Great! Good to see your gut feeling was at least close. So nice to see a problem fixed w/o having to throw lots of $$ at it.
D > On May 20, 2024, at 6:26 AM, Todd Zuercher via Emc-users > <emc-users@lists.sourceforge.net> wrote: > > I did to exactly that. With the dial indicator on the ends vs the center, it > moved 10 times more in the center of the gantry than it did on the ends. I > will be the 1st to agree that the servo tuning could probably be better. But > this thing really is(was) a wet noodle. At 12ft long, with the ends > disconnected from the ball screws, +/-1 inch differences between the ends of > the gantry wasn't difficult to achieve. The two servos driving them really > interact very little and behave independently of each other with one not > really affecting the tune of the other. More than likely this has been the > true root cause of the majority of my servo tuning/carving issues with this > machine since day 1. (We bought it about 15yrs ago.) Originally the > machine's two ends were driven by rack and pinions with a 12ft long torque > tube connected between the pinion gears. I had been blaming most of the > wobble problems on torsional twisting of tube, belt squirm on the 7":1/2" > sprockets on the belt reduction pullies for the servo, and a huge inertia > imbalance for the servo, being used with a gear ratio more appropriate for a > stepper motor. > > While I kind of liked the idea of using cable trussing, my colleges did not. > So we decided to go ahead with the steel tubing we had on hand. > > That said, I a cut a piece of the 2x4x1/8" wall steel tubing, drilled holes > in it spaced 1ft apart and mounted it on edge on the back of the beam. It > has made a huge difference, and now the gantry no longer wobbles when homing > and hitting the center behaves approximately the same as hitting it on the > ends. > > Todd Zuercher > P. Graham Dunn Inc. > 630 Henry Street > Dalton, Ohio 44618 > Phone: (330)828-2105ext. 2031 > > -----Original Message----- > From: Chris Albertson <albertson.ch...@gmail.com > <mailto:albertson.ch...@gmail.com>> > Sent: Tuesday, May 14, 2024 9:26 PM > To: Enhanced Machine Controller (EMC) <emc-users@lists.sourceforge.net > <mailto:emc-users@lists.sourceforge.net>> > Subject: Re: [Emc-users] Beam Stiffening? > > [EXTERNAL EMAIL] Be sure links are safe. > > I think I fell for the “beam is bending” idea too. It might be. The way > to find out is to measure the beam center with the dial indicator and then > measure the ends of the beam. It might be that the entire beam is moving > > Is the gantry belt driven? Long belts can act like springs. The solution > is wider belts. It is easy to see that a belt that is twice as wide is twice > as stiff. > > I’d measure movement at the ends before any more thinking about the beam. > > As for modifying the beam, you have to model it. Guessing and “eyeball > engineering” generally does not work well. Any fix is going to be very > expensive. It is best to know it will work. > > > Everything that you add to that beam also adds mass. Mass is what you want > to get rid of. > > > > > >> On May 14, 2024, at 1:56 PM, gene heskett <ghesk...@shentel.net> wrote: >> >> On 5/14/24 14:34, Eric Keller wrote: >>> Do something cheap because I'm not convinced it's the beam. I've >>> done troubleshooting on things like this, and sometimes it's >>> stiffness and sometimes it's not stiffness. But it really doesn't >>> make sense that it would sit there and ring after a move, so you also >>> may have some tuning to do. Possibly a notch filter? >>> Eric Keller >>> Boalsburg, Pennsylvania >>> On Mon, May 13, 2024 at 4:50 PM Todd Zuercher via Emc-users >>> <emc-users@lists.sourceforge.net> wrote: >>>> >>>> Anyone have any brilliant ideas to stiffen a woefully inadequate cross >>>> beam on a gantry router without adding too much mass? What is there now >>>> is a 4" x 8" rectangular 3/8" walled extrusion that is 145" long. >>>> >>>> Under normal jogging commands the two servos control the ends of this >>>> gantry reasonably well, but while the axis is