What's the value by stretching for preloading at both ends?Sent from my Samsung
S10
-------- Original message --------From: andrew beck <[email protected]>
Date: 2026-01-03 11:25 p.m. (GMT-06:00) To: "Enhanced Machine Controller
(EMC)" <[email protected]> Subject: Re: [Emc-users] setting up
dual PID loops for servo encoders and
scales hey stuartyeah the ballscrew is connected both ends. i think one end
has the bigangular contact bearings etcand the other only has deep groove ends
probably (its much smaller than thedriving end)on my other two cnc mills they
have angular contact bearings both ends andthe screws are stretched between
them slightly with a tiny bit of preloadhey guysi was reading the link that sam
sent two and it looks like the two Pidloops are running side by side and then
the outputs are added togetherbefore going to the servo drivewould i be correct
in thinking that they are using the "sum" component inlinuxcnc to do that?if so
this is getting pretty simplecheersandrewOn 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> >> > 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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https://lists.sourceforge.net/lists/listinfo/emc-users> >>>> --> Addressee is
the intended audience.> If you are not the addressee then my consent is not
given for you to read> this email furthermore it is my wish you would close
this without saving or> reading, and cease and desist from saving or opening my
private> correspondence.> Thank you for honoring my wish.>>
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