Re: [CAD_CAM_EDM_DRO] spindle counterweights

At 05:00 PM 9/16/01 -0000, you wrote:

Hello Jeremy,

You problems with Counter-Weights are common. A number of points come to
mind as I read
your posting.

1. Before you operate your machine too much longer, take the time to make
sure your
Counter-Weight chain is in good shape. Determining the proper distance
between the chain
links is a good indicator, as is excessive 'fretting' on or around the
chain surface.
If the chain fatigues and lets go, it is possible to have some problems. :-)

2. If the counter-weight 'bongs' and creates excessive following
errors when decelerating or
accelerating, you may be able to correct some of this by adjusting the
vertical guide rails for the Counter-Weight
( if your machine has them ) so that the weight is more constrained against
lateral movement.

>I have a CNC machine that I have retrofitted to a more modern
>control.
>It is a bed mill with a 42"x20" bed and a 5 HP spindle motor.
>It was previously only capable of 2 axis simultaneous motion.

This is a good size for a bed! Lucky find.

>It
>had a dec pdp control. We have are now running a windows
>based control with a galil servo card.
>

Is this machine by any chance a KT with a DEC PDP-8 ? or was it a
Micro-Swinc control ? ( LSI-11 )
Does the galil card have the tuning software bundled with it ? If it does,
you should be able to conveniently
pick up OverShoot and such.

>
>I have been planning on writing some software to preprocess
>the G-Code and look for rapid accelerations in the Z and add
>acceleration and deceleration for those lines but I was
>wondering how other machines tend to handle the
>counterbalance issue since I think some of our problems are
>due to that. You can hear the counterbalance bouncing around a
>little under rapid acceleration.
>
>

Alot of machines of the Asian (Okuma, Mitsui-Seki) and European variety (
ELB,Wahli ) use a Hydraulic Cylinder arrangement as
a counter-weight. Some American Tool Makers did too such as Sundstrand's
OmniMil. Other like Devlieg used a big hunk of concrete. I
support 8 such machines and have had all of your symptoms occur at one time
or another. You may very well have to play with the
Accel/Decel as alot of these 'CNC' machines evolved from semi-automatic
designs that were never intended to accel to decel from
300+ipm.

I hope some of this info is useful. Above all, after you have determined
that the chain is ok, have fun ! It will not be all
that much longer before some of these unique and intersting machines go by
the way-side because of the cost of critical spares.

Best Wishes, Wally