Using a DA sander to remove paint

[Palmer]

Once I get the Z back from the welder I'm going to start the paint removal process. I've been told that a DA sander works fine, but, I've never used one. So, if someone could recommend a brand first, I've got mostly Dewalt stuff, that would be helpful. I'm sure they are all pretty much the same. Next, pad sizes, grits or any other suggestions would be much appreciated as usual. I have been told the following though...If you work a particular area too hard you can warp the metal causing waves in the metal. Since the car will be painted black pearl, the darker the paint the more prominant the 'waves' would be. How easy is it to actually put flaws in the metal with a DA sander? I plan on taking things slow because I am in no rush to get this done quick. Any advice is helpful....

[EScanlon]

...snip...I'm sure they are all pretty much the same. Next, pad sizes, grits or any other suggestions ...snip...

I have been told the following though...If you work a particular area too hard you can warp the metal causing waves in the metal....snip... How easy is it to actually put flaws in the metal with a DA sander? ...snip.....

Regarding warping the metal with a D/A:

I've been doing bodywork for about 25 years on and off and I have to admit that this is the first time I've heard this. Is this the beginning of an autobody urban legend? If not, then could someone elaborate?

Metal will warp if too much heat is applied unevenly or if it's flexed / vibrated with a lot of force. While I CAN see this happening when using a large grinder, I can't imagine how you could generate enough heat with a D/A to warp the metal or oscillate the metal to do so.

As far as which brand D/A to buy, it really depends on how much you are willing to spend, how much you plan to use it, and whether or not you are looking to repair it when it requires repairs.

Harbor Freight has some excellent values on inexpensive tools. They also have some rotten deals on some CHEAP tools(*). If you are only planning on doing this one car this ONE time, go there. You'll probably pay anywhere from 15 to 25 dollars and when you are finished with the job you'll have definitely gotten your money's worth.

If you are planning on making a career out of bodyworking, then check with Snap-On, Matco, or Mac tools. They all have very heavy duty D/A's that will also set you back a pretty penny. The big advantage is that you will have a heavy duty unit that won't need repairs for a LONG time (unless you abuse it) and will have a source for replacement parts / accessories. I'm not sure whether they manufacture their own or have Chicago Pneumatic or Milwaukie Tool manufacture for them, but they will have their backing on the item. Expect to pay upwards of 75, for just the basic tool (i.e. no pad, nor fittings)

If you are someplace in the middle, check with Sears or Home Depot. Both of them have better than average tools and their prices will also be in the mid-range.

Regardless of how much you want to spend, as that is mostly determined by your willingness to part with the cash, look at some of the following features as being the deciding factors more than the money.

A D/A sander is a Dual Action Sander. It not only rotates the paper it also oscillates the rotation's center. The main purpose of this is to allow the pad to not rotate while still "jitter-bugging" the pad. Think of drawing little circles while drawing a large circle. Although you can find electric jitter-bug sanders, most guys buy an AIR driven D/A. A pneumatic D/A offers features that an electric one will not. (Most electric D/A's are used in wood working, and although you can use them on the car, their limitations outweigh their use.) Aside from being able to vary the air pressure at the compressor's regulator, D/A's usually have a feathering valve near the body of the D/A, on or near the handle. Although many D/A's come with a pad, look for a D/A that will allow you to change it, as you WILL find that it gets chewed up. Additionally, you may find that you want a beveled edge pad that allows you to sand into curves easier than a thin flat pad.

Some D/A's only allow the "jitter-bug" rotation. Others will allow you to lock the shaft going to the pad so that only ONE rotation type is allowed. You will usually see a sliding tab that slides into a hole or straight edge on the shaft to lock it in place. You should also see a counter-weight there. This counter-weight is important as it minimizes the vibration from the eccentric rotation of the pad.

Look at how much air pressure and cfm's the tool will require. More expensive tools will be better built and sealed and will have less "waste" air. This is important as the size of your compressor's pump and tank will REALLY limit what you can do.

If a D/A requires 65 psi it tells you where you will be setting your pressure regulator. But if it requries 10 cfm at that pressure, you're not going to be using it with your typical home compressor.

