If you ever need to draw a smooth, long, complex curve, say sixteen feet long, that follows a line of measured marks, here are some simple inexpensive tools that will do the job. Similar tools are used in certain specialized fields, such as ship design, where the drawings are so large that the draftspeople walk on them in their sockfeet. Professional tools are hard to get and very expensive, though. I draw boat hull designs and make models of them, using my FOAMBOAT method, such as this 16-inch long kayak. When it is time to scale up the drawing to cut materials for the 16-foot real thing, the somewhat ragged lines of measured dots need to be smoothed.To see my related Instructables, click on "unclesam" just below the title above or in the INFO box to the right. On the new page that appears, repeatedly click "NEXT" to see all of them.
Step 1: Limber Stick and Lead Socks
I could not find a wooden strip at the home center that was limber enough to follow tight curves and still be thick enough to stand up on its edge. I did find a very limber molding that consists of a foam core wrapped with a wood-grain plastic covering. It is 3/8" thick by 1-3/8" wide. I scarfed (look it up) two strips end-to-end, and the glue joint is a bit stiffer than the rest of the molding, so I try to place that part where a curve is not severe. This very long strip is fragile and difficult to handle, so I bought a long strip of 1" right-angle sheet metal, sold as edging around dropped-ceiling tiles. When I need to move the molding, I slide it across the table and into the metal angle, then I can safely carry it. I store it by laying it in its metal angle across several large nails driven into a wall along a high horizontal line.
A dozen soft weights were made by dividing a 35-pound box of lead shot (hunting goods store) into plastic sandwich bags (not zip-top) closed with twist ties, one tiny hole in the bag to let out air. Each bag was put in a child-size sock bought with non-slip pattern on its sole, closed with a knot. The plastic bag prevents lead dust from sifting out of the sock.
Step 2: Smoothing a Long Curved Line
Here the molding has been placed onto a sheet of MDF, medium-density fiberboard, that will be cut and its edges sanded smooth to be used as a router template for cutting pieces of very thin plywood for the boat.
By sighting along sections of the molding, flat spots and incorrect curves can be spotted and the molding adjusted. When all looks good, a pencil or marker can be run along the molding, in segments between the weights, as each segment is also held down by hand. Then, while holding each segment down by hand in turn, each weight can be slid along the molding a short distance and the missing bits of the line filled in.
I usually clamp the very ends of the molding to make it easier to sight along the end segments.