Circle/Arc resolution

[desman]

Has any one experimented with arc/circle resolution. Ellipses seem to be tough for me to get a smooth cut around the whole ellipse. The flatter the curve on the ellipse the bigger the steps the machine seems to take.

[Brady Watson]

Alan,
If you are using PartWizard, be sure to choose the arcs-inch post processor when saving toolpath files. The Shopbot-Inch version interpolates arcs as small segments, where the arcs-inch post uses CG commands to interpolate arcs. I think that you will see a noticable difference right away.

-Brady

[ribbons@newformresearch.com]

What is the downside of saving in the shopbot-inch version? Why would they have more than one format?

Regards,
John M.

[Brady Watson]

The downside is that if you have any circular movement of the tool, it will move the tool in very small linear movements. In gross exaggeration, this would be akin to asking the machine to cut a circle, and it in turn cuts an octagon.

The arcs_inch post uses a mathematically calculated arc, using the CG command, to create a closer representation of the arc compared to that of the standard inch post. The result is a much smoother movement when the tool makes a circular cut. While you will not see a difference in cut quality on totally square or straight parts, you will see an improved difference on rounded and circular parts. This is particularly true of plastic/acrylic parts where edge quality is important.

I am not sure exactly, when it gets down to the hardware level of movement, how the arcs post really is different than the standard inch post...since steppers move in discreet linear steps regardless of what you ask them to do.

The best illustration would be for you to take some scrap and toolpath a 4" circle. Save one with the inch post, and save a 2nd SBP as the arcs post. Listen to how the tool sounds when cutting each one, and note the edge quality. To compare apples to apples, do an outside profile cut using a Conventional strategy.

Hope that helps,
-Brady

[mikejohn]

If you draw an elipse and toolpath it in Vector, you get a series of CG commands (after the first J3 command)
If you draw the identical elipse in PW, and save as Brady suggests (you also get a similar result with mm,ARC)you get almost exactly the same number of lines, but the CG's are interspersed with straight line M3 moves.
Anyone know why, and whether one method will produce a smoother curve than the other?
You see Brady, I am learning PW with your guidance

...............Mike

[srwtlc]

The "Circle Resolution" setting under VU does help to make any M3 segments smoother. I've always set it lower even with all CG's from Vector and have noticed a difference with small arcs.