My random orbital sander on bennies.

[Packard]

I’ve had my current random orbital sander for about 7 - 8 years.  I like it.  It is small, light and fairly powerful.  The onboard dust collection works reasonably well and it will hook up to both sizes of vacuum hoses and with my shop dust collection it does not emit any noticeable dust. 

This afternoon it started running crazy-fast.  It was leaving burn marks on the wood and when I adjusted the speed downwards it had lost all or most of its torque and it would stall.

So what happened here?  I never experienced anything like it.  I will likely get another one.  When I bought it, it was about $50.00.  The replacement (not exactly the same) is $80.00.

I worked it pretty hard.  My only complaint is it is a nuisance aligning the holes for dust extraction. 

Any ideas why this is acting like a runaway banshee?

 

[luvmytoolz]

If it's using a pot (potentiometer) to adjust speed the wiper or contacts in it may be dirty. Maybe open the sander housing cap and give the pot area a really good blow with an air compressor. You can also get sprays specifically for cleaning the contacts in pots from most electronics suppliers.

It could also be that the controller board has developed a dry joint that just took some time to manifest. If the controller board isn't potted in resin you can just touch up all the solder joints lightly with an iron, this is perfectly safe to do.

 

[Packard]

I will take a look. I’m ready to write it off anyway, so little risk. Thanks.

 

[xedos]

The belt that controls the random orbit is broken.

Clearly the variable speed is still working.

 

[luvmytoolz]

The belt that controls the random orbit is broken.

Clearly the variable speed is still working.

Belt? Aren't pretty much all ROS's direct/gear driven?

 

[Packard]

The variable speed works, but there is almost no torque at the low speeds, and the high speeds are probably twice as fas as the had been.

I am almost certain to replace it.  But the symptoms are very curious.  When I disassemble it, I will post photos if there is anything to see.

 

[AlexThePalex]

Sounds to me like your pad brake is worn out. The pad brake is a rubber ring/skirt that sits between the pad and the housing of your sander.

 

[luvmytoolz]

Sounds to me like your pad brake is worn out. The pad brake is a rubber ring/skirt that sits between the pad and the housing of your sander.

Doesn't the pad brake only engage when the tool is turned off?

 

[AlexThePalex]

Sounds to me like your pad brake is worn out. The pad brake is a rubber ring/skirt that sits between the pad and the housing of your sander.

Doesn't the pad brake only engage when the tool is turned off?

No, it makes contact permanently with the pad. The motor often runs at 10.000 RPM, imagine that digging into your workpiece. The pad slows it down to a controllable speed. And when the pad break is worn, it doesn't do that anymore, hence the ridiculously high rotation speed you get.

The pad break is a wear item and meant to be replaced every few years, depending on use.

 

[Packard]

I will check that out. But what about the almost nonexistent torque at low RPMs?  I used to be able to use lower cutting speeds, but the sander stalls out when I try it now.

 

[Packard]

I completely disassembled the sander.  I was surprised that I had a full set of torx wrenches.  I had no idea I had these. 

The case yielded to the torx wrenches.  I found no broken parts, no obviously worn parts and nothing looking burned out.  It was fairly useless and i won’t bother to reassemble this. 

I bought the direct replacement (a Rigid brand from Home Depot).  It was a lot better than, and longer lasting than my much more expensive Porter Cable unit. The replacement appears to be exactly the same. 

If history repeats itself, I will get 7 - 8 years hard use out of this. (About $10.00 per year).     

Should I save any of the components from the older one?