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not circle that is a polygon
« on: August 25, 2010, 06:12:32 AM »
i want to make circle cutting but i failed. try all of CV settings.

g code example:
F400
G00 Z10
G00 X7.5 Y0
G00 Z1
G01 Z-0.5 F50
G02 X7.5 Y0 I-7.5 J0 F400
G01 Z-1 F50
G02 X7.5 Y0 I-7.5 J0 F400

i zoom toolpath screen. this is not a perfect circle. it is segmented. When i was cutting a circle, surface is choppy.



Online Tweakie.CNC

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Re: not circle that is a polygon
« Reply #1 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.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline RICH

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Re: not circle that is a polygon
« Reply #2 on: August 25, 2010, 06:49:57 AM »
The code looks fine. When you zoom in on the cricle you will see it segmented and doesn't affect the actual cutting.
Like Tweakie said the X and Y are moving in small straight lines, but......
How close to a perfect circle you can cut is dependant on your machines systems components. The better the resolution,
lead screw quality, micro stepping all come into play.


RICH
Re: not circle that is a polygon
« Reply #3 on: August 25, 2010, 07:38:07 AM »
i know perfect circle imposible for x.y.z machines.  But my surface is very bad. i am using servo system. My mechanical equipment is very good.
i think my mach3 setting is wrong or circular interpolation is not enough. i send my setting file.

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Re: not circle that is a polygon
« Reply #4 on: August 25, 2010, 08:47:20 AM »
I think that by using circular interpolation you will only cut a circle with 40 sides but the edge finish will be good. If you are getting a poor edge finish then it is something else which is machine related and probably, as Rich has said, mechanical.

These two discs have been shown before but the one on the left has been cut with straight but wobbly lines (bad finish) whereas the one on the right has been cut with 40 straight lines, using circular interpolation (good finish).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Hood

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Re: not circle that is a polygon
« Reply #5 on: August 25, 2010, 07:03:58 PM »
Your problem is likely to be you are using a pirate version of Mach.
Hood
Re: not circle that is a polygon
« Reply #6 on: August 26, 2010, 05:15:30 AM »
I am using 3.042.040 version of mach with license.
i dont think so my problem about license.
i count 40 segmented lines at one circle.

Offline Hood

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Re: not circle that is a polygon
« Reply #7 on: August 26, 2010, 05:18:32 AM »
You have a pirate licence.
Hood
Re: not circle that is a polygon
« Reply #8 on: August 26, 2010, 07:43:44 AM »
no. i have my own license. i purchased myself from scott nichols.
do you think my license is fake. this is a very big problem.
Re: not circle that is a polygon
« Reply #9 on: August 26, 2010, 11:27:41 AM »
I'm not arguing whether or not his license is legit.  Just curious how it could effect working quality?