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Re: [micRo-cnc] Re: Mods to the M3 ( and M2 )

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  • Dan Andersson
    On Mon, 15 Jul 2013 20:24:55 -0400 ... ( switch out aluminum for steel ways, or use larger aluminum ways ) Use larger ceramic coated aluminium ways High speed
    Message 1 of 25 , Jul 15, 2013
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      On Mon, 15 Jul 2013 20:24:55 -0400
      robin turner <rohabeen@...> wrote:

      > Ideas to improve the micRo:
      > thicker leadscrews 10 tpi: less resonance, faster speed
      > nema 23 motors, more power at higher speed
      > replace some HDPE parts with PET parts, less flex

      ( switch out aluminum for steel ways, or use larger aluminum ways )

      Use larger ceramic coated aluminium ways
      High speed ACME screws instead of standard ACME screws
      Add an extra way for each X-way
      Increase Z to 3"-4" ( allows for mounting of a 1" thick T-slot base extension )
      A more rigid base. Granite or 1"+ Aluminium. Maybe 2" with T-slots.


      Proper clamping is a problem. T-Slot seems to be given solution. Also, it doesn't matter what we do as long as the base flexes.

      //Danand
    • Ipeerbhai
      Ahh -- that makes sense on why you moved away from the supported ways -- it was the supports that were the problem. Out of curiosity -- did you have any
      Message 2 of 25 , Jul 19, 2013
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        Ahh -- that makes sense on why you moved away from the supported ways -- it was the supports that were the problem. Out of curiosity -- did you have any trouble with the bearing carriages clogging up?  Supported rail has huge gaps for crap to enter and clog up the ball bearings, and I didn't see any Bellows or the like in those old prototypes.  How did you keep the bearings from clogging?



        -----Original Message-----
        From: robin turner <rohabeen@...>
        To: micRo-cnc <micRo-cnc@yahoogroups.com>
        Sent: Mon, Jul 15, 2013 5:24 pm
        Subject: Re: [micRo-cnc] Re: Mods to the M3 ( and M2 )

         
        As far as straightness is concerned, it's a toss-up between aluminum rods and steel.  The shiny chrome coating isn't hard-chrome BTW (hard chrome is typically gray)- though there are processes for putting chrome on aluminum, most need an intermediate plating- effectively doubling the tolerance and the price.  The ceramic coating put on aluminum is harder than chrome anyway AFAIK.  We moved away from supported ways because of quality issues- the supports are basically aluminum extrusion (imagine the spaghetti extruded in a playdoh factory, and you get the idea), and typically come minimally machined.  The bearings had similar issues.  The biggest was getting the slop out of the bearing without stripping the adjustment screw.  seriously annoying.  

        Ballscrew and leadscrew are kind of a toss-up.  You'll sacrifice some accuracy with a ballscrew vs. leadscrew simply because there are a finite number of microsteps per revolution- but..  microstepping isn't known for its accuracy to begin with.  the tolerances of the screws themselves are typically something on the order of .005" (pulling this out of my ass) per 12" or so regardless of whether it's a acme lead or ballscrew.  

        Ideas to improve the micRo:
        thicker leadscrews 10 tpi: less resonance, faster speed
        nema 23 motors, more power at higher speed
        replace some HDPE parts with PET parts, less flex
        switch out aluminum for steel ways, or use larger aluminum ways



        On Mon, Jul 15, 2013 at 5:30 PM, Ipeerbhai <ipeerbhai@...> wrote:
         
        Yeah, I can't find the screw accuracy either.

        The ceramic coating is available for extra $ as a different part number -- but if you use a ceramic coating, no more ball bearings, as the bearings would wear the surface ceramic quickly.   AFAIK, Chrome--plating is stronger than surface ceramic, and has better wear characteristics and temperature characteristics.  I don't think you can chrome-plate Aluminum, so they use ceramic instead.   Ball bearings are 5x less friction than plain bearings.  Of course, ball bearings can clog...

        The laws of physics says, "Al rod must have a diameter = 2 times diameter of steel rod for same flexural stiffness, or there must be 4 of them if the same size."  So, in theory, a 12mm steel rod is as strong as a 24mm Al one, or as four 12mm thick Al rods( exponential function -- thickness increases strength more than number.)  Here's the formula and measured constants for some common materials: http://en.wikipedia.org/wiki/Young's_modulus.  
        In theory, these steel rods would have to be replaced by 40mm thick Aluminum rods for the same flexural strength.

