TO KERF OR NOT TO KERF...IS THIS A STUPID QUESTION?

[Micro469]

Just thinking out loud... When building the frame for the tear, I was thinking of kerfing the 1x2 as it goes around the front curve of the roofline. I know that many have used plywood to cut the curve, others have used blocks (Len), and others have glued pieces together and routed out the curve ( Steve). I tried it with a piece of scrap laying around, kerfing it every inch, then soaking it in hot water for a while. I cut the kerfs 3/4 the thickness of the wood, and when I bent it, it bent fairly easily. The only problem I found was that kerfing it every inch gave it a fairly tight bend. Is ther any Mathimatical equation that wil tell me how far apart to make the kerfs for a certain radius? Or is this a dumb idea and not structurally sound. Being in a wall sandwich and being used to hold up the inner roof AKA Steve Frederick style, I cant see why it won't work. I just want to cut out the least amount of wood that I have to.

[madjack]

John, there is no reason this wouldn't work that I know of...while there may be a formula(bound to be one) I have no idea of where it would be found...
madjack

[Miriam C.]

OK, Here ya go
(oops) first draw your curve on a pattern.

Take the outside measurement and divide into inches.
Take the inside measurement and divide into inches.
Take the difference and divide by the width of the blade. That will tell you how many cuts. Or you could talk to someone who has a clue how to do real math This is how I do guesstamates on fabric. Might work.
Just teasing ya. There is a formula I'm sure.

Miriam

[tonyj]

Miriam,
That's exactly the procedure I used when I kerfed the insulation panels and the method worked almost flawlessly. It was simple to figure, too.

Micro,
I decided for the time and effort involved, it was about as fast to use solid wood pieces and scribe to the curves between the spars--it also added the advantage that I knew I wouldn't be stapling into kerfed out spaces or spaces in between blocks.

[Todah Tear]

Enlighten me please. What is "kerfing"?

Todah

[Bandit]

kerf (kûrf)
n.
A groove or notch made by a cutting tool, such as a saw or an ax.
The width of a groove made by a cutting tool.
[Middle English, from Old English cyrf, a cutting.]

A kerf is made to shrink the inside radius of a bend or to stretch the outside radius of a bend and still keep the material flat.

[Todah Tear]

Thanks Bandit, you've expanded my vocabulary

Todah

[Micro469]

Miriam... That makes sense, Thanks.

Tony..."almost flawlessly"?........Almost????

[Miriam C.]

Hum. Guess I should have put that in metric.

Micro,
Before you rule out kerfing, Len used blocks and filler to make his curves. He probably planned where his screws would go.

Miriam

[Micro469]

Miriam, I saw the way Len did it. When I did my sample piece, I kerfed it 3/4 Of the width of the wood. I'll try another at 1/2 the width and soak it in hot water for a while and see how it bends. Since it's only on the bend radius, I really don't have to screw it down much, as long as I screw it before and after. The glue should hold it down, (I hope).

[tk]

from "Nick Engler's Weekend Projects Plus," p. 7:

To find the maximum kerf spacing for a bend, cut a scrap as thick as the wood you want to bend and about a foot longer than the radius of the bend. Cut a kerf in the board about 6 inches from the end. Measure and mark the length of the radius out from the kerf. Clamp the end of the board to your workbench. Lift up on the other end until the kerf closes. The distance between the bench and the board at the radius is the maximum kerf spacing."

Tom

[Miriam C.]

Thanks Tom
That one took me a few minutes to process but I think I got it.

Micro If its kerfed I don't think you should have to wet it. Maybe, I'll try tomorrow and see.

Miriam

Ut oh How deep do you make the cuts? Anyone????

[IndyTom]

Tom,

Thanks for posting that. I knew I had read something like that before, but I could not remember where. I have that book but I had not gotten to that one yet in my search for the answer.

Nick Engler is awesome. You can have Norm, I would take advice from Nick any day.

Tom

[cracker39]

I cut my framing to follow the roof line from pieces of 3/4" x 4". Depending on the amount of curve, they were from 18" to about 4' long. The curve was cut with a bandsaw, then the spar notches cut out with the bandsaw. These pieces were glued/screwed to the 1/4" plywood sides and attached to the ends of the vertical framing pieces with corrugated fasterners. I made sure that a piece overlapped each plywood joint for strength.

[josephhanson]

I kerfed all the rounded parts of my trailer then glued with P/L glue and clamped until set up. You don't need to wet the wood, it just bends.
Joe