Toolpaths are offset when selecting holes to avoid.

[j.n.c.hayton]

A parallel finishing pass for the outside of a mould has holes that need to be avoided. I have done this by selecting the holes as additional machining boundaries. This works, however, generates a strange offset in just one axis (See images below). I remember it working correctly in the past such that there was no offset, however I have not been able to reproduce it.

Note that actual parallel passes are not offset, so they mill the model correctly. It is simply the "avoided" holes that are incorrectly offset.

[seth.madore]

Create a Patch surface over the holes and select that in the "Model" tab in the toolpath (make sure "Include Setup Model" is checked as well)

[j.n.c.hayton]

Thank for the fast response. I have tried this and it works well for my application. However I am still intrigued as to why my initial problem occurred. Do you have any idea why/where this offset could come from? Based on your answer I assume that machining boundaries should not be used to "avoid" things? Should it only be used to define the outer perimeter of the machine boundary?

[seth.madore]

Could you share your actual file so I can see what was going on?
File > Export > Save to local folder, return to thread and attach the .f3d file in your reply

[j.n.c.hayton]

I have attached the file. The contours I am referring to are labelled "Edge finishing" in the setup "Right (long) Top". There is meant to be just one edge finishing pass, but I had duplicated it to play around with settings to try and resolve the issue. 

[seth.madore · Accepted solution]

I suspect it's due to the tool shape. For example, if I was to swap to a Ball Endmill, my result (over the holes) is this:

And this:

 

 

[j.n.c.hayton]

Oh right, thank you. Do you think it is a bug in fusion? Should it not also be possible with a flat end mill?

[seth.madore]

No, I don't think it's a bug