RE: Threading on a lathe with EMC

[Ethan Vos <ethan-at-forward.ca>]

Part of the issue has to be a reasonable amount of time cutting air before 
the tool hits the part. This will give the control a certain amount of time 
to figure out what it's doing and make any corrections.

Ethan


-----Original Message-----
From:	Paul [SMTP:paul.corner-at-tesco.net]
Sent:	Tuesday, October 30, 2001 4:02 PM
To:	Multiple recipients of list
Subject:	Re: Threading on a lathe with EMC



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