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]

So, I just scanned your last post and here it goes, flat end mill is wrong choice for any 3D profiling due to the fact that flat end mill is inadequate geometry for dealing with 3D surfaces of infinite number of arbitrary shapes not aligned with any plane that flat end mill can be in sink with.

So to get best out of Fusion, I would assume following the rule of thumb would compliment your expectations and produce desired result without tool being suicidal and turning on model in undesirable way that led you to this forum to declare "Fusion sucks", when in fact it was your lack of knowledge that prevented you from getting better result even with WRONG tool. 

In this one instant flat end mill happens to be able to substitute ball end mill with some extra work and you are saying that's better option then one intended to work without extra efforts to beat it into compliance, that's where we go separate ways, wrong logic.

In this case you can only drive tool from top to bottom or bottom to top, driving it side to side would leave stairs so again diminished options and wrong tool for the job.

[jw.hendy]

I think experience >> any degree. This is exactly why I'm asking you to tell me how your experience so adamantly insists that the flat mill is doomed in this scenario. I still haven't heard why, just that you insist it's "wrong." The only drawback I'm currently seeing is that it breaks Fusion's brainz to compute a non-colliding toolpath. This has nothing to with whether or not a flat end mill can cut a miter sufficiently well.

I'm asking how you could tell a miter made by a silly pants with a flat mill from the one professionally made with a ball end mill. One of them is obviously ridiculous to you, so I thought it would be easy to describe the drawbacks. You're still hung up on bread and soup! Tell me about the resultant miter.

[Anonymous]

You keep pounding on end result so I must tell you that end result in this case is not focus of right and wrong.

You can take .001 stepover with any tool and achieve finished surface associated with grinding rather then cutting so that point is well ...... pointless.

When you consider what tool to use for a job you need to consider how software works, some tools are less "wrong" then others but you can come to better conclusion if you consider that one tool is able to do a whole lot more than one which is less wrong, subsequently deciding which tool is right or wrong for the task.

Still able to stretch the possibility but two tools of different geometry cannot be equally right choice for job that by its nature calls for one of the tools as preferable and correct.

[jw.hendy]

Thanks for elaborating. I hear you and in most 3d applications, of course flat is going to suck. I would counter that the work piece doesn't know what's machining it other than the contact area. The ball end has an advantage of gradually biting in, but at full contact it's almost the same as a flat end mill. In metal I'd think twice about this as I'm sort of angled-plunging... but this is wood.

As to what Fusion is doing, I never declared Fusion sucks. You're cautioning me about staying respectful... but your insistence on hyperbole and getting into character attacks based on CAD/CAM usage is pretty ridiculous. This all started with "Fusion is machining into your part because tool center on boundary, tool center point, flat is bad for 3d and you have no idea what you're doing."

I'd appreciate input from Autodesk on resolving that. My assumption continues to be that Fusion intends to generate paths that don't machine the model, period. Subpar surface finish or e.g. stair steps by using a flat mill on an angled surface, sure. Machining into the part volume? I still don't get it. You also haven't explicitly stated that e.g. "it's a rule from pg. 378 of the Fusion manual that flat end mills will machine your part." I don't think you know this, I think you're starting with "flat is bad for 3d" and hand waving the rest. That's just my opinion, and I'm quite open to empirical evidence, or direct input from someone who develops Fusion software to clarify the behavior I see.

Ultimately there's only one tool path cutting this... I'm not sure why one orientation is a downside. What do I gain from the possibility of machining horizontally? Vertically along the miter is good enough. I do appreciate you sticking to the miter, specifically, though. If your hangup is on the direction the machining takes place, indeed, I guess we'll go our separate ways. If you ever get the chance, try it! It's simple, saves a tool change, you don't have to machine into your wasteboard, and the results are gorgeous.

[jw.hendy]

Fair, but then I don't know why it's "wrong." It works. Dunno what more to say.

The ball end mill is equally "wrong," as a tool which can't machine to the bottom surface and leaves material to sand/grind, or that forces you to machine your wasteboard over time when another tool doesn't cause this damage is sub-par. This is all I was looking for: why is it wrong. I can get behind all the above reasons when having this debate.

