I started by drawing the major and minor axes on poster paper. My ellipse was to have major diameter 15" and minor diameter 9".
 |
| Axes drawn longer than size of ellipse |
I set the two trammel points to a distance of 4 1/2" and 7 1/2" from the pencil - these are half the ellipse diameters.
Then got a piece of scrap with one square corner and laid that in one quadrant of the drawn axes. I used some plywood that was thicker than my trammel pins are long. That way, the edge of the trammel from which the pin protrudes (the wooden part) can ride on the edge of the board and the points won't dig into the poster paper.
Then, while holding the scrap board down firmly, I run the two trammel points along the two squared edges of the scrap board (both trammel points must remain in contact with the board at all times), while dragging the pencil trammel on the paper.
Then it's a simple matter of moving the scrap piece to the different quadrants and repeating that process.
And here is the result - a very pleasing shape.
I'll use this as a template for laying out the tops of the stools. More on that later.
 |
| Setting the trammel pencil and the two points |
 |
| Using a squared-up scrap to guide the trammel points |
 |
| Starting the ellipse - pencil point is right-most |
 |
| Sliding the trammel points along the board, keeping both in contact with an edge |
 |
| Finishing the first quarter of the ellipse |
 |
| Working the next section of ellipse ... |
 |
| ... and the third quadrant ... |
 |
| ... and the fourth |
 |
| Completed ellipse |
Works well with your framing square as the right angle.
ReplyDelete( you have a framing square, right? )
Not sure how accurate my framing square is, but it probably doesn't matter too much as long as it's close to square. Thanks for the tip.
DeleteOk I'll fess up. I had no idea what Trammell points were for until I read this. Thanks so much for sharing. Now I have to go read your post on making them.
ReplyDeleteAnd trammel points will do many more things. Probably the top one is marking out an arc, putting one pin as the pivot and the pencil on the arc end.
DeleteVery nice result Matt!
ReplyDeleteBut, if you ever misplace your beautiful trammel points, you can use two nails and a string. Like this:
http://www.thisiscarpentry.com/2013/09/06/drawing-an-ellipse-the-string-method/
OTOH, there might be more use for trammel points than for string. :)
Hi Bob. I've seen that method, but read that it's a little sloppy (due to stretchy string, etc.), for lack of a better word. The method described above can be sloppy too, if you're not careful to keep the trammel points in contact with the square. I guess any method is only as good as how careful you are.
DeleteIt's also called trammel of Archimedes. No surprise famous people get credited for many things.
ReplyDeleteGood to know. Thanks for that, Damien
DeleteNeat, but to me a simple jig with tracks at 90 degrees to each other, insert sliding blocks (use dovetail track and block so they stay inside track) with an arm attached to both, rotate and it will draw an ellipse. Change the lenght of the arm, ellipse size changes.
ReplyDeleteOr then again my other method work great... Stress free :-)
https://thevalleywoodworker.blogspot.ca/2015/05/figuring-sides-profile-of-my-saw-till.html
Aspirins not included Hah!
Bob, the jester
I'e seen both these methods. The string method I remember form childhood. But I've seen the 90° track method, too. That one works on the same principle as my trammel point method. Bottom line - whatever works!
Delete