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
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