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Author Topic: ellipse code using limited number of arcs  (Read 6475 times)

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ellipse code using limited number of arcs
« on: January 14, 2009, 05:26:22 AM »
I have used the ellipse formula with line segments and the angle for each segment and it works well, but it is very slow.
Each segment is an individual move with an accel and decel associated with it.
Can anyone help with the Gcode using a limited number of arcs to approximate an ellipse?
This would let me use circular commands and very fast smooth moves.
Any help or suggestions would be greatly appreciated.
Thank you.

Offline RICH

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Re: ellipse code using limited number of arcs
« Reply #1 on: January 14, 2009, 06:38:50 AM »
Csquared,
Have you tried one of the wizards called "SHAPES". It provides code for an ellipse , it may provide for
g2 or g3 coding which is what your after. LazyCam can be used also but i just don't remember what
gcode would be  generated. Hope this helps.
RICH

Offline zarzul

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Re: ellipse code using limited number of arcs
« Reply #2 on: January 14, 2009, 11:56:25 AM »
Are you milling or turning?  Have you tried it with exact stop off?  Or maybe accel and decell could be too slow?
Re: ellipse code using limited number of arcs
« Reply #3 on: January 21, 2009, 02:16:49 PM »
If you want a true ellipse then get the formula out of machinery handbook, I'd scan a copy and post it but my scanner doesn't work right now. It ends up with 4 arcs, ends and top / bottom,, so it is going to run with I J or R values. I tried a cad snap ellipse and it didn't fit but used the formula and cut my part and it fit perfectly. The project was an adapter to the intake of the vette motor I had in my Jeep sold and gone now.
CRUISER
  Don

Offline ger21

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Re: ellipse code using limited number of arcs
« Reply #4 on: January 21, 2009, 03:26:03 PM »
A true ellipse can not be made with 4 arcs. Or any number of arcs, for that matter. AutoCAD can draw one with 16 arcs, but it's still not a true ellipse. Sorry, but I don't know how they actually do it.
Gerry

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Re: ellipse code using limited number of arcs
« Reply #5 on: January 21, 2009, 07:08:56 PM »
I have used the Figure 1b construction from the following paper (i.e. draw the arcs centered at (h, 0) and (0, -k) and fillet with an arc that is the geometric mean of the first two arcs), and for ellipses of moderate eccentricity it is very close to the actual ellipse:

http://users.cs.cf.ac.uk/Paul.Rosin/resources/papers/oval8.pdf

Best regards,

Randy
« Last Edit: January 21, 2009, 07:20:04 PM by zephyr9900 »