Accuracy problems in Fusion 360 vs CC

Software Fusion 360
1

Hello,
I’ve got an issue that’s making my brain hurt. I’ve been using the 5 pro for over a year now, love the machine. Lately we’ve moved from CC to Fusion 360 due to some of the more complex geometries of guitar modeling and carving. I’m starting to get some pretty drastic inconsistencies in cuts - mostly pockets, and the inconsistencies are such that I can’t quite figure out if it’s machine related, software related, a tool issue, or something else.

I decided to run a test, using my main two end mills for the more precision bits of the carving (generally speaking, these are pockets and contours for pickup cavities, neck pockets, and truss rod/carbon rods in the neck)

The drawings I use for generating the sketches all originated in Illustrator, exported as .dxf, and conformed in CC and Fusion. Everything checks out in the sketches down to the thou.

BUT - my pockets in Fusion are distinctly smaller, enough that it’s a problem. I know I could sort out the gap and fix via some negative stock-to-leave, but this seems like a really clunky way to have to deal with the issue. Especially since (as you’ll see below), CC doesn’t have this issue.

In Fusion, I’m using the Carbide 3d Shapeoko 5 Pro post processor (carbide3d 02052026.cps).

Here are some screen captures of the sketches being used with expected dimensions. The carbon and truss rods are top-to-bottom, all milled with 1/8" endmill:
1st and 2nd: 2d pocket, machined to the sketch (both top carbon and truss rod below it)
3rd position: 2d pocket with .020 stock left, followed by a finishing contour (with ‘repeat finish pass’ checked)
4th postion: machined to sketch, but this one is 0.206" instead of the original 0.202"

The three pickups are:
Left: 2d pocket with .020 stock left, milled with 1/4" endmill, then a 2d contour finish pass with 1/8" endmill
Middle: 2d contour only, 1/8" endmill
Right: 2d pocket, 1/4" endmill only

Machining issues - Sketches
Machining issues - Sketches1610×2496 258 KB

and here are the results.

Machining issues - Cuts
Machining issues - Cuts1920×3813 1.08 MB

I know there can be some tolerance issues with any machine, and a few thou is totally acceptable (especially since we’re working with wood), but this can’t be where I should set my expectations.

I have done all the maintenance I can think of on the 5 Pro - oil and checking the mechanicals. I’m at the point where I’m pretty sure this is something I’m missing in my Fusion setup. I’ve checked, I’m not leaving any stock on the pockets (unless I’m doing it on purpose to follow up with a contour finishing pass).
I’m attaching my Fusion and CC files here as well. I’m still relatively new to Fusion, maybe 3 or 4 months of really serious diving into it, but I understand the basics enough that I’m pretty sure I’m cutting pockets right. :slight_smile: I could very easily be missing something glaring that’s causing my 2D pockets to be undersized. If so, I would be thrilled to find out what setting I’ve neglected.

Thanks in advance!

Truss and Carbon slot troubleshooting.c2d (96 KB)
Truss and Carbon slot troubleshooting - Fusion360.zip (675.4 KB)

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2

I don’t import DXF files into Fusion but I do import SVG files. Depending on which application generated the SVG file it may have to be scaled in Fusion to get the correct dimisions. I don’t have time now but I will look at you files later.

3

I’m not seeing anything obvious. Looks like your CC file is all down cut bits but feeds and speeds in CC with down cut is the same as Fusion with up cut cutters. When I first started looking I thought it might be feeds and speeds were different between CC and Fusion.

Fusion by default does climb cutting and it looks like CC is doing conventional cutting which could cause a difference. I assume you are using the same cutters and just changing between up and down cut versions.

Not much help here.

4

I took a look at the Fusion file and I can’t see anything that jumps out as a potential source of error. The simulation in Fusion is also showing me what I’d expect to see - it completely mills the pocket. Once I get my machine up and running, I will give this a test and let you know what I find.

It’s a bit of a silly question, but have you tried a simpler test of milling a single square pocket that’s an inch inset from the origin and is 1" x 1" x 0.25" to verify that an inch is really an inch according to your machine?

ETA: If you haven’t used the simulation feature in Fusion, it’s helpful and can show you where you’re going to do something REALLY bad (as far as Fusion and the post-processor know). The simulation will also show you where stock is going to be left once the operation is done. E.g., in the portion of the pocket where there are tabs to attach the pickups to the body you can see an small sliver where the cutter isn’t going to remove material (which is fine in your case).

image
image924×743 9.84 KB

2 Likes
5

Thanks gentlemen,
Yeah, I’ve done the simulations and am getting the same results you are, everything -looks- correct in-software, but clearly there’s something else going on. If it wasn’t for the fact that the CC version is pretty much perfectly cutting the stuff I’d chalk it up to, well, something.
I’m going to do the 1"x1" test, that’s a great idea. Will do a pocket and a contour with the 1/4" and then the 1/8" bit using both a Fusion generated file and a CC one.

In the Fusion version I am adding a finishing pass to the pocket that I don’t believe I did the first time. In other words I want to give it every opportunity to get as perfect a cut as possible so I’ll have a better idea of what may or may not be off. Also I’ll see if I can’t find a chunk of maple or something to test on instead of the pine I did with the previous test. Might as well use the kind of hardwood I generally am cutting for the guitars.

Stay tuned, I’ll post my findings later today.

1 Like
6

Maybe check the tolerances on the tool paths in fusion? IIRC the default tolerances can be kind of loose for some applications.

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7

I’ll check out the tolerances, I honestly haven’t played with any of that yet.

So here’s the 1"x1" test, pockets and contours, 1/4" and 1/8" endmills, Carbide Create and Fusion 360.
Not really sure what to glean from this. Attached are the files. Note - the tool name differences are simply because I built a new tool library in Fusion and organized things differently. The endmills used making this are the same for both versions.

1 inch squares
1 inch squares1920×1440 220 KB

I’ve included the .nc file from Fusion in case that’s of any help.

1 inch squares on 6 x 2.c2d (52 KB)
1 inch squares on 6 x 2.nc (28.1 KB)
1 x 1 test.zip (137.7 KB)

8

The default tolerance in Fusion is 0.004" which shouldn’t lead to this end result.

I have only been using Fusion or OnShape with my Shapeoko, so I don’t know much about what Carbide Create (with or without the Pro) is capable of feature-wise.

What’s telling here is that the contours have more variation than the pockets. Contouring like this is going to have the cutter at 100% engagement and puts a lot of stress on the tool, spindle, and stepper motors and can lead to losing steps in some cases. I don’t have access to Carbide Create Pro, so I don’t know if Carbide Create attempts a gradual acceleration here, but g-code generated by Fusion will rely on the machine to accelerate at the right rate. An actual ramp (helical or otherwise) is a better option since it will gradually lower the cutter into the material while also moving on the XY plane until the tool is at the cut depth you specified, then the cutting will begin. The end result is that there is less of the end mill engaged in the work piece, leading to less force on all of the equipment, and, in the case of open loop systems, less chance of dropping steps.

With a plunge ramping strategy, it’s possible to miss steps when using open loop steppers like the ones on the the Shapeoko. It’s odd that this doesn’t happen when you generate via Carbide Create, but maybe Carbide Create handles acceleration in software after a plunge, or you’re using Carbide Create Pro and it has more options.

I’m still doing machine maintenance and probably won’t get a chance to duplicate this today :frowning:

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9

The nc files I looked at in ncview for the 1/4 end mills have corner points .75 inches away from each other, so the data is good.

The material looks like pine, which will not clean up very well.

Try a hard wood or aluminum.

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