Continued…
Number Crunching Time!
This first set of numbers are the measurements taken after each wet-sanding step to show how much material was removed.
This second set of numbers are the measurements taken after each machine cleaning and polishing step to show how much material was removed.
Crunching the numbers, here's the results... 
Here's a graph showing the very small amount of paint removed during each procedure.
Most car manufactures say that .5 mils can be removed safely from a factory finish. During this entire process my goal was to approach the sanding and buffing just like I would if I were really sanding down the factory finish on a customer's car.
I let the PosiTest Paint Thickness Gage tell its own story as I measured after each step as accurately as possible.
From the measurements taken, it looks like the process in totality removed approximately .5 mils of film-build. This is at the safety margin.
This hood started out with the normal orange peel when we obtained it for our Advanced Class. During our Advanced class approximately 10 people were sanding both by hand and by machine and buffing using rotary buffers with wool pads and compounds. Pictures from this class can be seen here,
Pictures & Comments from October 4th, 2009 Sunday Detailing 102 - Advanced Class
This means by the time I did this demonstration there was no orange peel left on the hood so I was starting out on very flat paint.
Here's my theory...
Had I started out with pure, good old fashioned GM orange peel I would have only sanded enough to remove the tops of the orange peel and would have removed less paint overall, at least less than .5 mils of solid, uniform coverage. There would be less risk and more paint to last over the
service life of the car. At least that's my theory.
Big picture conclusion...
At least on this paint system being used in 1999 on GM Silverado trucks, the factory baked-on paint can be sanded and then buffed using a DA style polisher to remove 99.9% of the sanding marks.
Summary Dual Action Polishers
Then new generation dual action polishers like the Griot's Garage ROP, the Porter Cable 7424 and the Meguiar's G110v2 offer a lot more rotating power under pressure than first generation models and with the right pads, chemicals and techniques can remove sanding marks in the higher grit range.
Historically, the direct drive rotary buffer has been the tool of choice for removing sanding marks fast and effectively because of the power it provides from the motor and also the direct drive nature of the design of the tool. This direct drive design also brings with it some risk because if you're not careful you can easily buff to long in one area and remove too much paint and expose the color coat under the clear layer in the case of a basecoat/clearcoat finish or expose the primer under the color coat in the case of a single stage finish.
The new generation of DA style polishers offer more power and can do a better job of keeping pads rotating, this would include the PC 7424XP, the Griot's Garage ROP and the new Meguiar's G110
v2
As this demonstration has shown, a DA style polisher can be used successfully by enthusiasts and Pro Detailers to remove sanding marks as long as they have the right tool, the right pads, the right chemicals and use good technique. It's a given that you should always try to finish out with the highest grit papers possible to make the buffing process the easiest and fastest.
Of course a HUGE factor that will determine how easy or difficult it is to remove sanding marks with a DA style polisher is how soft or hard is the paint. A better way to say this is actually, how workable, or polishable is the paint and this is something you don't know until you do some testing in a small area.
Because paints vary after they are cured in polishability, it's not wise to make sweeping generalizations like, all Honda's have soft paint therefore they are easy to sand and buff. The truth is, you really don't know if a paint is going to be hard or soft until you test.
Fresh paint versus Factory paint
There's also a huge difference in working on fresh paint, paint that is less than a week old and typically in a body shop situation, less than a few days old when they do the sanding and buffing, and sanding and buffing paint that has been baked-on at the manufacturer's assembly line. By the time a car leaves the assembly line the paint in most cases has already reached full cure and is completely dried and hardened to as hard as it's going to get. Again, hard or soft or how polishable or workable the paint is on each car is a variable that you won't know until you do some testing.
Risk Factor - Thin Paint
Factory paint tends to be thin, at least thinner than a good quality re-paint at a reputable body shop. Keep this in mind should you decide to sand an isolated area or an entire panel or an entire car. Thin paint means there's not much room for error. Also remember that sanding removes a measurable amount of paint and so does the step where you cut the sanding marks out with an abrasive compound or swirl mark remover.
That said, I know a lot of enthusiasts and even Pro Detailers do this, or are planning to do this so I did my best to show the results from a standard and simple hand-sanding technique.
Next, I demonstrated that fine or shallow sanding marks can be removed using a quality dual action polisher with foam cutting pads and in this case, a quality swirl mark remover. In their simplest form,
swirls are a type of scratch and the Wolfgang Total Swirl Remover 3.0 is an excellent swirl mark remover and capable of removing at a minimum, #3000 grit sanding marks, at least on the factory baked-on paint used in this demonstration.
Before you decide to sand down an entire car, if it were me, the first thing I would do is a
Test Spot to insure your choice of pads, chemicals, tools and your own personal skill level will be good enough to remove the sanding marks in your Test Spot.
Use the results from your test spot to confirm your plan of attack and give you the confidence to proceed, or if you run into problems, come back here to the Autogeek forum and ask for help and our online community will go out of their way to see you through to success.
While a rotary buffer with a wool cutting pad and an aggressive compound is the best tool for removing sanding marks, I know that a lot of people don't own a rotary buffer and/or are not ready to move up to a rotary buffer but do own a dual action polisher.
In this demonstration I used 5.5" pads and one thing to consider is that you can also use 4" pads for even more correction power as the smaller diameter will enable a dual action polisher to better rotate the pad.
Paint is removed best when the pad is rotating, not merely vibrating or jiggling against the paint, so be aware of this and always mark your backing plate with a black mark so you can easily see that your pad is rotating, or if it's simply jiggling against the paint.
There's a huge difference in the quality of sandpapers on the market, and whenever you do any wet-sanding on clear coat paints it is important to use the best quality paper you can obtain.
Avoid basic wet-dry papers as there's little or no control over grit particle
size or grit particle
distribution. These papers will put horrific tracers into the paint and the only safe way to get them out is to re-sand using premium quality paper like the Nikken brand. So start out working smarter instead of harder and just get one of the best papers available before beginning any project.
List of products used Griot's Garage Random Orbital Polisher PosiTest Paint Thickness Gauge Brinkman Swirl Finder Light Wolfgang Total Swirl Remover 3.0 Wolfgang Finishing Glaze 3.0 Nikken #2000 Finishing Papers Nikken #2500 Finishing Papers Nikken #3000 Finishing Papers Meguiar's E-7200 Rubber Backing Pad Lake Country 5.5" Yellow Foam CCS Cutting Pad Lake Country 5.5" White Foam CCS Polishing Pad Generic Spray Bottle with Clean water and drop or two of
Pinnacle Bodywork Shampoo 3M Scotch 233+ Premium Automotive Masking Tape 18mm x 32m GritGuard 5-Gallon Bucket System with Dolly - Red Autogeek Complete Two Bucket Wash System - Red Brass Shut Off Valve Brass Quick Connector Set That's all, let the discussion begin! 
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