Kerfing plywood. Cone shape

[Jeff Todd]

ok.. I have never used this technique and was wondering a few things..How much does it effect the strength of the plywood? I know that is a loaded question. but just generally if were to want to make like a coffee table with plywood base kerfed in a "u" shape is that just kinda out of the question because of strength issues.. it has to be stronger than just using 1/16-1/8 plywood right?? if the kerfs were vertical I would have no questions. What about filling kerfs with epoxy than bending it to add strength back also the ability to hold its shape.. what about bending it in a cone shape? making 1/4 spaced on one side of sheet and like 3/4 on top? i am looking to make a few "corner tables" in a kids room and was going to make them 1/4 rounds. and put a "1/4 cone" shape on the bottom to add strenght like a leg. kinda hard to explain picture a 30" radius 1/4 round. in a corner. under it a "1/4 cone" that tapers from about 15"r at the top to 5"r on the bottom about 30" tall.

thanks in advance JT

[Peter Quinn]

I'd be looking at 3MM plywood bent lamination, or a build up of bending ply for the core with 1/8" skins. The lamination technique is a Lot stronger, less likely to be segmented, not even sure you could successfully kerf bend a conical shape unless you taper the kerfs to adjust for the change in radius, that wood take some figuring. Otherwise you are over bending at one end or under bending at the other. Kerf bends are stronger if you can fill the kerfs with thickened epoxy or similar, but in my mind they are never the best way to do anything, occasionally more economical if there is a substrate or frame to which you can attach he curves, but often just fast and dirty.

there is also some kerf board MDF product meant for bending, you bend one in, one out, or maybe 3 layers, it's around 3/8" thickness IIR and the kerfs are tightly spaced, makes a decent paint grade curve with no segmented look if the radius isn't too tight.

[Kevin Jenness]

I would second Peter's advice. Nominal 3/8" lauan bending ply for building up thickness (min. 6" radius, rough surface and inconsistent thickness), 1/8" birch or poplar bending ply for smooth surfacing (min. 3" radius), prekerfed neat flex or kerfcore for moderate bends and less strength. Don't bother kerfing it yourself unless you have a cnc router available. You can wrap the bending ply or kerfcore around a conical shape.

[Jim Matthews]

You'll need to layout your shape with some kind of frisket or layout paper.

Once you're happy with the shape, apply it to whatever ply or Kerf board you've chosen.
I don't know of any that can be set tighter than a 12" radius.

I've tried Kerf board, but it's REALLY heavy when filled.
I used Durham's Rock Hard putty, other fillers may be lighter.

Don't go cheap on bending plywood.
"Wacky wood" has given me poor results.

http://www.columbiaforestproducts.co...nding-plywood/

[Kevin Jenness]

In regard to minimum radius of bending ply, we have a serpentine bench seat project in the shop now with a minimum radius of 3 7/16"". The bending forms were made with 3/8" lauan wacky wood- i think that was forced to its limit, but it worked. The lauan was faced with p-lam to get a smooth waxable surface, and the actual panel substrate was made with 6 layers of 1/8" bending poplar and epoxy with zero springback. The form skins and the panels were all done in a vacuum press, that is, not with crushing force.