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!

[Anonymous]

Tool overlaps selected faces because you are using flat end mill and "Tool center on boundary", tool center is what it is and because it is flat end mill, tool overlaps edges by its radius.

Typically, you wanna use ball or bull nose end mill to do any 3D finishing work, bull nose will not be good choice in some instances just like case in point with flat end mill.

[jw.hendy]

I guess I find that explanation odd? This isn't about not "overlapping," it's about the z height it uses for a plateau after the ramped section being below a model surface. A 3d contour doesn't do this, despite being a 3d path. I get that this is "atypical," but Fusion is also well aware of the tool geometry, and it's not about the outer edge of the cutter hitting a vertical wall, it's about the tip being buried into the part.

Actually, I just tried using a 1/4 ball end mill and the same thing is happening. It seems this is about the z of the tool being too low (which affects a ball or flat end mill equally). Look at how those toolpaths are well below the shelf:

You can see the toolpath disappear into that area again after switching to a 1/4-ball.

Maybe a side question: regardless of the boundary chosen... are you saying Fusion will readily generate toolpaths that create a situation where the tool volume (e.g. a 1/4 cylinder in my case) readily crash/collide into the model? I have certainly run into issues where the wrong boundary type won't reach a given area (e.g. choosing center and I want "outside" so it cuts a perimeter), but I've never had the selection dictate that I must cut my actual model surfaces?

[Anonymous]

First of all using wrong tool for the job opens can of worms in disagreements you see as "odd explanation", simple fact is that using wrong tool will produce garbage result.

I find it odd that you selected flat end mill to profile angled surface even though direction of cut theoretically should produce decent finish, tool programmed point is center of end mill, not the edge and tool is inadequate for type of operation.

Tool dipping into model on top surface is result of confusion in settings and tool type, or more to the point not knowing what you are doing.

Using ball end mill, below tool path shows programmed point (red dot) when tool is tangent to surface of model.

There is no evidence of ball end mill dipping into top surface as you have it with flat end mill, although tool does not complete bottom edge and needs adjustment to bottom height to allow tool to go deeper.

So, it looks like you are awfully unhappy with good and free advice I offered,.....  how can I be at your service in more gentle, considerate and productive way !?🙄

[jw.hendy]

It seems I've riled you up. I didn't meant to. I read your explanation, didn't think it answered my question, and said so. There are now two topics going on: my original inquiry, and your assessment of the validity of what I'm doing.

The actual question

Fusion generated a toolpath where the tool is machining into my model, both in theory (Fusion shows it) and in practice (my machined result). I want to understand why this is the case, and if it's potentially a bug. Your response about the horizontal boundaries of the machining area did not satisfy me. This is about the height of the path.

I'm still looking for some explanation and/or solution to this:

I can understand how the "wrong tool" would yield a subpar machined result, but I expected and have experienced Fusion to always err on the side of leaving more stock. Thus, the "garbage result" you hypothesize will be due to excess stock or poor surface finish. Are you saying it's quite expected that Fusion will readily machine into the model?

What bit is the best for this situation

Despite your readiness to judge that a stranger on the internet has no idea what he's doing, I already said why I wasn't using something else, but can reiterate: (a) I avoid a tool change, (b) I avoid re-zeroing/homing error, and (c) I simply wondered if it would be good enough. Turns out, it's more than good enough.

What does a ball end buy me when the motion is in line with the gradient? From the point of view of the motion, how is one of these guaranteed to produce a "garbage result"? This is looking in line with the miter, down the slope (profile view for reference):

Moreover, exactly as you said: I'd have to drop the bottom height (i.e. into my wasteboard) if I want to machine the surface fully with a ball end mill. If I don't want to machine my wasteboard... now that miter would be a garbage result.

In any case, the miter itself was sufficiently perfect. What's not perfect is Fusion generating a toolpath that eats into my surrounding model volume rather than avoiding it.

In your test upload, you changed from touch to avoid surfaces. If I change back to touch surfaces with the 1/4 ball end mill, the toolpath looks to do the same: when it plateaus at the top of the ramp, it's machining into that shelf vs. on top of it. Are you saying this is not the case?

If I run the attached test piece and the ball end mill (will have to be 1/8 as I don't have a 1/4) machines into the top surface, can we shift to discussing why this happens and/or if this is a bug instead of whether or not I know what I'm doing or if tool choice correlates to intelligence?

