Re: [CAD_CAM_EDM_DRO] spindle forces

----- Original Message -----
From: "Jon Elson" <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, June 16, 2002 2:34 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Power Supply Circuit


> Les Watts wrote:
>
> > Well, I have horrible power quality here and often ride through dips as
> > well. A computer
> > without an ups simply will not function around these parts.
> >
> > What is most important to me in a power dip or loss is not to have
continued
> > machine
> > motion after the SPINDLE has wound down.
>
> Yes, I've had this happen. I now have the fault relay in the VFD hooked
into the
> e-stop chain, so if the VFD loses power long enough to drain the cap bank,
it
> will e-stop the machine.
>
> Jon
>

That's a good idea.

I am using router motors rather than vfd driven induction so I would have to
do something different. They are prob series or compound wound
universal motors with built in phase control. I could get some kind of
rpm signal from them- they may even have a tach but more likely use
ir comped back emf for the phase control.

I still would like to software clamp spindle side thrust force. I did some
calculations
and find that my total transmission (preload) drag torque is about the
equivalent
of the torque required to exert 250 lbs force on the tool! A simple
subtraction
may not be enough if there is a higher static friction coefficient on the
preloaded
bearings. I will just measure it. I have found that drag force is constant
over
a wide rpm range once it's moving at least.

One might wonder why I am so concerned. Well the calculated peak force on
my machine is a whopping 2550 lbs!!! As I said before high forces are needed
to get 1000 lb of gantry zipping around like a plotter pen (and it does).
But I don't
want the spindle to ever see it.

Now something would break if I drove the thing into work or something. I
chose
to have the router end bearing housing be the weak link. I was going to beef
it
up but didn't for that reason. I would rather lose that than other expensive
machine
components.

But better to clamp spindle force- either software or shear pins.
That would protect from all but impulsive impacts.
Soon semi skilled labor will be pressing the buttons.
That might even be me...
heh heh....

Les

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.rabun.net/~leswatts/shop.html