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Motor bounce & motor mounts

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  • Alys & John Vreede
    Hi guys I ve only encountered bounce like Steve described when the blade started to crack, but it broke within a short time. A poorly welded join also bounces
    Message 1 of 1 , Oct 6, 2013
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      Hi guys

      I've only encountered bounce like Steve described when the blade started to
      crack, but it broke within a short time. A poorly welded join also bounces
      but that's easy to see as it happens whenever the weld passes over the work

      People also commented on the poor motor mount contributing to sawing

      My saw had sheet metal motor mount with a tensioning screw like Robert's
      until I had to remake the motor mount, the catalyst for which was burning
      out the motor when it jammed in some sticky 3x2 aluminium bar I was cutting
      and I couldn't get a like-for-like replacement.

      I remade the motor mount to fit the new motor from 4mm thick aluminium plate
      and made a tensioning arm with one of those multi-position clamp levers
      locking it, mounted on the top of the gear box. I also bushed the M10 bolts
      to fit the holes in the casting so its not loose like the old one.

      There are a few photos of it in photo folder John Vreede
      (http://groups.yahoo.com/neo/groups/4x6bandsaw/photos/albums/1809245338 )

      Single phase motors inherently vibrate as part of the way they're made, so I
      vibration isolated the motor with high shear rubber mounts from RS Spares
      (http://newzealand.rs-online.com/web/p/stud-mounts/7773190/), which made it
      much quieter. NB. Hanging the motor like this puts the mounts in shear so
      make sure the vibration isolation mounts can stand shear loads of 3kg or
      greater (even though they look alike some can and some can't stand shear).
      RS Spares is an electronic component distributor so Radio Shack or similar
      probably will have them.

      Now the motor is solid and it's a 5 sec job to change ratios so no excuse
      for running wrong speed.

      The lever locking system can be made to work with the OEM sheet metal motor
      mount too. There's a photo sequence of what to do in the last half of the
      photos above. If you'd like to have a better tensioning system but don't
      want to remake the motor mount you could try this.

      Cut off the thumb-screw thread and turn the plate around 180 deg. with a bit
      of banging and grinding it fits, though you'll have to elongate one of the
      mounting holes to fit the belt cover.

      You'll see from the pictures that the rod with the rose joint didn't line up
      when I transferred it from the new motor mount to the old one. Its only a
      few millimetres out in sideways alignment but that's enough to make it jerky
      when changing pulleys - when its properly lined up its smooth as silk.

      Also the up-stand of the angle bracket across the top of the gearbox needs
      to be cut back to let the motor swing forward more.

      You might need a different vee-belt too (I don't know because my new setup
      has a shorter belt than standard). While you're at it get an AX-section
      belt not A-section as the grooves on the inside let it form around the
      smaller diameter pulley better with less HP and vibration. People on the
      forum have raved about the A-section Link belts as being the quietest and
      most vibration free. I haven't tried one as they're 4x the cost here in NZ
      but that would let you custom fit the length of the belt with known
      improvements over std and maybe wouldn't need anti-vibration mounts.

      Rgds - jv

      From: 4x6bandsaw@yahoogroups.com [mailto:4x6bandsaw@yahoogroups.com] On
      Behalf Of wa5cab@...
      Sent: Saturday, 5 October 2013 4:58 p.m.
      To: 4x6bandsaw@yahoogroups.com
      Subject: Re: [4x6bandsaw] Motor bounce

      My 4x6 (from the 1970's or 80's) came with a tension screw on the motor
      mount. It's a 5/16"-18 thumbscrew (plastic knob for a head) through a
      tapped hole in the pivoting (cast) motor mounting plate, above the pivot
      point. The screw bears against the end of the saw base casting. To change
      pulley grooves, you have to loosen it before you can swing the motor up.
      But with it tight, the motor cannot move.

      Robert Downs - Houston
      wa5cab dot com (Web Store)
      MVPA 9480

      In a message dated 10/04/2013 19:00:49 PM Central Daylight Time,
      stevetroyer56@... writes:

      I have in the past, had a problem when cutting metal the blade runs into
      resistance which changes with the thickness as the blade slices through the
      metal. I ti salmost impossible to set the arm tension correctly when cutting
      through tubing or metal at angles.

      What that does is make the motor move up and down in order to keep the blade
      running without binding. But what then happens is that the arm starts
      bouncing up and down causing blade damage as the teeth bite into the metal.

      So what I did to stop that was add a bungee cord to the mounting base of the
      motor and then to the stand of the saw. (off the back of the saw)

      What that did was stop the oscillating bounce and keeps a steady blade
      movement and a much smoother cut.

      Give it a try. It is a cheap trick to do and will keep your saw blade from
      bouncing off the metal.
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