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Saturday's Advanced Class was the first such class where most of the participants were already pretty experienced with the rotary buffer. Wet sanding, however, was still new to them so there was plenty to learn!
As usual, we spent time with both hand sanding and DA sanding, and the differences in technique between them.
Although this picture may say otherwise, this is not a "contest"!
As a first go, not bad. But the overlaps could be tighter, which comes with practice.
Hand sanding in two directions; one for the first cut, the second for the finer cut to take off the tops of the sanding scratches from the first cut. The idea is to refine the surface as much as possible, while taking off the least amount of paint.
DA sanding; while similar to DA polishing, you don't use anywhere near the level of pressure when doing this. Pad rotation, overlapping strokes, back and forth motions are all the same as used when polishing with a DA.
Nice uniformity of sanding marks, except for that section in the middle. That's the reflection of the overhead fluorescent lights showing up in the middle of the picture, along with a dirt nib. So why do only see this in the middle? Check the next image below.
A broader view shows that panel has a slight concave to it so the sanding media was bridging across the lower portion, making only very slight contact with the paint. The mottled appearance is due to only the tops of the texture being sanded, leaving slight reflections emanating from the untouched paint in the low spots.
A second pass of the same area, using the DA sander from two different angles, removes the texture and evens out the finish. Even very fine, gentle contours can pose issues when sanding.
Hand sanding into a tighter contour forces you to change things up a bit. The flexible backing pad is curved to better match the radius of the contour. In this situation, a tighter curve on the pad is likely called for, but you can see it's actually lifting off the paint on the side closest to the operator's body. That means the curve of the pad is tighter than the contour being worked on, which is desirable. If the curve of the pad wasn't tight enough, it would bridge over the lower portion of the panel contour and you'd get the same sort of non-uniform sanding shown in the images above.
Historically we used rotary buffers to remove sanding marks as the DA just wasn't up to the task. Today's technology in both tools, pads and compounds - and even abrasives - is changing the industry dramatically and it's now common to remove those sanding marks with a DA. Here we're using the new MT300 DA buffer, a microfiber Xtra Cut disc, and M100 at 5800 OPM.
Sand and buff!
Revealing the gloss after compounding out the sanding marks!
So what kind of results were the guys getting? This is a "before" shot of the recently painted panel, showing a lot of micro texture in the surface.
After some sanding (either 1500/2500 by hand or 1500/3000 by DA) and then a bit of compounding and polishing the difference in clarity and gloss is huge!!!
As usual, we spent time with both hand sanding and DA sanding, and the differences in technique between them.
Although this picture may say otherwise, this is not a "contest"!
As a first go, not bad. But the overlaps could be tighter, which comes with practice.
Hand sanding in two directions; one for the first cut, the second for the finer cut to take off the tops of the sanding scratches from the first cut. The idea is to refine the surface as much as possible, while taking off the least amount of paint.
DA sanding; while similar to DA polishing, you don't use anywhere near the level of pressure when doing this. Pad rotation, overlapping strokes, back and forth motions are all the same as used when polishing with a DA.
Nice uniformity of sanding marks, except for that section in the middle. That's the reflection of the overhead fluorescent lights showing up in the middle of the picture, along with a dirt nib. So why do only see this in the middle? Check the next image below.
A broader view shows that panel has a slight concave to it so the sanding media was bridging across the lower portion, making only very slight contact with the paint. The mottled appearance is due to only the tops of the texture being sanded, leaving slight reflections emanating from the untouched paint in the low spots.
A second pass of the same area, using the DA sander from two different angles, removes the texture and evens out the finish. Even very fine, gentle contours can pose issues when sanding.
Hand sanding into a tighter contour forces you to change things up a bit. The flexible backing pad is curved to better match the radius of the contour. In this situation, a tighter curve on the pad is likely called for, but you can see it's actually lifting off the paint on the side closest to the operator's body. That means the curve of the pad is tighter than the contour being worked on, which is desirable. If the curve of the pad wasn't tight enough, it would bridge over the lower portion of the panel contour and you'd get the same sort of non-uniform sanding shown in the images above.
Historically we used rotary buffers to remove sanding marks as the DA just wasn't up to the task. Today's technology in both tools, pads and compounds - and even abrasives - is changing the industry dramatically and it's now common to remove those sanding marks with a DA. Here we're using the new MT300 DA buffer, a microfiber Xtra Cut disc, and M100 at 5800 OPM.
Sand and buff!
Revealing the gloss after compounding out the sanding marks!
So what kind of results were the guys getting? This is a "before" shot of the recently painted panel, showing a lot of micro texture in the surface.
After some sanding (either 1500/2500 by hand or 1500/3000 by DA) and then a bit of compounding and polishing the difference in clarity and gloss is huge!!!
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