Controlling Blend strategy cut direction (preview feature)

[zach.allaun]

Hi friends,

I've been using the blend preview feature to great effect for a number of months now. I'm finding that there are a number of cases where it is superior to 3D contour or scallop, both in the smoothness of the resulting toolpath and in ease of selection.

The biggest issue I've run into is reliably controlling the cut direction. Like many other strategies, the cut direction is specified as "one way", "other way", or "both ways". I'm finding that very minor changes will cause the resulting toolpath to flip between climb or conventional even though the cut direction hasn't changed. It seems that sometimes nothing changing will cause it to flip -- just regenerating the toolpath yields a different result. But in particular, seemingly unrelated changes like adjusting radial stock to leave will cause it to flip.

This is a preview feature so I don't expect 100% stability, but I would love to know if there's something I'm missing -- what's actually driving the cut direction?

As an example, I made an unrelated change and regenerated the toolpath. Out at the machine walking through the program, I stopped it because I realized it had flipped to conventional. I came back inside, saw that it had generated a conventional cut, flipped the cut direction, and it was still conventional! I've now flipped it back to the original cut direction and it's generating climb!

🤣

Would appreciate any insight into this toolpath and how I can better anticipate the result before starting a lengthy calculation.

(Quick edit: In the meantime, I'll just Protect these toolpaths, but I generally don't like doing that.)

[Anonymous]

A lot of reading there,.... anyway, I think you can control direction of cut by making drive curves that are different from those on edges of model, since direction of cut is parallel to selected drive curves, you can manipulate direction of drive curves to drive tool in desired direction.

You can do that by offsetting planes at angle and / or distance then use them as cutting tool in splitting surfaces into sections, subsequently being able to drive tool in different directions on parts of same surface by selecting edges resulting from splitting faces at desired angle or location.

[Anonymous]

As for climb or conventional, you have option of "one way", "other way", and "both ways"

[zach.allaun]

Thanks for taking the time to reply, Vic.

I'm not sure I fully understand your first response. The drive curves do not have a direction in the UI in the same way that curves do when selected in a 2D Contour (indicated by a red arrow that you can click to toggle between sides of the curve).

I also understand the options of "one way", "other way", and "both ways". This is the source of the problem: Using the same set of drive curves and surfaces, sometimes "one way" will be climb, and sometimes convention. Making a seemingly unrelated change like adjusting radial stock to leave will cause the cut direction to switch, even though I have made no changes to the drive curves or surfaces and have not changed the cut direction selection.

Is there some underlying curve "direction" that is not visible in the UI that is the result of selecting the curves in some way? I know that surfaces have a "hidden" normal, but I am not sure that the same is true for the direction of an arbitrary curve selection.

[Anonymous]

What I called "drive curves" is actually labeled as "chains", notice that when you select wrong edges, the error message makes reference to "drive curves" because those selected face edges are the drive curves, tool runs parallel to those selected edges.

In regards to climb or conventional, I find it interesting that one of the choices is labeled "other way", sort of working with the fact that initial direction may be one or the other and therefore, if you don't like it, ... select  "other way".

On left side of my sample model, I deliberately used lines at 45 degree angle and cutting from top to bottom, the other way can only be cutting from bottom to top,..... or "other way"🤣

[Anonymous]

There are more possibilities and initial direction of cut will be determined by first of two selected edges, after which you can correct direction of cut by selecting other way or both ways if you like, just experiment with settings to learn the limits and behavior.

All passes start in upper left corner and spread across selected face, cutting from top to bottom.

Or the other way, cut from top to bottom with  all cuts ending in lower right corner of selected surface.