Parabola Issues

I need to create a 2D drawing of a parabolic mirror for a piece our lab requires. As of this post I have created 2 pline script files in WORD using EXCEL data. They each have 120 points along the verticle axis, with one holding the positive x values and the other holding the negative. Here are the issues I am running up against.

1) The script files ONLY work when they are named eq.scr , no other name will load into acad. This requires me to keep the files in two seperate folders. Not really a big deal but a little unsettling that acad can't deal with any other file name.

2) The negative end of the parabola, when loaded, has the final value missing. Basically, the right end of the mirror in the drawing is longer by 1/120th of its total length. I've checked the scripts and their values are the same, so why is this happening?

Just in case anyone has a script (lisp?) that can create this monster, the equation that drives the parabola is:

y=17.1*(x^2) - 0.02736

the mirror's total length is 3.560 in.

This may need to be done with Lisp. Hopefully, Lee Mac will stumble on to this post soon and be able to help you out.

Hopefully that happens. Just a note, if you make a lisp and test it out, there is a hole at the bottom of the parabola. This is supposed to be there.

PhysycsCAD

Maybe this old link could help you: http://www.cadtutor.net/forum/showthread.php?t=4943

Or if you work more comfortable with Excel, see this: http://www.cadtutor.net/forum/showthread.php?t=1186

Good luck, keep posting about your progress.

Fuccaro....you're good.

That old Excel copy and paste trick worked, and it didn't cut off the end point. So step 1 is complete, I will post my progress/questions for the rest of the piece as they come.

Well, just off the cuff, this will plot the equation you posted:

(defun c:para (/ x y)
 (setq x -60)
 (command "_pline")
 (while (<= x 60)
   (setq y (- (* 17.1 x x) 0.02736) x (1+ x))
   (command "_non" (list x y 0.)))
 (command)
 (princ))

But, I know that you are looking for something more than that.

I see Fuccaro is nearer the mark, let me know if you get stuck

Oh, and just a tip - when doing plotting operations like this, switch off the OSNAPs

Is the parabola meant to be that narrow? The proportions seem more regular if the 17.1 is used as a reciprocal.