Most home compressors (under 5hp and 30 gal.) will NOT have enough air to power a D/A for long periods of time. The smaller your tank, the oftener that you will have to wait for the compressor to catch up with you. How long you wait will depend on how strong your compressor is. Conversely, the larger your tank, the stronger a compressor you will need to fill it quickly.

Look at the location of the feathering valve. Is it located CONVENIENTLY and does it have an easy to move lever or knob? A "thumb-lever" will allow you to change pressure as you work which in turn affects the speed of rotation. A knob will require you to stop in order to adjust, and you won't be able to do it as it is running. Also look at the On/Off valve. Is it a nice long lever that allows you to grip the tool and by tightening your grip run the tool, or is it a short lever that will tire your hand out.

Check where the exhaust air vent is. Since air tools require lubrication, if the exhaust is aimed downwards onto the pad, it will eventually oil up your pad and you'll be having to replace it more often. If on the other hand it vents to the side, you might find that you are oiling your work. This is a definite NO-NO for paint. The best design I've seen has the exhaust going back under the handle to exhaust via a small muffler near where the air inlet is.

Lastly, check how easy it is to change pads. It's no fun having to disassemble a D/A just to change a pad. It should be as easy as locking the shaft and unscrewing the pad.

That should help in finding the D/A you want to use.

Sandpaper is your next consideration. This will be your next largest area of expense.

The size of the paper will be determined by your D/A pad. Sanding paper grit will be determined by the job you are doing. You can get as coarse as 36 grit to as fine as 600 or 800, with the last two being rarely used. Most of your work will usually be done with 180, then 220 or 280, and finishing with 400. But these aren't hard-fast rules. It all depends on what you are doing, on to what kind of surface and what is below that surface.

For extremely fast paint removal start with 80 grit, then 220 and finally 400. But these are MY preferences for paint on steel with no filler underneath.

Well, I hope I gave you some answers. Feel free to ask more.

Enrique

[jackboxxx]

that about covers it all Enrique's the man

[hls30.com]

One note to add-I am currently stripping three layers of paint from a '70 roadster, and I am using a RotoZip with a right angle adaptor with scotchbrite pads.

The pads extend past the backing/mounting plate by about 1/4" inch when new, I use that portion to get into the dual plane corners of the body, and after the edges of the pad have worn, use the rest of the pad to take off the paint, too "spongy" to do anything but lightly burnish the metal, but very effective on the paint-just keep it moving-as the pad collects paint(and it will), it will generate heat and could create issues if held in place too long. I could have used my airtools, but there is on a strong enough compressor where the car is, and I could not find my old D&D side arm grinder.

One other note of interest.

This car is outside, and will remain there until it is painted. When I finish stripping paint for the day, I spray all of the exposed metal with a mist of Metal Ready several times, and follow that with three complete wipedowns with a paper towel saturated with Metal Ready. I then tarp the car. As the Metal Ready dries it etches the sheet metal and leaves a zinc-phosphate coating which will protect the metal for about 2 weeks as long as rain does not collect. When I am ready to move on with etching primer, I will take a scotchbrite scourning pad saturated with metal ready and scrub the surface of each panel. This removes the excess zinc phosphate and collected dust while still treating any newly exposed metal. After that step and before the Metal ready has dried fully, I will wipe down the panels with laquer thinner to remove everything left from the scrubbing, and then, after the panel has dreid, wipe down again with laquer thinner, and prime with etching primer.

Will

[EScanlon]

Will: for those odd areas where it is real hard to get the D/A pad into, try a different technique.

Take your small air grinder, the one that looks like a pistol and uses small grinder disks / sandpaper with a stiff backing that is smaller in diameter than the disc you are using. Next, with your metal shears make diagonal cuts all around the circumference of the pad. You don't have to make them very deep, a 1/4" is sufficient. You will end up with a many pointed star.

Next, using very light air pressure--just enough to get the pad rotating and very light hand pressure, walk your grinder into the area just lightly touching the "V" on the paint. You'll be surprised at how fast you'll literally RIP the paint off.

