Anybody have any definitive guidance on how to kerf bend lumber? I need to bend a piece of 2×8 treated syp on a 16′ radius. My guess is 3/4″ deeep kerfs about 1″ apart.
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There's a formula....may help. You should have stock longer than the radius required. Make two kerfs....the distance between is the radius of the curve....depth is optional (it should be deep enough to make the curve, but not deep enough to telegraph through....judgement call.Two thirds of the way through might be a starting point though).
What you do is clamp one end of the board...outside the kerf (on the extra length of the board)....to a table. Then you lift the other end (by the extra stock on that end) until the two kerfs close up. Measure the distance from the bottom of the board to the table....at the second kerf mark... and that's the spacing between kerfs. Takes some fine tuning, but that gets you in the ballpark. If you cut the kerfs on an angle, you can do spiral curves.
Disclaimer: I've never done 16' radius though. Don't know how well this works on something that size. Guess you have to find an 18' table too.
cabinetmaker/college instructor. Cape Breton, N.S
Ok, here's the results. First one is a mostly dry 2x8 #2 treated syp, bent around a 16 ft radius. Kerfs were 3/4" deep and 1-1/2" apart. It bent easily. "Mostly dry" means that it sat out in the south Texas sun for two weeks.
Second one is a very wet 2x8 #2 treated syp bent around a 15 inch radius. Kerfs were 1" deep and 1/2" apart. It was a bit of a struggle. The tips of the kerfs did not touch, but the depth should have been increased to 1-1/4".
The bend looks fine but how are you going to hide the kerfs, and is the syp going to do anything when it dries out more in the sun?
Not trying to rain on your deck just wondering.
Doug
Go on over to HD and pick one out of the pile......pre formed. I've seen them.
I don't know what to do about the kerfs. Maybe explain them as part of the design? Fill the top 1/2" with epoxy or wood filler? Suggestions welcome. There weren't any visible signs of stress, so I'm hoping it just dries and doesn't go bad. I had a board delivered in the original shipment that I was planning to use, but when I got to it I discovered that it had a real bad case of wane edge that couldn't be hidden, so I went to HD (not my regular supplier, but they were open late on Saturday, and close to the project) and pulled a clean board from the pile. Man was it heavy. Took two of us to get it to the truck, and when I screwed it in place, water oozed out.