Ball Nose Mills and Cusp Height Calcs

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Ball Nose Mills and Cusp Height Calcs

Postby TReischl » Sat Feb 23, 2019 9:52 pm

For some odd reason it started bugging me that I really did not know what kind of finish I was going to get based on the stepover settings for a ball nosed endmill.

There are some obvious issues, stepping over by a fixed amount produces different results depending on the radius of the ball nose. The same is true for percentages, but those are a little bit better.

But what I really understand is cusps. The ridges left between passes. I have a sense for the difference between .0001 cusp height and .0003.

When I checked how I had my tools set up in the database I was amazed at how different the cusp heights were from tool to tool.

Sooooo, it was time to get out Excel and do a spreadsheet. Warning! The ball nose info is entered as a radius, so if you are using a .25 diameter ball nose it should be entered as .125. I did this because some ball nose tools are spec'd as radii and others as diameter. Had to choose one or the other.

Also included are two jpg files that can be printed that show settings for both metric and imperial tools.

Here is the formula I used in case any of you want to set up a sheet yourself or just calc a few tools you have and you do not like my choices.

Stepover = =(SQRT((R^2)-((R-CH)^2)))*2

Where R = radius of the ball nose tool and CH = the desired cusp height.

Ball Nose 1.jpg


Ball Nose 2.jpg


I would have included the Excel spreadsheet but the software does not allow .xlsx files to be uploaded. Sorry about that.
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Re: Ball Nose Mills and Cusp Height Calcs

Postby Rcnewcomb » Sat Feb 23, 2019 10:03 pm

I would have included the Excel spreadsheet but the software does not allow .xlsx files to be uploaded.

You can compress it as a ZIP file and upload the ZIP file to the forum.
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Re: Ball Nose Mills and Cusp Height Calcs

Postby TReischl » Sat Feb 23, 2019 11:28 pm

Thanks Randy! Done.

Excel Spreadsheet file:

BallNose StepOver.zip
(8.18 KiB) Downloaded 92 times
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Re: Ball Nose Mills and Cusp Height Calcs

Postby Bob Jr » Sun Feb 24, 2019 12:21 am

Thank you for your help Ted.
These charts answer a lot of questions, and will be a valuable resource when designing!
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Re: Ball Nose Mills and Cusp Height Calcs

Postby WNC_Ed » Sun Feb 24, 2019 6:26 am

I have added "Cusp Height" to my vocabulary and you spreadsheet to my toolbox.
Thank you for sharing!
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Re: Ball Nose Mills and Cusp Height Calcs

Postby Leo » Sun Feb 24, 2019 4:59 pm

Best thing since sliced bread - that is awesome Ted - thank you.
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Re: Ball Nose Mills and Cusp Height Calcs

Postby jarm2 » Sun Feb 24, 2019 6:31 pm

Thanks, Ted. Appreciate the thought that went into this. I have wondered how to eliminate most of the cusp lines on projects and this will help optimize my stepovers to accomplish this. Have a great Day. :lol:
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Re: Ball Nose Mills and Cusp Height Calcs

Postby TReischl » Sun Feb 24, 2019 7:51 pm

Glad you folks find it useful.

Hopefully the Vectric Team will take a look and incorporate it in a future version.
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