laying out curves


Sorry for the basic question, but I find I have a lot of trouble laying out accurate curves when marking out cuts. For example, right now I am making a small table for a theater set that will have flat cutout cabriole legs cut from 1/2" plywood. When I am marking the curves on the wood to be cut, I can't seem to get a smooth single line. Any suggestions?
Thanks, Richard
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if you can get a set of french curves to the scale of your work, they help a lot. they take a bit of fussing with, but the result is worth it.
you can also use a sprung lath and some ducks or pins.
sometimes I do a lot of it by eye- first at arms length with a big pencil, get the curve approximate- really just to scale. then use a rule and find any spots that have to be located- the length of the leg and the points where it fastens to the apron in your case. then lay it flat on a high bench and get your eye down to a low angle so you are seeing a lot of foreshortening. at this angle you can only judge a short section of curve at a time, but you can really see the fairness of that section. you'll have to rotate the sheet about to maintain a useful angle and stand it up frequently to check it at arm's length. with this method it is possible to make some very pretty curves at any scale you wish.
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I personnaly use CAD and just plot it out but you can create a ships curve by just using a very thin piece of stock or edge banding and setting some pins (nails) at specific points on the curve and bending the stock around the pins. Just do some grid work on the original drawing to determine the x-y location of the salient points on the curve.
You can create a thin piece of stock by ripping a 4/4 board at the table saw just to straighten one edge, then kick the fence over the thickness of the blade + a shy 1/8" and rip it again, leaving a nice thin piece of drop.
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Get a set of "ships" curves, they are longer and more suitable than "french "curves...........mjh
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Richard wrote:

The magic word is "Batten", basically a flexible straight edge that allows you to connect the dots along a curved shape.
You lay out a lot of cambers building a boat.
The following are a few methods I've used.
Large cambers, say 10-15 ft long.
Layout the points, the use a pilot drill for an 8d finish nail and insert nail.
Use a flat aluminum bar, say 1" wide, 1/16" thick a8 96" long as a batten placing it against nails and tracing the curve.
(SFWIW, have even used a piece of 1/2" PVC water pipe as a batten in a pinch)
Cut curve proud and finish as req'd for the piece.
Small cambers such as might be found on a piece of furniture.
Use a flexible spline curve sold by a good drafting supply house.
They are about 18" long and can bent by hand to conform to the curve, then trace curve.
Again, cut proud and finish as req'd.
HTH
Lew
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Richard wrote:

Buy a French curve. Available at fine (and not so fine) art and drafting supply stores.
-- Will R. Jewel Boxes and Wood Art http://woodwork.pmccl.com The power of accurate observation is commonly called cynicism by those who have not got it. George Bernard Shaw
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Do it first on suitably stiff cardboard. When "close" with a heavier line, cut that carefully. Use as a template and draw easily around it on the wood. ...unless you're a total klutz, then get someone else to do that part. I did a toybox, and put on some cartoon drawings I'd spent a week [it felt like a week] copying from drawings copied through the internet. Several stages to get what I wanted, since I draw stick-people. My daughter painted the characters when the outlines were done, or it would have looked like Hell. It now looks great.
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http://www.tools-for-woodworking.com/index.asp?PageAction=PRODSEARCH&txtSearch=curves&btnSearch=GO&Page=1
has several "solutions" for curves of various sizes.
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Yet another way: get a cheap metal yardstick or ruler, drill holes in each end, loop string or wire through the holes, tie the ends together, put a stick in the string, then twist the string to bow the yardstick. Twist until you get the curvature you want. Of course, if you want it TOO curved, you'll end up making a permanent kink in the yardstick/ruler, but I'm sure you can find other springy materials to make a bow from.
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darkon wrote:

this is ok for regular curves- ones with a single radius. a trammel is better, though, if you have room to use it.
a cabriole leg wants curves with smoothly changing radii, though.
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Make a template of 1/4 to 1/2 MDF or plywood. Freehand the curve onto that and sand it to shape. Easier to sand something smooth than to sand something jagged. Sanding will naturally flow things together. Once completed, use to mark workpieces. An advantage is that they will all be the same.

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Thanks for all the help everyone! I had never heard of ship curves, but that is exactly the solution I was looking for. I have no trouble laying out the lines in a scale plan with a french curve, but even using a grid I was unable to connect the points smoothly. I think the flexible straightedge will work perfectly.
Thanks, Richard
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