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Creating a Step-off Chart for Turning Radii

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Jasonb:
I just tend to pull it off the CAD drawing.

1. Draw a line that follows the curve that is spaced away from the surface by the radius of the cutter if a button tool or its tip radius if a normal insert

2. Draw a line and then pattern that as many times as needed at a spacing to suit the increments you want. You can vary the line spacing too.

3. Take the lengths of the points where the lines meet the offset curve from your datum Zero.

Best thing with this method is it will do blended curves/shapes where you may have a circular fillet flowing into an angled line and ending in part of an ellipse.

gbritnell:
I have been modeling curves by the step-off method for most of my building career.  Back when I started my apprenticeship there were no computers or even calculators so each of the journeymen on the machines had a little black book of radii calculated bu using several different sized ball end mills.  All these numbers were generated using trigonometry with the sin cosine functions. It took hours to create these charts using longhand math so the books were closely guarded.
The biggest thing to keep in mind is the size of the cusp or the amount of material left between cuts. It's a happy medium between taking forever to machine or taking forever to finish out by hand. Today with a computer and a simple CAD program one can make a whole surface of curves, radii and connect surfaces in no time.

Dave Otto:
Jason, this is exactly what I have been doing.
Depending on how many points you want it can get pretty laborious.

Dave
 

Mcgyver:
Likewise, it works so well I've just never had much (any?) motivation to make or buy a ball turning tool.   I usually use a couple of thou for the step and have a simple excel sheet I use and have posted it for who might find it of interest (attached hereto).   Afterwards, file for a minute or two then polish.

Kim:
McGyver, that's a nice spreadsheet.  Simple and straight forward.  Thanks for posting it.

I've never used a CAD program like that for taking off points from, Jason.  I considered it but it always just seemed easier to do the spreadsheet rather than make the curve in CAD and figure out how to transcribe all the data points.  Plus, it wouldn't help for a tool with a radius tip.  I'm sure there's a way to do that with CAD too, but as I said, using the spreadsheet just seemed more straight forward to me.  Probably because I know Excel well, and am still quite the novice with Fusion 360.

Kim

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