Thread: Machine Slow on Curves
You can make CamBam curve fit a polyline using the "edit/polyline/arc fit" menu option.
You are prompted for the tolerance so you can choose the tradeoff between accuracy and minimising the number of curves.
CamBam has a very good forum for asking these sort of questions. It is also deceptively simple and it's worth (never thought I'd say this) reading the manual to find out all the things it can do.
I don't think that any of the inexpensive 3D CAM programs can output arcs instead of straight line segments. I talked about this with the MeshCAM developer several years ago. You should be able to fit an arc to the first 3 points, then check the next point, if it lies on the same arc, then continue. Otherwise, start a new arc. I think the issue is that the entire internal structure of the program needed to be changed to accommodate this.
I've read somewhere about someone writing a utility to read the g-code and convert the line segments to arcs, but I don't recall ever seeing it anywhere. Since Mach3 doesn't have any issues with the straight segments, there was no reason to pursue it.
Its not that i don't have an arc in cambam that is the problem. I do. The problem is when cambam creates the gcode it turns the arc into a series of lots of small straight lines. Im then having a problem with linuxCNC not giving a smooth output to the machine.
What i find weird in cambam is, you go to the postprocessor for linuxcnc, you then go down to 'Arc Output' and there are three options to choose from
convert to lines
Helix convert to lines
So i assume normal would mean it makes a curve using lots of small radius. This isnt the case though
Last edited by swisscheese; 09-04-2014 at 12:15 AM.
In your original post, I think you said that it was fine when you cut a circle, but not a curve made of arcs of different radius. My experience with LinuxCNC cutting circles is that even with a circle made from four quarter-circle arcs (which is what Vectric VCarve seems to generate), the arcs themselves cut at full speed but LinuxCNC slows as it goes from one arc to the next, even though it's still a smooth curve. I want to follow up the ideas already given about G64 and so on, but it may well be that even if you have a series of arcs, it's not going to make much difference as you still get slowing going from arc to arc. However, you did say that your curve was a series of arcs of different radius so it's possible that Cambam can't actually do much optimisation into constant-radius arcs which is why it settles for a series of straight lines and lets the machine controller do any optimisation.
Personally I feel your not going to get what you want because like as been said this is how 99% of Cam packages output there code for 3d surfaces. Obviously linux as a problem with this and CV or again you need to go ask the Linux technical guys over at there forum but again I don't think you'll have much "Simple" joy because I've heard complaints from several experienced CNC users that Linux is rubbish at CV.
I quote "simple" because like the post Ger linked to shows there is a Planner in progress that may solve this but then I think you'll be into messing with compiling machine code and programming etc which if your not into programming isn't simple. It's also IMO why Linux CNC gets labeled with the GEEK factor and what lets Linux CNC down because the answer all too often is you have to resort to DIY programming machine code to get something fixed or working like you want it.!! . . . . . Which you shouldn't have to do this and esp for such a basic function as CV to use a CNC machine.
Last edited by JAZZCNC; 09-04-2014 at 08:21 AM.
If you're having problems with the machine running slow, like you are with the circle made of four different arcs i suggest you play around with G64 G61, P and Q parameters like has been suggested in this thread and you should be able to get it to work.
Have you tried changing the 'P' setting with the G64 command to something other than zero? For example, if you put G64 P0.02 that will allow deviation of up to 0.02mm from the programmed path. That will reduce the amount the machine has to slow down when changing direction, for a given acceleration.
Also, what have you set the acceleration to for all of your axes?
Yes I've played with values of both p and q and the change was minimal, if any.
The acceleration of x and y is about 110 mm/s^2 and z is about 95.
You're running linuxcnc aren't you? Does your machine act the same way with curves made of small straight lines?
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