Don't apply too much pressure, nor allow the pad to spin too fast. Your intent is to literally whisk the paint off and not grind / burnish the metal.

You can also do this with the D/A, just by using the next higher diameter paper.

The technique and product that you mentioned is an EXCELLENT way of getting into deep areas where the D/A simply won't do and your knuckles and fingers would suffer. Although the Scotch pads are real good and do a FAST job of removing paint, look for another product of Scotch's that I've used to make it even faster.

Look for the Yellow and Green Rubber "Finger" disks. These are available in 1.5 and 3 inch diameters. The two styles are different "coarseness", but I can't remember which. They look like the type of brush you use to groom a horse or short haired animal, or simply these small diameter rubber tubes on a rubber base mounted on a shaft. I used up the box I had otherwise I'd give you a part number.

These "finger" disks literally ERASE paint, rust, bondo, and just about anything except the metal (unless you really press down, but even with a lot of pressure you will only see a few sparks). I used these to remove the undercoating under the front fenders.

You posted that you can't get enough air pressure to use your D/A or other air tools, and your idea of the Roto-Zip is excellent. I'll have to remember that one.

Enrique

[=Enigma=]

Very nice guys. Thanks for all the great info. I use an electric Porter Cable random orbital or D/A(now that I know what that means) for polishing and waxing my cars, in combination with products from Griots.com. It's a huge time saver and leaves absolutely no swirl marks or burns, even with excessive pressure on the pad. I imagine that this could double for use when doing body work. It is a very high end model so I plan on getting many years of use out of it. I found a great deal on it at wordworkers.com. Porter Cable also makes the sort of full-featured air powered model Enrique was talking about.

http://woodworker.com/cgi-bin/FULLPRES.exe?PARTNUM=130-715

[EScanlon]

Enigma: Wait up, your random orbit polisher is NOT a D/A Sander although it does have "dual-action" rotation. A D/A is understood as the body working tool and not the polisher.

The polisher is an excellent tool for waxing or polishing but it is NOT designed for sanding, nor would I recommend you use it as such.

Enrique

[=Enigma=]

Enigma: Wait up, your random orbit polisher is NOT a D/A Sander although it does have "dual-action" rotation. A D/A is understood as the body working tool and not the polisher.

The polisher is an excellent tool for waxing or polishing but it is NOT designed for sanding, nor would I recommend you use it as such.

Enrique

Point taken, however the Porter Cable 7335 is actually a random orbital sander converted by me to be used as a polisher. I replaced the 5" adhesive ready sanding pad with a 6" H&L pad incl. new matching counter weight and added task specific polishing and waxing pads.

Porter Cable 7335

Polishing Pad

Waxing Pad

[EScanlon]

Whereas this:

http://www.eastwood.com/shopping/product/detailmain.jsp?itemID=5212&itemType=PRODUCT&iMainCat=608&iSubCat=609&iProductID=5212

is the "typical" D/A sander.

And this:

http://www.eastwood.com/shopping/product/detailmain.jsp?itemID=14433&itemType=PRODUCT&iMainCat=608&iSubCat=609&iProductID=14433

is your typical D/A polisher.

E

[=Enigma=]

So it simply seems to be about the form factor, not about the action or features. BTW, I wouldn't let that low-end Eastwood polishing unit near any of my vehicles. Not on yer' life!

[EScanlon]

While both rotate and oscillate in the same manner, the two are quite different in their use.

The unit you showed is closer to a production polisher and not related to the one in the second picture I posted.

The one you posted is actually closer to what we used to use for heavy grinding and for polishing lacquer paints with the wool bonnets and polishing compounds, although ours didn't d/a.

The typical D/A if I recall correctly can actually rotate higher than 6k orbits.

But no matter, as long as you are careful and EVEN while sanding they'll work.

E

E

[jackboxxx]

Whereas this:

http://www.eastwood.com/shopping/product/detailmain.jsp?itemID=5212&itemType=PRODUCT&iMainCat=608&iSubCat=609&iProductID=5212

is the "typical" D/A sander.

Do you guys Prefer the handle with thumb trigger Over a "palm"

type control DA? Personally I like the palm type better.