        So, a misumi rod with a metric rolling insert bearing should be:
        1. Stronger in flex -- a lot stronger.  Just replacing the rods in the existing micRo with these rods from Misumi( and ream to 20mm ) should increase stiffness considerably -- and at very low cost.
        2. roll much more smoothly.

        Downside -- rolling bearings can clog and can need oiling from time to time..

        I saw that LL had originally used chrome-plated steel supported rods in an earlier versions of the machine, then switched to Al/machined HDPE motion system.  I can't figure out why, and I'm trying to figure out what they learned before they made the switch.  Was it just the cost( they used supported steel rails -- pricey, even from China, and often with months of delay time to get... ), or was there a technical reason?


        I've been leaning towards dropping the ballscrew.  This conversation seems to have sealed the deal.  The ballscrew added so much cost, and I wasn't sure it would return in both accuracy and backlash as much as I hoped...  I'm still in the steel camp for now, but maybe a hybrid.  main ways of steel, secondary Al ones( much thinner ) to help stop any rotations...

        I have one design constraint I want to keep -- no hand-work.  If I need to tap something, it's out.  I have carpal tunnel, and turning things by hand weakens me for weeks...  So, if I use ACME rods, then I have to have matching nuts.  

        -----Original Message-----
        From: Dan Andersson <dan@...>
        To: micRo-cnc <micRo-cnc@yahoogroups.com>
        Sent: Mon, Jul 15, 2013 1:48 pm
        Subject: Re: [micRo-cnc] Re: Mods to the M3 ( and M2 )

         
        Misumi does the rods but no alu ceramic coating. I don't like the dead weight of the steel rods.
        Accuarcy ok.

        Screws, looks like 380mm is max and I can't find the accuracy that easy.,

        //danand

        On Mon, 15 Jul 2013 21:38:47 +0100
        Dan Andersson <dan@...> wrote:

        > The ceramic coated Alu rods have Dia. Tol -0.0004" to -0.0012". That is -0.010mm to -0.030mm.
        >
        > And dirt cheap! 20$ for 2' of 3/4"
        >
        > The screws -
        >
        > Travel accuracy per foot is better than 0.009"
        >
        > And around 60$ for 6'
        >
        >
        > ////
        >
        > Now take some time and compare this with the garbage you find on Ebay etc!
        >
        > I need to take a look at Misumi but your number is a decimal of for worse...
        >
        >
        > Buy American or German stuff. Swedish stuff is probably way to expensive for semi-pro hobby stuff.
        >
        > //Danand, M0DFI
        >
        >
        > On Mon, 15 Jul 2013 16:11:06 -0400 (EDT)
        > Ipeerbhai <ipeerbhai@...> wrote:
        >
        > > Misumi's PSFJ20-600.
        > >
        > >
        > >
        > >
        > > Hard chrome plated. 20mm thick ( aka 0.8mm thicker than 3/4" -- so we'll call it 3/4" ). Tolerance spec to .03/300 ( probably the same as the Al used by LL ). $25.20 for 600mm ( or 2ft. ).
        > >
        > >
        > > Misumi has a nasty habit of overnighting everything via Fedex, even if you select UPS ground shipping. Get yourself a shipping account and FOB it... Or call them and order by phone...
        > >
        > >
        > >
        > >
        > >
        > >
        > >
        > >
        > >
        > >
        > >
        > > -----Original Message-----
        > > From: Dan Andersson <dan@...>
        > > To: micRo-cnc <micRo-cnc@yahoogroups.com>
        > > Sent: Mon, Jul 15, 2013 12:52 pm
        > > Subject: Re: [micRo-cnc] Re: Mods to the M3 ( and M2 )
        > >
        > >
        > >
        > >
        > >
        > >
        > > On Mon, 15 Jul 2013 15:00:51 -0400 (EDT)
        > > Ipeerbhai <ipeerbhai@...> wrote:
        > >
        > > > Do you think milled HDPE blocks inserted as a liner into a printed part with an Al/Ceramic bearing would yield better tolerances than a chrome-plated metric steel rod with a ball-bearing liner inserted into the same printed part?
        > >
        > > Yes.
        > >
        > > I haven't seen reasonably priced "chrome-plated metric steel rod with a ball-bearing liner"
        > > with better accuracy than the LL solution.
        > >
        > > If you really(!) have a deep wallet, sure.
        > >
        > > //danand
        > >
        > >
        > >
        > >
        > >
        > >

