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Our first Advanced Class of 2016..... after a late reschedule and it falling on Easter Weekend, we had a slightly smaller class than usual, but that just meant the students had more hands on guidance!
We started with our usual classroom discussion of the processes involved in both hand sanding, DA sanding and rotary polishing. Then it was out to the garage for a hands on demo, a quick lunch break, and then a couple hours of hands on time for the guys.
DA sanding is a quick and easy way to remove heavy paint defects, level texture, etc. With a variety of grits available, plus media that is either a texture leveling disc or a texture matching disc, you have plenty of options when DA sanding. Options not only in terms of materials available, but in what goal you want to achieve. One quick thing to note in the blow image: the DA sander is being moved from operator's left to operator's right (bottom of image toward top) and you can see that the size of the "footprint" left by the sander is narrower than the width of the abrasive media. This should be a quick visual reference to you that you are not keeping the abrasive disc flat against the paint, and you want it as flat as possible to avoid uneven sanding. In this class we demonstrate the right way to do things, but also show what can happen when things are done incorrectly. Sometimes the consequences are minor, sometimes they're pretty major - as you'll see later on in this article.
Our first cut was with a 1500 grit sanding disc. Notice all the residue on the face of the disc after our initial cut - that's clear coat residue that has been sanded off the paint surface. This needs to flushed away regularly in order to work clean and avoid the creation of pigtails in the paint surface.
An area full sanded with 1500 grit - note the absence of any sort of reflections in the sanded area.
Toward the outer edge of the sanded area we see this mottled effect. The mottling comes from dull spots and shiny spots created by the abrasive media only sanding the tops of the orange peel texture. The shiny spots are the bottom of the "waves" in the orange peel that have not been sanded.
Next, we refine our sanding mark using a 3000 grit finishing disc. This reduces the depth of the sanding marks, making final buff out much easier. An easier buff out means you're introducing less heat to the paint, and modern catalyzed clear coat just doesn't like heat.
On the left side is an area sanded with just 1500 grit via DA; on the right side we followed up the 1500 grit with 3000 grit. Note that there is a reflection in the 3000 grit side but none on the 1500 grit side. Remember that reflectivity comes from flatness and smoothness of the surface; 1500 grit is anything but flat and smooth, but 3000 grit is making great progress toward that goal.
This quick video clip shows the difference from a different angle, with the lack of reflection on the 1500 grit only section seemingly cutting off the head of a student. We assure you, no students were harmed in the course of this program!
Hand sanding is a whole different technique, and technique is really critical here because hand sanding can actually be more aggressive than DA sanding, even with equal grits of abrasive media. Note the tight overlap of the stokes as evidenced by the stripes of residue.
Again, this short video clip shows the sort of hand motion we're looking for when hand sanding.
The resulting area should be very uniform in appearance when you're done sanding.
Very close inspection reveals straight line sanding marks, something you will not see when DA sanding.
Sanding on an edge requires you to change up your technique a bit. Remember that the thinnest paint on a given panel is on the very edge of that panel, so you want to avoid sanding right over the edge. If you sand over the edge, you then have to buff over the edge, and that gets real dangerous real fast. Don't do it. Keep this in mind: don't sand where you can't buff!
For the record, the rotary in the below picture is spinning at 1400 rpm - it's easy to control if you just relax and don't fight it!
An initial buffing with a wool pad and M105 shows that we still have a bit of work to go. That haziness around the light is actually the remnants of our sanding marks.
A second pass eliminates the remaining sanding marks and clears up the haze. You must fully remove the sanding marks with your compounding step before moving on to your finishing polish. Don't think it's close, or good enough, and expect your finishing polish to complete the task.
See that little dull oval just about dead center in the image below? That's a burn through mark. It took a split second for this to happen....
This video shows how quickly things can go sideways with a rotary if you're not paying attention, or you do something silly with the wrong combination of product and pad. In this case, using a burgundy foam cutting pad at just 1400 rpm, we tipped the pad up on edge for just a split second, using nothing more than the weight of the tool. The edge of the pad is dry and, being the edge of the pad, it has the greatest velocity and therefore creates the greatest friction. Keep your pad flat!!
With the demonstration portion over, and a quick lunch out of the way, it was time to cut the guys loose and let them get some experience with these various techniques and processes.
We talked about keeping your hand flat against the backing pad when hand sanding so as not to create pressure points with your fingertips. The image below is a perfect example of what not to do when hand sanding.
Below is an indication of incomplete hand sanding. Notice that the sanding marks go in two different directions. That's all fine and well, and actually recommended as you step down to finer and finer grits of sand paper. But in this case, there is a definite lack of uniformity of sanding marks in both directions. We guarantee that buff out of this set of marks is going to be frustrating at best.
This is properly DA sanded section, using 1500 grit (notice the lack of reflections).
A bit of hands on guidance as he works into the tight contour on the hood.
With the introduction of our DA Microfiber Correction System and SMAT abrasive compounds like M105, M100 and M101, plus the higher torque output of DA polishers like our MT300, we can now often times remove sanding marks with a DA polisher and skip the rotary all together. In this case, a DMC5 cutting disc is paired with M100 to quickly remove 3000 DA sanding marks.
