DeWalt DWMT70780 air DA sander - is this right?

[DGersic]

https://www.dewalt.com/products/power-tools/air-tools/dual-action-sander/dwmt70780

Bought a new DA sander. Supposed to be a variable speed tool. There is a speed adjustment knob, you can see it in the picture, right by where your index finger would be if you were holding it.

The owner’s manual (yes, I read The Friendly Manual) says that this knob adjusts the speed of the sander. It has that “ramp” icon above the knob to show this.

So far, so good.

In practice the knob does adjust the speed of the disk rotation. The knob is smooth turning, no detents. But the speed adjust is not smooth. It goes from slow to not working, then to medium, then not working, then fast.

“Not working” here means that air is going through the tool, but the disk no chooch.

Anybody know if this is how it’s designed to work? Don’t want to return a perfectly good tool if it’s working correctly.

I called DeWalt today. Friendly customer service. They don’t know either. We read the manual together, and agreed that it could go either way. They connected me with a service center guy, who also didn’t know, he’s never had one of these come in for repair. The parts list just tells him that there’s a speed adjustment knob.




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[Wamsutta]

Is the adjustment knob the kind that limits the travel of the trigger?

 

[DGersic]

No, the trigger is on/off.


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[bullnerd]

No, the trigger is on/off.


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Doh! Not the trigger, the speed adjust!

Does it turn 360? I think that's how my old old DA was. It just turned and changed speeds.

Probably just limiting the airflow through an orifice to change speeds, when you rotate it, its closed until it gets to the next orifice.

If it works it works.

 

[DGersic]

Turns about 180 degrees from slow to fast.

I expect it to be a variable orifice to adjust airflow, based on how the knob works. Instead, it’s more like an impact wrench, with three distinct settings, just no detent on the knob to indicate where they are.


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[bullnerd]

Set it to fast and mat it and go for it!

 

[DGersic]

Set it to fast and mat it and go for it!

Yeah. That wasn’t the question.



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[bullnerd]

Yeah. That wasn’t the question.



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lol! DA's have one speed...full throttle!

 

[DGersic]

Well, mystery solved. I just returned and exchanged a perfectly good DA. Got a new one. Exactly the same. Slow/Medium/Fast on the continuously adjustable knob, with most of the knob range being “doesn’t spin”. Kind of a weird design choice there, and The Friendly Manual could do a much better job of explaining it. Maybe this will help the next guy that buys one and wonders if it’s working correctly.


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[bullnerd]

That is weird.

How does it work besides that?

Hows the power?

PSA or hook n loop?

I need a new one. My 30+ yr old one died in a fire.

 

[DGersic]

Seems good. Runs fine. Peel and stick.


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[KenC]

Probably just a ball valve. Thru hole full diameter when lined up with the passage and less when not in line. I'll bet it really does vary, but just takes a very small movement. full speed to closed would be 90 deg. another 90 to full open again.

 

[DGersic]

No, it’s not a ball valve. Rotates 180 degrees.

It’s on slow, then off, then on medium, then off, then on full.


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[tarbellb]

Well.... Dewalt isnt known for their pneumatic tools.

Personally I would shop Ebay for a new/like new reputable brand (Mirka, CP, Dynabrade, Suix)