How accurate is simulation?

[Helmi74]

Hi,

i wonder how accurate simulation is intended to be and what it is used for? Especially for a new CAM user like me simulation is extremely helpful to find out what special parameters do and how they are intended to work.

I have prepared piece with some pockets. I managed to setup the stock easily (this really improved since i looked at it last time - good job!). Then i setup a 2d pocket, selected my pockets and was quite a bit surprised as it looked like the lines showing the toolpath looked way to near at the outer edge of the pocket. I started simulating and saw this: http://note.io/1C1RW5s

As you can see on the image the tool is crossing the the models edge (the darker one) removing stock (the brighter material) but not showing any possible conflict there. If i wouldn't look closer at the simulation but only look at the result i would see a proper result as it just seems to show my model and not whats the result of the milling process. I guess this is not how it should be and most probably i'm just doing something wrong, right?

Frank

[fonsecr]

The stock simulation is an approximation - which more of less tries to follow the tolerances of the toolpath being simulation. That said, however, your issue is unrelated to this.

Looking at your picture you are showing cutting into the part. Note that when using 2D strategies these only look at the contours you specify. The 3D surface model is not used for these strategies. You need to use the 3D surface strategies to automatically gouge check against the surface. For 2D strategies it is your responsibility to make sure the settings are appropriate for their purpose.

The cutting issues can be categorized into 2 groups. Gouges and Collisions. Gouges are loosly defined as cutting more than desired into the part. And collisions as cutting into stock when not allowed (e.g. moving the holder into stock). Only Collisions are detected by the simulation since the system doesn't know when the user intends to cut into the part and when not to.

We are adding more options for Simulate which will allow you to visually compare the part and stock so you can verify that the machined part is as desired.

[Helmi74]

Thanks for your explanation, fonsecr.

Actually the mistake was different like you suggested. I selected the bottom faces of my pockets for pocket operation and i don't know why the pocket it created was much bigger than the edges of the pocket actually.

I did select the contours instead which is a bit more complicated and now i'm coming close to what i want.

May i add another question here as it is somehow related.

Is there any option to clear corners? Example here. My pockets are slots with around 3mm width and 100mm length. I will use a 2mm flat mill which will of course leave material in the corners at around 1mm radius. In the woodworking tools i used so far i have the option to clear these corners. In this case the outer boundaries of the pockets somehow get ignored and the tool moves a little bit out to the corner. This is to make sure that other parts fit in there (you may imagine like a tounge and groove connector).

Is there an intended way how this can be done with Fusion360 CAM?

[fonsecr]

I think I need a picture 🙂

Some general notes:

However, for woodworking and cutting slots I think 2D Contour would normally be what you want to use (to ensure nice tangential cuts - without rolling around your corners). You can control the stock to leave on the side using the Stock to Leave feature. When full engagement is an issue you can do a center cut first - also using 2D contour - either with proper offset specified or with actual center line selected. And then finish the 2 walls with a separate 2D contour operation.

[Helmi74]

sure, here's a picture of these slots/pockets. Like i said they are around 3mm wide making room for 3mm plates that should slot in there later. To make them fit perfectly the corners need to be cut. Unfortunately tools tend do be round 🙂

http://note.io/1yluhvj

let me know if you need further input or an impression how other tools solve this issue.

[fonsecr]

Ok so you want to cut the closed end of the slot. You can use rest machining for a 2D contour operation using a smaller cutter in that case.

[kb9ydn]

I think he may be looking for something more like this (the slot on the left).  The only way to do this is to model that feature into the part.

C|

[Helmi74]

Exactly this is what i'm looking for. Several tools are offering this feature so i thought Fusion360 CAM maybe offering it too.

[jeff.walters]

I understand what you’re looking for its called corner relief. The thing is that’s a designee feature not a CAM feature. If you want it contoured you will have to add it to the model. You could do a drill operation using your mill and selecting the corners.

[HughesTooling]

Some CAM programs do give you corner options without having to draw them.

Here an image from BobCAD.

Mark.

[kb9ydn]

I think Mastercam does something like this as well.

To me this is kind of a hobby use vs. industrial use thing.  Industrial users are more interested in design maintenance and will normally want the design file to match the finished product as closely as possible.  So the corner reliefs would be designed in.  But hobby users are likely more interested in the finished widget, and don't care so much if the design file doesn't exactly match the finished product.  Personally I tend to have the industrial mentality even for my own personal stuff (because I design and fabricate for a living already), but I can see how strictly hobby users just want to get from idea to finished product as quickly as possible.

Fusion is sort of an interesting case, since it seems to be trying to bridge the gap between industrial use and hobby use.  Therefore, I think it would be good to at least consider the idea of a corner relief function.  If it were me, I would want to see it as a design tool, where maybe you pick a corner edge and set a radius, and it creates a relief in that corner.  A simple hole with the center at the corner vertex will work, but that removes more material than is necessary.  I think it's better to have the hole coincident with the corner vertex.  It's not that difficult to model this in with the tools available now, but if you have a lot of corners to do a dedicated tool might be nice.

C|

[jeff.walters]

thats not overcutting the model is it?

[kb9ydn]

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@jeff.walters wrote:

thats not overcutting the model is it?

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Well I guess any corner relieving done during machining would technically violate the model (if it's not modelled in).  That's why I would rather see it as a design tool.

C|

[lukepighetti]

I find simulation to be very accurate. I wish there was a tool for analysing stock left, or a way to add a pocketing operation to remove what I call "hanging chads" (blast from the past!) before they occur.

What I do notice, is that sometimes after the simulation has stopped due to a crash (because you checked that checkbox) it will stop simulating cutting the stock. But other than that, it's dead on. I spend a LOT of time in simulation before heading out to the machine. Saves me a ton of time.