If you need to make a perfect oval for putting up beaver and you don't have the patterns you can make "perfect ovals" using a string and 2 nails. All you need is length and width of 1 oval and your good to go.
Here's a link that shows you how:
http://books.google.com/books?id=f_ViRN4...o7ovFY#PPA46,M1

Thought maybe this might help someone else

ttt

Very good!

That's a good description of how to make a perfect oval (ellipse).

Now, you only need to know how to calculate the required two axis dimensions based on the size of the pelt or carcase. I have seen a couple formulas, but wouldn't mind seeing a little discussion on it.

The measurements for the seven rings measured from center on a beaver board from smallest to largest are:

1--11 1/5 X 9 5/8
2--13 X 10 5/8
3--14 1/2 X 11 5/8
4--16 X 12 5/8
5--17 1/2 X 13 5/8
6--19 X 14 5/8
7--20 1/2 X 15 5/8

once you do the large ring and have your nail position established all you have to do is move your nails 1 1/2 inches in on each nail and the next ring will be 3 inches smaller in length. And shorten the string!

I think that perfect ovals are a bit over rated LOL. I have been eyeballing my beaver stretching with no lines at all for the last umpteen years. The length to width ratio isn't that important as long as you get a semi natural SYMETRICAL stretch. I believe that having lines on your boards tend to influence over stretching trying to get that next size up.

well newhouse, for someone like yourself who has been doing it for a long time that might be ok, but for a newbie like myself I need the lines. I don't try to over stretch I'd rather it be one size smaller.

ttt

thanx