homing the thing shakes and >>>> wobbles terribly bad. >> >> This, on 3rd or 4th read, sounds as if the two servo's are not in tune with >> each other. Tuning servo's is not my strong suit, (and the only servo I had >> was destroyed by the new autotune pid in linuxcnc, it found settings that >> mde it ocillate and fried a $125 motor in around a minute. But this would be >> a lot easier to synchronize if stepper/servo's were used. Rigged with a home >> switch, maybe a prox switch since its non contact, with logic rigged so they >> can back away from home and move in sync the rest of the day, getting sync >> is running toward home until the switch trips on that end of the beam, run >> toward home until both ends have tripped, call that home. From then until >> powerdown, both motors getting the same step/dir signals will be in sync >> till the powerdown. No fighting because the two servo's are not in an >> identical state of tune. Hanpose has nema 34 and 42 motors of 12 NM, >> probably with more torque and speeds than your servo's. The best description >> is that they just work. And they use much less power than regular steppers >> to get the job done. A diff you can see in the power bill if replacing burn >> your hand regular steppers. >> >> How fast and how strong are the servo's you are using now? Gear ratio's too. >> >> Also If I put a dial indicator in the center of the bridge and hit the >> bridge forward or backward it will flex and wobble enough to displace the >> dial indicator +/-0.03 and it takes nearly a dozen wobbles to dampen it. >> But on the ends the servo's only have a few thousandths of give. >>>> >>>> I'm less concerned about the actual stiffness and more worried about >>>> dampening the wobble. >>>> >>>> Todd Zuercher >>>> P. Graham Dunn >>>> Inc.<https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F% >>>> 2Fwww.pgrahamdunn.com >>>> <http://2fwww.pgrahamdunn.com/>%2Findex.php&data=05%7C02%7Ctoddz%40pgrahamdunn >>>> .com%7C6070adc9473e4c46b7d908dc747e32b9%7C5758544c573f47cebee96c3e08 >>>> 06fb43%7C0%7C0%7C638513332582699305%7CUnknown%7CTWFpbGZsb3d8eyJWIjoi >>>> MC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C >>>> %7C&sdata=5MAm0wOGv2qUSXp%2BbOD8xlARLMutz9xrf1XwGcuWc0M%3D&reserved= >>>> 0> >>>> 630 Henry Street >>>> Dalton, Ohio 44618 >>>> Phone: (330)828-2105ext. 2031 >>>> >>>> >>>> _______________________________________________ >>>> Emc-users mailing list >>>> Emc-users@lists.sourceforge.net <mailto:Emc-users@lists.sourceforge.net> >>>> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fli<https://li/> >>>> >>>> <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fli%3Chttps://li/%3E> >>>> sts.sourceforge.net >>>> <http://sts.sourceforge.net/>%2Flists%2Flistinfo%2Femc-users&data=05%7C02%7Cto >>>> ddz%40pgrahamdunn.com >>>> <http://40pgrahamdunn.com/>%7C6070adc9473e4c46b7d908dc747e32b9%7C5758544c5 >>>> 73f47cebee96c3e0806fb43%7C0%7C0%7C638513332582707658%7CUnknown%7CTWF >>>> pbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI >>>> 6Mn0%3D%7C0%7C%7C%7C&sdata=v%2BrBMdjjefXrHu1Zs9o5%2Fxmf%2BT0M1Jo%2BJ >>>> pEsrrTyCpc%3D&reserved=0 >>> _______________________________________________ >>> Emc-users mailing list >>> Emc-users@lists.sourceforge.net <mailto:Emc-users@lists.sourceforge.net> >>> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flis<https://lis/> >>> >>> <https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flis%3Chttps://lis/%3E> >>> ts.sourceforge.net >>> <http://ts.sourceforge.net/>%2Flists%2Flistinfo%2Femc-users&data=05%7C02%7Ctodd >>> z%40pgrahamdunn.com >>> <http://40pgrahamdunn.com/>%7C6070adc9473e4c46b7d908dc747e32b9%7C5758544c573f >>> 47cebee96c3e0806fb43%7C0%7C0%7C638513332582712504%7CUnknown%7CTWFpbGZ >>> sb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0% >>> 3D%7C0%7C%7C%7C&sdata=1bx91xrXWuZJtO%2F%2Fp%2BGImuWvoA6Vx0dCo7cY2njCA >>> hY%3D&reserved=0 >> >> Cheers, Gene Heskett, CET. >> -- >> "There are four boxes to be used in defense of liberty: >> soap, ballot, jury, and ammo. 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