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-   -   Tip: Cutting and Buffing Paint (https://vansairforce.net/community/showthread.php?t=60631)

DanH 07-26-2010 05:54 PM

Tip: Cutting and Buffing Paint
 
So how do you get paint with a perfect surface? You sand, compound, and polish. It is not technically difficult. The hardest thing is finding the courage to pull the trigger on the sander after all the time and money you spent to get shiny new paint on there in the first place.....

What follows is my current favorite cut and buff process. There are variations in individual methods, and everyone's methods change as products develop. As a used car dealer I've been doing this sort of thing on and off for 30 years. Even so, this particular 3M system is new to me, and auto panels don't have rivet lines. More education and recreation! Refinements always welcome.

3M has a YouTube channel;

https://www.youtube.com/channel/UCN4...dxk7v8_8gh6iDw

Paint finishing playlist here:

https://www.youtube.com/watch?v=mkwF...ia290Luw-rO4p7

I'm cutting a light color so I can get away with a few less product steps. For me it's a 1500 grit Trizact disk, 3000 grit compound/white foam pad, and machine polish/black foam pad. Dark colors are far more sensitive to swirl marks and visible sanding scratches, so you'll perhaps you'll need 3000 and maybe even 5000 sanding before going to compound. My main focus in this thread is simply removing orange peel.



Gather (1) a bucket and a spray bottle, both with plain water, (2) a washrag and a few handfuls of drying rag or towels, (3) some 600 and 1500 grit wet-or-dry paper and assorted sanding blocks, and (4) some masking tape. The random orbital sander is equipped with the appropriate hook and loop pad, and a soft interface pad. Later you'll need a good buffer. Pro buffers run at 1500-2000 RPM. You'll need a hook and loop pad for the buffer too.

Work someplace with good overhead lighting, preferably fluorescent tube. The entire process revolves around seeing the contrast between shiny surface and dull surface. Dull is where you've sanded away a high spot. Shiny is a low spot not yet sanded. It looks like this....the band of shiny speckles you see below is the reflection of an overhead lighting tube. They're your indicator. When they're almost gone, you're done cutting. You must be able to see, so don't skimp on lighting.



Start by taping all panel edges and screw lines. You can't accidentally cut through a taped edge. Well, you can, but you'll need to work at it:


DanH 07-26-2010 06:00 PM

Pick up the spray bottle and squirt the pad, then mist the entire surface of the panel. Take a deep breath and start sanding.

It is very important to be consistent. Sand in rows, overlapping each pass on the previous much like how you run a spray gun. Do not move the sander in random patterns. Your goal is to remove the same material thickness everywhere on the panel. Random sanding tends to remove a lot over here and not enough over there....too easy to get a thin spot.

Sheet aluminum over ribs means the panel is slightly wavy; high at the rivet lines and low in the middles. Most of your sanding should be in rows parallel to the rivet lines, although early in the cutting process you can run patterns across them without risk. Keep the pad flat and don't press; just let it float. You want the foam interface pad to conform to the surface. As you near the end of the cutting process, just ease the pad edge up next to the rivet lines rather than over them and keep the bulk of the cut in the middles.



You'll build up a nice froth of powdered paint and water. After a few passes (in a pattern!) stop, grab a wet rinse rag (remember the water bucket?), and wipe down the surface. Grab a dry towel and really wipe the surface nice and dry. Now you 'll be able to see exactly how deep you've cut. Here is the surface after the first round, uncut on the right for comparison. See the shiny speckles in the tube light's reflection? Needs more cutting.



Ok, so mist it again and cut some more. Stop from time to time, rinse and dry, then examine the surface again. Move your head around to walk the reflection across the panel and look at all of it. You might spot an area with no more speckles while the rest still needs more cutting. No problem, just mark it with some tape dots. It may be thin there or it may not, but there's no point in taking a chance. That spot has been cut enough.



Continue working the panel. Eventually you'll reach a point where you can still see just a little bit of shiny speckle, the very last vestige of the demon orange peel:



You're done.....move to the next panel. All that's left is the buffer, which we'll get to in a future installment. And yeah, we'll fix a run too....

Mike S 07-26-2010 07:39 PM

BIG THANKS
 
Dan, good info, well presented, thanks a bunch.:D

DanH 07-26-2010 10:39 PM

Thanks Mike....gotta do something nice for the diligent ants, slaving away at home while the grasshoppers play at OSH :p

Let's fix a run.

Grab a razor blade and a piece of 400 or 600 grit paper. Hold the blade at a slant as shown and drag it across the paper a dozen times. You just put a microscopic curl on the edge:



Now bend the razor blade like so, curled edge on the convex side:



Here's our run.....ugly, ain't it?



Drag the edge of the blade across the high spot in the run, holding it nearly perpendicular to the surface and using only light pressure. Don't try to cut or dig or anything like that...just sort of drag it. It will scrape very light feathers of material off the run with each pass. The bend in the razor isn't strictly necessary in this example, but if the run was on a flat surface it would prevent you from dragging the corners of the blade and making a scratch. In this case it just shows you which side has the curl.


DanH 07-26-2010 10:50 PM

When your fingers almost can't feel the lump any more, quit scraping. Grab some wet 600 grit paper and wrap it around a small hard block. This one is balsa. Hard rubber blocks work nice too. Foam blocks are too soft for this task.

Using light pressure skim the surface over the run. The idea is to cut the remaining high spots without skinning the surface around them. It will only take a few strokes to flatten the surface:



Now switch to some wet 1500 grit, which you can hold freehand. Make a few more passes. Your goal isn't to remove any significant material. You just want to remove the 600 grit scratches. After that you can go straight to compound. It can wait until later when you're running the buffer, but for this example I just hand rubbed it a few minutes. Run all gone:



Ok ants, let's get some work done....

E. D. Eliot 07-27-2010 01:50 AM

Great Presentation
 
Dan, please give us info on the brand name of the paper that you use. Also, if there are any product numbers on that paper, please give that info too. that way, we may order the paper by name and product number .Thanks:cool:

DanH 07-27-2010 09:08 AM

Quote:

Originally Posted by E. D. Eliot (Post 453193)
Dan, please give us info on the brand name of the paper that you use. Also, if there are any product numbers on that paper, please give that info too. that way, we may order the paper by name and product number .Thanks:cool:

Ordinary wet-or-dry sheets for hand-sanding, 3M or Norton, common as dirt. Keep them soaking in your water bucket.

The purple P1500 Trizact clearcoat sanding discs are 3M # 02088. You also need the matching 05551 and 05777 pads to equip the sander:

BTW, don't confuse 3M's "Hookit" with "Hookit II" products...they're not interchangable.

Buffing: 06085 compound and 06064 polish, 05737 and 05738 foam pads:

Your buffer probably has a hook-and-loop backing pad.

Yeah, it's about $250 for all of it, but......




mculver 07-27-2010 10:09 AM

Wow, this thread should be sticky. Thanks Dan

panhandler1956 07-27-2010 05:54 PM

Thanks Dan!
 
I too am stuck at home while OSH is in full swing - thanks for thinking of us that couldn't make it!

chinch 07-27-2010 08:44 PM

Meanwhile...
 
...in unrelated news, 3M shares have risen two hundred points this morning on unconfirmed reports of a massive and as yet unexplained spike in sales by their cutting and polishing products division....


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