On 12/3/22 22:56, John Dammeyer wrote:
From what I understand you're talking about a normal parallel lathe so here
are my thoughts:
Yes. And thank you.
The Z axis is more interesting. Before homing I imagine the tail stock
has to be loosened and moved all the way to the right as far away from the
headstock to ensure finding a home switch. Or a home switch could be
somewhere in the middle but then which direction to search?
I think the safest setup in this case (given your Z axis can crash with
the tailstock if you forget to move it all the way to the right) will be
having the home switch towards the chuck side (with a proper
independent limit switch right at the left of the home switch to avoid
crashes when homing). This way you can set up your homing sequence to first
home the X axis to move it to a safe place and then home the Z axis towards
the chuck.
I'm guessing you are suggesting something like what Gene was that the home
switch isn't at the end of travel but somewhere else and once activated never
goes inactive in that same direction. So if you start a home sequence and the
switch is ON you know you have to go to the right until it goes OFF. It can't
over travel past the OFF position and go ON again. That approach lets the Home
Switch be pretty well anywhere.
Unless the limit switch is movable it's useless. My carriage can go much
further to the left to turn near the part held in the 5C collet than it can
with the part held in the 3-Jaw. So a crash into the spinning 3-Jaw can happen
without ever touching the limit. And if the limit does prevent that one can't
turn a part close to the collet.
How does one determine, with that tool tip, where the lathe centerline is
and set that so G54 X is 0.000?
I think you're asking about tool setting. If you have tool fixtures that
ensure that whenever you change your tool you get the exact same tool
position then it's just like a CNC turret. You just take a skim cut on the
diameter (or maybe use some fine paper to gauge the tool against the
workpiece) and then measure and input the diameter (or radius depending if
you're in G7 or G8) in the touch off popup.
Thanks. I'm going to have to study that a bit further.
I understand that the machine coordinate for x at the home switch is 0.000.
And measuring the tool tip relative to how it mounts into the AXA holder can be
done creating an offset from the home switch.v Now each time the tool holder
+tool is put into the AXA the distance from the tool table is offset from that
home position and LCNC knows where the tip and can turn a diameter.
Theoretically.
However as soon as the holder is pivoted even slightly the distance of the
tool tip relative to the home switch changes. And it changes differently
depending on how far the tool protrudes out of the AXA holder right?
So the tool measurements are only useful with the AXA in one position and that
can change really easily in the home shop. We're not talking a commercial
production operation where the setup is the same over a long period of time.
I suppose if you can touch of or measure the new position of the tool tip you
can then use simple trig to determine the angle that the AXA holder has
pivoted. Unless it also slid in the T-Slot which now moves it in more than one
dimension.
Doe my explanation make sense? A small shop lathe where the operator can shift
the tool bit around relative to the X home switch and even on the carriage
relative to the Z home switch suggest a tool table for a LCNC lathe is
virtually impossible.
So I can manually turn that shaft. Leave the X axis where it is and measure the diameter; say
exactly 1.000". Then click on the "Touch Off" on the display and enter half the
diameter (0.5") for the offset.
Now a request to move the X to 0.480" to do a 0.020" deep pass should work
right?
But the tool table and for that matter the home switch and machine coordinate
system is pretty well useless. Or have I missed something?
John
Don't adjust your antenna, you got it, John, the reception is perfect.
The main reason for a home sw is the let the machine know where its at
in the absolute sense, I've surveyed my bed for wear, and corrected it
with a lincurve/offset module combo. Rather satisfying to see the X
motor turn a bit as the Z is scanned. But, its effect is determined by
the absolute z position established by the home switch. It does not
respond to z touch off, only to the real position.
Threading to any std, or to one you've invented is nothing but arguments
to the G76 routine. I've even abused G76 to make compression fittings
The main advantage to cnc'ing a lathe is that its far faster at
executing the move codes than you can squint at a dial and do it by hand
in between cuts, it turns the crank in milliseconds and gets on with the
job.
With no compound, mine was broken beyond redemption by a fall over no
one mentioned before I bought it, so LinuxCNC IS my compound, and far
more accurate than you can turn a compound and set it, fraction of a
degree several digits right of the decimal point with submicron errors
can be done by LinuxCNC. W/o a compound.
It is all done with 2 stepper/servo motors and a raspberry pi4b, and w/o
a PID module anyplace. The driver does it all, including stopping
LinuxCNC in a millisecond if a motor can't get to where it was told to
go. I can set a stopped chuck jaw in the way, and program a .2" a second
move into the chuck jaw, it touches the jaw and springs back about 10
thou as the drivers shut down, without marking the jaw, or damaging the
carbide chip in the tool. Tested many times doing that, but it has yet
to actually shut down a job.
And if you want to step out of the way of burning swarf, the programs
linear speed can be turned way up, w/o worrying about getting holes
burnt in your clothes by white hot swarf. Carbide tooling is right at
home with those temps, human skin isn't. Coolant would be nice, but this
80 year old Sheldon has no way to collect the coolant to reclaim it.
Cheers, Gene Heskett.
--
"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
Genes Web page <http://geneslinuxbox.net:6309/>
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