The only one I can't get behind is "Fusion can't handle a flat mill and so it eats into the part." After all of this dialog... I'm 100% still inclined to think this is a bug. If Fusion ever responds, I can't wait to hear. There is no mathematical issue with simply going a hair higher to the real model surface before traversing sideways... why would they intend to do that? I think it's an oversight or a bug. I mean, what other toolpath can you name where by changing from ball to flat, I will eat into my part? Why doesn't this happen with adaptive clearing? Why don't I have to check all my toolpaths just to be sure Fusion isn't weirdly eating into a finished model surface? I don't! The number one rule of a CAM program should be: at the very least, don't machine the freaking part itself!

In any case, I'd choose a 90-deg v-bit/chamfer bit for this before I'd ever think a ball end was more "correct" than a flat end mill. There is zero chance a ball end mill is the right tool for this. The only reason it works is due to your 0.001 stepover comment.

[Anonymous]

In my 4 years of using Fusion, I have seen two extremes on this forum, one has to do with stretching the limit of what can be done in Fusion and the other is fenomena that identifies with users who have zero experience in machining and programming but they are trying to cut highly complex model on $200 router, sure, swim or sink, it works,.... right?

Between those two you get professional and amature crowd making enormous number of claims that are highly beneficial and those that just don't make any sense, and the worst part is when you respond to any post you really have no idea who is behind the curtain.

So, what triggers short fuse are those ridiculous claims, questions, actions, words, lock of behavior that inspires cooperation for mutual benefit, making it hard for someone to help by bragging nonsense and uploading pictures but not the file of a project.

It can be difficult to make the call, and someone's insistence on going against the grain just aggravates the progress in right direction.

My analogy with chainsaw and fork is equivalent of using microscope to overcome limitation of human eye, magnify it to insanity and analyze detail to draw conclusions.

You started with a problem, wrote a book on subject and are walking away with skill or discovery presented to you in samples of files and screenshots, you haven't taught me anything I didn't already know so you demanding that I explain this or that is just ridiculous but here we are, just another thread that will live forever in cloud and amuse someone years later.

What do you think, which one of us will be considered less of a clown, less wrong in overall picture if our dedicated efforts are being judged by combined activity on this forum and other posts that we so proudly upload for others to consider as "solution" to their issues or just wisdom that has roots in experience, in Fusion or elsewhere, with intent to help, even when insult is detected or perceived based on few words of bad choice in trying to penetrate thick skulls ?

[Anonymous]

Because flat end mill is not preferable tool type for 3D strategies, there are no safeguards that prevent it from "eating the model", that part is up to you, there are techniques to avoid that from happening, choice of settings in operation and other methods mentioned, like dummy surface or model, don't you see that all your problems are product of using (wrong) less favorable choice of tool and lock of skills to avoid issues of "tool eating model"?

That's done deal for me, just take collective assessment of two scenarios, riding risky trails requires skills and techniques to avoid problems, live and learn, accept occasional failure and say "thanks" when it counts. 

[daniel_lyall]

You have been give advice by people who have done this for year's you can do it the slow way if you want or how ever you want by by.

[jw.hendy]

Can you back up any of this "safeguards" talk with any evidence at all? This is the same toolpath with a 1/4 ball. The only reason it's not worse is that the tool doesn't traverse as far onto the flat surface. It still eats into. How is this not a bug? Fusion is computing a path that puts the tool into the part. Period.

Daniel's answer made the most potential sense by far: Fusion ignores the rest of the part if you use touch surfaces. That would certainly be non-intuitive news to me, but I can live with that and log it away in my mind if this is truly a Fusion limitation.

[jw.hendy]

Seems like more exaggeration. I gave pictures and my file, asking a simple question: why does Fusion generate a toolpath that machines into the part?