M205 on a yellow polishing pad generates crazy gloss after M105 on wool knocked down all the sanding marks.
We started with our usual classroom discussion of the processes involved in both hand sanding, DA sanding and rotary polishing. Then it was out to the garage for a hands on demo, a quick lunch break, and then a couple hours of hands on time for the guys.
DA sanding is a quick and easy way to remove heavy paint defects, level texture, etc. With a variety of grits available, plus media that is either a texture leveling disc or a texture matching disc, you have plenty of options when DA sanding. Options not only in terms of materials available, but in what goal you want to achieve. One quick thing to note in the blow image: the DA sander is being moved from operator's left to operator's right (bottom of image toward top) and you can see that the size of the "footprint" left by the sander is narrower than the width of the abrasive media. This should be a quick visual reference to you that you are not keeping the abrasive disc flat against the paint, and you want it as flat as possible to avoid uneven sanding. In this class we demonstrate the right way to do things, but also show what can happen when things are done incorrectly. Sometimes the consequences are minor, sometimes they're pretty major - as you'll see later on in this article.
Our first cut was with a 1500 grit sanding disc. Notice all the residue on the face of the disc after our initial cut - that's clear coat residue that has been sanded off the paint surface. This needs to flushed away regularly in order to work clean and avoid the creation of pigtails in the paint surface.
An area full sanded with 1500 grit - note the absence of any sort of reflections in the sanded area.
Toward the outer edge of the sanded area we see this mottled effect. The mottling comes from dull spots and shiny spots created by the abrasive media only sanding the tops of the orange peel texture. The shiny spots are the bottom of the "waves" in the orange peel that have not been sanded.
Next, we refine our sanding mark using a 3000 grit finishing disc. This reduces the depth of the sanding marks, making final buff out much easier. An easier buff out means you're introducing less heat to the paint, and modern catalyzed clear coat just doesn't like heat.
On the left side is an area sanded with just 1500 grit via DA; on the right side we followed up the 1500 grit with 3000 grit. Note that there is a reflection in the 3000 grit side but none on the 1500 grit side. Remember that reflectivity comes from flatness and smoothness of the surface; 1500 grit is anything but flat and smooth, but 3000 grit is making great progress toward that goal.
This quick video clip shows the difference from a different angle, with the lack of reflection on the 1500 grit only section seemingly cutting off the head of a student. We assure you, no students were harmed in the course of this program!
Hand sanding is a whole different technique, and technique is really critical here because hand sanding can actually be more aggressive than DA sanding, even with equal grits of abrasive media. Note the tight overlap of the stokes as evidenced by the stripes of residue.
Again, this short video clip shows the sort of hand motion we're looking for when hand sanding.
The resulting area should be very uniform in appearance when you're done sanding.
Very close inspection reveals straight line sanding marks, something you will not see when DA sanding.
Sanding on an edge requires you to change up your technique a bit. Remember that the thinnest paint on a given panel is on the very edge of that panel, so you want to avoid sanding right over the edge. If you sand over the edge, you then have to buff over the edge, and that gets real dangerous real fast. Don't do it. Keep this in mind: don't sand where you can't buff!
For the record, the rotary in the below picture is spinning at 1400 rpm - it's easy to control if you just relax and don't fight it!
An initial buffing with a wool pad and M105 shows that we still have a bit of work to go. That haziness around the light is actually the remnants of our sanding marks.
A second pass eliminates the remaining sanding marks and clears up the haze. You must fully remove the sanding marks with your compounding step before moving on to your finishing polish. Don't think it's close, or good enough, and expect your finishing polish to complete the task.
See that little dull oval just about dead center in the image below? That's a burn through mark. It took a split second for this to happen....
This video shows how quickly things can go sideways with a rotary if you're not paying attention, or you do something silly with the wrong combination of product and pad. In this case, using a burgundy foam cutting pad at just 1400 rpm, we tipped the pad up on edge for just a split second, using nothing more than the weight of the tool. The edge of the pad is dry and, being the edge of the pad, it has the greatest velocity and therefore creates the greatest friction. Keep your pad flat!!
With the demonstration portion over, and a quick lunch out of the way, it was time to cut the guys loose and let them get some experience with these various techniques and processes.
We talked about keeping your hand flat against the backing pad when hand sanding so as not to create pressure points with your fingertips. The image below is a perfect example of what not to do when hand sanding.
Below is an indication of incomplete hand sanding. Notice that the sanding marks go in two different directions. That's all fine and well, and actually recommended as you step down to finer and finer grits of sand paper. But in this case, there is a definite lack of uniformity of sanding marks in both directions. We guarantee that buff out of this set of marks is going to be frustrating at best.
This is properly DA sanded section, using 1500 grit (notice the lack of reflections).
A bit of hands on guidance as he works into the tight contour on the hood.
With the introduction of our DA Microfiber Correction System and SMAT abrasive compounds like M105, M100 and M101, plus the higher torque output of DA polishers like our MT300, we can now often times remove sanding marks with a DA polisher and skip the rotary all together. In this case, a DMC5 cutting disc is paired with M100 to quickly remove 3000 DA sanding marks.
M205 on a yellow polishing pad generates crazy gloss after M105 on wool knocked down all the sanding marks.
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