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Thread: how fast should the disk of a random orbit sander spin ?

  1. #1
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    Default how fast should the disk of a random orbit sander spin ?

    Hello,

    I just bought a new random orbit sander, the small festool one, and was wondering how fast the disk should spin. In my memory the disk of my old machine, a bosch spun much faster, but that one did not have a brake system. I used the sander on surfaces with various curvature and using only little pressure, but the disk doesn't spin that fast. Is this normal?

    I am just afraid to mishandle or break it, after all it was quite expensive. but the dust collection is awesome !!

    Thanks and regards,

    Duncan

  2. #2
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    According to their website, the ES125:

    "Speed: 6000 - 13000 orbits per minute"

  3. #3
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    Thanks Donn,

    But I think that refers to the small orbits, the 2mm radius orbits. If I understand correctly the 'global rotation' of the disc is superposed. Or am I completely wrong?

    Duncan

  4. #4
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    According to page 3 of the owners manual, these are the speeds:

    No Load Speed ES125Q 13,000RPM ES125EQ 6,000-13,000RPM
    No. of Strokes ES125Q 26,000SPM ES125EQ 12,000-26,000SPM

  5. #5
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    Interesting question. I just googled around and couldn't find an answer either. But I just looked at mine and it goes fast enough to trick the eye into thinking it reverses its direction, ya know, like the wagon wheels in the cowboy movies, however fast that is.
    Last edited by JimD; 07-21-2007 at 02:13 PM.

  6. #6
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    The disc should not spin much. The rate of spin will be least if the disc is flat to the victim.
    After years of use, the bearing the disc mounts into can stiffen up and the disc will spin at the high rate and will be hard to rotate when the tool is stopped. On the P-C sanders, this is an easy and inexpensive replacement.
    The 'Rotex' Festool sanders have a mode where where the disk spins at a considerable rate, making them a pretty aggressive tool.

  7. #7
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    I had mine turned upside down to watch it spin. It was easier than holding it over my head and looking up

  8. #8
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    Quote Originally Posted by JimConlin View Post
    The disc should not spin much. The rate of spin will be least if the disc is flat to the victim.
    After years of use, the bearing the disc mounts into can stiffen up and the disc will spin at the high rate and will be hard to rotate when the tool is stopped. On the P-C sanders, this is an easy and inexpensive replacement.
    The 'Rotex' Festool sanders have a mode where where the disk spins at a considerable rate, making them a pretty aggressive tool.
    Ok, so if I understand correctly miminal spinning means optimal orientation of the sander?

    If I understand correctly the festool has a sort of brake which stops the spinning completely when the machine is completely clear of the object, and the disc can not spin freely. When the machine comes in contact with the object the spinning starts, if I understand correctly.

    Duncan

  9. #9
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    my dewalt uses a couple of nylon "friction discs" to convert the motor's rotation into the orbit mode on contact with the surface being sanded. if held off the sanded surface the disc will stop orbiting and eventually catch up to the spindle speed and rotate at the motor's rpm. these discs are replaceable when the friction gets so low that the random orbit funtion becomes so slow that it leaves orbital marks on the sanding surface.

  10. #10
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    The disk on a random orbit sander should hardly spin at all when sanding. If it did it would leave swirl marks like a disk sander. The disk assembly is attached to the motor eccentrically, which moves the disk in an orbital motion. The disk itself is attached at it's center so it can spin freely. It's not attached directly to the motor. When the sander is held in the air centrifugal force sets the disk spinning. A breaking device is usually installed to reduce the spinning to prevent swirl marks when the running sander first touches the work. The old PC right angle RO sanders didn't have this and would leave swirl marks unless the sander was in contact with the surface before turning it on. The combination of the orbital motion from the eccentric and the slow spinning of the disk gives a random orbit that doesn't leave swirls like a disk sander and doesn't leave little round circular scratches like a plain orbital sander.

  11. #11
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    The reply above explains how it should be. However, not all orbital sanders are created equal. My small (115mm) Bosch sander does NOT have a brake. It spins like crazy if not in contact with the work. So the routine is always push down on the sander first before turning it on. It will then orbit nicely, the perceived disk rotation being quite slow.
    Klaus

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