On 4/22/26 10:44, Dave Engvall wrote:
Hi Andrew et al
I have a cinci contourmaster set up with US made glass scales and a rotary
encoder on the ballscrew. I’m in transition to stepper-servos but progressing
slowly.
When I started this process I did a manual check with the hand crank vs the X
axis scale. Proceeding in the positive direction I manually moved in 1”
increments, ie 4 turns of the hand wheel. Even in this early 1960’s machine the
glass scale was dead on. Since I’m protective of the US scale I removed it and
installed a Chinese scale.
Both scales have a reference channel spaced with markers 50 mm apart I suspect
the US made scale has guard ticks either side of the reference mark. I know the
Chinese one's do.
Homing procedure was simple. I installed a laser diode and a tab with a hole in
it at the end of the axis and manually homed to that before kicking off a home
of the machine. Z was done by manually moving Z to the upper stop. If I
positioned the tab and or Z stop correctly it never had to move more than ~ 3
mm to index. All of this used the normal homing procedure. Scan past the index
and capture the position of index then move as necessary to home. It is my
impression that homing should be done in that manner and not dual channel but
after homing position seeking uses both signals but I have no data to back this
up! However, given the nature of linear scales one might do just as well to use
linear scale for position and shaft encoder on the motor for velocity. The
system on my Mazak used a resolver on the servo motor geared (?) 7:1 and 1.6:1
to the ball screw. Those numbers are from memory and a long time ago i.e a
couple of years before we did the Mazak at Galesburg.
When I get the machine running with stepper-servos I will probably try using
the R channel for homing. Thanks for listening. Rant OFF.
Dave
I have a much simpler setup, the only fully stepper/servo is my sheldon
lathe which is all stepper/servo, or about 1/2 of my 4 axis 6040 mill.
I have motors and drivers to do the same for my ball screw converted
go704. configurable as 3 or 4 axis. Home is the closing of the $2
switch on each axis. The 6040 is the odd man out, There, z & b are
stepper/servo's where xy are just steppers. I can have a 1 second power
failure in the middle of a threading operation, remove the tool, rehome
the machine, I have notches in my r8's to replace the lack of tooing
keys go thru the rehome, replace the tool and hit r, all in the middle
of a 50 tpi threading opertion. That is plenty accurate enough for the
girls I might go with. The only none hard switch is the inductive home
switches on the 4th axis for z & a or b. My biggest problem is the.3mm
back lash in g7O4 z if the gibs are too tight. & I forget to oil it.
On Apr 18, 2026, at 10:49 PM, andrew beck <[email protected]> wrote:
hey guys
just reporting back here with my success with the dual feedback
i have 0.1mm backlash still in the ballscrew or somewhere
and i have a magnetic scale on the machine also
with a encoder on the end of the ballscrew
i copied the examples on online of how they did that massive mill and its
working awesome
the mill rapids down or feeds down to 0.02 to 0.05 and then the I value
from the second PID takes over and moves the last tiny bit
which takes a second or so
and it stops right where it should everytime within 0.01mm the scale says
it's perfect to 0.003 on the screen. and no dithering
next issue thought is homing with index
either to the motor encoder or scale z pulse
i have my x and y axis homing perfectly with encoder index
but i can't get linuxcnc to home this z axis to index. homing without
index works fine though.
i think it is because linuxcnc internals throws a hissy fit because i have
a hacked up PID system with two forms of feedback getting summed together
any ideas would be great
cheers
Andrew
On Mon, Jan 5, 2026 at 11:04 AM gene heskett <[email protected]> wrote:
On 1/4/26 01:36, gene heskett wrote:
On 1/4/26 00:23, andrew beck wrote:
hey stuart
yeah the ballscrew is connected both ends. i think one end has the big
angular contact bearings etc
and the other only has deep groove ends probably (its much smaller
than the
driving end)
on my other two cnc mills they have angular contact bearings both
ends and
the screws are stretched between them slightly with a tiny bit of
preload
Probably should clarify here. The tension isn't meant to stretch the screw,
but to pull it tight enough there's no lengthwise backlash under normal
working loads despite a few microns of wear. On my sheldon, the z screw
has only a sliding ball bearing on the right end, so the double bearing on
the left controls the end play. After a decade of light use, I'm still
under 2
thou of play acc a .0001 dial.
hey guys
i was reading the link that sam sent two and it looks like the two Pid
loops are running side by side and then the outputs are added together
before going to the servo drive
would i be correct in thinking that they are using the "sum"
component in
linuxcnc to do that?
if so this is getting pretty simple
cheers
andrew
On Fri, Jan 2, 2026 at 3:07 PM Stuart Stevenson <[email protected]>
wrote:
HI,
I don't think the LinuxCNC control scheme is cascaded or nested. I
would
call it parallel.
The only backlash problem I can imagine is if the backlash causes the
motor to dither trying to maintain position because cutting forces
move the
axis enough to cause the control to try to correct the axis position.
Is the ball screw supported on each end? If it is, then, is it
possible
the screw has some stretch preload.
regards
Stuart
On Thu, Jan 1, 2026 at 4:10 PM andrew beck <[email protected]>
wrote:
hey guys
sam i just looked at that link you sent
that looks pretty cool
only thing is i don't know is if it will work to reduce the backlash
issue
i am getting. I have about 0.10mm of backlash on each axis. half of
that
is from the thrust bearings which is fixable with new bearings
the rest is from the ball nut i think and i am not willing to fix that
Those tiny ball screws stuart sold me 25 years ago were just a hair
sloppy.
I found the balls .001 bigger on ebay and restuffed the nuts. One of them
is in the Y of my sheldon, and has about a thou of backlash today I had
to make a cage for the nut with teeny grub screws to stop the nuts end-
play in the cage. So oversized balls are one possibility. Ticklish
work tho.
but i can only try it.
does anyone want to have a go with making a config like they did? one
axis
would be best I am struggling to get my head around the different
layers.
i probably need to write it all out or use a diagram or something.
regardless i am sure i will work it out. just might take some brain
cells
cheers
Andrew
On Fri, Jan 2, 2026 at 4:54 AM Sam Sokolik <[email protected]>
wrote:
This was also John k.. I would trust his solution. He is the one
that
came up with hal in linuxcnc... (Among other things).
On Thu, Jan 1, 2026, 9:49 AM andy pugh <[email protected]> wrote:
On Thu, 1 Jan 2026 at 15:41, andy pugh <[email protected]> wrote:
On Wed, 31 Dec 2025 at 22:14, andrew beck <
[email protected]>
wrote:
just looking for a config example if possible for a mesa card
from
someone
that has this nested PID loop setup.
This may not be as effective as you would hope. Cascaded PID
loops...
Actually, what was done with the MPM jigmill wasn't a cascaded PID.
What was done there was to run a P + FF control based on the motor
encoder and an I control based on the linear scales.
Then the two controllers were summed together to create a PID
controller, but with I using a different feedback source than P and
D.
--
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
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
Don't poison our oceans, interdict drugs at the src.
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
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
Don't poison our oceans, interdict drugs at the src.
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
