Problem with Circles

[djh82uk]

Heya

guys

I am trying to make a flywheel resonator for my steppers, I did the drawing in Corel Draw and exported to DXf, imported to lazy cam, set layer depth, post to Gcode and Mill

But in lazy cam and the mach2 toolpath pane the circle is not round, it has 4 straight lines with curves connecting them, it looks like a circle, but it ain't.

Any ideas where I am going wrong? I am usless with cad, hence the corel draw, however I did have to convert all the objects in corel to curves before they would appear in lazycam.

I thought originally it was uncompensated backlash or something, but one stepper completley stops on the straight line so I guess not

then i noticed it not looking round in lazy cam? Any ideas?

DJH

[ger21]

Try exporting hpgl if you can. I've heard of a lot of problems with Corels' dxf export.

[djh82uk]

Thanks

I will give it a go, I had the same problem making Cat name tags with corel, will also try and draw up a quick circle in a cad app, and see how that previews in lazycam too

DJH

[djh82uk]

Well

Just in case anyone else has this problem, i tried it as hpgl and it was more of a circle, but rather than a continuos curve, the circle was made up of lots of small straight lines, so was more of a polygon.

So i then exported in WMF (Windows Metafile), and it appears how it should in lazycam

DJH

[NC Cams]

Essentially it is impossible to make a ROUND circle on a computer.

Why? Because you simply can't move perfecty diagonally on a computer screen due to pizelation - you have a very tiny step function that nets what APPEARS to be a circle but really can't be " a locus of points that is perfectly equidistant from a common fixed point".

Thus, you're always working with the "how close is close" scenario. WIth small enough resolution, you'll come up with somtthing that APPEARS to be a circle. IF your DXF exports well and "translates well" (not always the case), you'll get a "circle".

However some DXF exporters don't translate well - your "read me" someplace should provide you with the necessary caveats - my cad program does. At that point, you might be able to come up with alternatives but it is not an unheard of problem.

[Al_The_Man]

The main difference between images is between bit mapped and vector based, Vector is always used for Cad or higher end graphics drawing because the vector is based on mathematical equation not independant pixel.
This is why you can enlarge a vector image without losing resolution like a bit map does, they both of course display as pixels on the PC but are completely different in structure.
I have had fairly good success transfering Corel DXF to Autocad except for some text styles for some reason.
Al.

[djh82uk]

Hiya

Yes I don't expect it to be perfect, i just want it to pretty much be a circle

DJH

[Andre' B]

Originally Posted by NC Cams Essentially it is impossible to make a ROUND circle on a computer. Why? Because you simply can't move perfecty diagonally on a computer screen due to pizelation - you have a very tiny step function that nets what APPEARS to be a circle but really can't be " a locus of points that is perfectly equidistant from a common fixed point". Thus, you're always working with the "how close is close" scenario. WIth small enough resolution, you'll come up with somtthing that APPEARS to be a circle.

Same is true for making a circle out of metal, you can't have half of an iron atom.

[djh82uk]

well my circle looked like it was a square with filleted corners

As I said i don't need it perfect, a pixel here or there is nothing, besides the pixels on the screen are just a representation of a vector

DJH

[djh82uk]

Problem Solved, am now using artcam