2d Trace, with angled tool does not follow selected geometry or model surfaces

[emk2501]

I have a part that requires a 2mm radius fillet cleanup at the base of angled tubes that protrude from a plate.  To gain access for the fillet, I angled the entry of the ball nose end-mill (with the 4th axis) to get under a lip on the tube (Refer attached files of selected geometry and video of machine path simulation).

My problem is... the tool path does not follow the geometry, it ramps down from entry and ramps back up towards exit, not following either the selected geometry or the model surfaces. 

I have found that if I reduce the angle of the tool, it reduces the ramp deviation from the selected geometry and if I align the tool with the axis of the tubes the deviation does not occur.  

I do not understand why this is happening, can anyone advise?

I can forward the file if necessary.

[Schillertb]

try swaping to a 3D tool path like "pencil". trace will follow a contour no mater what. It dosent look at the part geometry.

[seth.madore]

Would you be able to share your Fusion file here?
File > Export > Save to local folder, return to thread and attach the .f3d/.f3z file in your reply.

[emk2501]

I have attached the .f3z file.  The problematic manufacturing processes are 'T12 Trace 6', (2), (4) and (3).

I have a workaround for this by using a lollypop mill to get under the tube lip, but using an angled ball has advantages for rigidity and it avoids cutting on the ball end.

[emk2501]

I tried Pencil but can't seem to select acceptable target geometry, I keep getting 'Empty Toolpath'? ..... I will have to read up on it .

[emk2501]

I did a bit of reading and now understand how to constrain a pencil tool path, and I can use it to do my fillet, angling the tool in.   Thank you for your advice.

I still would like to understand what is going on with the Trace tool path and the odd deviation from the selected geometry.... hopefully Seth may have an answer for me?

Cheers...

[seth.madore]

Yep, I've got an answer:

The Trace toolpath is not aware of the model, only the selected curve. It does exactly what you ask of it, within the context of its limitations. When the toolpath is at 0 and 180 degrees of arc, you'll see that it does a decent job following the selected curve. however, when it approaches the 90 degree point, it's gouging well into the part. This is how the toolpath is driven, which is something you can see in the Simulation using "Programmed Point". 

Long story short; Trace is a very poor toolpath choice when it comes to 3D Surfaces and trying to blend anything more than a very small section/area. Best recommendation is to stay to the many 3D toolpaths that ARE model aware and have the ability to machine what you're looking to do.

Steep and Shallow would certainly be my first choice in a part like this (supports undercut machining)

What sort of a machine is this going on?

[emk2501]

Seth, thanks for taking the time to explain and your suggestion. I have taken Schillertb suggestion and used 'Pencil', which after I read up on how to constrain its tool paths, works great.  

Although I'm still yet to fully get my head around all what you have said, I now know some of the limitations of 'Trace'.

Cheers..... Ed