Questions about wrapping fourth axis toolpaths in Fusion 360 using Wrap Y to A post

I am attempting to use fusion to create continuous fourth axis toolpaths without paying for the $2k mutli axis extension.

I can definitely achieve the shape I am currently aiming for using multiple tool orientations(using the A-axis as an indexer), but I would like to see if it is possible to get fusion to create a continuous toolpath that could save some machining time.

I wrote a grasshopper script that does some coordinate transformation and unrolls my vase shape, shown here:

I imported this into fusion, created a parallel fininishing toolpath and posted this:

It doesn’t appear to do the Y to A transformation that I was expecting. There is only one line in the g-code that calls out an A rotation, at the very start. Furthermore I am not sure if my input surface length is correct. I am currently using the max circumference of the vase, shown here:

Does anyone have any advice on why fusion is not posting g-code that wraps the y-axis of the file around the a-axis, or what to use for the input surface length?


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The wrap toolpath is a very specific functionality. It only works with a small set of toolpaths on geometry that is on a cylinder. See this video:

There might be a way to let Fusion do the carving toolpath and wrap it yourself. You would have to load the G-code and transform the Y moves to A moves, possibly with inverse-time feeds. This might introduce an error because your transformation deforms the surface without a corresponding change in the cutter shape. If your cutter is small, that shouldn’t matter.

Another option would be to do the indexing on a small slice and then write a script to rotate and repeat. This would work if your pattern repeats, which I think it does but can’t quite tell. You could use Fusion’s stock bound feature to choose a slice that’s off-center to get better cutter engagement.

I was hoping that the post processor for fusion from avid called “Avid CNC Wrap Y to A.cps” would do exactly that, transform the Y moves to A moves. Is this not the case?

Yes, there could be some cutter shape issues if the pocket is too small.

As far as I know, that is not the case. In Fusion, Avid’s wrap post-processors only handle 3+1 indexing and this functionality.

@Eric might know more.

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The “Wrap to A” posts will do basically what they say… They take X or Y (depending on how you have your rotary mounted) and wrap those moves to rotary moves.

Using these posts essentially makes your 4 axis machine work like a 3 axis machine with one of those axes being swapped to a rotary.

To put another way: “Turkey on a spit”.

I believe you can do this type of toolpath in Fusion, although I don’t know how to set them up because it’s been a while.

What I did in some of my other posts here is to find another true 4 axis post, create code with that and then just massage it to work with Mach 4.

It should be noted that Mach 4 CAN do all 4 axes at the same time, our post doesn’t do that.

For the model above, the “turkey on a spit” approach with a ball nose would yield great results, and you might be best off using Vectric Aspire or Vcarve as that toolpath would be pretty easy to make in one of those.

@Eric That was what I was trying to achieve, the turkey on a spit 2+1 using an unrolled version of my vase. As you can see, despite using the Y to A post my g-code still has Y moves, and only references A once at the start of the file to zero it:
T41 M6
S18000 M3
G0 A0.
G0 X9.8532 Y-0.2305
G43 Z5.2259 H41

I know you can do this the “right” way by buying the multi-axis extension for fusion or by using the fourth axis as an indexer which seems to post just fine after enabling the A axis in the default fusion post, although I haven’t tried it on my machine. Not sure why the g-code still has y-axis moves, they should be A axis moves if the post truly translates y axis moves into a-axis moves. I may be missing something fundamental, I am new to fourth axis g-code.

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Made a little progress, I made the part in fusion 360 inches long, then made a parallel finish with a 1" stepover. I posted the g-code, and used find and replace to swap all “Y” to “A”. Nc viewer now shows this, which is what I was looking for:

I think this method will not work because the tool contact point calculations will be off. Could work for cylindrical parts but I think anything concave will be off due to how I had to stretch the part to trick fusion into outputting the correct A angle.

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Uh, actually you can just buy cloud credits and use what you need. You don’t have to buy the full subscription.

3 of my machines are 4 axis and I rarely do 4 axis work. It’s like 1% of your job unless you specialize in that kind of work.

Just rent for the day.

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Biting the bullet does seem like the best solution here. But I cringe at 11 credits ($33) a day.

Back in 2010 I built my first 4 axis machine. It was a Sieg X3 conversion. I used a Sherline rotary table for the 4th axis and a Probotix custom controller. Cost me about $4,500.

Long story short, the CAM to drive that 4th axis was $50,000 per seat.

Consider yourself lucky. $33 a day is still peanuts compared to any other provider.

PS. For the record I still use the X3, original PC but the latest LinuxCNC build.

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That sure puts it in perspective!