"DoN. Nichols" wrote:

On 2012-03-18, Pete C. wrote:


trimmed


Most any CNC mill can be used manually if it has an MPG. Just select the
axis and a suitable step rate and crank away. I can't really see why you
would want to though when you can just "manually" machine one line of G
code at a time in MDI mode.

By MPG I presume you mean Manual Pulse Generator. The
Bridgeport did not have that, and while there were complete schematics,
the CPU was a DEC LSI-11, and there was no source code for it to allow
adding such things to it. (Not to mention that it was limited to 64K
bytes (32K words) of memory -- both the G-code program memory, and the
machine language code (in ROMs) which translated the G-codes into actual
motion. This was in the early days of CNC. Bridgeport's BOSS-3 was the
first model to escape form the factory (nobody seems to know what
happened to the BOSS-1 and BOSS-2 -- presumably died of too many bugs to
be released. :-) They stayed with the stepper motors up through the
BOSS-6, and I'm pretty sure that the BOSS-8 was servos, but I don't know
whether the BOSS-7 was similarly invisible or not. :-)

Nobody ever released a version of EMC/LinuxCNC for the LSI-11,
and I doubt that anyone would bother with the limitations of memory.
(Back then, they even measured the memory in "feet" (feet of punched
paper tape, at 10 bytes per inch. That whole address space would only
hold 546.1333 feet of tape -- even if no space were being used for the
code in ROM. :-) This is one reason why they came fitted with a punched
tape reader. If you set your program up right, you could load almost as
much as memory was available for, then run that part, and when it was
done, it would automatically read the next chunk of tape to proceed with
the program. Then, you were only limited by how much tape you could get
on a reel. (Or maybe even more, if you could swap tapes while it was
running the last chuck which would fit on one tape -- but that required
being a bit more alert than CNC made common.

Why not three MPGs -- one per axis, so you could crank two axes
at once -- or even three if you put one in reach of your knee. :-)

Obviously, as I convert it to servos, a MPG is a nice feature to
add for positioning and for testing layouts with the system serving as a
DRO.

It's kinda fun sitting on the table of a large gantry machining center,
MPG pod in hand, dialing around the table you're sitting on (X) as well
as the gantry (Y) and head (Z) as you reinstall the spindle cartridge
after rebuilding it.