topic Re: Inability to do true 4th axis toolpathing to remove stock behind a feature. in Fusion Manufacture Forum

Inability to do true 4th axis toolpathing to remove stock behind a feature.

kineo_wood — Sun, 08 Jun 2025 08:51:50 GMT

I genuinely feel like I shouldn't be here right now writing a forum post.

But Autodesk has decided that people trialing their software, who are considering giving them several thousands of dollars per year for the machining extension and multiple seats - don't deserve to get support from Autodesk. We're only allowed to get support *after* we decide to buy their product. What an abysmal business model.

I've already typed out a long, detailed explanation on three other websites, on top of exploring rhinocam and spending dozens of hours trying to get that to do what we wanted first. So this post will be comparatively short, as I've pretty much lost my patience with this whole situation.

Here's a sample piece. Being cut on 4th axis. (Ignore the sloppy conversion from mesh to solid, its not relevant to this)
You can see generic 4th-axis toolpaths.
I need a toolpath that will come in at an angle, and clear out the back side of those block features (ala green lines).

For the purposes of this sample piece, it does not matter that a ball nose bit will create a radius on the back of those blocks where they meet the center basin area.

I can guarantee you that this operation is physically possible. It will require the software to generate a toolpath that is off-axis, with both C, Y, and Z moving at the same time (X is rotational axis, so X doesn't need to move more than once per pass to step over the cut). The only other thing this needs is the software being able to handle variable tool contact (which shouldnt be a problem seeing as I want this done with a ball nose), where the tool will shift the angle of contact as it cuts behind each feature (a limitation of having to fit between two blocks on the top side, and also why both C axis and Z axis will have to move during the cut along with Y).
This is possible enough that it could be manually jogged to put the bit where I want it on the machine, but obviously there's no scenario where its cost effective for anyone to be manually writing the gcode for this. This is possible on a true/simultaneous 4th axis machine with a small enough ball nose bit, ***IF*** the software plays ball.

I've already tried every single machining-extension exclusive operation (ya know, the $1500/yr addon that Fusion wants me to buy so they give a trial period for, but refuses to provide any support for during that trial period, and where its price will probably balloon to $2500 or $3500/yr within the next 5-6 years at the rate that autodesk raises their prices), but not a single machining-extension operation gave me a result with the bits going ANYWHERE other than straight dead center on the axis. Ironically, the only toolpath that cleared this out was multi-axis finishing, and that's because it pretended this is a 5 axis operation, and I couldn't find a way to limit it to 4.

I honestly don't know if Fusion can handle variable contact angle though, since their tool orientation dropdown for every single operation I've looked at, does not include a "Z, X, Y" option. Only "Z, X" or "Z, Y" so on.

Maybe someone can help me here, but I'm not holding my breath. The best source for this answer would be Autodesk themselves since this is a relatively niche operation, but again - they refuse to provide support since I've not forked over thousands of dollars to them yet, and as far as I'm concerned, they won't be getting those thousands of dollars from my company or I based off a "maybe".

Autodesk - if you're going to provide trial periods for software, a marketing tool that exists solely to try and drive more sales, you need to provide support during that trial period. I'm confident I'm not the only customer Autodesk is about to lose (or has lost) because they needed a specific feature, and when they went to ask you about that feature, they got a box pop up saying "oh you're not good enough for us to waste support time on".

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

a.laasW8M6T — Sun, 08 Jun 2025 18:45:32 GMT

This should be possible with several of the 3d toolpaths in 4 axis mode.

I would start with Geodesic set to 4 axis

You probably want to use a primary mode of lead/lean or From point

From point you would need a sketch point probably in the middle of the opening the tool will be going through to allow the tool to "Pivot" around that point

Turn on collision avoidance

You will likely have to reduce the shaft and holder values from the defaults to get a toolpath

If you can share the file we can provide better guidance on how to achieve this

Goto File>Export>Save as .f3d/.f3z and attach to a reply here

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

kineo_wood — Sun, 08 Jun 2025 19:45:40 GMT

Thank you very much!

