to be shaped will be ebony.
Something like this may work. A small blade in the TS may give acceptable results.
David, note that making coves on the table saw will NOT make a consistent radiused curve. It's the curve of an ellipse.
Here's how you do it:
The depth of the cove will be the final height of the blade. The width of the cove is determined by the angle you run the board over the blade. Note that in doing this you must take very little off the cut every pass, perhaps 1/16". You must start with the blade just protruding above the table.
Anyway, back to the setup. Make yourself a jig: Take some straight 1" wwide boards, two 6" long, two 36" long, and attach them together making a rectangle using a screw in each corner. This allows you to skew the rectangle into a parallelogram.
Raise the blade to the final depth of the cove, and place th parallelogram over the blad so that the leading and trailed edge of the blade just touches the inside edge of the jig. The angle that the jig is sitting relative to the blade is the angle you have to run the board over the blade. The sharper the angle, the more out of round the cove will be.
Once you have that angle marked on your table saw (just use a pencil and draw it on), get yourself a straight edge, and clamp it on the table saw parallel to the line you just drew, spacing it properly for the stock that you're using. Put the blade just protruding, and slowly run the board over the blade. Raise it 1/16" and do it again. Slowly. Keeping doing it until the proper depth is reached. It takes a while, and you have to clean up the cut with a scraper and sandpaper.
You can also tilt the blade, which make the height of the cove offset from the center of it.
The final height will be the "radius" = 1.5" so raise the blade this high and measure across the blade.
Theoretically: If a 10" blade, the part hidden will be 8.5. Using Pythagoras [can't get away from it] half that distance across will be the square root of (10 squared - 8.5 squared). I get 5.2678269.
To get an effective total distance across of 3, you have to rotate through an angle, and its cosine will be 1.5 / 5.2678269. This makes the angle 73.5 degrees. You may need the complementry angle, 16.5 degrees.
Way past bed time here, so you'd better check it out yourself. Bear in mind you won't have a circle shape, but an ellipse. Close enough.
On 28 Feb 2005 16:29:47 -0800, the inscrutable "David Ford" spake:
Google for "cove cutting table saw", David. Essentially, it's angling the panel across the raised blade 1/16" deeper each time.
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