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Re: [mach1mach2cnc] Re: stepper motor losing steps - swapping X and Y

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  • Lester Caine
    ... I ve been following the exploits of one of my Taig customers who has recently bought a larger router table for a job. I will not name the supplier, but
    Message 1 of 54 , May 1, 2012
      composite_airplane_pilot wrote:
      > bottom line, in spite of all my changes it fails identically, except the failure this time was pronounce after 30 minutes instead of 11 hours. I believe the root cause is misalignment of the stepper motor axis with the shaft of the ball screw.

      I've been following the exploits of one of my Taig customers who has recently
      bought a larger router table for a job. I will not name the supplier, but there
      are not many in the UK. The machine shipped was supposed to have been the demo
      machine so one would have perhaps expected that it had been used? Well it took
      them two weeks to get the 'x' and 'y' axis cleaned up and moving smoothly. Now
      they just need to sort ot the 'z' axis which as a FIVE mm miss-alignment between
      motor and leadscrew and no way to even adjust it out ... perhaps they should
      have started with 'z', found the problem and just shipped the whole lot back.

      Since the stepper motor can warm up a lot, there needs to be some leyway for
      expansion of the leadscrew. One nice thing about the oldham couplings is that
      the plastic plate provides a thermal break, while the solid spring like coupling
      is quite efficient at passing the heat on into the bearing on the leadscrew.
      Just another potential pinch point after running a machine of a period of time.
      One of the car programs yesterday was changing the wheel bearings on a big
      american import ... Tighten the nut then back off 1/4 turn before fitting the
      split pin - otherwise the whole thing will seize when hot :)

      Most of my recent problems with machines 'losing steps' were down to mechanical
      problems ...

      --
      Lester Caine - G8HFL
      -----------------------------
      Contact - http://lsces.co.uk/wiki/?page=contact
      L.S.Caine Electronic Services - http://lsces.co.uk
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      Model Engineers Digital Workshop - http://medw.co.uk//
      Firebird - http://www.firebirdsql.org/index.php
    • composite_airplane_pilot
      and the rest of the story is that the job I thought would take 16 hours based on the software s estimator ... ended up taking 18 hours And, near the end, the
      Message 54 of 54 , May 11, 2012
        and the rest of the story is that the job I thought would take 16 hours based on the software's estimator ... ended up taking 18 hours

        And, near the end, the other axis began to fail. So now, with the axis with the Oldham coupler stays square and true but the axis with the helical beam coupler, even a well aligned one, begins to fail on a very long job.

        I'll put that on my list of changes to be made .. soon



        --- In mach1mach2cnc@yahoogroups.com, "composite_airplane_pilot" <lobo.jk@...> wrote:
        >
        > I took apart the mount for the stepper motor and reversed one aluminum mounting plate per advice from the manufacturer. In the new configuration the shafts line up better. I've put a smaller oldham coupler (from Ruland, one of their smallest Oldhams) in place of the helical beam coupler.
        >
        > The machine ran a 7 and 1/2 hour job without error this week and, right now, it is 11 hours into a 16 hour job with no error.
        >
        > I have my fingers crossed.
        >
        > Here's my list of changes
        >
        > 1) Changed the mount to make the alignment of stepper shaft to ballscrew better
        > 2) installed a better fitting Oldham coupler in place of the awkward helical beam coupler
        > 3) added a fan to cool the coupler and motor (I now think this is superfluous)
        > 4) I've slowed the feed rate to 400 mm/min (16 in./min) which is a 10% reduction.
        > 5) I've changed the way the litho is cut so that the x-axis, which has broken two helical beam couplers, does much less work
        >
        > I've got my fingers crossed that the machine in this configuration will have a much longer Mean time to failure!
        >
        > Thanks for the support here folks!
        >
        >
        >
        > --- In mach1mach2cnc@yahoogroups.com, "Dr Mark Vaughan" <mark@> wrote:
        > >
        > > Yep don’t use a rigid coupling.
        > >
        > > It’s OK on really big motor shafts where you bolt up the coupling and then the motor so they are aligned, but for small motors as Gaston has pictured it will wreck the motor.
        > >
        > >
        > >
        > > On bigger machines where some misalignment is an issue I tend to use Oldham couplings.
        > >
        > > Have a look on this site which shows a variety of couplings, and when to use what.
        > >
        > > http://www.techdrives.co.uk/html/shaft_couplings___collars.html
        > >
        > > Beam couplers like you are using are good to 5Nm, as guidance a CNC mill would typically be fitted with 6 to 7Nm servos, the Oldham couplers are good to 21Nm.
        > >
        > >
        > >
        > >
        > >
        > > Regs Mark
        > >
        > >
        > >
        > > From: mach1mach2cnc@yahoogroups.com [mailto:mach1mach2cnc@yahoogroups.com] On Behalf Of Gaston Gagnon
        > > Sent: 01 May 2012 17:00
        > > To: mach1mach2cnc@yahoogroups.com
        > > Subject: Re: [mach1mach2cnc] Re:stepper motor losing steps - swapping X and Y
        > >
        > >
        > >
        > >
        > >
        > > On 01/05/2012 10:43 AM, Dr Mark Vaughan wrote:
        > > > At least we know where the failure is.
        > > >
        > > > With the limited lifetime, it has to be too much misalignment, there are other couplers which work with larger misalignments, but they introduce radial errors and resonances which we don’t want, so the best thing to do is to correct that misalignment as you’ve already decided and fit yet another coupler.
        > > The coupling is gone but at least the motor was saved. See what happens to
        > > me with a rigid coupling
        > > http://public.fotki.com/Gaston-Gagnon/fireball-cnc/machine-problem/
        > > Gaston
        > >
        > > [Non-text portions of this message have been removed]
        > >
        > >
        > >
        > >
        > >
        > > [Non-text portions of this message have been removed]
        > >
        >
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