solekeeper said:
I have contemplated switching to DA or machine wetsanding for my shop. Looking for some beginners tips. Here are some variable for my particular shop. I usually use 2000 for post paint operations. (Removing tiny dirt nibs, take away minor OP etc.) We do not do reduction sanding. We have done this on many paint finishes, without issue.
Can someone break down WHY I should switch from handsanding? I'm thinking, it's faster, less messier, and a better finish? The the only downside to the DA polishing i guess would be that the possibility of burning the paint would be greater.
I'm in the dark ages, i know.. so I'd like to switch... Which DA would you guys recommend? I know the sandpaper i'd probably end up using is the 3M triczact system. Thanks for all the feedback guys.
Sounds like for the type of sanding you wish to accomplish, DA sanding would be a great choice for your shop. Since you are using 2000 grade papers for the majority of your work, I doubt you are having many paint burning issues at the moment (perhaps "over-thinning" of the paint might be a better term than "burning" in this case). Should you decide to switch to DA sanding (assuming you will use similarly fine grade of discs to accomplish your work), I doubt you'll have any major complications.
I hope you don't mind if I get a bit "entry level" here, for the benefit of other readers.
In the case of de-nibbing, that can still be accomplished by hand pretty rapidly. You can either use a small piece of sandpaper and cross-cut or approach the dirt at a few different angles (which is what you're likely doing now), or you can use a de-nibbing rosette and holder, or a dedicated de-nibbing machine:
Mirka 1-1/4" Vinyl-Faced Sanding Drum
Or you can use a de-nibbing tool:
I mention these tools because whatever paper or disc you use, the backing or the item that the paper or disc is attached to needs to be rigid enough so that the abrasive particles will push through, cut off, or wear down the dirt particle without conforming around it and affecting the surrounding paint.
The Trizact system has film-backed discs as well as foam-backed discs. You'd want to use the film-backed to level texture, and then use the foam-backed afterwards to refine the scratches before final polishing. You can also use the foam-backed discs to remove micro-shrinkage of the paint, which occurs independent of how the paint surface is formed as the paint is sprayed or is curing.
You don't
have to use dedicated de-nibbing rosettes or tools. You could typical sanding discs (3", 5", 6") and tilt the machine a bit to shrink up the footprint of the discs. To do this, its best to use very low speed and perhaps an interface pad if you're de-nibbing on curves surfaces.
Once you get to the large-area work such as leveling paint texture, the DA can save you lots of time. If you are just trying to eliminate some of the orange peel but wish to retain a factory-peel or textured surface appearance, the Trizact foam-backed discs can work remarkably fast, and will deliver a consistent finish. Once again, use of an interface pad will allow the disc to more readily contour to curved panels.
There is a bit more to consider when making the transition to machine sanding, but all in all it will save you lots of time and can deliver a better result. The main drawback to DA sanding has to do with difficulty in
leveling textured surfaces. It most certainly can be done, but it is important to keep the sanding disc as level to the panel you are sanding as possible. In other words, if you tend to tilt the machine off-kilter while you're moving it along, the edge of the disc may dig into the paint (causing hard to remove pigtail marks). Edge-digging can occur when you hand sand too, but you're not moving your hand back and forth thousands of times per minute (typical speeds used when DA sanding range from almost nothing to 10,000 RPM). Even at a a "slow" setting of 3,000 oscillations per minute, the sanding disc is orbiting at a rate of 50 times per second! If it just so happens that you've added tilt to the machine and consequently caused the edge of the disc to dig into the paint for even half a second, there's a chance that you'll see 25 "pig-tail" shaped gouges in the paint. It's not a deal breaker... just wanted you to know why there is a leveling
limitation.
Interface pads can help to control edge digging. There are interface pads available that are designed to allow excellent leveling potential while still giving a bit of cushioning action so that sanding discs can contour to shaped panels.
An EXCELLENT thread about sanding:
http://www.autopia.org/forum/machine-polishing-sanding/135397-wetsanding-buffing-fresh-paint.html
More about interface pads:
Interface Pad Facts
Meguiar's Unigrit Discs (featuring Trizact-style technology):
All About Meguiar's Unigrit
