[Path Blending G61/64] Question for CAM programmers.

Firstly I'm new to Lcnc's path blending features, never used them extensively. I'm currently rewriting a post-processor for a 3ax milling machine with stepper motors (32mm/s vel, 300mm/s/s accel). My question; I'm wondering how CAM programmers set-up their contour roughing & finishing operations for a similar machine-tool driven by Linuxcnc. In other words; how, when and where to take advantage of the G64 P and Q params.

If you have experience with the path blending algo and have cons/pros insights to share, that info would be invaluable. 

My goal overhaul: 
Contour Manufacturing Tolerance: +/- 0.05mm
Contour Roughing Operation: +0.1mm (remaining material)
Contour Finishing: 0.0mm

not sure how you cam, or what your deal is. personally i dont run production cnc. I keep my roughing stock material larger than my g64 path deviation tolerance , and for finishing contours, I dont usually do finishing contours fast enough that path deviation/velocity is an issue.

cakeslob wrote:

not sure how you cam, or what your deal is. personally i dont run production cnc.
 

Deal's for a personal 3axis mill sitting in my garage. But yeah, I also do prod elsewhere, unfortunately. Would rather beach-side doing nothing but the reality is we need to machine molds and fixtures alot. Most of our HSM CAM smoothing is automated via several algorithmic cycles (built-in modern controls, not ours). That will optimize best cutting & surfaces based on the velocity and acceleration for a given Rough, Semi-Finish and/or Finish operation. Takes linear toolpaths, and output to nurbs/splines and does all the interpolation using a combination of proprietary secretive magic & voodoo. 

And so nothing 'manual' involved. Zero experience with the Lcnc G64 Pn Qn, its cornering behaviour, tolerance output, what's best what's not etc etc. Obvious way to find out is to throw scrap at the machine and test toolpaths, which I plan on doing this weekend. 

In a meantime I'd still like to hear how CAM programmers does it. 

damn ok. premachining or hardmachining? I guess it depends what kind of mold is for also. , ok well the first part still stands. set your roughing stock larger than your g64 tolerance to be safe. Its the same when I do molds. Im not usually doing a finish path fast enough to cause noticeable issues.

If you are doing finish 3d contour hard machining for like space ship molds then that changes things.

If I did feel the need to add this to my post, I would probably have it as a variable option for the header of each toolpath, and either set 1 of the 3 options on a per toolpath basis, or set the p and q variable option for toolpath.

I'm not making space molds out of my garage's 3 steppers mill. I was trying to say that my only CAM smoothing exposure is with commercial cycles that does it all for you (the company I work for). Compcad/surf/curv, cycle832 to name just a few out of several others that we use and which dynamically sets soft & brisc path modes based on the velocity, jerk and acceleration of the machine params. You end up with near perfect surfaces and within microns tolerances, effortless. 

At home that is NOT the case. Nothing space here; I have G64 P & Q only and have no clue how to make the best of that with my advertised poor'ish steppers and acceleration. If I understood that path blending should always be ON for contours and surfacing with a tol half the thickness of the material remaining. And so in post and for non-drilling operations, the logic should be:

There's some clues about Q in the docs for G64:
linuxcnc.org/docs/2.6/html/gcode/gcode.html#sec:G64

Not far off, Jacob. Interestingly the answer was in the planner. Linking up in case someone else gets to writing a CAM post-processor for Lcnc, and like myself need to understand the concept so to be able to write the needed vel & accel algo logic output to match roughing/semi/finishing throughout the operation.

Thanks everyone.

linuxcnc.org/docs/2.9/html/user/user-con...gramming-the-planner