All I could get out of anyone is how this is "well, it's just wrong, darn it!" No evidence, no explanation, no acceptance of inquiries I proposed to A/B test, and no answer to why the holy ball end mill also machines below that surface (despite it's "geometric safeguards"). Where is the evidence what you're saying is correct? There is none.

You could have learned something: a 1/4 bit works like a champ for miters, far better than a ball end mill. You just have to know what Fusion will machine surrounding areas if you use touch surfaces for a reason no one has explained. Awesome, lesson learned and now I know.

I 100% am sure that you have helped many others and that your experience is extremely valuable. You just didn't use it to answer my actual question, and the proposed answer (ball end) is no better than what I'm doing. I don't mean to upset you by this fact, but you can either provide evidence for what you're saying or... just stay upset and write me off, I guess?

[Anonymous]

Somewhere along the line I mentioned that set of choices in settings of operation are going to produce difference in proficiency of tool path.

The very first post in which I responded to you I used ball end mill WITHOUT refining detail, main point being tool does not cross over selected surface and it does not eat the model.

You can finish that surface with at least 3 different 3D strategies and all of them will be at home with ball end mill while only parallel and direction of cut you used will be acceptable using flat end mill and careful tweaking of settings.

It sounds as if you prefer fewer options just so you can justify this one instant in which you can get away with flat end mill.

You are free to do whatever pleases you just don't bother trying to sell the concept to me. I have done enough milling to know few things for a fact but will retire as "lathe guy" for the record.

That screenshot in your post has no meaning to me, I don't associate it with anything, could be a sail on a sailboat as much as a detail of a tool path.

I have cheated Fusion in few instances with great success but those are times when Fusion just did not have other option, why is it that I think you are doing exact opposite, using less effective option first in face of more adequate choice?

[Anonymous]

First of all, I am not upset, I am dedicating this time to defeat any and all claims you have in favor of using flat end mill when there are options that show better result without elaborate scheme of beating flat end mill into compliance.

There is one post in which I am showing you screenshots but not f3d file from which I derived them, why not?

Let's just say that your appreciation was not on level worthy of further free handouts.

I showed you result from flat end mill that is as clean as a whistle and one using ball end mill that needs no explanations.

You should look for ways to use Fusion that compliment your philosophy, the proof and evidence you seek is earned thru learning efforts so nobody owes you anything, I never claimed that Fusion is perfect but you have to know your stuff to squeeze the best out of it.

If you believe there is a bug, by all means, report it, get your money's worth and demand explanations,.... from right source.

[jw.hendy]

In your own test file if you change from avoid surfaces back to touch, then simulate and zoom in, you will see the 1/4 ball does eat into that surface as I've shown. It's not like I can just pull it up and show it to you so we can look together. I have other shots showing the lines below that plane. Now I'm just doing the same. Nothing to hide, it's not secretly a sailboat sail, it's me zooming in on what a 1/4 ball end does with my exact settings.

I don't prefer fewer options, I'm just asking how more options helps when you can only ultimately use one. And yes, I chose parallel because it is, indeed, the only one that works with a flat end mill. But it does work.

You're painting this like I'm sitting in this world of hurt over here, barely able to go on with CNC-life. I changed to avoid surfaces and... voila, problem handled. Great, whatever, workaround for Fusion's inabilities and/or bug is handled. Not even any "careful tweaking of settings." I just clicked two surfaces and would have had to change all the other settings anyway. Getting (a) an awesome miter, and (b) saving a tool change.

I wish I could think of some better analogy for mill/lathe work but I can't. I'm trying to imagine some age old adage like you can't climb mill, or you must always run steel at [formula I'm blanking on related to tool dia]. You ask about something you think shouldn't be the case in Fusion, and all you hear is that you can't freaking climb mill for crying out loud! But imagine climb milling was working great. "Yeah, sure, but why isn't Fusion generating what I expect?" Because you're climb milling you dummy! You don't even deserve to have a mill! Go cut some bread with your $200 cheap toy! I think you'd find that a frustrating interaction as well.

This whole interaction has felt like machinists fighting me on the internet over a belief that a baby seal dies every time someone does 3d toolpaths with a flat end mill!