Using geodesic set to lead and lean without any specified values got it to work.
I don't see the plugin symbol on this operation, even though this is definitely a true 4th axis operation generated. Is lead and lean locked behind the extension, or something else required to make this work?

I also tried flow after changing the same settings to tool shaft clearance, and setting it to lead and lean, since flow was one of the only true 4th axis operations I found in youtube videos, and flow definitely failed. Reading it, it sounds like flow is constrained to be perpendicular to the surface being cut, and lead and lean can only specify a specific angle, instead of allowing flow to have a variable angle of contact, where as lead and lean appears to allow geodesic to have that variable angle required for this path generation.

Now a question on optimization.

It seems like setting geodesic to blend is a little more efficient than scallop, however both of them still have these unecessary retractions (green arrows). In scallop it uses the retraction to switch to the other side, but on blend its retracting the tool until it reached the gap at the top its poking through, then its putting the tool back down to the surface. Its retracting for no apparent reason at all, including to switch side.

How can this be cleaned up so its not retracting, but instead just looping over (red arrow)?

Thank you again on your help in suggesting this operation. I find it funny this 3D operation generated a workable toolpath when none of the multi-axis options worked.

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

a.laasW8M6T — Sun, 08 Jun 2025 20:08:22 GMT

Basically all of the 3D toolpaths are Multi axis capable.

But the multi axis toolpaths are generally NOT 3axis only capable

All the 4/5 axis options for the 3d toolpaths are only available with the Manufacturing extension(Geodesic/Flow etc are 3 axis only without the extension)

Lead/Lean should behave the same with geodesic and flow.

They both will maintain a specified lead/lean value from the Surface normal.

Collison avoidance can modify this as required to machine the part without colliding.

did you have collision avoidance turned on for Flow?

As for the retracts, generally it will retract if it deems it cannot fit the lead/link in without colliding

You can modify the lead in radius to be smaller

also you may find setting the retraction policy to Minimum retraction helps(I don't think it will in this case)

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

kineo_wood — Sun, 08 Jun 2025 20:09:41 GMT

Quick followup, it looks like the tool shaft clearance had no impact on it, as it still generated the toolpath just fine with the default 0.04 inch clearance setting.
I did try switching it to a slightly larger bit, and now I have this strange gap.

(0.01 tool shaft clearance)

The strange things are the gaps are pretty much only in the middle of an approach angle, and changing shaft clearance has no impact on it.
Also minus one small spot in the center, those gaps disappear when switching to scallop, while retaining the larger tool.

(default 0.4 tool shaft clearance shown)

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

a.laasW8M6T — Sun, 08 Jun 2025 21:56:06 GMT

With multi-axis toolpaths there can be quite a few settings that affect the outcome of the toolpath.

Without seeing the file I can't really offer any more suggestions as to why your seeing that behavior.

If your able to share it it would be a great help

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

kineo_wood — Mon, 09 Jun 2025 04:00:05 GMT

I remade the design in fusion to a rough extent since its going to have to be remade anyways. - I was hoping this would resolve the issue with gaps, but not quite.

This is my result now with lead and lean

its only approaching from a single opening, and not machining the entire surface.

Where as here is a version with "from point" option enabled.

Despite a single outside boundry line being selected as "from point" in this (red arrow), it still approaches from both openings.
So I'm still seeing some weird behavior.

Also on the second example, the toolpaths were generated where the ramp downs line up, instead of the cut paths lining up left to right.
This is creating a peak between the two sets of toolpaths.

How can I get rid of that? (How can I make the left and right set of toolpaths overlap better)
Also, is there a way to do one side at a time instead of the current nonsense where its doing one X axis step at a time, and moving from the left to right opening on every single line.

I've attached the fusion file so you can see the model and current toolpaths, now that I've rebuilt the model.

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

a.laasW8M6T — Mon, 09 Jun 2025 07:37:30 GMT

See video

(view in My Videos)

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

kineo_wood — Mon, 09 Jun 2025 09:48:17 GMT

That's amazing, thank you! I really appreciate the video detailing everything.