[daniel_lyall]

You are using the wrong tool for the angled faces flat yes sure but that big of an angle needs a ball nose or bull with a tinny step over there is no way around it yes it looks fine but you can see the toolpath lines A bull would have done a better job.

This looks good but the sim is only a Guide 

A back plot looks good

Where the arrows are pointing is the problem there is a difference between the first and second and the first is the problem, why is there a difference 

[daniel_lyall]

What you would be better doing is selecting what to cut not just forcing the toolpath to cut these faces for the first parallel the second use a 2D pocket it's way faster with less stupid moves.

On a Different note what are you using to set the Z height and what type of machine is it?

For some reason, I am not see tool paths in the wrong places.

[Anonymous]

So we have second reference to wrong tool being used for the job, at some point you just have to ask yourself what is it that you are trying to achieve and why.

Does it not make sense that using correct tool gets the job done and there is no sign of any weird behavior ?

Your issue is equivalent to asking ,... "Can Fusion tie my shoes?",...... NO,......... what do you mean ...NO?   why not?????🤣

[jw.hendy]

Thanks for taking a look. Could you clarify this? "Where the arrows are pointing is the problem there is a difference between the first and second and the first is the problem, why is there a difference"

I'm not sure what you are highlighting or explaining.

Re. the "wrong tool," could you define this more explicitly? As in (a) "a tool that will machine into your part when used in a parallel toolpath" or (b) "a tool that generates a poor surface finish?" I'm only interested in (a). I get the theory behind (b)... but it's my project/part, to my knowledge I'm the only one who's cut this in real life, and I'm saying I'm happy with it. Try to cut it with my settings and have a look yourself..

I'd just like to understand the machining into the surrounding material, where the z height of the parallel toolpath is lower than the z path of the contour toolpath.

[jw.hendy]

Could you upload an example file? Maybe do it using my test piece attached to a post above? That is just a simple miter and I'd like to understand what you mean by using a 2d pocket. For the miter? The piece in general?

It's a Shapeoko hobby CNC. I just touch off against the table.

Have you zoomed in from the side really far like I have shown in other pictures? I only did this after seeing each of my 4 sides have the phenomenon I showed. The tool ramps up the miter, then runs horizontal. The 2d contour that follows is running at a higher plane (the actual model surface) vs. those extensions on the parallel path, which eat into the model. If you zoom in really far looking perpendicular to the miters, you will see the lines are below that surface. You can also zoom in far and compare to the 2d contour to see it.

[jw.hendy]

I think what I'm doing is perfectly reasonable, I'm the only one's who's machined it and I'm reporting that I liked how it turned out, except for machining into the surrounding area on my part. No one has clarified exactly what they mean when they say it's the "wrong tool." Would you kindly do so?

- Are you saying that using "the wrong tool" is expected to result in Fusion machining the part itself?

- Or, are you saying that using "the wrong tool" will produce a bad surface finish for the desired miter?

Also, what did you think of my proposal: I run a part with a 1/8 ball end mill, parallel path, touch surfaces, and will show that it eats into the surrounding part. Isn't that a straightforward way to empirically answer this?

[daniel_lyall]

Each type of tool has a standard use flat for a flat round for round yes you can do other things with them that's a given.

I asked about machine you have as most have the option of adding probing If you did just for the Z things will be easyier 

Your first parallel toolpath is set to cut these faces so it is doing just that cutting those faces and bugger anything else and on your pick where the part is cut too deep it lines up with the toolpath(What I was pointing To), this could be your machine losing steps or fusion being silly.

To sort this you will need to run the toolpath again done how you have done it and done how I have done it.

The standard to do the angled faces is a V bit, ball, or bullnose or custom shaped cutter for a custom shapes the reason for this is the surfaces that get cut if it is to a speck the chances of it failing is massive if you just use a flat endmill visually it may look fine but it will be bad it is all to do with the shape of the cutter if you do it for roughing a part that's fine I do that on a bevel for something I make then I come back and clean it up with a ball nose end mill the reason I come back and do it with a ball nose is the endmill leaves cusps you can really see it when it is sanded so to get a good surface it has to be done with a ball noise never tried it with a bullnose. future more it's faster with a ball nose

The sim is showing the cusps with a flat endmill

You can do it however you want if you are happy with the finish go hard but you should expect to get told the standard way of doing things 

The standard is if it is a flat surface being cut use the toolpath that is made for it the top flat faces of your part are flat so using a toolpath made for cutting flat surfaces will be faster as that's what they are for so taking this the 3rd toolpath to cut the flat areas you are using the parallel toolpath what's also going down the miters 6.06 min if you use a 2D pocket its 2.36 mins for the flat areas then if you do a parallel with a ballnose after just on the angled surfaces its 1.26 mins total 3.62 mins instead of 6.06 mins and the parallel toolpath has a .1mm stepover. You can just change the first parallel to a selected toolpath and turn touch faces off you could even set it to a .1mm steppover what will give you below but there is the chances the samething will happen again.

