Generated parallel toolpath is cutting into the part itself?

[jw.hendy]

I recently made a 4-sided case and used a new technique for the mitered corners. I've used the 90-deg v-bit trick before, but I don't like the variability in re-zeroing after a tool change, and I wondered if I could get away with a parallel toolpath using the 1/4in bit used for everything else. It worked great! ...

...except it cut into my part in the surrounding area during the operation. Like all things I suspected myself, but I just looked more closely before I go to make a second, and it looks to be real in the generated toolpath.

Can anyone illuminate on why it would generate a path that cuts into the final model?

Here's the part for reference. I will note that this was made in SolidWorks and imported to Fusion. Not sure if that matters or not.

Here is the parallel operation cutting my miter:

I adaptive clear to rough everything out, then run the miter parallel toolpath, and then clean up the "shelf" and walls with this 2d conI also have this contour cleaning up the "shelf" and protruding walls after this miter operation:

Now I'm orienting to the front view (looking at the miter/shelf from the side) and zooming way in:

Here's the contour, which makes that shelf disappear behind the toolpath lines:

Now here's that parallel path highlighted, which is clearly below the shelf as I experienced in real life:

Here's the geometry tab, which I'd think is the most relevant?

I thought it might have been the use of touch surfaces, but here's with turning them off. In this view from the side, you can see the toolpath line disappear right into the part!

Any other information that would be helpful for me to provide? All other cuts/passes seem correct, and in checking other dimensions, things seem well within what I'd expect. My walls should be 4.37mm and I get 4.34-4.37mm with my caliper away from the ends, but 4.19-4.22mm where the parallel path hit.

I appreciate any suggestions, and again am happy to provide other details/settings that would be needed to troubleshoot further. I've never had this happen so I'm not sure how to diagnose!

[HughesTooling]

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@Anonymous wrote:

2 - The main reason for creating offset surface is to isolate main body that caused odd tool path or "tool eating the model" under certain choices made in operation.

Therefore, when selecting model in operation, in this particular case, you wanna unselect option to use setup model which results in only machining duplicated surface.

Operantly, because you extended top edge of new surface, tool still avoids "eating the main model" even though you left setup model selected in operation.

Devil is always in the detail, isn't it ? 😁

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If you want to suggest unselecting the model then you should warn people the rest of the model is then invisible to the op. In this example it doesn't matter but we've had lots of times people on the forums whining about toolpaths going through the job because they've unselected the stock model.

Never noticed any problems with overlapping surfaces, seems safer to me to leave the model selected but each to their own. Might be worth unselecting the model for big complex models so only the area you're machining is used in the calculation but something this simple the calculation time isn't a problem.

As for extending the surfaces all round, I just prefer to have the toolpath machine past the surfaces on all edges. Could reduce the overcutting distance to save time. Would be nice if there were options for tangential extensions in the parallel op so no need for extra surfaces.

Mark

[HughesTooling]

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@Fabbunny69 wrote:

@jw.hendy  

If some body has advise of how to project a profile without constraints please share!

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There's an option on the project dialog.

Mark

[Fabbunny69]

Thanks @HughesTooling but I don't seem to have that option.

[HughesTooling]

Not sure why you're not seeing that option. Looking at the old What's New it was added in 2018 and I don't think there's an option in preferences to enable it. @Phil.E  any idea why this might be missing?

This is from the 2018 What's New.

• Unlink projection from source
  Another thing you couldn’t do before, but now you can link/unlink the projected geometry from the source. If Projection Link is unchecked, any changes you make to the source sketch will not affect the projected sketch. Yaasss.

Mark

[daniel_lyall]

Do you have the timeline turned on?

[HughesTooling]

@daniel_lyall  Got to wonder why the projected curves are created as projection curves when there's no history, might make more sense if they were locked. Either way the option for projecting without link should probably be available with or without history.

Mark

[Anonymous]

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@HughesTooling wrote:

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@Anonymous wrote:

2 - The main reason for creating offset surface is to isolate main body that caused odd tool path or "tool eating the model" under certain choices made in operation.

Therefore, when selecting model in operation, in this particular case, you wanna unselect option to use setup model which results in only machining duplicated surface.

Operantly, because you extended top edge of new surface, tool still avoids "eating the main model" even though you left setup model selected in operation.

Devil is always in the detail, isn't it ? 😁

---

If you want to suggest unselecting the model then you should warn people the rest of the model is then invisible to the op. In this example it doesn't matter but we've had lots of times people on the forums whining about toolpaths going through the job because they've unselected the stock model.

Never noticed any problems with overlapping surfaces, seems safer to me to leave the model selected but each to their own. Might be worth unselecting the model for big complex models so only the area you're machining is used in the calculation but something this simple the calculation time isn't a problem.

