Though that is aluminum and it really shouldn't occur, that looks like oxidation probably caused by a damp, humid environment or some wood reacted with the metal that you may have left on the bed of the saw for a while. It won't have any effect on anything other than appearance. A Scotchbrite pad may shine it up a bit. Wax will help prevent further oxidation.

 

That appears to be from some moist contaminate of some king. I would buff it clean with a mild abrasive (0000 steel wool or 3M pad) then treat it with CRC 3-36 spray. It is a silicone based product that seals and lubricates so it will resist any moist contaminates in the future. I also use the CRC 3-36 on my cast iron tool tops. Fine Woodworkers magazine rated it as one of the top products for those purposes.

 

Thanks. I actually have some silicone lubricant spray, not sure whether it's CRC 3-36 - will check.

 

DON’T use steel wool on aluminium. The steel imbeds itself into the softer metal and will speed up corrosion when conditions are right again. Use the Scotchbrite. It is made of plastic with aluminium oxide abrasives.

Pete

 

I would not use a silicone based product on my tool surfaces. It may be unlikely but if any silicone gets on the wood surfaces, it will play havoc with finishes and you may not know it is there until it is too late. It can also be difficult to remove. That said, looking at their website, I do not see that CRC 3-36 has silicone in it?

 

Oops....I was looking at a different product when I came up with the silicone content. It is a petroleum product; no silicone.. At any rate after reading the Fine Woodworking article I have been using it for a couple of years and it works great.
I too agree about using silicon in places where it might contaminate the wood.

Another testimonial from 2017: CRC 3-36 Multi-Purpose Lubricant and Corrosion prevention

 

So what should I use? I have some off-brand Scotchbrite pads (I bought a box of them to apply Osmo), but can I just use... what's that stuff like Ajax or Comet that doesn't scratch... I forget the name?

 

I suppose that you could try Barkeepers Friend or Bon Ami. Supposedly, vinegar or lemon juice will remove corrosion from aluminum but the problem with the that and the mild abrasive cleaners is that they usually require water so you might have to be careful not use too much water. Personally, I would probably just use use the gray 3M abrasive pads. Just use a little WD40 or something as a lubricant.

 

Bon Ami is what I was thinking of.

Well, I'll try the pads first. Thanks.

 

I just read that one thing to try is rubbing a ball of aluminum foil (shiny side out) on it to remove the corrosion. As with anything, Try a small area first.

 

When I polish aluminum table

I use WD-40 and a scotch brite pad under a random orbital sander

 

3M makes an aluminum polish for boats that should do the job....it is not for use on anodized aluminum.

I would be careful using Barkeepers Friend on non anodized aluminum because the primary ingredient is Oxalic Acid which could etch the metal.

 

Is the aluminum on the saw anodized?

Thanks - and thanks for the great replies, everyone.

 

The corrosion would suggest it is not anodized.

 

Makes sense!

 

And should I put on paste wax on my magnificent DeWalt DWS779 miter saw to stop it from continuing?

(It looks a hundred times worse in this picture than it really is.)
I maintain 1500 tools here in Hawaii for a tool library. Our location is 50 yards from the ocean. The salt air will oxidize aluminum and cause pitting on steel or cast iron. I use fine grit wet/dry sandpaper to remove the worst and smooth out the surfaces. Once pitting is too bad it is hard to smooth/slick the surface of table saws etc. Then I was treating with paste wax but it doesn't remain for long. Treating with a spray that leaves a lanolin coating seems to work best. You don't want to treat with something that will leave too much residue that might stain wood materials. It is a continuous maintenance situation.
TIA

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Good comments above. I have not used a protective coating on the aluminum rails or beds. What I probably would use on the surfaces are Search Results for "dry lube spray" at Menards® These cost less verses some of the other protective sprays
B'laster® Advanced Dry Lubricant - 9.3 oz. and
WD-40® Specialist® Dry Lubricant - 10 oz. with PTFE


Look for the one that are silicone free. The silicone if it gets on the wood surfaces, you may end up with poor results when applying stain & finish.