Hi All,
At 2000 RPM cutting 20 threads per inch, my Z axis would have to move
at 100 IPM, ( I think).
Although my top speed is 180 IPM I wonder what distance it would take
to reach that speed. I think my acceleration is set at 3.5 but I
don't know 3.5 what. Can someone tell me what distance it would take
to reach 100 IPM at that setting?
I assume the deceleration would be the same so that potion of the
thread would be useless, No?
Jerry
--- In mach1mach2cnc@..., Art <fenerty@a...> wrote:
LatheHeads...
to thread with and I couldn't get the spindle speed where it
had to
be to get the best finish
Interesting note here on speed. Early on I was told that flashcut
had a
problem with threading above a certain speed, so I tried to design
the
compensator to allow any speed. This is, of course, impossible, but
I am
interested in any experience in this area. The technique is a
little unique.
I use a bresenham algorithm within the main bresenham algorithm to
slow down
time if the spindle slows. The design assumes the spindle will not
speed up
above the starting RPM during a thread (hopefully a good
assumption) so time
simply slows down for the pulser which has already computed the
pulse timing
using the original algorithm based on the originating spindle speed
feedback. This time slowing is done useing a time constant derived
on each
revolution as the adder to the bresenham. There is no way that one
pulse per
rev can do the job in the end I think, but I am interested in how
fast
anyone CAN do a thread using this technique.
This algorithm within an algorithm was the only way I could
think of to
do this reliably in a buffered pulse engine, the results will be
interesting.
To see your theoretical maximum thread pitch at any speed easily ,
you need
only set a spindle speed, and then jog back and forth in the Z
axis. The
reading of the Velocity/Rev DRO at full speed jog is your maximum
threading
pitch in your setup. This, of course, is because your rapid speed as
compared to the spindle speed is your maximum pitch per
revolution.You'd
need a fast Z carriage to do 2000RPM threading at any but a very
fine pitch.
The engine uses the number of 40us intervals between rotations as
the
constant for the algorithm as measured when the G32 is begun. So at
500RPM,
the engine has a count of 3000 intervals per rotation, It can
correct pretty
finely at that high a number, but at 2000RPM, the count is only 750
so the
ability to compensate has dropped by almost 75% from the 500RPM
mark. This
is all at 25Khz. At 45Khz you have 22us periods so the numbers get
better.
At 500RPM you get 5454 pulses per rev and at 2000RPM you get 1363
pulses per
revolution. So the quality at 500RPM in 25Khz mode should be equal
to the
quality of the cut at 909RPM in 45Khz mode. So just in case you were
wondering if 45Khz mode was any better even if you can't drive your
motors
faster, in this case it is because the thread compensation will be
more
accurate even at lower speeds.
Just an application note on threading...
Art
www.artofcnc.ca
