hey guys finally made a thread on the forum
lots of photos and this youtube video for those that are interested cheers https://youtu.be/AmQGh_Cwff0?si=ZIihICf10Gto2px7 https://forum.linuxcnc.org/show-your-stuff/58689-large-fil-cnc-machine-retrofit-12-ton-larger-maching-running-linuxcnc#345849 andrew On Thu, Apr 23, 2026 at 7:37 AM andrew beck <[email protected]> wrote: > Hey guys > thanks for the replies > > the homing is a interesting issue > > I had a bit of a play and made a copy of my config that i hacked. > > What i found was that if i combined my original 2 PID loops into 1 loop > and used the scale for position and used the motor velocity on encoder for > velocity all in one PID then homing to index enable worked perfectly. > > but doing it that way the motor tuning was not as good. backlash is a > constant of 0.1mm and the motor just jumped across that backlash whenever > it moved. in practice that meant that the absolute scale position hovered > by +-0.01 or so. > > this was not bad and totally usable. If i had done this option first i > would have called it good and just used it. but the movement was much > louder and less smooth than the two PID loops which get run through a sum > component. As the original two PID loops was much much smoother, it was > perfect and once i come to a stop the drive rapids to within 0.01 or 0.02 > and then creeps the last 0.02mm (using the integral value which takes about > a second) and ends up in the right place within 0.005mm or less. > basically perfect every time with no dithering. > > It is now my most accurate machine. and really nice > > also the homing when homing I home all axis at the same time. X and Y get > homed to index enable like normal. > > and the Z value i trick the home switch by checking the joint state. How > this works is the Joint2 switch state goes form 7 when searching for switch > the first time to 12 when latching on to switch slowly the second time > > so in classic ladder i set up two compare functions that basically choose > whether to listen to the main home switch or the z axis motor encoder Z > index pulse. (this is different to the index enable pulse and this is > possible to miss when only checking in software not hardware. but at a > slow speed i haven't found any issues yet, and when testing with a dial > indicator i can't see any changes between homing. I can rehome linuxcnc up > the top of the travel beside the home switch and then rapid down to the > table which is about 1m away and the dial indicator is definitely within > 0.01 each time. i can't really see any movement on it. > > So pretty happy all in all would like to fix the index enable issue in the > future but for now it's working fine. > > this is a 40 year old machine and weighs 12 ton. and when i got it the > backlash was 0.40mm. I replaced all the thrust bearings and changed from > reduction gearbox to a nice mazak flexible coupling and direct drive. The > timing belt was T8 timing belt so not even HTD profile which has more > backlash which didn't help. The FIL factory actually got the location of > the Z axis 2nd ballscrew mount out by 2.4mm which i was shocked by. i > double checked measuring against the slideways at the top and bottom of the > screw and yeah it was out 2.4mm from factory! so that is why all the > thrust bearings were stuffed. > > anyway just about to get it running into production. this machine will be > running like 16 hrs a day shortly probably. > > cheers > > Andrew > > > On Thu, 23 Apr 2026, 5:11 am gene heskett, <[email protected]> wrote: > >> 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. >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> 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>>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>>>> 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 >> > _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