As for extending the surfaces all round, I just prefer to have the toolpath machine past the surfaces on all edges. Could reduce the overcutting distance to save time. Would be nice if there were options for tangential extensions in the parallel op so no need for extra surfaces.

Mark

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"Each to their own"....  fully agree😋 (order of words does bypass potential filtering by forum but as you see, it works both ways), however, my point is misunderstood.

1 - Extending surface below model bottom is unnecessary due to flat end mill reaching bottom without that extension.

OP rejected using ball end mill because to make it cut to the bottom edge, tip of tool dips into spoil board.

Of course there is a way around that but he made it main issue in selecting flat end mill so it is a factor that needs to be accounted for.

2 - If the main purpose of creating dummy surface is to isolate model and restrict tool path to the surface itself

as in this particular case, selecting setup model as well contradicts the logic.

If surface is used as a patch over hole for example, then selecting surface and the model is correct.

Far back in my initial posts and before hell broke loose, I made a point of using Selection in geometry tab instead of Silhouette, my claims are based on my own tests and result as evident in screenshots below, I have no desire to negotiate facts, they are what they are.

[Phil.E]

"Either way the option for projecting without link should probably be available with or without history."

Link = parametric. There is no way around that. Do you mean to say there should be other options in the non-parametric sketch projection tool?

[HughesTooling]

@Phil.E  With history enabled you have the option to project with or without a link but in direct mode you don't get this option.

This is the project dialog with the timeline.

In direct mode the Projection Link option is missing and you get curves that are of the Projection type. This actually seems odd as in direct mode the projection is not linked, I guess it does give you feedback as to how the curves were created though. So all I was suggesting is that there should be an option to create ordinary curves from the project dialog in direct mode. I guess you might not want to use the same wording as "Projection Link" in direct mode might cause confusion.

Thanks Mark

[Fabbunny69]

Thanks @daniel_lyall the Projection Link button appeared with time line on. @HughesTooling that saves me a heap of time I use these feature a lot with customer supplied models.

[anthony.a.douglas]

This problem is very similar to the one I have had a problem with many times over the years.  I just posted about it in the forum.

What's happening is that you have contact point boundary selected, which makes the machining boundary larger than you thought it was.  See the pop up tooltip that occurs when you hover long enough over the option for an explanation. Uncheck that and you will probably immediately get almost what you want.

It always does this thing where it goes whooo, way down or around the sides of a surface like that, either at the top edge or the bottom edge.  The way pro machinists prevent such behaviour is with so called runoff surfaces.  I was a cnc machinists with a 4 axis machine for several years there, mostly working with soft materials.  They are a pain in the ass to produce, and this sort of geometry creation and modification is part of why getting a custom part costs so much...

I do apologize for the... unproductive, shall we say, attitude some other people exhibited. Don't take it too seriously, this is a thing that happens in the industry for some reason.  There is clearly a lot of sense in using flat and bull nose end mills for finishing soft materials with the right toolpath.  Indeed, they are superior, producing smaller cusp heights for the same toolpath length, in many circumstances.  Different circumstance, different approach.

Ultimately, fusion and other cam software I have seen just isn't nearly as sophisticated as you are assuming.  It doesn't know where the part is.  Only the surfaces, machining boundaries etc. , it is not smart enough to not gouge the part, you have to hold its hand and lead it on.

The way to fully complete the surface in this case would be to select the flat level areas and the slanted area as machining surfaces, but then use the slanted area with the "select boundary" option for machining boundary, and go tool on the outside, and a small positive offset.  Thus, the tool is allowed outside the boundary of the slanted area, but it won't gouge the part, nor will it try to do all that flat level area.  However, it will still stab downwards at the  sides of the slanted area.  To prevent that, you can use the methods of making enlarged offset surfaces, as people above have said.  Another approach is to offset the slanted surface downwards without changing its size, and use it as an avoid surface by setting a sufficiently large avoid distance.   This only works with some toolpaths.  This should prevent stabbing, but I haven't tried it recently.

[BjoernJohnsson]

To answer your original question, the toolpath cuts into the part, but only by about 0.002 mm, which is 1/5 of the tolerance of the operation (0.01 mm).

The toolpath calculation is aware of the entire selected model, and will avoid gouging it, but due to the tolerance it doesn't detect this as gouging. If you use a smaller tolerance, the toolpath will respect that and not go below the surface by more than that amount. I've tried you example with a tolerance of  0.001 mm instead, and can see that the result looks better and is much closer to the surface.

[jw.hendy]

Sorry on the delay and thanks for the explanation! I followed along with the followups on projection vs. linking. I don't know enough of the Fusion internals to know which is expected/normal/proper, etc. Either way, not too bad to turn on the timeline (and wouldn't be an issue if I hadn't imported from SolidWorks) and use this trick. I've used project followed by offsetting from that linked path before, which works nicely enough. In that way, you're linked to the model, but if it changes you still get the desired offset.

Thanks again!