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Old 03-20-2004, 04:16 AM
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DA sanding vs hand sanding

How do most of you do it now. I've had quite a few tell me the way to do it is to hit the paint with a DA and 320 grit. I started on the hood with that and was very disappointed with the results. For one the DA always has to be tipped slightly. Of course I'm Old School and can see the DA being used for small repairs but not to prep for paint. I tossed it aside, grabbed the block and 400 paper and proceeded to block the whole truck (it's gonna be BC/CC and I want a mirror shine). By blocking I found numerous places that the DA missed. Also by blocking I can find every little door ding, etc, that would normally be missed with a DA or even by hand sanding. It's a little more work but I feel well worth it in the long run. How do you prep you cars. BTW almost the whole truck needs no primer. Just a spot on the hood and a couple of spots on the roof so it makes it real easy to see flaws.

Kevin

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Old 03-20-2004, 05:32 AM
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I've always hand (wet) sand last coat of primer or redoing paint,I agree feel like got better results.Then I've gone over again with fine scotch brite pads,clean about 4-5 times with pre-cleano.
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Old 03-20-2004, 07:03 AM
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I used to wet sand, but in the past 4 years, I have'nt even ordered a single peice of wet/dry paper. I even dry block primer with 320, then DA over it with 400.

I've cut my prep time almost in half by dry sanding, and the job turns out so much cleaner.

I use 320-400 for new parts, and 500-600 for blend panels, then scuff around the edges with scotch brite. Most of the jobs turn out with only a few nibs.
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Old 03-20-2004, 07:27 AM
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I start with the DA 320 grit, this takes it off fast, Then fix the places that show up. Next a couple of coats of primer, then block dry with 320, this is called the leveling stage. And keep repeating until it's as level as you want it. Next, after a good cleaning,wipe down with final prep and a good blow job. Apply a tinted urethane sealer. another light wipe down for over spray dust and sand any nibs out (or runs). Then paint.

DigitalW, (why block first, then da?)


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Old 03-20-2004, 12:28 PM
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Nanotechnolgies

Great topic!
It's the last chance to get it level or really screw things up before paint. Why spend all those hours, weeks, months, sometimes years getting ready to paint and then risk it all to a machine to save a few hours?

If your painting a wheel barrel on a Saturday afternoon nobody will notice where you changed directions with a DA in the same spot to many times while thinking your foucusing on another spot/problem hence digging a low/flat area in the soft primer where it was just right a second ago. That's gonna show man!

The mistake I see the most in preping for paint is in the absence of thought given to what happens when the block or DA for that matter changes direction at the end of a sand or cutting stroke. If it is changing direction in the same place again and again the result is a low spot (burn with a buffer) (scalp with the lawn mower)(run with the paint gun) in that "turn-around" location. The princible is the same with the hand block too but there's more time for control and to reflect back to this thread while keeping it a hobby
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Old 03-20-2004, 01:34 PM
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Sanding is a skill, an art, that special touch, and you don't learn it over night or by sanding one or two cars. The final look depends on the sanding and prep work.

Troy
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Old 03-20-2004, 04:00 PM
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You are NOT supposed to tip a d.a. at an angle.I see too many "bodymen" do it and it aggrivates me.You are supposed to do it flat.
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Old 03-20-2004, 04:26 PM
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Quote:
Originally posted by jimk
You are NOT supposed to tip a d.a. at an angle.I see too many "bodymen" do it and it aggrivates me.You are supposed to do it flat.
i tip mine for stripping

i wouldn't use it like that for prepping tho

did i screw up?
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Old 03-20-2004, 05:04 PM
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Tipping the DA makes it work faster, all right, but are you looking for speed, or results? Keep it flat at all times. But, for final leveling, there is absolutely no substitute for block sanding, and not only once, but several times. The more you put into it, the better it will look!
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Old 03-20-2004, 09:07 PM
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OK I may be wrong but a DA has to be tipped slightly to have control over it. When it is PERFECTLY flat one side of the disc pushes and the other side pulls allowing it to grab. By tipping it ever so slightly it gives you control over the direction. By that I mean that the front leading edge has slightly more pressure than the back edge, or the back edge has slightly more pressure than the front allowing control. But with a blok you are insured that the panel will be flat by showing areas that was missed that otherwise you could have hit with a DA and never had them show up. Then afterwards I give it the dry rag test. By that I mean put a soft cloth on the flat of your hand and go over the complete vehicle. This way you can feel any imperfections that you otherwise may not see by looking at it. If you know what you arre doing you can see way more with your hands than you can with your eyes.

Kevin
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Old 03-20-2004, 09:20 PM
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I'll go with troycurt says, been doing it this way for many years. I haven't had any problems keeping a da flat, is it spinning like a grinder or oscillating? The weight on the side of the shaft will determine this. Check it out. Dan
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Old 03-20-2004, 10:05 PM
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Feeling the sheetmetel or surface of a car is a lot like sanding, you have to acquire the touch. If you rub enough, you will know when shes ready. My wife used to get jealous of the petting the cars got.lol

Yeh, you have to tip the da ever so slightly to make it do what you want it to.

Troy
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Old 03-20-2004, 10:45 PM
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Re: Nanotechnolgies

The mistake I see the most in preping for paint is in the absence of thought given to what happens when the block or DA for that matter changes direction at the end of a sand or cutting stroke. If it is changing direction in the same place again and again the result is a low spot (burn with a buffer) (scalp with the lawn mower)(run with the paint gun) in that "turn-around" location. The princible is the same with the hand block too but there's more time for control and to reflect back to this thread while keeping it a hobby






Ever end up with 3 low spots where once there was 1?
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Old 03-20-2004, 11:21 PM
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You guys mention hand blocking primer with 320 dry. I like the results from this but have trouble with the paper clogging. It builds up what seem like little primer rocks then those little rocks end up scratching the freshly sanded surface. What do you do when this happens? I switched to wet 400 because of this but would rather use the 320 dry if I can figure it out.

-Max
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Old 03-20-2004, 11:55 PM
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Keep the air hose handy, to keep the paper clean, don't let it build up, time and experience will tell you when it is getting ready to start clogging, watch the tracks the paper is making, and you will see it. When you have it like you want it , shoot one more coat and wet sand it with 320 or 380. Then dry it as soon as you can.

I haven't had any 400 in the shop since the days of lacquer.

Troy
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