Merry Christmas, all!
I'm about to attempt cutting a cove on the table saw, for a
picture frame moulding. This will be my first attempt at this.
I have a nice hunk of 8/4 poplar 8 inches wide that I'll be cutting.
Once the cove is done, I will rip the board down the middle to yield two
lengths of moulding. The board is flat sawn, and the arc of the growth
rings is fairly symmetric. Should I cut the cove with the arc up (so the
cove will follow the rings) or with the arc down (so the cove will cut
through the rings)?
I imagine that cutting so the cove follows the growth rings would
result in a stronger moulding. But I'm not sure about that and other
issues, such as wood movement.
Easy to do, a bit fussy to set up, but safe, fun, and satisfying ...
providing you think it all out carefully beforehand and have enough stock on
hand for some test passes.
IME, probably the only thing you'll gain by grain orientation with the flat
sawn stock on a TS cove cut is maybe a bit more smoothness, and slightly
less clean up, by cutting "downhill" instead of "uphill" (IOW, looking at
the edge of your board, I would generally tend orient it to make a right to
left pass over the blade with the grain sloping to the right).
... but in actual practice I really don't think you gain too much either
way, including the issue of "strength" in the final product. At least that's
been my experience.
How much "strength" to you need in a molding anyway? I would go with a
couple of test cuts to see which makes the best/most pleasing grain pattern
for your project, and not worry too much about strength.
As a side note, the TS cove cut can end in some unusual grain effects ...
take a look at the corner cabinet project on the following link and notice
the "half moon" effect of the medullary rays in the cove cut on the quarter
sawn crown molding in the last couple of pictures:
On Mon, 24 Dec 2007 17:00:44 -0600, Swingman wrote:
I think whatever happens (short of not cutting it straight, or the whole
thing turning to dust after its cut), the result will be OK. This ain't
furniture I'm making (not yet, anyway). I figure a picture frame will be
a great learning exercise.
OK, thanks. I hadn't thought about the grain going lengthwise. So you're
suggesting I look at this in the same way I'd approach jointing, going
in the direction that will minimize tearout?
Perhaps I didn't state my question clearly. Looking at the end of the
board, I can see the growth rings. The rings are symmetric. (i.e., if I
come off the centerline of the board at a 90 degree angle, that line
would go through the center of the tree.) This means the arc of the cove
will either be concentric with the growth rings if I have the "open"
face of the board down when I make the cut, or it will intersect them if
I have the "open" face pointing up.
Something to consider when I'm making something out of a nicer wood than
poplar. I intend to paint this piece. But once I've got a little
experience with this under my belt, I can see myself making some
mouldings out of figured maple.
Very nice, Swing. I always enjoy looking at your work. We don't share
the same style (I lean heavily toward modern/contemporary), but you
provide plenty of inspiration nonetheless.
Thanks for your input, very much appreciated.
I built a fireplace mantle with a 5" radius 90 degree cove. If you
place the arc of the growth rings up so the cove follows the growth
rings, you will get only a few grain rays spaced far apart, sort of
like rotary cut plywood. If you put the arc of the growth rings down
so you cut through more rings, you'll get a grain pattern more like
dimensioned lumber. If you can find a way to hide it, glue a piece of
plywood to the back surface of your cove. That will stabilize the
cove where it gets thin. Be prepared to do a lot of hand sanding to
smooth out the cove surface. Even with a fairly thick blade, it tends
to chatter a little. It just wasn't made to take that side load. I
took a scrap piece of the cove I had cut, dammed up each end and
poured it full of plaster of paris. Then the plaster is used as a
custom-made sanding block to smooth out the cove.
Good Luck with your project, and Merry Christmas.
"Every man is my superior in that I can learn from him." - Thomas
None of the passes cut more than 1/8 or so of material. All of the
last 10 or so passes were at 1/16" or less. The final pass was
probably 1/64" or so, then a cleanup pass without moving the blade at
But you have to understand that I had several things working against
me. I was moving the wood directly in line with the axis of rotation
to get the widest cove possible from a ten inch blade. Narrower coves
would move at an angle to the blade, which should cause less chatter.
The piece being shaped was over 8 feet long and it had a very slight
bow in it that had to be pressed flat to get a consistent depth of
cut. And the cove was so deep that at the final cut, a full quarter
of the blade's circumference was in contact with the wood. A good
deal of feed pressure was required. After the operation on the table
saw, the cove surface was about as rough as rough-sawn lumber from the
sawmill. I spent about an hour with each sandpaper grit, starting
with 60 grit and ending with 220. In the end, it turned out
beautiful, but it was a lot of work. I'd do it again.
"Even an old blind hog finds an acorn every now and then."
No, my best blade is a Freud Glue Line Rip Blade. I use it for
everything. I considered trying one of several other blades I have,
but I would have had to move my guides I had clamped down in order to
access the blade. I didn't want to risk losing the alignment I
already had started, so I kept going.
"There's a difference between doing things right and doing the right
How do you intend to finish the molding? Poplar is a very stable wood but it
doesn't offer much in the way of "grain". If you're planning to paint the
molding, grain orientation is a moot point.
The earlier suggestion about gluing a plywood backer board for added strength
may seem like a good idea but you'd likely experience problems due to the
differential in how the plywood and poplar would react to seasonal changes in
humidity. If you feel the need to add a backer board for additional strength,
use a piece of wood with the same response to seasonal changes.
On Tue, 25 Dec 2007 21:40:13 GMT, toolman946 via CraftKB.com wrote:
Yep, I did say poplar. I probably should have mentioned that I'm going
to paint it. I didn't think anyone would start discussing grain effects.
I am concerned with proper technique, and strength of the finished
I'll probably have enough material behind the cove (at least 3/4 inch)
to assure it will be strong enough. This isn't for a crown moulding, its
for a picture frame. As I mentioned in my original post, I'm going to
rip the piece down the center once the cove is cut, to create a picture
frame. After ripping, the thinnest part will be the inside of the frame.
Thanks to all for your suggestions!
On Tue, 25 Dec 2007 07:27:55 -0800 (PST), DonkeyHody wrote:
I'm not really concerned with the appearance of the grain, as this is
poplar. I'm going to paint it. Sorry that I wasn't explicit about that.
It won't be very thin, its going to be a relatively shallow cove in 8/4
material. After I rip it, I need to cut a rabbet in the back on the
thinner edge to mount the picture. So I'll need enough thickness there
to do the mounting.
Yeah, that part I was wondering about. I have a curved scraper that I
was planning to use. The custom sanding block is a neat idea, too.
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