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Formula for calculating number of required stepovers.

Message 1 of 7
271 Views, 6 Replies

Formula for calculating number of required stepovers.

Hello there F360 Manufacturing,

I was wondering if anyone had a formula to automatically calculate the number of required stepovers, for roughing passes in 2D Contour, when machining a feature, such as a counterbore, that has a pre-existing hole?

The example: I have a Ø5mm end mill plunging directly down into the centre of a Ø8.2mm hole. I want to machine a counterbore of Ø15mm taking 0.15mm roughing steps and a 0.1 finishing step.
I want my number of passes to be enough that the tool begins its toolpath at the wall of the Ø8.2mm hole with a gentle engagement angle but not so many that I waste time cutting fresh air.

So far my attempts at working this out have not been successful when changing the variables and I'm sure it's something basic that I'm missing! Help would be much appreciated!

Message 2 of 7
in reply to: AidenSG

Use a 'model aware' toolpath like 3D Adaptive and select the pre drliled hole under the linking tab, you can constrain the toolpath by using the Selection feature bounding


That will use a constant stepover (you said .15mm) to mill out the counterbore pocket, select a 'Stock to Leave' value (default .5mm) , and clean it up with a 2D Contour utilizing something like a Wear cutter compensation path to cut on size


For the finish pass make sure to use an Internal Feed calculator to adjust for the 15mm path with a 5mm endmill, the speed / feed to cut in a straight line is too fast to interpolate without adjustment, if you want to cut close to on size

Message 3 of 7
in reply to: dwilliamsFM6K4

Thank you, dwilliams, I'll give the 3D adaptive path a go. 

Also I had not heard of an internal feed calculator before so thank you for mentioning it. I have some research to do.

Message 4 of 7
in reply to: AidenSG

Hi @AidenSG, just a small thing to think about and feel free to ignore me, but if you spend 10 min to eliminate 3 min of air cutting you are not saving anything. This is the dilemma of all folks that work in both analog and digital fabrication.

Good luck with your project, and keep learning!

Joshua Aigen
Workshop Supervisor
Message 5 of 7
in reply to: AidenSG

Here are 2 good resources for that, note this really only matters for Finish toolpaths where you are expecting to hit a certain dimension, I do not feed adjust a constant stepover roughing toolpath

Message 6 of 7

A tip I always use, if you define a stock contour it automatically trims the passes to be optimal. So you can put 1000 passes in and it will not only produce the correct number of passes but also trim their length. 

Richard Stubley
Manager - Manufacturing Specialist Team
Message 7 of 7
in reply to: Richard.stubley

Thank you for the tip. I shall try this in the future also.

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