> > Paul wrote:
We do need something fast as a lot of material is removed.
Especially on something large like a 3D contoured bell housing
pattern.
Many many tool paths are involved to get the smooth surface finish
necessary.
You won't machine anything at 300 IPM, at least not with that spindle.
With your spindle turning 7000 RPM, 300IPM would be a feed per tooth
of
0.020" on a two flute mill. For an end mill in Alloy you are looking
at a
max of about 0.011", less for a ball.
With a 1/4" ball end mill, you would be looking at about 548 SFM,
which is a
low for alloy .
Drive a 1/4" ball though foam at 0.020" feed and 548 SFM, and you will
just
tear it apart, not cut.
In practice, you will machine far below the rapid speeds of the
machine, so
whether the machine can do 300 IPM rapids, or only 120 IPM rapids
won't make
much difference in run time.
To do high speed machine you would need a much faster spindle, and an
effective cooling system.
Regards,
Mark
Let me see if I understand what is going on here. It is up to the PC Intel
processor
to repetitively send 3 bits through the parallel port that move the 3
axis's, .00001
inch each, at rates that result in smooth 3D motion. This is why feed rate
is limited.
Correct? The Geckos receive these bit rates and convert them to analog
voltages +/-
70 Volts for the servos. This is done in hardware (resister-capacitor
integrators and amps) with no processors on the Geckos. Correct?
If so what are typical bit rates for 1 gig processors running DOS?
Paul Lamar
The main limiting factor would be the Geckos supplying ~70V (Max is 80V, but
you need a little headway in California with your utilites :) to your 100V
motors . I think thats what Harrison said they were. That is why you would
not get 300 IPM rapids, rather around 200 ipm, unless you went to the more
powerful Rutex drivers. I really don't think you should hang up on that max
speed.
Parallel port frequency can become a issue on Servo systems, because there
are some extremely fine resolution encoders out there.
Take the example of a 1000 line encoder. You have 4000 discrete positions
per rev (quadrature). If your machine has a direct driven 5TPI ballscrew,
you are looking at a resolution of 4000 *5 =20000 increments per inch
(0.00005" per increment). If you want 300 IPM (5IPS) you would need 100kHz
from the LPT.
Under DOS, the new timing module in TurboCNC V4 is testing at about 100Khz
on a fast CPU, but you would be on the ragged edge. The current V3.24
doesn't seem to correlate well to CPU clock speed, with K6-2's delivering
the highest port frequencies.
Mach2 does 45Khz under WinXP.
I have placed the question on the CAD_CAM_EDM_DRO group as the max frequency
of the LPT under RT Linux.
All is not lost. The resolution in the example is unnecessary. You will
never see that sort of accuracy on this mill. Thermal expansion alone across
20" of table is about 0.001" per °C.
To get around this problem you have three choices, replace the encoder with
a 200 line encoder (yielding 0.0001 resolution, thus 20Khz for 300IPM),
used the G340 geckos instead of a G320. The G340 can be set to move 5
encoders increments for each step pulse (or 10 or 2 or 1) achieving the same
result. Or you just limit your max rapids to whatever the LPT will deliver,
say 150IPM, which you will likely do any way.
Regards,
Mark
wankel.org
American Flyer wrote:
Mark,
The problem with the Geckos only being rated for 80V is not so much that
we couldn't use full 300IPM speeds, it's that the power
supplies in our mills produced in excess of 100V. The Geckos can't
take this as an input which means we would have to come up with a
way to supply only ~70V at ~40-60A (at this point I'm assuming
that Paul's mill and mine have identical servo power supplies). The
motors are actually rated 92V.
The servo drivers on my mill are working fine, but are the old
original ones which PWM at about 5KHz. They squeal, and being 20
years old it is questionable how well they can be supported when
they eventually break. Regardless of which USB controller I end up
using (my own or the G2003), I think I'm going to put Rutex servo
drivers on my mill. Since they are rated at 200V, they will be in
no danger of damage from the 100V+ supply input, even if the power
company decides to send some bonus volts. The Rutex also have the
nice feature of being able to software adjust the PID settings
via an SPI port. With the right software, the PID alignment could be
completely automated.
By the way, I've been running my mill at 300IPM (no cutter)
to see what it's like. It's easy to envision major carnage if anything
goes wrong at that speed.
Harrison Young
Harrison, I have new servo amps from Servo Dynamics in Chatsworth CA.
Got everything working today except I have a continuous chatter or low amplitude
oscillation in the x axis servo. What could be causing that?
Z and y axis are working fine as does the tool changer.
The knee goes up and down properly after I swapped one 3 phase wire.
Paul Lamar
-American Flyer wrote:
P.S.
Have you tried the serial port on your Bandit yet? I'm just in the process of
wiring up a cable for mine. I hope to try some DNC
aircuts tomorrow.
Harrison Young
That is down the road a bit but I do have a spare connector from DigiKey if you
want it.
Paul Lamar
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