Terry, I think I confused you again. I was not using the flat length (chord length), but rather the distance across the flats - what you actually measure with a caliper across flats. You can call it the inscribed circle diameter otherwise.

Dan

Wonder if we can make this as the next stage:

http://www.youtube.com/watch?v=FpP7iTKuWpw



Dan

Amazing work you fellas are doing here, thanks for sharing-

Dave

OK Makes sense. What you are describing would be the Root Radius of the flats?  Hard to measure diam across a 3 sided object (;-)

One easy way at this point to make it multpass would be to scale the routine oversize on the first pass then reduce the scale for each pass down to the root diam of the flat.

We do this with cam grinding to make it simple as the math there is horribly complicated.

(;-) TP

This is VERY neat and interesting to follow.

I have questions though.
Would this have any practical application, other than just in certain plastics ?
With a neutral top rake tool, a 4 sided shape would transition from +45 to a -45 top rake angle. 8 sided, 22.5 degree. The more flats, the better.
You can almost see the effect of this in the Delrin oct. sample....(and BTW, the little metal hex sample looks surprisingly well.
Russ

Practical Application ??  Probably not as you see the rake angles are extreme and the Power needed to  rotate the shaft slowly and cut is HIGH  and not readily available on a DIY type lathe. ALSO most lathes do NOT have an encoder to run it as a 4th or follow mode.

IT is just NEAT to think about.

(;-) TP

Thanks T.

I agree !  A very cool exercise.

You and Dan do good work.

In envy,
Russ
 

Terry, yes, that would be the root radius. Sorry for the confusion, but always had the hexagon in mind while doing this and assumed it was obvious. I will have to give it a bit more thought to make it multipass. Don't want it to cut air at any point.

Russ, I agree, squares may not be practical, but I believe hexagons and above should be doable in metals provided the rake angle is correct. We shall see this. Now I really think eccentrics should be next... what do you say, Terry?

Hmm... didn't notice the metal hex sneaked in - obviously they have some better ways to make hex shapes out there...

Dan

So are Cams lobes next?

  Now I really think eccentrics should be next... 

Hmm... didn't notice the metal hex sneaked in - obviously they have some better ways to make hex shapes out there...

Dan

Hi Dan,
 Cams and eccentrics would do OK ou to a point where the offset becomes so great as to require the other axis, ie. the tool moving up and down to maintain tangency to the surface.
Graham posetd some cool references earlier, will try to find them.
Thanks again for a great topic,
Russ