I don't find what I'm doing that much of a stretch at all. Again, zoom in on a ball end and you'll see Fusion does the same, just not as far into the part.

[jw.hendy]

"...there are options that show better result without elaborate scheme of beating flat end mill into compliance."

I haven't heard a definition of "better result," and you already said it's not in the end result. I'm also not "beating" anything into compliance. It took one shift in strategy, that's it.

You're saying you're not upset, but you withheld a file as a sort of punishment? I went back and re-read my very first response to you after you replied, and it seemed you mistook it for something it wasn't. All I said was that a flat tool and tool center on boundary did not explain Fusion eating into my part. That's all. You described me as being awfully unhappy, threw in some condescending tone, and an eye roll emoji. I saw no justification for that. That set the tone for me. I'm not going to come crawling on my knees for your files. Sorry things went that direction. This indeed seems like it could have been a lot more pleasant and frankly I found this pretty jarring.

Re. this post, I guess I made a mistake. I thought I'd posted here before and had seen Autodesk replies and thought this was the sort of place for a bug report. I now see one is to use the Fusion 360 Support board, whereas I was just picking the closest related subforum that made sense.

My philosophy is "get good results in an efficient manner." To that end, being creative and trying a flat tool for a miter to save a tool change struck me as aligning with my philosophy greatly, to subsequently be surprised by behavior I've never seen in ~2yrs of using Fusion. That's all this was about.

[Anonymous]

I will agree to disagree, I have a problem consuming your phrase "tool eats the model" or "cuts into the model".

When you select a surface to cut and assign tool, stepover, boundaries and the rest, you end up with texture that is determined by tool shape, stepover, variable pressure of hitting those heavy steps you have after adaptive  clearing, feed rate, number of flutes and probably few more factors. 

So tool will leave concave passes and there will be a ridge between two passes, you can make smaller stepover and reduce them but they will still be there, do you require finish equal to glass before you stop claiming that tool "eats into the model" ?

How about transition of tool between those steps, tool suffers load of taking out peek height of each step then falls to very small amount of stock between ridges, having no load and springing into it after coming out of ridge, I would expect some horizontal tool marks indicating wavy surface as a result of that uneven surface.

I think I am losing you as far as your climb milling chapter that may be related to some other experience.

Anyway, just because something works, doesn't make it best option,...... I can assure you that slicing bread with chain saw can work beautifully with correct preparation of task but again the fact that it will work doesn't make it a preferable choice.

[Anonymous]

Oh, just one thing, I don't represent AD and AD does not represent me in any way, shape or form.

I preach what I believe to be the fact and I will accept guilt for occasional irritating response to what I perceive as juvenal behavior, like.... "odd explanation" .... that actually benefits your case,....  but we are bound by rules of conduct in forum so rest assured someone is watching and filtering this.

Again, can you for sake of understanding supply clear and definitive explanation of "tool eating the model" in form of file and outlined screenshot of "byte", something that is not result of expected texture or fighting grossly uneven surface left by adaptive clearing.

Also, does your machine have rigidity of commercial grade equipment or are we talking about router from Amazon and similar sources, may make a world of difference?  

[jw.hendy]

I think I follow, but you're talking about the miter and I'm talking about the surrounding area. It did eat into my model! If the toolpath went a little higher before traversing, it wouldn't have. Same miter, no bad result. I thought this was clear and maybe you saw this, but here it is again. Your connection of "eats in the model" to the quality of my miter surface lead me to believe you might not understand what my issue is. No, I don't need "glass" for my miters. They are great as-is. I need Fusion to stop eating other parts of my model while it cuts those miters.

I 100%, no hesitation whatsoever, love the blue. This post is about the red, which it cuts as it ramps to the top of the miter and then extends sideways.

It does this prematurely before it's level with that neighboring surface. This is where all my confusion is coming from. Fusion is part aware and cutter aware, not to mention it's technically machining into what I selected as a touch surface. Why would it stop short and cut into parts of the model that should remain?

