On 3/15/24 11:33, Chris Albertson wrote:
If you are using it as a probe, why not put the drill in the chuck backward,
then you have a precision rod, not a drill.
Then I'd have to stop and turn it, loosing my z calibration. It is an r8
an r8 spindle, no built in stops.
Spinning seems like an interesting idea, moving fraction is always less than
static friction. You would likely need to spin a 3mm rod fast enough so that
the tangential speed is comparable to the up and down speed. Let's see,…
spinning a 3mm drill at 60 RPM, one rev per second you have 3 * 3.14 mm. per
second tangent speed. That is something close to 9mm/sec. that might be too
fast, I don’t know
Since this is all taking place at servo_thread rate, the usual spin rate
is much higher that that, 1000 or more.
Even if used “point down”. My guess is is that you want the tangent speed
comparable to the Z-speed.
No z speed, I am already positioned inside the SHCS portion of the
bolthole at the start.
I'm doing two passes, updating the center "home" position after every
finding of center. Then recalling the same sub to do it again but slower
tangental speed deep enough to be inside the 3mm boltholt at the bottom
of the SHCS countersink.. All under 5mm/minute. That gets me (using a
probe wire) close enough I can go to the center and lower the probe wire
into the hole another 4mm and do it again, except this time I'm not in
the 5.7mm dia SHCS countersink but inside the deeper 3mm bolt hole.
wash rinse repeat.
Then I'd do a g38.2 Z to a point where the conductive carbon fiber stops
it and save that from 5063. Here I haven't written it yet but I need to
move it just enough Y to probe down beside the rail, recording the depth
of the cf trigger obtained there so I can compare, in case some side
contact stopped it early before it triggered on the cf at the bottom of
the hole. If it gets to the cf, within .5mm, its time to stop it, M5, G4
p1.5, m3 to turn it fwd, and drill the hole.
And it is those speeds that are are what I'm looking for. I've already
drilled the 3 thru holes that will bolt the ends to the Y carriages I've
already changed from 2.75" sq 8mm thick solid steel to printed in PETG
with corrected belt geometry to replace the bad geometry tronxy used,
cutting that flying weight by 50% or more.
Those 12 holes were drilled with a more conventional 3mm up spiral tool
and are very rough and ragged on the inside. A nearly solid infill 18mm
sq with a corners sanded a bit will fill the ends of the cf tube
preventing it from being crushed by the tension of the bolts mounting it
to the new Y sleds.
This piece I'm doing on a CF tube replaces a solid alu extrusion about
20x20 with two steel 8mm rods inlaid to it, that weighs 24 ounces! I
could kill a horse that wants to buck by laying it between his ears hard
enough.
And tronxy expected a couple 48mm nema17's to move it? Silly people. Up
to around 45 mm/sec, then step skips. Those motors are now 60mm long
Hanpose stepper/servo's with optical encoders running on cl42
controllers at 72 volts. With adequate frame bracing I hope to get
400mm/sec speeds and 20k accel's.
History Chris:
I am using similar stepper/servos on 2 of my cnc'd machines in the
garage already. A layer shift is a lost step to a 3d printer, these can
hit the immovable object and lcnc is shut down in it tracks 1
servo-thread time later, but not something klipper is considering, I've
asked. Well tested on the Sheldon, but has never occurred while running
gcode.
Another advantage, they use the error signal magnitude to control the
motor current, motors at work will heat a few degrees but never get burn
your hand hot. You can see that in the power bill, the machine is
running on 10 to 20% of its former power consumption. Yes if they do get
up against something, they use every amp the supply has for about a
millisecond, if that fails to reduce the error, the motor driver
transistors are turned off to save them and the motor, and linuxcnc is
signaled an e-stop. That on my stuff toggles F2 off and totally powers
down the whole machine. Move whatever it ran into, pull the tool, power
it back up with a tap on F2, rehome everything, put the tool back on the
toolpost and run from line.
Just one problem, I haven't had to do it in the about 3 years since I
put the first 2 on the Sheldon. Running w/o PID's they simply do what
motion tells them to do. I have enough motors, controllers and BIG PSU's
to convert this machine, collected to replace the XYZ's, A already is.
All I gotta do is find a round tuit, which at my age is getting harder
to find. 3 PID's will disappear, they are a source of error, and these
simply do what motion tells them to do.
I use those very cheap 2, 3 and 4mm drillig for 3D printed plastic to ream the
holes if they print undersized. The cheapest Aliexpress drills I can find are
good enough. Good that you have found another use for them. The diameters
are spot-on, or as good as I can measure.
Same here, I already checked.
Is the coating on the bit electrically conductive? I know some oxides don’t
conduct electricity.
My cheap go704 has steel balls for spindle bearings. So the spindle has
a decent ground. I have not encountered a coated tool that was an
insulator yet.
The only insulator I worry about is the coat of alox that forms on an
alu part nominally a microsecond behind the passing of the tools cutting
edge. Raw alu exposed to the oxygen in the air is a very active metal as
it will burst into an almost invisible flame, converting that raw alu
surface instantly into alox, the ash of its burning until its thick
enough to to block the burn in a few microseconds. 95% of the heat
produced from machining alu, is actually the heat produced by this burn.
A mist sprayed at the back of the tool blocks the airborn oxygen and
stops the heating by sealing the surface, straight water, very dry but
add a wee bit of koolmist, which contains contains something that makes
it wetter, so less of it is needed. I use an 8 oz coke bottle for src
and cut out the two wrenches I made for the collet on that motor, a half
inch thick, going around the outline 25 thou deeper per pass with an
eight inch tool. Used about 2oz out of the coke bottle per wrench. Std
open end pattern, one to fit the collet nut, one to fit the double d
flat on the shaft. both fit precisely enough I can let go of them w/o
them falling off. You cannot find a layer line from the .025 per layer
feed.
The oxidation continues on a longer term basis, which explains why you
can do a mirror like surface. set it on the table and its dull gray the
next day.
Alox is a perfect insulator, you have to apply enough voltage to punch a
hole in this film of alox before /any/ electron flow can occur. Good for
around 50 volts a minute behind the tool. Set it on the shelf and it
takes 400 volts or more 2 years later. The alox coat has gotten that
much thicker.
That 4 bearing water cooled motor I put on the 6040 after the EOM
version died in about 3 hours, has ceramic bearings that insulate the
spindle. So if I want to use a touch off pad, for tlo setting I need to
put a clip lead on the tool to ground it. PITA. Someday I'll print a tlo
setter with a builtin grounding spring. One of those round tuit projects
we all have. ;o)>
But this question is still valid:
What revs and feed rate stands a chance of doing a decent job of making a clean
hole w/o excess tool wear? Max revs about 2750/minute.
Thanks Chris, take care and stay well.
Cheers, Gene Heskett, CET.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
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