What you said about the ball noise going below the bottom surfaces it does that 

I have the attached model how I would do it with a parallel toolpath using a flat endmill set so it only hits the angled surfaces, I changed your first contour so it does the finish it one run.

[Anonymous]

---

@jw.hendy wrote:

I think what I'm doing is perfectly reasonable, I'm the only one's who's machined it and I'm reporting that I liked how it turned out, except for machining into the surrounding area on my part. No one has clarified exactly what they mean when they say it's the "wrong tool." Would you kindly do so?

- Are you saying that using "the wrong tool" is expected to result in Fusion machining the part itself?

- Or, are you saying that using "the wrong tool" will produce a bad surface finish for the desired miter?

Also, what did you think of my proposal: I run a part with a 1/8 ball end mill, parallel path, touch surfaces, and will show that it eats into the surrounding part. Isn't that a straightforward way to empirically answer this?

---

I try to give good advice where I thing I know what I am doing, when someone insists on doing dumb things for no logical reason, I loose interest in debating the issue.

However, it is possible to cheat the system into compliance despite better choices and here is example of managing wrong tool to do good job.

Yes I am telling you that using wrong tool for the task will result in problems,  but if you do things that promote failure and problems, learn techniques that help you manage bad effects of doing the wrong thing.

Like, if you want to bang your head against the wall, strap a pillow on your head 😁

The "pillow" in this case is a dummy surface with extended edges to avoid tool hitting model where it's not supposed to , but using ball end mill instead is still better choice.

Also, using Selection rather then Silhouette keeps tool edge on selected surface without spilling over.

[jw.hendy]

Thanks for the suggestions. For my sanity, can you clarify this? "I try to give good advice where I thing I know what I am doing, when someone insists on doing dumb things for no logical reason, I loose interest in debating the issue."

As in, what is the outcome of doing something "dumb" like this? I still can't tell if you're saying "a flat tool is bound to give errors in Fusion" or "a flat tool will give you a subpar surface finish"? I think you bolded that line to indicate it's the former?

As I said, with the same settings, a ball-end is showing the same result. If I make that test miter and a ball-end machines the flat face... would you change your opinion? Do you have any reasoning/explanation for why you think it's expected for Fusion to machine into the part simply by choosing a flat end mill? And what, precisely, is it about the flat end mill that makes it "wrong" for this task?

I guess my point this whole time has been: if the result is acceptable to me, it's my choice to machine it like this. I don't know why you're so hung up on it. The resulting miter is beautiful. Thus, by using a ball end mill, I'm working around the software behaving how it shouldn't, not anything to do with reality.

Is this at the core of what you're saying as well? Namely, Fusion can't handle this and that's why I'm to do it this way? Or are you saying something in reality is worse about using a flat mill vs. a ball?

Thanks for the idea on the extra surface. Do you have a quick shot of the model, or how you added it? I've not used a "dummy surface," so I'm curious if this is a sketch or full on e.g. extrude to pad the surfaces. And then does one have to export the miter toolpath, then suppress the feature, then re-export the other toolpaths? Cool technique.

[jw.hendy]

Will take a look at the part later tonight. I appreciate the response!

Indeed... z probing would be great. Just haven't bought one. That is half the reason I wanted to avoid the tool change. It still adds time and from a surface finish perspective, I assure you the result is amazing. I can take one pass with a hand plane on a mitered shooting board and I'm done. There is just no reason for me to seek anything better. And I agree, if I did want it absolutely dead perfect, the answer would be a 90deg v-bit, not a ball end. I've done that, too, I just wondered if I could avoid tool changing altogether.

The only bummer was machining into my part. I have zero worry about the result of the miter. It is amazing.

