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Creating a Step-off Chart for Turning Radii

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Jasonb:
Kim, it works for a radius tip as I said. You can either draw the offset line to the radius of a button tool eg 3mm away for a RCGT 06 or if using say a CCGT 060202 with a 0.2mm tip radius you just draw the line 0.2mm away from the curve you want. That is the insert I am using in the photo

Spreadsheet is OK for just a constant radius or ellipse. But where the CAD comes into its own is when a shape is made up from several components like angled line, radius ellipse.

You can also draw the offset lines at different spacings to keep the scallop or cusp length more regular as it follows the shape

petertha:
<edit I was typing as Jason was posting, I think it says much the same with different words>
CAD programs vary so there is no good universal advice here. Here I have  curve, happens to be a simple ellipse but it could be a complex spline for that matter. If you have a command to divide/overlay the curve with user defined N points it looks like this. Then you can define a tool tip radius (circle) & then copy paste that to each point. But its easier to work from an offset curve, its the same thing. The circles must be both tangent & coincident to the part curve. So now you have a bunch of coordinates in oddball X & Y values. My program does not have an easy way to export a table of these positions directly, that would be the ideal output to bring to the shop. I have made a screen grab which works but is unwieldly with high density spacing. There is another trick (again software app specific) where you can specify the circles as 'holes', as in drill holes. That then allows a 'hole table' output which is a quick 1-step command & prints as X,Y format on center. So a net longer workflow, but doable.

That's why for the few curve surfaces I've had todo this far, I just revert to the so called square profile parting tool profile with X,Y directly on the curve so the steps can be defined & managed completely in the drawing itself. In reality a square parting tool still has a radius, its just teeny. And you can build in a little bit of on-the-fly tolerance by cutting just short of the actual curve value which is desirable anyways come filing & sanding time. So if the theoretical infeed is 1.257", take 0.005" off & go in 1.252". Its not uniformly oversize depending on the curve shape, but it provides a bit of finishing buffer.

I wouldn't trust these techniques to more critical surfaces, but that's for the user to decide. 0.010" deviation on a cosmetic nose case is of no consequence, but it may well be on a small cam or combustion chamber for example. Speaking of cams, this is where some of the same issues come about, or at least where I stumbled n them. Here you have to be concerned about the profile of a cutting tool shape traversing over the cam X-Y coordinate at different setup rotational angles. Or a cam grinding machine that uses enlarged templates & a roller follower mechanism. Save that for another discussion.

Jasonb:
Radii are also possible with a lot of DROs. usually called the "ARC" function

I've only used it on the mill as my lathe does not have one but you just enter radius, tool offset and the increments along the actual curve that you want so gaps between cuts constant along the face. Works like moving around a PCD pattern, you just press the down arrow and it gives the co-ordinates for the next cut

Gives results like this and that was with a square edged milling cutter.

Kim:
Yes, I see what you guys are saying.  I don't know if I have an ARC function on my DRO. I'd imagine I do. But that will only work for a single arc shape, not an elipse or a compound curve, right?

Kim

Jasonb:
Just just a single arc much like your spreadsheet so you would have to enter a new datum and radius for a second one that blends to the first

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