How would you get the top flat (quite a lot of bumps and pronounced lines left after the geodesic cleans up the backside of the blocks)?
Like this:

I'm trying a contour path, and it clearly gets the job done, but my, it is very ugly with a lot of spots where the tool is almost stuck/idle for prolonged periods.

I can't help but feel like this is exactly the use case for how "swarf" is described (A multi-axis strategy for machining with the side of the tool), but it just seems to refuse to work for this.

Additionally, I'm trying to get it to put a V-bit into these corners in order to get nice sharp corners.

However every toolpath I try to use to accomplish that, throws an error about how the toolpath will only work with a ball nose bit that isn't tapered.
For example, I try to use multi-axis contour, which literally has a picture of a v-bit or other tapered bit cutting into a model

But when I go to use it, it throws this at me:

Obviously, because of how this corner exists, the Y axis just needs to approach it from off the X axis line, and it should be able to cut in with a V-bit to produce a nice squared-up corner. I may have to tweak some angles a little bit in order to make it work with a standard 90 or 60-degree V-bit, but there shouldn't be a physical limitation. Is the software capable of doing this?

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

a.laasW8M6T — Tue, 10 Jun 2025 18:26:58 GMT

are you trying to finish this face, its not quite clear?

Your really going to struggle to find any good solution to machine that from the side, Swarf is not designed for machining that sort of geometry.

You would save a considerable amount of hassle by machining all of these features by standing the part up on the table, using 3 axis toolpaths to mill everything very simply then transferring the part to the rotary to finish the outside features(That how I would do it If i was making this part)

As for getting a sharp corner you can use trace, but with a 45° tool it will gouge

(view in My Videos)

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

kineo_wood — Tue, 10 Jun 2025 20:02:43 GMT

Thank you.

I'll try a 60-degree V-bit then, and maybe that'll be narrow enough it won't gouge. The geometry is already going to be mostly formed around that area with a 1/32nd tapered ball nose, so I really just need any kind of point to get in there and square it off, even if it takes 2-3 passes per corner due to being a tighter angle bit.

And yes that is the surface I'm trying to finish. Though I'm not sure that finish is the right word. I just want it flat, even if the surface quality isn't ideal.
I ended up cleaning up that toolpath a bit with the delete passes and lead and link options, so maybe it's good enough now.

And yes, multiple jigs would probably be easier, but I really want to do this in such a way that it can go from raw stock to a near-finished part ready for any hand finishing that would already be necessary, without any operator intervention. Reduce labor cost. Potentially allow setting up an autofeeder, and then the machine can spit out a few dozen almost finished parts without the operator being anywhere nearby.

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

kineo_wood — Tue, 10 Jun 2025 20:17:59 GMT

By the way, I want to go back to clearing out the back side of the blocks, with geodesic.

I'm having issues in the simulation where the shaft is colliding with the blocks at the entrance,

There's clearly tons of room on the right, but instead its deciding it should touch the block on the left.
Collision avoidance is turned on.

However it doesn't seem to matter what settings the shaft and holder are.

The default shaft clearance is 0.04in, but changing it to 0.001" or 0.1" doesn't impact the toolpath whatsoever. Fusion generates an identical toolpath no matter what I put in. Cranking it up to a 1 inch shaft clearance causes the toolpath to fail to generate, but since the gap at the entrance is only ~0.18" or so, and the tool is 0.125", even 0.1" *should* be failing, but its not. It just doesn't seem to care what the setting is, and it'll keep colliding the shaft with the body.

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

a.laasW8M6T — Fri, 13 Jun 2025 05:39:11 GMT

I'm afraid I do not know why Geodesic isn't avoiding the part correctly. It should be working in theory but appears not to be.

Re: Inability to do true 4th axis toolpathing to remove stock behind a feature.

kineo_wood — Fri, 13 Jun 2025 06:48:52 GMT

It appears that for whatever reason, the Amana default library (the one built into the default fusion library) has the majority of the shaft defined as the shoulder.

setting the shoulder clearance to a non-zero value got it to clear the wall.