> 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.
Good. The cable idea would not have worked. You would have done better with a steel rod the same diameter as the proposed cable. The rod is stiffer than the cable. But either way, the cross sectional area of the cable or rod is tiny compared to the beam. It would have a small effect because of the small amount of steel added. What you did with that steel tube is you made the beam much wider. Stiffness goes up with the cube of the width. If the beam is now twice as wide, it is 8 times more stiff. > > 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. _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
