Hi folks:
I read an article somewhere about bending plywood through a technique called “kerf bending” — making multiple cuts right up to the top layer from behind, with the kerf of the saw blade equally spaced the length of the plywood, which then allows it to be bent into curves. I can’t find the article in my library. Can anyone tell me the basics of what needs to be done, especially the spacing for the kerfs?
Thanks
Josh Gressel
Replies
Kerf bending is more typical for carpentry, particularly in the stair building trades. It's avaialble in Kerfcore MDF. Typically it's done in solid wood and the spacing and depth varies depending on wood species. Improperly done it will break or show flat spots. It's not used in furniture making. Laminate or steam bending is the norm in furniture. Wacky bd plywood is a much better option or birch bending ply for furniture. You will find more on kerf bending in BreakTime or Fine Home Building or stair making books.
There are better ways to achieve a smoothly curved wood surface, but kerfing is an option. The depth and spacing of the kerfs (I've always used standard blade widths of 1/8") is best determined by experiment and trial using the stock you wish to use. You can do this with either solid lumber or hardwood faced plywood. Once the kerfs are cut, the inner core material doesn't matter.
The method has been used in all possible applications.
Josh,
Even kerf spacing and depth is critical for a smooth bend. Experiment with the same material to see if the curve you want can be attained.Brace or otherwise support the backside if possible.
Paul
Works best if the grain wraps around the curve. Vertical grain often snaps if too tight!
7/8ths depth of kerf.
spacing depends on radius.
Expert since 10 am.
Hello Adirhu,
I buy special bending ply and that works better and looks smoother.
This ply has a thin core layer and the outside layers run in the 4 foot direction, not the 8 ',
this gives a very bendeble and smooth face.
Cheerio Bernhard.
I've successfully bent hardwoods ,never tried plywood. I would think that you would kerf down to the depth of the last lamination, 1/16" at the least thickness. If the bend is not severe you can kerf to a thicker dimension. The kerfs have to be exactly the same centers. I index the the kerfs with a hardwood slice the thickness of the saw blade.Tablesaw is best if the stock can be easily manuvered. I have used a hand circular saw and a router as alternatives.The distance between kerfs depends on the radius.The closer the kerfs the better the bend ,no matter what the radius.Usually I wind up with 1/4" inbtween each kerf.This is about 1/2" center to center if he blade is 1/8" thick.
If the bend is tight and you have any chance of breaking the board,then take this next step.
Get a small bottle of Downy Water Softner.You need a container of some sort and hot or boiling water.The container has to be large enough for the stock to submerge in. I have used a bath tub a couple of times. Fill the container with water,add downy and stir a bit.Place the stock in the water and keep it sumerged until the water is tepid.
Remove the stock and make your bend. I have bent 9" radiuss for custom stair risers,although not plywood.
mike
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