Rotary continuous 4 axis

Now that laser is out I can get back to posting some of the shop projects I’ve been messing around with.

In the past I’ve done some 3 axis rotary work… Essentially where you wrap X or Y to the rotary axis.

I wanted to play around with some continuous 4 axis machining. To do that I whipped up this little test block in Fusion:

I had to hand-edit the G Code to make it work, but it proves that it works!

Has anyone else attempted continuous 4 axis machining?


Can I ask if you need to pay extra beyond the fusion subscription to do this? I’ve seen varying things about if you need an extra plugin for continuous machining or just a subscription.


Very cool.

What edits did you need to make to the G Code?
And what’s that red tool length sensor you’ve got sitting there?


Yes you do need the manufacturing extension to be able to do simultaneous 4 axis machining.

I actually used another post that supported simultaneous 4 axis and altered a few commands to work with our rotary. There were some G91 commands that needed to be fixed, and I had to change the rotary axis letter too.

That’s a little tool height sensor I 3d printed. Basically it lets you measure your Z offset once and then switch tools during a job to maintain that same Z offset. I have some VERY hacky code to make it work. Several other users have done similar (And much better) takes on the Z height sensor on their ATC builds.

Corbin Dunn and Jason Parker on this forum have done a lot of work in that deparpment.

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In this example it looks like you could have used standard 4 sided machining but in general you won’t be able to achieve the desired detail. How does this compare with the standard Avid rotary post processor in performance?

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What I was trying to do here was really just test if my G Code was working properly. Some things that you wouldn’t be able to do with a wrapped rotary post are those side cuts and the slots I made.

I think if you’re doing something like a baluster or something artistic the simplicity of doing a wrapped rotary in Aspire is the way to go, if you’re doing something more… mechanical this approach would be better because you can be really specific about how things are machined and where.


@Eric next time you are recording, the quickest way to verify the full 4 axis operation is record looking down the A axis towards the tailstock. You will see the end mill come off that centerline of the A axis and machine outwards to the edge of the stock.

A great way to see this is to put undercut features on your model so the CNC has to tilt the A axis and move the end mill off the centerline to reach the undercut. So all 4 axis will be moving at the same time.

From the video its really hard to see but the model you are cutting doesn’t actually require true 4 axis paths to cut.

Let me get you a demo model to play with. The problem you will discover is getting a long enough end mill to actually get in there and cut with without the tool holder or the spindle itself colliding with the stock.

** Update; this model will make the end mill have to move off the A axis center line to mill the undercut angle of 15 degrees. It should work for a 1.25" flute length 1/4" ball nose. (4.5 KB)

PS. Remember any operations in Fusion 360 that are named "Rotary … " is turkey on a spit. You will need to enable the multiaxis machining and preview stuff in the preferences. You will also have to check the box to limit 5 axis milling ops to 4 axis (which is the key to making all this work). Then you will need to enable the new Flow ops as well.

Then you use the multiaxis versions of flow, trace, contour, blah, blah. Never the “Rotary” ops as I said before as they are all 2.5D.

Here is a “rotary op” on the model above;

Here is a “flow op” on the same model;

Yup I am using all of the preview stuff. What I was going for with this test was just to see how Fusion/The control handled continuous 4 axis… anything.

Now that I have that box checked I’m going to design a wood dead blow mallet of some sort. I suspect that the way I want to do the handle will require some real 4 axis work, and the head will likely be more simple 3+1 stuff.

I have a trouble ticket out right now because the limit to 4 axis switch isn’t working for me. It’s giving me that 5th axis whether I want it or not.

I bet that’s a post-processor issue. I haven’t seen that in the post I’m using.

Let us know what they say. I am assuming you’re on Fusion Preview as well?

Oh, my problem was a corrupt install. I was setting the flag but it wasn’t being honored.

I’ve done some 4-axis simultaneous work but not with Fusion. I was interested in parametric design (the algorithmic architecture kind, not the parametric CAD kind), so I wrote my own toolpath and G-code generation to have more control over the process. Basically, you solve for XYZA based on your geometry and then use G1 commands in G93 inverse time mode based on the desired feedrate and the distance between steps.

If either of you know of a walk-through for Fusion, I’d be interested in seeing it before activating my machining extension trial (I think I still have one). When I search for “Fusion 4-axis simultaneous” on YouTube, I see several 3-axis XZA or YZA examples. I didn’t see any clear XYZA examples.

When I’ve looked, they haven’t had the operation I’m most interested in, which is swarf-type contour cutting limited to 4-axis operation. It looks like the Rotary Contour operation handles contours only if they pass through the rotary axis and the Swarf operation doesn’t support reduction from 5-axis to 4.

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Correct, true 4 axis milling is actually very limited. If you notice the images of the models and operations I posted above you really aren’t getting a whole lot extra detail. You are able to achieve undercuts around the width of the A axis but not the length of the axis.

So like if you had a bird with spread wings or a bust of a person you could machine the tips of the wings and behind the person’s ears but not under the beak or person’s chin.

I would advise doing the 3 axis rotary thing until you know how to design for a true 4 axis process. Since the limitations of the process are so pronounced it really becomes very specialized and not something that would produce an artistic product. Meaning just grabbing a scan and trying to turn that would result in very noticeable “missed” spots on the finished product. Whereas if you have a clear understanding of the process and design around the limitations then you are good.

Also, just a little note; in order to use true multiaxis machining you really need to model your CNC machine. That is how the CAM package figures out collisions and keeps you from wrecking your machine.

Eric, this is super cool! I’ve finally got some designs that require a rotary axis. I’ll probably be getting one in the near future and experimenting with the continuous 4th axis machining in Fusion. It looks super fun! I’m a bit weary of the Machining Extension cost; it’s pretty pricey for hobby-ish projects.


Here’s one of my new ideas; wrapping X or Y to A would probably work fine for a project like this, but pocket machining the cuts with a proper 4-axis motion might produce a sharper corner.