Concave profile groove cutter needed
 

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?

David Ford wrote:
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.

snip

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

You can do this to a flat board by running at an angle across a low blade.
Wilson
"David Ford" wrote in message
oups.com...
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?

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.

http://www.binkyswoodworking.com/CoveMouldingTip.htm

David Ford wrote:
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.

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.

On 28 Feb 2005 18:49:38 -0800, "David Ford"
wrote:

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.

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:

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?

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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