A very kind chap on cnczone helped out on the issue of rotary cuts below the rotary axis.
Although the somewhat cryptic Help entry gives no hint of this it’s the Base Point which needs to be set to define an axis within the part, paths can then be generated down to this Base Point. (Base Point isn’t even a point, it’s an alternate axis for the part parallel to the defined rotary axis.)
If your rotary axis is in X then use Y and Z to define an alternate axis parallel to the rotary axis and use this to generate paths for the problem section.
Parts with multiple sections where one axis will not suffice can be processed as several sections, each with it’s own appropriately set Base Point (It’s not a point it’s an axis).
For my S shaped part I needed 3 Base Points with the job split into sections along the axis, see image attached
Thanks Nick that sorted things out. I have been following this on CNCzone too.
The help is a bit vague on these base lines.
Are you able to get roughing passes with as much surface height differences that you have?
I’m having trouble with differences of approx. .75 inch it will give me large rapids in to part to lower surfaces maybe you won’t get them if don’t have sharp drops.
I’m not sure what you are getting at. What I have done is use multiple 4th axis rotary features with decreasing allowance, 20mm down to 1mm, then do a finish pass. I did this because the Multiple Passes option of the 4 axis rotary feature didn’t give the results I expected, might now that I understand the base line better. Is there another way to do roughing? Guess I could use 3d features and indexing, still have a lot to learn.
Help entries describe parameters from poorly to entirely inadequately, it’s no wonder we’re struggling.
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