Re: Bridgeport retrofit servo questions

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "braidmeister"
<braidmeister@y...> wrote:

>
> Mariss,
> In all of my research I haven't been able to get a consistent
> reposonse regarding the original steppers and new drives. Some say
> they use Geckos and they only get 50 IPM reliably, others use

Larkens

> others say they are getting 200 IPM rapids with stock

steppers...So,

> not to doubt anyone, but I just can't get a straight answer about
> what really works reliably in this particular scenario and what
> doesn't. I hear stories of poor low speed performance and drives
> burning out left and right. I REALLY don't want to deal with that.
>
> If I heard from a few people that were using a certain driver
> reliably with good performance and few headaches, then I would
> strongly consider it. Looking on various boards though, I get
> conflicting stories regarding steppers and drivers on the BP.
>
> Just about every retrofit 'kit' available for a Bridgeport is

servo

> powered. If steppers are cheaper and easier to setup, then why

don't

> they offer them in a retro kit?

There are many models of bridgeports ( both CNC and retrofits), some
are and were junk, some are so old, and/or were exposed to extreme
coolant chemicals and temperature environments, that the insulation
is sloughing off the wires in the spindle and drive motors. Some
models, when new, blew power transistors like popcorn, most would
pop a few corks if the Z axis was crashed ( a very common occurance
on these sort of conversational machines).

The reason that the servos are offered is because the retrofitter
knows what you have and has a reasonable chance of assuring you that
you will have a reliable and operating machine when you are done.
There is very little dependence on your ability and skills to dig
into 20 year old powersupplys and drivers and hack a workable
solution. If you have this ability and skill, clearly you can save
some money. The "but" is that you will also have to provide your own
maintenance and support, some of which is rolled into the commercial
retrofitters prices.

Steppers do not perform as competitively on this size machine as
servos. That's the bottom line, and the reason that later model
Bridgeports, and most new industrial machine tools have servos
instead of stepper systems. Performance means positioning speed,
and cutting speed for modern materials (like aluminum, plastics, and
composites), not just die steels and exotic alloys, which have
slower cutting speeds. 200 inches per minute rapids is a slow
machine by today's industrial standards. The Haas minimill for
instance has 600 ipm rapids, and 6000 rpm spindle on a 16 x 12 x 10
envelope.

Fred Smith - IMService