Re: [CAD_CAM_EDM_DRO]doodling with ideas

Lobes and cams, yes. Squares and Hex (es) are another story. Having said that, you need control over the spindle motion to
produce your off round shapes.
Let me state that more plainly. You need co-ordinated motion between the spindle and the carriage and cross slide. Equivalent
of X-Y and Theta (or is it Y, Z, Theta?). Some downfalls are that the spindle speed must be VERY slow to turn a cam. OK if you have
a live tool doing the cutting (grinder or spindle). Not OK if you are using a "regular" lathe tool.
The limitations have to do with the inertia of the cross slide and the capability of the control system. Imagine turning a
simple one lobe cam. At 180 RPM you would have 3 points of inflection every second to move your cross slide (accelerate,
decelerate, 6 times). Depending on the eccentricity of the cam, most cross slides would have no chance of keeping up. Of course
the bigger the part the bigger the slide, more mass to move, slower..... Mass compounds mass quickly.
Most vanilla CNC lathes are 2 axis with an encoder on the spindle so that it "knows" where the spindle is so that it can do
threading. Being able to move the spindle and the other axes in co-ordinated motion is way beyond vanilla and is not really a
"lathe".(more like a 'turning center') Being able go 3600 rpm and then stop and hold the spindle still while you machine the part is
an expensive trick.
I have had plans to build a lathe with stepper control of the spindle, but I have not figured out how to overcome the above
problem.
Lathe parts with flat sides can be produced on special "square turning" lathes that have floating spindles, but it is much more
cost effective to do it will live tooling on a lathe with spindle control. The srew machine method of getting square or hex on a
part is to use square and hex stock. It is much easier to put a round on a square than a square on a round.
Fin.


BillDarby wrote:

> Was just sitting here wondering if anyone has used any CNC lathe software that would allow you to turn shapes, other then just
> circular. It occures to me that under CNC control, a lathe should be easily capable of turning all sorts of shapes (squares, hex,
> lobs, cams)????
>
> Bill Darby
>
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