Re: [CAD_CAM_EDM_DRO] Bridgeport Milling Machines

info.host@... wrote:

>
> I suspected the idea would not work from the moment I dreamed it up, it was
> just a thought. Perhaps another way would be to make the tracer probe think
> it's hitting the sides of the part to be traced so you don't have to muck
> about with the hydraulics themselves? Does the tracer's table sit still and
> the guy moves the probe by hand or does the tracer trace something sitting
> on the end of the mill's table?

There are a bunch of different tracer systems. The simplest scheme is a one
axis tracer on Z, where the operator arranges for the machine to sweep back and

forth with a power feed in X, say, and bumps it in Y after every sweep. The
tracer
probe makes the mill's Z axis follow a pattern bolted to the table, and the
cutter
duplicates the shape on the workpiece.

Then, there are 2-axis contour tracers, that will hog out arbitrarily complex
pockets to a set depth in a part, or the exterior. These can generally follow
the contour all the way around the part, switching from X to Y, or using both
at the same time to work its way around the shape. I'm guessing that this is
the sort of machine you were talking about. There were also 'electronic eye'
tracers that would follow a line on a drawing. There was a platen with a
drawing
taped to it on one end of the mill's table, with the eye looking down onto the
drawing. It follows the line, moving in X or Y to follow wherever the line
takes
it.

I don't believe I've ever heard of a full 3-axis all-hydraulic tracing machine.

For one thing, it would need a lot of hydraulic gadgetry to be able to program
the most desirable scanning grid over the pattern, and I doubt many shops
would buy such a beast unless it was fairly flexible in the way is scanned
the pattern. Somewhere around that level of complexity, they would just
go to a full CNC system.

Your idea is not completely crazy, but I think it is harder to do than you
think.
Also, to make the tracer work as a servo amp for a CNC, you need position
feedback to the computer. With leadscrews, you can always put a shaft
encoder on it, and you've got feedback at relatively modest cost.
Without leadscrews, you are stuck with expensive linear scales as the
only way to measure position. There are a variety of technologies out there
for linear scales, but they are ALL expensive.

There's one other thing you should know. The proportional valves have
VERY tight tolerances, that have had hydraulic fluid forced through them
at 1000+ PSI for years, and they are almost always in a state of poor
performance when a machine is sold. So, the extremely tight control
of position it once had is no longer there, and the valves are rather
intricate and hard to repair.

Also, these machines are not only noisy, they use a HUGE amount of power,
somewhere between 5 and 15 HP even when standing still, for the hydraulic
pump. That could be a big problem in your garage.

Jon