## Ball Nose Mills and Cusp Height Calcs

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TReischl
Vectric Wizard
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Joined: Thu Jan 18, 2007 6:04 pm
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### Ball Nose Mills and Cusp Height Calcs

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.
I would have included the Excel spreadsheet but the software does not allow .xlsx files to be uploaded. Sorry about that.
"If you see a good fight, get in it." Dr. Vernon Jones

Rcnewcomb
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### Re: Ball Nose Mills and Cusp Height Calcs

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.
- Randall Newcomb
10 fingers in, 10 fingers out
another good day in the shop

TReischl
Vectric Wizard
Posts: 3568
Joined: Thu Jan 18, 2007 6:04 pm
Model of CNC Machine: 8020 Build 48X36X10 RP 2010 Screenset
Location: Leland NC

### Re: Ball Nose Mills and Cusp Height Calcs

Thanks Randy! Done.

BallNose StepOver.zip
"If you see a good fight, get in it." Dr. Vernon Jones

Bob Jr
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### Re: Ball Nose Mills and Cusp Height Calcs

Thank you for your help Ted.
These charts answer a lot of questions, and will be a valuable resource when designing!
Bob
hammer...nails...stuff

WNC_Ed
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### Re: Ball Nose Mills and Cusp Height Calcs

I have added "Cusp Height" to my vocabulary and you spreadsheet to my toolbox.
Thank you for sharing!
Maker of sawdust

Leo
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### Re: Ball Nose Mills and Cusp Height Calcs

Best thing since sliced bread - that is awesome Ted - thank you.
Imagine the Possibilities of a Creative mind

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jarm2
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### Re: Ball Nose Mills and Cusp Height Calcs

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.
Vectric Aspire 10, AutoCAD lite, Corel Draw 2019, ViaCAD Pro 9, W 10

TReischl
Vectric Wizard
Posts: 3568
Joined: Thu Jan 18, 2007 6:04 pm
Model of CNC Machine: 8020 Build 48X36X10 RP 2010 Screenset
Location: Leland NC

### Re: Ball Nose Mills and Cusp Height Calcs

Glad you folks find it useful.

Hopefully the Vectric Team will take a look and incorporate it in a future version.
"If you see a good fight, get in it." Dr. Vernon Jones