      • robin turner
        If I remember correctly, the bearings for the supported ways had way wipers, and I personally never had a problem with the bearings getting clogged. Having
        Message 3 of 25 , Jul 19, 2013
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          If I remember correctly, the bearings for the supported ways had way wipers, and I personally never had a problem with the bearings getting clogged.  Having said that, I wouldn't want to machine too much abrasive material with the early micros



          On Fri, Jul 19, 2013 at 4:13 PM, Ipeerbhai <ipeerbhai@...> wrote:
           

          Ahh -- that makes sense on why you moved away from the supported ways -- it was the supports that were the problem. Out of curiosity -- did you have any trouble with the bearing carriages clogging up?  Supported rail has huge gaps for crap to enter and clog up the ball bearings, and I didn't see any Bellows or the like in those old prototypes.  How did you keep the bearings from clogging?



          -----Original Message-----
          From: robin turner <rohabeen@...>
          To: micRo-cnc <micRo-cnc@yahoogroups.com>
          Sent: Mon, Jul 15, 2013 5:24 pm
          Subject: Re: [micRo-cnc] Re: Mods to the M3 ( and M2 )

           
          As far as straightness is concerned, it's a toss-up between aluminum rods and steel.  The shiny chrome coating isn't hard-chrome BTW (hard chrome is typically gray)- though there are processes for putting chrome on aluminum, most need an intermediate plating- effectively doubling the tolerance and the price.  The ceramic coating put on aluminum is harder than chrome anyway AFAIK.  We moved away from supported ways because of quality issues- the supports are basically aluminum extrusion (imagine the spaghetti extruded in a playdoh factory, and you get the idea), and typically come minimally machined.  The bearings had similar issues.  The biggest was getting the slop out of the bearing without stripping the adjustment screw.  seriously annoying.  

          Ballscrew and leadscrew are kind of a toss-up.  You'll sacrifice some accuracy with a ballscrew vs. leadscrew simply because there are a finite number of microsteps per revolution- but..  microstepping isn't known for its accuracy to begin with.  the tolerances of the screws themselves are typically something on the order of .005" (pulling this out of my ass) per 12" or so regardless of whether it's a acme lead or ballscrew.  

          Ideas to improve the micRo:
          thicker leadscrews 10 tpi: less resonance, faster speed
          nema 23 motors, more power at higher speed
          replace some HDPE parts with PET parts, less flex
          switch out aluminum for steel ways, or use larger aluminum ways



          On Mon, Jul 15, 2013 at 5:30 PM, Ipeerbhai <ipeerbhai@...> wrote:
           
          Yeah, I can't find the screw accuracy either.

          The ceramic coating is available for extra $ as a different part number -- but if you use a ceramic coating, no more ball bearings, as the bearings would wear the surface ceramic quickly.   AFAIK, Chrome--plating is stronger than surface ceramic, and has better wear characteristics and temperature characteristics.  I don't think you can chrome-plate Aluminum, so they use ceramic instead.   Ball bearings are 5x less friction than plain bearings.  Of course, ball bearings can clog...

          The laws of physics says, "Al rod must have a diameter = 2 times diameter of steel rod for same flexural stiffness, or there must be 4 of them if the same size."  So, in theory, a 12mm steel rod is as strong as a 24mm Al one, or as four 12mm thick Al rods( exponential function -- thickness increases strength more than number.)  Here's the formula and measured constants for some common materials: http://en.wikipedia.org/wiki/Young's_modulus.  
          In theory, these steel rods would have to be replaced by 40mm thick Aluminum rods for the same flexural strength.

          So, a misumi rod with a metric rolling insert bearing should be:
          1. Stronger in flex -- a lot stronger.  Just replacing the rods in the existing micRo with these rods from Misumi( and ream to 20mm ) should increase stiffness considerably -- and at very low cost.
          2. roll much more smoothly.

