Makeing Plywood curve using kerf cuts.

Im making a 1/2 of cylinder 3' outside diamter - 2'7" inside diameter to be used as a base of a table Im making.
I tried using bending ply w/ veneer - but I can get the color to match w/ what is on the rest of the project (1/2" oak ply) So im going to use the 1/2" oak ply - kerf cut it and bend it around the staves (or ribs or what ever you want to call them) Is there some general rule of thumb on how far about the kerf cuts want to be and how deep?
Thanks Rob
You can reply to me at r_b_v at v_e_r_z_e_r_a doht c_o_m
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Distance between cuts is dependent of how much you want to bend the piece. I make the depth of my cuts about 1/8" shy of all the way through. The best is to try this on a scrap piece the same length and start with the cuts about 1" apart. If the piece does not bend enough add cuts between the previous cuts. For the smoothest curve you do not want the kerf gaps to close on the back side. If the kerf gaps close on the back side the front side may end up looking like a curve made up of a series of short straight lines.
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veneer. attach i to the bending ply. much easier than kerfing and all that. just a thought
skeez
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Assuming a 1/8" kerf, you will need 5/(1/8)@ cuts as an absolute minimum.
Jay

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I just did something similar for a piece that I am making for my daughter, but my radius was quite a bit tighter than the 3 feet you are doing. My radius was only 10" and I was using the cheapest plywood that Home Depot had since it would all be covered.
Before I went to HD, though, I had a scrap piece of 1/2" (and it was 1/2") mahogany plywood that I used to see if this could even be done and still look ok. I cut a few kerfs that were about 1/2" apart, then a few that were only about 3/8" apart, and finally some that were only 1/4" apart. I did as a previous poster suggested and made the depth 3/8" which would leave about 1/8" thickness. This was not deep enough and the veneer started to crack. I recut all the kerfs leaving only about 1/16" (barely more than the mahogany veneer itself), and the pieces of plywood where the kerfs were 3/8" and 1/4" apart wrapped arount the curve very nicely. The part where the kerfs were 1/2" apart looked a little bit like narrow strips. You had to look for it and I could have used that spacing in this particular project, but I went with the 3/8".
When I got the cheap plywood from Home Depot, it was the "new" 3/8" which is actually 11/32". I went with the thinner plywood because I was thinking that I needed to keep the weight down. I am going to have to lug this piece up a flight of stairs when I get it done. But this stuff was so dry and so brittle that it still cracked a little with the kerfs as deep as I dared make them without cutting all the way through the wood. I happened to see the front of the piece with the sun shining through the back and you can really see the kerfs.
So what I am trying to say with all these words is that if there is a general rule, it would have to be modified for many factors including the thickness of the piece you are kerfing, probably it's moisture content, type of wood (and veneer), radius of the bend, thickness of the kerf (I was using a standard width blade so mine were 1/8" wide), and there are probably more factors. If you do this often, you will probably come up with your own rule of thumb and then you can share it with us.
As for your case with a 3' diameter, I would think that the kerfs placed 1/2" apart, and leaving 1/8" thickness should be good. A trial piece will tell you fer sure, dude.
Sorry for being so wordy.
Wayne

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proposed a theory ......and in reply I say!:
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To actually remove enough wood in a half circle of 1/2' ply, you need pi / 2 * 8 = 1.6" inches or so of wood removed by the kerfs. But because that's only 13 * 1/8" cuts or so that will make a lot of straight bits. So if you are cutting 1/8" cuts, basically I would practice on scrap first, starting with that number and going between until it's smooth.
Cut nearly through. Make sure you are working on a very flat, stable surface, as you are working right on the edge of _cutting_ right through. You want the ply to be held down flat on a flat surface.

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Make a kerf in the center of the board to within about an eighth inch of the face veneer.
Clamp one of the edges that is parallel to the kerf, to the bench, with the open side of the kerf up.
Make a mark at a point equal to the length of the radius away from the kerf.
Lift the board up until the kerf just closes. Measure the distance from the bench top to the top of the board, at the point indicating the length of the radius.
This gives you the spacing between kerfs.
Regards, Tom.
"People funny. Life a funny thing." Sonny Liston
Thomas J.Watson - Cabinetmaker (ret.) tjwatson1ATcomcastDOTnet (real email) http://home.comcast.net/~tjwatson1
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You could try using 1/16" or 1/8" solid oak sheets and glue them up on a form. Seems to work well for Norm. I'm gonna try this soon with some white mahogany.
Bob

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It seems like your project would be much stronger if you laminated 1/8" or maybe 1/4" strips together around a form.
If you go with the kerf-cut method, you might want to steam or otherwise moisten the outside veneer to keep it from cracking.

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