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4th Axis - External Contour - Not Working In Practice

Message 1 of 5
224 Views, 4 Replies

4th Axis - External Contour - Not Working In Practice

I hope this is the right place to get some help and advice with this.


I am practising my 4 axis machining and am machining test pieces to try to get the hang of it.  I have set up the attached Fusion file for one of these test pieces and written out the attached .nc file from this, using the post, "HAAS - A-axis (pre-NGC)/ haas with a-axis".


According to the simulation, after operation "[T1] 2D Contour 3", I should see this


but, when I run the .nc file on an actual machine (a HAAS TM 2p 4A), I actually see this


This operation is carried out using this tool


Again, according to the simulation, after operation "[T3] 2D Contour 3 (2)", I should see this


but, when I run the .nc file on the actual machine, I actually see this


This operation is carried out using this tool (16mm)


Can anybody give me any advice as to why the actual machined fillets look nothing like they should, please?  I feel like I am missing something to do with the tool geometry and its interaction with the tool path, and doing something silly but can't work out what it is.  I've had a go at this a few times now and keep getting the same result; and it is now driving me mad.


I would be very grateful for any advice, at all, that anybody can offer.


Apologies, if this is the wrong forum.  If it is the wrong forum, could somebody recommend a good forum for this question.


Thank you,





Message 2 of 5

I think the problem in this case is two factors.


1st factor is probably some tool deflection, a 16mm endmill is quite large for a wee TM2

2nd and probably the largest contributor is that in reality Flat endmills actually have some end relief towards the center of the tool


Like the above picture, which is exaggerated.


under normal flat machining operations this isn't an issue as the tools periphery generates a flat surface as it travels along, but when you machine with a rotary motion the tool can no longer generate a flat surface.


The only way around this is to use quite a small stepover for finishing, or to travel with a spiral motion along the rotary axis 

EDIT: using a smaller diameter tool will reduce the effect of the dish quite a lot as well, if you went down to say a 6mm tool for finishing you would get better results

Message 3 of 5

Thank you very much for your reply.

The 16mm endmill I used for the finishing operation ("[T3] 2D Contour 3 (2)") was this one: (for some reason, the link in my original post linked to the wrong tool).


According the that link, this should be a centre cutting tool


Doesn't that mean that it can plunge into stock (like a slot drill) and has a perfectly flat bottom or is that not so?  Apologies for asking but I'm still fairly new to a lot of this.


Thank you, again, for coming back so quickly with some advice.

Message 4 of 5

center cutting does mean it can plunge straight down into material, but no it will not leave a flat bottom, basically all endmills are ground this way.


For flat bottom holes using a tool the same size as the hole you need to use a counterboring tool like these: 


But I have no Idea how they would work in a normal milling application.


Like I mentioned earlier, you need to use a small stepover and ideally a smaller diameter tool would help too as the effect of the dish goes down with tool size and as the part diameter increases(but you cant change the part size in this case)

Message 5 of 5

Thank you very much for your advice.  That has really cleared it up and been very useful.  I can now try different toolpaths to see how they come out.


Thank you, again,






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