2D face milling CAM - passes - problem defining stepover - toolpath

[michele4_rota]

Hi,

I am a student and I am trying to understand how Fusion360 generates toolpaths. I'm also new to the forum.

I want to create a simple 2D Face Milling operation on a plain surface. I want my tool to enter the material by 4/5 of the diameter (I'm using a mill 50mm diameter) and so I set the Stepover to be 40mm. But when I create the toolpath and look at the Toolpath Data, I discover that the tool is not following my instructions and it's using an other value for the stepover. I mean, the tool is not moving on Y axis by 40mm as I specified.

[jhackney1972]

Please attach your model.  Open it in Fusion 360, select the File menu, then Export and save it to your hard drive.  Attach it to a reply post using the Attachment section of the post.

When asking a question concerning a model, it is always a good practice to attach it as well as screen captures as you did.

[michele4_rota]

Okay, sure. Thanks for replying me. The problem is that the Stepover is set to 40mm, but when I simulate the operation, the tool is moving by 32.09mm (I identified this distance from Y-coordinates). I don't understand how the toolpath is generated because it seems the Stepover is not the value I put.

[jhackney1972]

I do not see an issue, your Stepover is working fine.  In the video I changed it to 10mm Stepover to show the difference.

Edit: I can see the Stepover is not exact by the Toolpath table but is probably due to the calculation to the width of the facing surface , otherwise I do not know.  Maybe @seth.madore could explain it better.

[michele4_rota]

Sorry but I don't get it.

I understood that if I change Stepover, the path is changing. But it changes randomly.

I mean, for example my stock has a width of 160mm and so, if the Stepover is 40mm, theoretically I can cut the surface in 160/40=4 steps, but in your video I see 5 blue lines which means the working engagement of the tool is not 40mm, but less.

Infact if I try to visualize the position of the tool during its motion, the tool is following these positions (I can see them in the "info tab" during the simulation):

Y=-72.51mm, Y=-40.42mm, Y=-8.33mm, Y=23.76mm, Y=55.85mm

And the distances between these positions along Y-axis are 32.09.

So my question is: what is the Stepover in Fusion360? Because at this point i think it isn't the distance between blue lines in CAM.

[seth.madore]

That's actually an interesting observation, and one that I've never picked up on. I just use the toolpath and produce parts, I never inspected the actual X/Y values to see how close they adhered to target values. 

I'll have to ask around on this and get a better understanding of the logic behind it..

[seth.madore · Accepted solution]

Had a chat with a developer, and the Stepover is a "Maximum Stepover" with the goal being to produce equal stepovers across the selected contour.

[michele4_rota]

Ok, now I understood. Thanks for help.

[programming2C78B]

It's always acted as a Maximum for me, and if you set it to MORE than your part width, the facing toolpath will run right along the center of your part in a single pass! A great trick not many know about, since Fusion lacks the "single pass" option that Mcam does for facing.

[leo.castellon]

Great find! I usually draw a centerline through the part, this will save time, thanks.

LeoC