          Downside -- rolling bearings can clog and can need oiling from time to time..

          I saw that LL had originally used chrome-plated steel supported rods in an earlier versions of the machine, then switched to Al/machined HDPE motion system.  I can't figure out why, and I'm trying to figure out what they learned before they made the switch.  Was it just the cost( they used supported steel rails -- pricey, even from China, and often with months of delay time to get... ), or was there a technical reason?


          I've been leaning towards dropping the ballscrew.  This conversation seems to have sealed the deal.  The ballscrew added so much cost, and I wasn't sure it would return in both accuracy and backlash as much as I hoped...  I'm still in the steel camp for now, but maybe a hybrid.  main ways of steel, secondary Al ones( much thinner ) to help stop any rotations...

          I have one design constraint I want to keep -- no hand-work.  If I need to tap something, it's out.  I have carpal tunnel, and turning things by hand weakens me for weeks...  So, if I use ACME rods, then I have to have matching nuts.  

          -----Original Message-----
          From: Dan Andersson <dan@...>
          To: micRo-cnc <micRo-cnc@yahoogroups.com>
          Sent: Mon, Jul 15, 2013 1:48 pm
          Subject: Re: [micRo-cnc] Re: Mods to the M3 ( and M2 )

           
          Misumi does the rods but no alu ceramic coating. I don't like the dead weight of the steel rods.
          Accuarcy ok.

          Screws, looks like 380mm is max and I can't find the accuracy that easy.,

          //danand

          On Mon, 15 Jul 2013 21:38:47 +0100
          Dan Andersson <dan@...> wrote:

          > The ceramic coated Alu rods have Dia. Tol -0.0004" to -0.0012". That is -0.010mm to -0.030mm.
          >
          > And dirt cheap! 20$ for 2' of 3/4"
          >
          > The screws -
          >
          > Travel accuracy per foot is better than 0.009"
          >
          > And around 60$ for 6'
          >
          >
          > ////
          >
          > Now take some time and compare this with the garbage you find on Ebay etc!
          >
          > I need to take a look at Misumi but your number is a decimal of for worse...
          >
          >
          > Buy American or German stuff. Swedish stuff is probably way to expensive for semi-pro hobby stuff.
          >
          > //Danand, M0DFI
          >
          >
          > On Mon, 15 Jul 2013 16:11:06 -0400 (EDT)
          > Ipeerbhai <ipeerbhai@...> wrote:
          >
          > > Misumi's PSFJ20-600.
          > >
          > >
          > >
          > >
          > > Hard chrome plated. 20mm thick ( aka 0.8mm thicker than 3/4" -- so we'll call it 3/4" ). Tolerance spec to .03/300 ( probably the same as the Al used by LL ). $25.20 for 600mm ( or 2ft. ).
          > >
          > >
          > > Misumi has a nasty habit of overnighting everything via Fedex, even if you select UPS ground shipping. Get yourself a shipping account and FOB it... Or call them and order by phone...
          > >
          > >
          > >
          > >
          > >
          > >
          > >
          > >
          > >
          > >
          > >
          > > -----Original Message-----
          > > From: Dan Andersson <dan@...>
          > > To: micRo-cnc <micRo-cnc@yahoogroups.com>
          > > Sent: Mon, Jul 15, 2013 12:52 pm
          > > Subject: Re: [micRo-cnc] Re: Mods to the M3 ( and M2 )
          > >
          > >
          > >
          > >
          > >
          > >
          > > On Mon, 15 Jul 2013 15:00:51 -0400 (EDT)
          > > Ipeerbhai <ipeerbhai@...> wrote:
          > >
          > > > Do you think milled HDPE blocks inserted as a liner into a printed part with an Al/Ceramic bearing would yield better tolerances than a chrome-plated metric steel rod with a ball-bearing liner inserted into the same printed part?
          > >
          > > Yes.
          > >
          > > I haven't seen reasonably priced "chrome-plated metric steel rod with a ball-bearing liner"
          > > with better accuracy than the LL solution.
          > >
          > > If you really(!) have a deep wallet, sure.
          > >
          > > //danand
          > >
          > >
          > >
          > >
          > >
          > >


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