Vectric Aspire makes a mess of a circle?

[John S]

Does it matter whether it uses one line or 4 quadrants ?

post processed literally 1,000's of programs thru Vectric with no hickups

[Ger21]

I believe that Aspire always does circles as 4 arcs.

[Neale]

Slightly different cutting strategies. Aspire plunges vertically, then cuts the circle in 4 arcs. Sheetcam ramps down in one partial arc, then completes the circle at constant depth (I think - haven't decoded all the coordinates). There also appears to be a 0.05 difference in radius. But I wouldn't worry about the 1 arc/4 arcs difference - in practice, Mach3 is going to optimise its cutting strategy based on looking ahead at a group of moves and the machine parameters and I doubt if it cares!

[Davek0974]

Doesn't really matter of course, i just like to know whats going on thats all :)

Sometimes Aspire seems to resort to making curves from many lines and these were visible in the finish, especially if feed rate override was in use.

[Clive S]

Sometimes Aspire seems to resort to making curves from many lines and these were visible in the finish, especially if feed rate override was in use.

Not sure what you are saying here. If Aspire generated code with arcs then you turned the federate up in Mach3 that could not change it into small lines.

I think there is a setting in Mach3 CV that can be ticked.

[Neale]

I'm guessing a bit here, but one reason for Aspire's 4-arc strategy might be potential problems with motion controllers. I seem to remember a gcode manual mentioning that some motion controllers could get a bit confused by full turns, so breaking it into arcs could be more reliable. If that was true once, it's probably not relevant any more with the motion controllers we use today but maybe it's just a historical thing?

There's a discussion of a possible reason here, to do with rounding errors in start/stop points in nearly-full circles. I used to use a free CAM package with LinuxCNC and it often threw up errors with these kind of arc calculations in g2/g3 moves. When I moved to vCarve all those problems went away, so maybe there's sense in it!

[Davek0974]

Interesting.

The one time i noticed it, i was doing a dummy run so had the feedrate turned up to max, it was very jerky on curves, thats what made me think.

I will need to do some more observing but at least i know now its probably just normal :)

[Ger21]

so had the feedrate turned up to max, it was very jerky on curves, thats what made me think.

This is a known issue with Mach3 and Feedrate Override. It works fine when below 100%. but it can cause jerky movement when turned up a lot above 100%.
I don't recall if there's a safe max to use, but I would keep it below 125%.