I think your description of the milling is great and those are all awesome points. A ball end would lead in and ramp into the cut vs. hitting it all at once. That said, this is a 0.5mm stepover and wood, so I'm really not worried about constant load, tool deflection, chatter, or anything. I am getting great results. I haven't wrapped my mind around the projection of a cylinder vs. sphere onto a 45 deg surface, but I doubt at 0.5mm stepover the inevitable ribs are significantly different between flat vs. ball. In the extreme case if our parallel path was in z with a y stepover, the two bits would produce identical results. Still, you are absolutely correct that a ball handles this with more finesse.

I'm fine with this minor tradeoff as it's not affecting my machine, the flat can reach the bottom surface, and I save a tool change, which I lose using the ball end.

My bad on the analogy. Basically I wanted you to think of a time you've been told "it's just the way it's always been done," yet you experienced something different. I have only minimal true mill/lathe experience so I couldn't think of anything obvious. I know there are opinions about climb vs conventional... so that was my best attempt to propose you asking about thing x and all anyone can tell you is you can't climb mill in that situation, which you would feel has nothing to do with that you asked.

[Anonymous]

I stopped reading half way thru as things are starting to repeat, so here is what you have been waiting to hear.

Look back on my posts and screenshots. I am showing you tool path done by flat end mill where tool spills over into areas you marked red but it is 1 mm above the surface, how do I know that ?, I made it go higher to clear those surfaces.

The other screenshot you need to pay attention to is one with tool path showing only on slanted surface with flat end mill in corner of screenshot.

So in my mind we resolved this issue long time ago, all you had to do is ask how that was done but I lost interest in the whole think because I was not perceived as contributor to your cause.  

I believe Daniel also supplied a file that is nearly identical to one I was working on.

So the issue of tool eating the model is solved more then once using both flat and ball end mill, strange to see that you have missed it but if it's important to you it can all be fixed in a flash,.... or soon after.

[jw.hendy]

Understood re. Autodesk (and not being affiliated). I posted in Support with a replicate of this to find out if it's a bug. I meant to have illustrated "eating into my model" in the very first post:

• in Fusion, the toolpath looked like it came up the miter and extended onto the neighboring horizontal surface. All good. Let's go make chips.
• while making my case (four mitered pieces), on every one of them the bit would come up the miter ramp, and traverse sideways onto that surface...
• except, when my cleanup 2d contour ran (I'm leaving 0.5mm stock in my first adaptive), it didn't get rid of the parallel path cuts. In other words, the 2d contour and the horizontal segments of the parallel cut are happening at different z heights.

This caused me to go look at the Fusion file itself and observe that those sideways passes really are below that surface (and indeed occur lower than the 2d contour passes). This was my best attempt to explain what I'm asking (somewhere in a previous post):

Keep in mind, I've selected that entire miter surface as a touch surface... yet by stopping short/lower and traversing sideways, Fusion is actually clipping the top of that surface by machining into it (and the neighboring material).

As I mentioned to Daniel when he asked, it's a Shapeoko. I mean, certainly not my dream machine and firmly in hobby land... I don't think this is about deflection on something like this cleanup cut? Those gouges are pretty obvious and I have never noticed this before (this being, random gouges into good material due to deflection).

In my opinion I get rather great results. Here's pictures of the most challenging thing I've ever made, and it involved 2 sided flipping. I don't think I could have pulled that off if my machine yielded z deflection from a light 0.5mm stepover cut (or other errors that would have factored in and stacked up by using locating pins and 3 tool changes)! If you have a way to diagnose deflection as the cause, I'm willing to try.

[jw.hendy]

You asked what I meant, so I assumed you didn't know. You also conflated "eating into the part" with how the miter is machined, when it's never been about that. It's been about the surrounding material. Both the indirect (confusion) and direct (asking) evidence suggested you didn't know what I meant. So... I indeed repeated what was already said.

Yes, a workaround was identified (though you didn't respond to me asking about dummy material). Solving it by workaround isn't what I came to ask. It's why Fusion would force a workaround in the first place and by default machine into the part.