Curves

[Tom Bender]

There was a post in the Neander forum about how to transfer and cut a curve. Plenty of suitable advice was given about tools but there is more to the subject. Before worrying about how to cut the wood, start with a satisfying curve on paper. This can be from a plan but if not then you are on a challenging and rewarding path. Over years and many pieces your eye will mature and you will like different materials, styles, balance and of course different curves. Part of a circle is ok at first but later will seem simplistic. Part of an ellipse is much more elegant and owing to it's flexibility will fit much better. Sometimes part of a parabola or hyperbola is better. These constructs can form a basis but you will want to fair them to the piece at hand. Combine bits of curves into ogees and cloud lifts. Enjoy the journey

[Yonak Hawkins]

I have found a CAD program is very helpful in designing and implementing custom curves. Access to a plotter to make templates makes cutting large, extended or complex curves quite easy, short of access to a CNC machine.

[Edwin Santos]

There was a post in the Neander forum about how to transfer and cut a curve. Plenty of suitable advice was given about tools but there is more to the subject. Before worrying about how to cut the wood, start with a satisfying curve on paper. This can be from a plan but if not then you are on a challenging and rewarding path. Over years and many pieces your eye will mature and you will like different materials, styles, balance and of course different curves. Part of a circle is ok at first but later will seem simplistic. Part of an ellipse is much more elegant and owing to it's flexibility will fit much better. Sometimes part of a parabola or hyperbola is better. These constructs can form a basis but you will want to fair them to the piece at hand. Combine bits of curves into ogees and cloud lifts. Enjoy the journey

Given your last name, this is an ironic post.
Kidding aside, this is good advice and a good subject. I'm on the journey myself. A helpful tool in the FWW tips section a while back. It involves using a thin strip of wood or plexiglass, some string and a small turnbuckle to create and adjustable curve scribing jig. Lee Valley makes and sells a posh one for symmetrical and a tapered one for asymmetrical curve layout.
Thanks for your post,

[Lee Schierer]

You have to be careful when using wood strips to define a curve. Unless the grain is pretty straight along the length of the piece, you can easily get uneven bending, which won't result in an even curve.

[Dave Richards]

I learned a trick when I was building the sailboat. Sight down the length of the curve. It's much easier to see if it's fair or if there are places that need attention.

Bending a thin batten around three nails will produce a curve that is closer to parabolic than circular. And as Yonak points out, a CAD program can be useful especially if you then print out a full size pattern to create the template from. Model it in 3D and you can sight down the draw curve just as you would a curve cut in wood or drawn on paper.

[Alan Caro]

Tom Bender,

Some of the consideration of how to draw the curve for cutting depends on the complexity and size.

The curve might be drawn directly onto the piece to be cut: Plant a nail somewhere that is level to the target piece and can be kept in place but moved when necessary.Attach a pen such as a BIC or standard wood pencil with vertical sides to a non-stretchable cord and pass through the arc while holding a small square (such that the square and pencil can be handled with one hand) against the pen of pencil to keep it vertical. If the arc is symmetrical, draw a line on the working surface perpendicular to midpoint of the intended perpendicular chord. That is: draw the two end points of the curve, draw a straight line connecting them, and then draw a perpendicular line for the midpoint of the straight line. Extend this line using a straight edge until the center can be established. Moving the arc center along the chord perpendicular is the way to experiment with different radii: the curve can be sketched and revised until the results are working. This technique can be useful especially if the radius is very large as it's possible to set the center of the arc across the workshop. If the curve is complex, the cord and pen/pencil can be moved to change the radius and/or reset to new chord perpendiculars:

Drawing Curves_SMC_12.19.jpg

The other technique is to draw the curve(s) to scale, using 1/2" = 1'-0" or larger on an 8.5 X 11" or better 11 X 17" piece of paper. This is useful if the curved piece is especially complex or has to fit into other components as those can be accurately depicted. Use a compass or round objects to draw the curve(s). When the scale drawing is finished, draw a grid that is referenced to the drawing scale and the points can be connected on the full scale piece. This is very useful when it's important to establish the origins of complex curves- it sets the point at which the connecting curves start and stop and then filling in the smooth curves if quite straightforward- at least they will connect! If the design is quite complex, such as a decorative corbel or bracket, then the scaling up can use a combination of the cord and pencil and standard compass to smooth the cutting outline. Plan the side of the cutting for the saw thickness and make V- marks on the cutting side.

Alan Caro

[Edwin Santos]

You have to be careful when using wood strips to define a curve. Unless the grain is pretty straight along the length of the piece, you can easily get uneven bending, which won't result in an even curve.

Absolutely true in theory. But as a practical matter, any curve you draw will then need to be sawn or at least faired anyway so a slight deformity due to grain is not usually going to make or break your project.
But yes, if it were a concern you could use a strip of plexiglass or thin MDF.

This raises an interesting point about the human eye and it's ability to distinguish slight errors. In a hand made piece of furniture, the four legs are never going to be absolutely identical but I was trained that the human eye cannot pick up the minor differences and I have found this to be true. If you get on the floor and start sighting down the curves then maybe then you will see the errors, but it is a rare person who would do this.
My point is you don't have to kill yourself striving for perfection. I think Sam Maloof talks about this in one of his interviews, and who knows more about curves in wood than Sam?

[Tom Bender]

Sometimes I use a spline or a template but more often I just sketch by hand in pencil. I usually start with any hard points I want to hit and connect with straight or templated lines then adjust till it looks right.

For small things like moulding it helps to draw bigger first then scale down. Big curves may be easier to rough out smaller and scale up. The scaling activity usually results in an improved curve, if we allow ourselves to make changes and not work robotically.

[andy bessette]

Frequently I will draw only 1/2 the curve of a sprung batten onto pattern stock and use that (flipped end-to-end) to draw the other half, in order to make the curve perfectly symmetrical.

[Mel Fulks]

You have to be careful when using wood strips to define a curve. Unless the grain is pretty straight along the length of the piece, you can easily get uneven bending, which won't result in an even curve.

I see a lot of segment arches with too straight ends,due to using bent strips. I always insisted on figuring what radius was
needed and striking it. Same for ellipses, I don't like the two radius method and will only use trammel system.