Re: Threading on a lathe with EMC

[Paul <paul.corner-at-tesco.net>]

Hi Ethan

As far as I'm aware, EMC does not have a facility to vary spindle speed 
(yet). The only control is on/off and direction. I have two machines here, 
one with a vari-speed head controlled by an air motor - The other is a 
standard gear box and three phase motor powered by a VFD. Both have differing 
requirements for speed control along with vastly different response times. 
Hacking a subroutine to control the spindle speed via a spare DAC and/or IO 
pins shouldn't be too involved if it is needed.

Using the C axis as it currently stands is far from ideal - Some thought of 
mine on the subject:
Regardless of direction of spindle rotation, the encoder count should 
increase - This makes the trajectory calculations trivial.
Some way of handling the counter overflow cleanly needs to be defined. 
Setting the counter to roll over to zero at each index pulse is probably the 
neatest.

Syncing the movements to the spindle is going to be the major stumbling block 
as far as I can see. If the tool is positioned at the starting point of the 
thread and a G33 move commanded, there will be a delay before the tool has 
synced. There would be a momentarily high commanded velocity that probably 
exceed the following error and acceleration parameters and so cause an E-stop.

It seems that each time I look at the problem, I find another piece of the 
puzzle needs to be kicked in to place - I feel another ini parameter will be 
needed to define a time period to ignore following errors during syncing.....


Regards, Paul.



On Tuesday 30 October 2001  3:12 pm, Ethan Vos wrote:
> I'm looking at it from the perspective of replacing the control on an
> existing CNC lathe. It has the proper spindle encoder.
>
> What controls does EMC have for the spindle? Is it just an on/off or is
> there an analog out?
>
> All I need to do is to write the IOSH stuff to handle the turret and the
> gearbox spindle and I'm away.
>
> I think a re-setting rotary axis would be a good idea.
>
> Ethan