Ok, so this is absolutely getting to the root of my question, if true: "Your first parallel toolpath is set to cut these faces so it is doing just that cutting those faces and bugger anything else..." I would not have expected that at all, but I've only been using Fusion ~2yrs and have not run into a ton of these situations. Internally, if using touch surfaces does something weird, like making the rest of the part completely off the radar and invisible to Fusion, that could make sense to me. I sill would have assumed it respects the rest of the model volume and that this is at least undesirable if not striking me as a bug... but if this is reality, that would explain why it's happening.

Thanks for explaining the parallel thing. I've never used a 2d pocket and will take a look for sure. And speeding up is cool (plus way lower step size is a bonus as well). I appreciate the input.

[Anonymous]

I'll give Daniel credit for providing more in depth explanation of how different tools are related to operations.

If a tool is not first choice for the kind of operation you intend to do, then forcing it to comply is really dumb, as you see it can be done, but question is why take hard route when you have better choice?

Good advice is considered to be just that, someone knowing better gives you advice that benefits you so why would you turn it into contest of opinions or imply that it is the software that is somehow wrong.

I don't use chainsaw to slice loaf of bread,..... but by your logic, nothing wrong with that, it should work just as good as knife designed for that purpose right?

I don't eat soup with a fork either, there is right tool for everything.

[jw.hendy]

What you're saying just words with no justification. Explain what you mean a bit. Your hyperbole situations are not at all like this topic. Eating soup with a fork and cutting bread with a chainsaw are easily identified as subpar fits. Soup isn't contained by a fork. A chainsaw would destroy the plate, shoot bread everywhere and stink up my house.

Why is a flat end mill wrong for this? You haven't said. You just keep asserting. I hand you two miters, one cut with your perfectly suited ball end mill, one cut with my idiotic flat end mill. What will you see that reveals one of them to be lovely and the other atrocious?

Everything else ("wrong," "bad," "hard path," "I know better") amounts to your opinion. I want to give you a wonderful opportunity: I present you with an open mind, ready to change his foolish machining habits for all time, ready to cite the illuminated wisdom of VicKosta for all eternity... if you can simply use your words and wisdom to explain why the flat end mill is wrong and bad.

So far, everything you've said amounts to "because we have to work around Fusion's limitations." Otherwise again, the floor is all yours: just explain why the ball end is better than the flat for this situation, without citing Fusion in the answer.

Until then... I know what's coming off my machine and I save a tool change and re-zeroing. Why should your opinion trump the evidence in my hand?

[Anonymous]

I explained all that I cared to explain, now I have better things to do, have a nice day.

[jw.hendy]

Aw, bummer. Since you had time to spend on exaggerated analogies, I thought you'd have time to share how you would easily tell which miter was made with the "wrong tool." I guess I will stick with my experience using this technique after all. Shame to lose the opportunity to help a fool see the light.

[Anonymous]

Machine I am waiting for to continue my project will be delivered on Thursday of this week, as you noticed I have been very busy beating some logic into heads of posters that seem lost in their own skin or I can just stare at the ceiling and burn the clock.

I was interrupted earlier by having to do a chore and help out with shipping, but I am here now and just wanna let you know that using your analogy, I think using chainsaw to slice loaf of bread is a **** good idea, full credit to you my friend for inspiring my imagination.

Of course, using food grade lubricant on a chain and wearing safety glasses is mandatory, what do you think?

I do have regular serrated knife which many would regard as being the right tool for the job but what about being innovative, thinking outside the box, exploring potential where others don't see it,.... I know it would work so don't even think about trying to convince me otherwise,........ oh, I think I should freeze the bread first to make it more manageable,..... would you agree or disagree? 

I do have some basic experience in handling chain saw, don't you worry about me.

And,.. I just realized, eating soup with fork can really help out as part of new diet I am working on, the energy spent to capture soup on fork will greatly reduce intake of calories and miraculously promote weight loss.....would you agree or disagree?

Now, you had an issue ?, something I need to explain ?, did I get myself in circle of claims that don't make any sense or is it just you not being able to make any sense out of it?

Go easy on me, I am just an old school lathe and mill-turn guy, basically self thought in things I do with very small margin of outside help, in fact go ahead, find one of my posts where I am seeking help, educate me, I trust that you are far ahead of me in milling, for all I know you may even hold a degree in engineering and here I am ,.... a lathe guy showing you better way or at least better way to do the job the wrong way,.... which you perceive as .... neverming.

I am all ear, lets keep it civil and respectful, there are people out there trying to learn something from professionals on this forum.