random orbital sander wanting to go orbital

[Electric Comet]

I don't use my dewalt sander that much but it's handy and useful. Using it the other day and I held it off the workpiece for several seconds while I was looking for dips, etc. The sander started spinning very fast and I shut if off before starting to sand again.

I don't remember this ever happening so I guess something's either broken or maybe it's dirty and instead of spinning randomly and orbital it's only doing random or orbital. This make sense? Anyone seen this? What's the cure? It's spinning so fast that if I were to continue sanding without first shutting it off I'd be destroying the work unless I was able to lay it perfectly flat on the surface.

When it's on the work it seems fine but without any resistance it starts spinning very fast.

[Leon]

Pretty common for an order ROS. My 25 year old PC ROS did this for day one.

[Artemus]

My PC333VS did that when the silicone(?) friction band broke. A new band solved the problem. Art

[woodchucker]

if it's like the pc you wore out the O Ring belt. get a new one, it controls the speed.

[Leon]

That is what the new ones do. ;~) I'm talking 1989. My Festool has a similar brake but the old PC's had nothing at all.

[Electric Comet]

Will take it apart and see what I need to buy. All the rubber on this dewalt has crumbled so I guess I'm not surprised. Well at least all the seals for the dust trap. The rubber on the switch cover's fine. Even the power cord is crumbling.

[Brewster]

I have the exact same sander, same problem (broken belt).

The PC part costs several dollars, I just went to the local hardware store and bought a generic black 'o' ring, costs $0.50 and has been working perfectly for several years now.

-BR

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[Electric Comet]

Good call. I know the rings you mean. Once in a while I wander the aisles just to get ideas and I remember looking at these o-rings. Now to test my memory of what aisle that was.

[Martin Eastburn]

Sounds like extreme heat or gasoline or oil. Bet on the first two.

They dry out the 'softness' material in the plastic/rubber and leaves a matrix.

[Electric Comet]

Took the dewalt apart and no bands inside. I discovered that the problem was due to build up of very fine dust in two places on the cast fan. That gave the fan just the right balance to allow the pad to spin at incredible rates. Like the perfect storm. A design flaw but not one that would be easy to test or model but I wonder if they've since fixed this.

With the pad removed the shaft would only spin so fast but with the fan and pad attached it really got moving.

[Leon]

More than likely it would always spin fast if you simply let it spin freely, especially if it is an older model similar to my old PC. FWIW with the pad removed from my old PC the shaft would hardly spin at all too. I remember when the brake feature was a selling feature on the newer models. ;~)

[Electric Comet]

No, it's back to normal again. Cleaning it out was the fix.

The brake's not needed if designed properly. It's all about the proper balance. I'd bet that an engineer figured that out at some point.

[Leon]

Gotcha, I misunderstood.

[Brewster]

After removing the pad on my PC (and seeing the broken belt), I thought that there had to be a better way, this is a really lame way to control rotation.

-BR

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