On 06/13/2013 07:22 AM, andy pugh wrote:
> On 13 June 2013 14:47, Kirk Wallace <kwall...@wallacecompany.com> wrote:
>
>> Depending on the thread pitch, there are one or two threads per
>> leadscrew revolution.
> ...
>> The ELS takes the place of the spindle to leadscrew and indicator gearing.
>
> My point is that the indicator measures the carriage position (modulo
> several threads) but an ELS does not know this position.
> (If the machine has linear scales, then the problem I am describing
> does not exist).

Looking at the Autoartisans ELS the X and Z positions are known by 
counting steps from touch-off, there is a spindle index and the position 
is probably interpolated (a la Mach).

> And there are many thread pitches where you can't use a threading
> indicator anyway (cross-standard threads with the 127 tooth gear, for
> example)
>
> I worked out all the change-gear settings for my Chinese lathe (before
> I thought of doing CNC). There are actually several changewheel
> combinations per pitch, but on that lathe 1.2mm pitch couldn't be
> disenaged.
> The summary table is on sheet 3 here, the workings on the other
> sheets: 
> https://docs.google.com/spreadsheet/ccc?key=0AhjJW1-T6n7CdFFSbTQwTjFmWlg3ZXVtUnNxSHo0dlE&usp=sharing

A limitation might come about if one is tied to the stock gear spider 
and change set, but as long as there is a ratio between spindle revs to 
leadscrew revs, there is a gearing of some sort that can provide the ratio.

It just seems easier to dust off an old PC and use LinuxCNC.

-- 
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/

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