Re: [CAD_CAM_EDM_DRO]doodling with ideas

Hi All.

There was an article in Engineering in Miniature a few years ago describing
just this process being used at I think Woolwich Arsenal to "turn" complex
shaped rifle stocks in wood. A similar process was used to make wooden
pulley block housings for sailing ships.

Jim Gregg.

At 11:48 AM 10/16/00 -0400, you wrote:

>Thanks Joe
>
> I must admit I laugh to myself when I imagine a lathe trying to

turn a square at a high RPM (My mind inevitably pictures that

>classic clip if the early whirling / flapping attempt at the helicopter.

But seriously I can vividly recall pictures of the german war

>production of propeller blades and they were being cut essentially on a

lathe with power tooling while the "tool post motion was

>controlled by a cam follower against a "master" of the prop.
>
> Now,, if I dismiss any notion of "high RPM" I can visualize a tool

post moving back and forth in sync with the normal spindle

>(non moving [not precluding the rotation of the spindle]) computer

controlled to to trace the desired path on the part, over and over as

>the carriage feeds along the bed. Power tooling would be needed for

shapes which preclude the use of the standard cutter and careful

>speed control of spindle rotation would have to be programmed in at abrupt

changes in direction.

>
> I am sure you could have some colossal screw ups but with careful

programming I cannot see why such shapes could not be

>produced. ?????
>
>
>
>Bill Darby
>
>Joe Vicars wrote:
>
>> 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