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jim barter
05-22-2004, 9:12 PM
Hi / I've been trying to find a plan to make a oval tracing jig.I've seen them (the jig) in pictures.I believe that you need to cut dove tails in an X and install sliding dove tails and from here you attach a pencil to mark the ovals.Need to make some for bases for song bird carvings.Any help would be appreciated.Thanks :confused:
Jim

Ken Fitzgerald
05-22-2004, 11:15 PM
JIm, see if this will help you.


http://www.popularwoodworking.com/features/fea.asp?id=1260

I hope I'm not violating any SMC rules. Not my intention!

Daniel Rabinovitz
05-23-2004, 1:18 PM
Jim
Draw two lines at right angles to each other and bisecting(crossing)
Measure the length on one line and width on the other

With the top point as the pivot point, and the outer length point to the center - as the radius. Mark an arch, with that length, from the top point. Radius marked from length line to length line ending on each side of center.

These two points on the length line are used for push pins or nails.

Make a loop (circle) out of a piece of string with a length - around the two nails and up to the top point. So you have a triangle made out of string.

Keep the string, around the pins, and with a pencil stretching the string and positioned at the top point (taught). Make a line, with the pencil, to make the oval.

Boy is that tough to explain without a picture. I hope that I got it out correctly and that you are in the same frame of mind as me. I will go into deep thought at exactly 6:10 PM eastern time and you can concentrate and we will have mental telepathy. Now Concentrate!
Daniel
:D

jim barter
05-23-2004, 9:49 PM
Ken / Thanks alot I'm going to build one of these so I can make some bases for the bird carving guys at the club.
Jim

jim barter
05-23-2004, 9:52 PM
Daniel / I guess I missed your mental telepathy ,however, I'm going to the shop and try to unravel this string. I'll let you know how I make out.Thanks
Jim

Dale Thompson
05-24-2004, 9:41 PM
Jim,
If you have a large shop with lots of storage, multiple jigs may come in handy. On the other hand, even if your shop is 80' x 80', I see no need to make a jig for ovals. An oval is nothing more than a simple ellipse. Using the math is a lot easier and more versatile than any jig which you could make. In fact, with a long enough string, you could make a VERY accurate oval which stretched from Canada to Mexico and New York to California.

In my humble opinion, Daniel's approach is the one I would definitely choose. All it takes is a calculator, two tacks and a piece of string. It is also VERY accurate.

Try this. Let's assume that you have an oval which has a long dimension of 16" and a short dimension of 10". Cut both dimensions in half and you have 8" and 5". Take the square of the larger dimension (8") which is 64 and subtract from that the square of the small dimension (5") which is 25. The result is 39. Take the square root of 39 which is 6.24. All you do now is double the 6.24" dimension and drive in your brads or tacks at 12.48".

Lastly, cut your string so that there is the original 16" length of string when it is tied to the two brads. In this example, you will have about 3.5" of "slop" in the string. Take your pencil and push it into the string until the "slop" is removed. Move the pencil, keeping the string tight, and trace the upper portion of your oval. Repeat the process for the bottom half of the oval.
Compare the time required to that of making a fancy jig. :) Not only that, but your oval will be more accurate. (I'm sorry to disagree with the Author of the link referenced above but math beats human accuracy EVERY time! ;)

As a test: Let's say that your oval is 87 miles long by 72 miles wide. Using the above, the distance between your brads would be 48.8 miles and your "sloppy" string between the brads would be 87 miles long. After a LONG hike and a LONG pencil, you would have the desired oval. ;) :)

Good Luck, (Work SMARTER not HARDER!) :cool:
Dale T.