4 axis toolpaths create paths as if the spindle is moving rather than the part.

[pad00000]

On any 4 axis toolpath I try to create fusion 360, before post, moves my axes as if my spindle is rotating around the part rather than the part. I'm not talking about the simulation preview that simply shows the spindle rotating but the actual paths are working as if the spindle is rotating around a stationary part. ex. as it mills around the object the Z and Y axis have negative values as they move towards the "bottom/sides" of the part. I can't really explain it better, sorry for that, maybe that's why I haven't found a solution in the forums yet. Attaching pictures to make it clear. Thanks in advance guys. (noob with 4th axis here, just installed it) - I'm attaching only the Z axis as an example since I can only attach 3 attachments but its the same with the Y axis as well.. just in horizontal orientation.

(I think I'm in the wrong board for this.. if anyone can verify that I'll delete the post because I'm not sure, thanks)

[karina.harper]

Hi @pad00000 

Those position values aren't correct for 4 and 5 axis operations - those are really only 3 axis reference. If you want to validate the code/positions, you could throw it into ncviewer.com to preview the code. 

Happy to take a look at the part if you attach it here!

Karina

[pad00000]

Thanks a lot for replying, my problem is that the g code comes out exactly as in the simulation. In this particular file/g code you will notice the Y axis making two sets of negative moves and then two sets of positive moves, this is because it assumes the spindle is horizontal to the work ,my rotary is X, so the Y axis moves "away" (negative) from the work at 0 degrees and when it turns 180 degrees to machine the other side the Y axis moves opposite (positive). In reality the Y axis should be relatively stationary only making small moves during this op. This means that the machine will behave by trying to move the spindle around the work rather than the other way around. I am attaching both the sample fusion file, the g code generated along with my post p. Thanks so much for divulging time to try and help me out )

[karina.harper · Accepted solution]

Hi @pad00000 

Hm, so I think something is up with your post. I'm a bit confused by what you're describing, but the code doesn't look right to me. An ordinary 4th axis operation that I'm used to would really have something more like:
A90
X1Y1Z1 ... with XYZ moves (as if it were in a 3 axis mill)

A0 

Yours is more like this:
A90
Y-15 
X1Y-1Z-1

X.Z..

X..Z..

A0

So it's almost still thinking that it's machining on the side of the machine, using the side of the tool rather than repositioned to top down. I think this is what you were saying above, but I'm finally understanding. Where was this post processor customized? I am not a post editing expert, but testing the same toolpath with the Haas with A-axis post outputs correctly so I think there's something incorrect with your post.

Sorry for the delay in replying, I was on vacation last week!

Karina

[pad00000 · Accepted solution]

You are right, it is a post issue. What threw me off was that fusions simulation was treating the operation as if the tool was moving as well. I though fusions issue with the 4th axis was only visual but apparently it calculates the paths in that way as well. Unfortunately the solution is to fix it in post, which is what I’m dealing with now.. regarding the post it is a custom one for my machine alone. Thank you for your time and the reply, you were right it was a post issue.