Re: spindle counterweights

Thanks to everyone for the helpful suggestions. I will have to
look into implementing some of them.

The machine is a Hamill. I don't think there are many of them in
existence. They were made by a guy here in Massachusetts.
The control was a PDP-11 (I think, I haven't looked at it in a
while).
We bought the machine and control for $500.
Pretty good for a 7000 lb machine.

The counterweights aren't constrained against lateral movement
at all. The just hang from the chain.
I think it is a chunk of concrete in a metal box with two chunks of
plate on top to adjust the weight.
Anyway, I'll have to go to the shop and look at the machine to see
what I can do to make it better. I will also look into reducing the
acceleration.

Thanks for all of the suggestions.

-Jeremy

--- In CAD_CAM_EDM_DRO@y..., Wally Daniels <wdaniels@g...> wrote:
> 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