[CAD_CAM_EDM_DRO] Homing position

Hi All:
     Here is some food for thought!!!!
Last year I run a 72 piece lot that had five tool indexes per part for a total of 360 indexes.
About two thirds the way through I had to drill a part deeper because it slide back in the
three jaw chuck.  In the process of running the drill cycle over a block of information was lost.
The next time it came to the drill cycle it rapid traveled the drill (3/4" Silver & Demming) right 
into the part before the drill was on center.  Bent the shank good!!!  I was running it the way
the machine owner wanted to run it and had set it up.
     Now, consider this,  when I had made the prototypes in the manual lathe and run the threads
manually I could consistently stop the threading within a quarter second.  If the owner had
set the tool turret home position one third a second back from the part I could have stopped the
machine because I was watching it carefully with my hand on the E stop button.  How much more
would it have cost me in machine rental time.  About 120 seconds, two minutes or less then two
dollars vs the $18.00 for the drill plus the time lost to get a new one and set it up.
     SO MY POINT!  I think it is better to set the tool turret index position (part home to some)
a distance of about one seconds rapid travel time away from the part (+Z) plus the length
of the longest tool.  This may take a few seconds per part longer but it gives you a safety
factor if you are watching the machine.
                                                                             GOD'S BLESSINGS
                                                                                  Bill Thomas

   

On Wed, 14 Mar 2012 22:24:07 -0500, Jon Elson wrote

>  
>
> Roland Jollivet wrote:
> > Thanks. Thats what I wanted to know.
> >
> > I will be repeating different parts on different days using jigs, so I want
> > to regain my setup as quickly as possible. I can't imagine trying to run a
> > cnc machine without home positions.
> >
> If you have encoders with index pulses, then you can reestablish the
> home position
> with the accuracy of a single encoder count. If you only have the
> switches, then
> you need to determine the actual repeatability of them to know what kind of
> accuracy you can get from day to day. Many people report sub-thousandth
> of an inch repeatability with micro-switch limit switches, but I'm just
> a bit
> skeptical.
> > I am familiar with cnc mills and lathes, but was uncertain about the
> > tailstock on a manual machine. cnc lathes usually run the tailstock on a
> > separate slide so it's not in the way of Z travel.
> >
> One trick I would certainly do is to put a microswitch on the carriage
> that would cause
> an E-stop before the carriage hits it. In fact, my manual lathe has a
> big bolt on the
> carriage that will hit the tailstock to protect the DRO scale from being
> the first thing
> to make contact.
>
> Jon
>
>

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