7671
General Mach Discussion / Re: not circle that is a polygon
« on: August 25, 2010, 06:41:12 AM »
It is not possible to cut a true circle with a flatbed X-Y-Z CNC machine. Because the machine can only move in straight lines the circle must be comprised of straight lines and so is really just an approximation of a circle. (A CNC lathe would, of course be entirely different).
Mach outputs step and direction signals which are also a series of straight line moves - that is the way it works.
The circle quality starts to improve as you get more (shorter) lines up to the point where the GCode gets too long to be practical.
From tests using acrylic and relating to the optical quality of the edge I have found that a 50mm disc comprising 400 straight lines is about the minimum I would like to use. If the diameter of the disc is increased then so does the number of lines used and so on...
One trick with CAD is to draw many times full size then scale the GCode at run time.
Hope this helps.
Tweakie.
Mach outputs step and direction signals which are also a series of straight line moves - that is the way it works.
The circle quality starts to improve as you get more (shorter) lines up to the point where the GCode gets too long to be practical.
From tests using acrylic and relating to the optical quality of the edge I have found that a 50mm disc comprising 400 straight lines is about the minimum I would like to use. If the diameter of the disc is increased then so does the number of lines used and so on...
One trick with CAD is to draw many times full size then scale the GCode at run time.
Hope this helps.
Tweakie.