Math whiz question

It would be better to clarify the problem before running off and letting mayhem ensue as people guess what you are talking about. Is the overall shape of the part a long cylinder? What's the diameter and the material? Do the holes go in one side of cylinder and out the other, or just into one side? Is the cant angle relative to long axis of part? (Ie, is long axis of the ellipse aligned with long axis of part, or across the part?) Is the Bridgeport head tilted to 40 degrees?

The hole is going through one side of a 2 inch square tube. The wall thickness is .125. The holes are to accept an .834 dia tube canted over at 40 degrees relative to the long axis. I just need to know if I need to make the ellipse longer or shorter along the long axis. The short axis will of course stay the same if my thinking is correct. Eric

snipped-for-privacy@whidbey.com fired this volley in news: snipped-for-privacy@4ax.com:

Longer.

Your problem was clear from the beginning, despite the last poster's comments. It wouldn't matter through what (flat) surface you were making them.

FWIW, a single-point tool simplifies the math. Otherwise, you have to make the "effective" radius of the tool when canted at 40 degrees less than or equal to the minor axis of the ellipse, or it will cut over- sized.

I know you're not canting the tool, but viewing it as if it were will be useful to you.

Lloyd

This is what CAD programs are for. spend the time to get a good drawing, then only cut once.

karl

Greetings Lloyd and Karl, I do have a good CAD program. That's how I drew the first ellips and generated the toolpath. I know my cutter needs to be smaller than the small dimension of the ellipse. Eric

snipped-for-privacy@whidbey.com fired this volley in news: snipped-for-privacy@4ax.com:

You should not have had to draw elipses. You should be able to spiral- drill a round hole on any angle, using XY interpolation; that is, presuming the material is thin enough such that the vertical tool shank doesn't impinge on the top end of the hole.

Perhaps that's the missing piece for you.

Lloyd

Well, first I thought that I could just feed at the 40 degree angle with a tool that had the proper relief. That didn't work. What I got was an oval. Sort of. That's when I realized that of course that wouldn't work. Another way to look at what I did was to divide the hole into steps. So there was a round hole on top of another and so on with the holes displaced in one axis. But a hole penetrating a plane surface at an angle makes an ellipse. So that's when I realized that I needed to program an ellipse and feed that in a helical fashion at the

snipped-for-privacy@whidbey.com fired this volley in news: snipped-for-privacy@4ax.com:

What I meant was to draw a circle on a plane 40-degrees off the horizontal, and drill it perpendicular to the plane using XY interpolation rather than a tilt axis.

Another way to get the elipse you need would be to draw a cylinder of exactly the size hole you need, then slice that cylinder with a plane 40- degrees off horizontal. Then erect the shape resulting.

From the web, here's the formula for the elipse formed such:

The intersection will be a ellipse with semi-major axis r/Cos[a] and semi-minor axis r where r is the radius of the right-circular cylinder and a is the slice angle.

That formula is correct, from the geometry, but if a Woodruff cutter of thickness t is used and descends through the part, it will overcut the major axis length by a distance of t*tan(a). If you shorten the ellipse by that amount it will have the wrong shape, so some other method (like cutting half the ellipse from above and the other half from below) might be needed if tolerances are tight.

James Waldby fired this volley in news:k0c6qg$n77$1 @dont-email.me:

Use a double-angle cutter instead. It will behave like a single-point tool, but with more teeth, and a smoother cut. Using it will not require that you adjust for the thickness of the tool, since the cutting edge is still a "single point".

LLoyd

2. That's the answer to life, the universe, and..... EVERYTHING!!!!

Christopher A. Young Learn more about Jesus

"Lloyd E. Sponenburgh" fired this volley in news:XnsA0AED686F142Alloydspmindspringcom@216.168.3.70:

I should have said "... or a dovetail cutter of >40 degrees."

Lloyd

"Lloyd E. Sponenburgh" fired this volley in news:XnsA0AED77A2FE74lloydspmindspringcom@216.168.3.70:

And then I should have said... either will require making a starting hole at least as large as the tooth gullet diameter of the tool...

(duh!)

I think that's OT and isn't specific enough to answer Eric's question. Here's a very slightly more relevant "42" link (still OT) that has some great advice:

Thanks, that's a good link. You have acted well, thy part.

Christopher A. Young Learn more about Jesus

I think that's OT and isn't specific enough to answer Eric's question. Here's a very slightly more relevant "42" link (still OT) that has some great advice: