Random orbit sander for clear vs wet sanding?

jcclark;2415 said:
You don't have to use a hard block on clear to get a straight finish,
if you sand with coarse paper, like 400 grit.
Anything above 600 will basically not straighten but only smooth.
So a soft block with 400 on those curves will get it straight if you
sand it properly, then the finer grits won't change it.
You have to be careful how you sand, not little overlapping strokes
but long strokes to cancel out each other otherwise you'll
create waves that appear like lines from bad bodywork.
I hope that makes sense. It's hard to explain without showing.
Click to expand...

Thank you for your reply. I have been doing a lot as far as different technique, varying types of soft blocks as well as varying the angles of the crosshatching, sanding direction, etc. I'm not sure if I am splitting hairs (no one sees a problem but me) or if there is a small but fundamental flaw in my process.

Most of the time my customers don't have the budget for a second round of clear, so on a lot of these jobs I have to make do with 3 coats of clear, and the amount of urethane wave that can be removed is minimal. So I want to get to a point where the applied finish is straight enough so that a fairly conventional sand and buff is all that is required.

Sometimes, the gun finish looks nicer in a way to me, because the natural texture of the clear coat will not reveal the things that I see once it is removed.

I may be asking too much out of the process.
 
There are alot of different causes of the wave to begin with. Slight changes may be all thay is necessary to correct or reduce the problem. Biggest thing is spraying too wet and heavy. Thicker clears add to it as well. Those sealers that spray glossy and thick like clearcoat will add to it also.
 
I don't think I am spraying too heavy. Around here the adjusters never pay for sand and buff unless the car is a Lexus, etc.

So painters here are expected to produce a gun finish that is passable, and that means no runs 99% of time.

Basically my jobs usually come out with similar or less orange peel than the factory job, and maybe my completes are a bit wetter than that, I will usually find at least one small sag in a complete, usually around a side marker hole or the like.

Like I keep saying, this is something that only I see, and it's only after the buff job that these tiny waves are revealed. Even at that it's only in reverse curves. I have a feeling that a lot of guys are getting similar results to me but either don't see it, or pass it off as "normal."

There are still plenty of things to try.

BTW, sorry to the OP for the hijack, maybe I ought to get my own dang thread, lol.
 
"BTW, sorry to the OP for the hijack, maybe I ought to get my own dang thread, lol."

Crash, no apologies needed! Its all about the good info for everyone :)
 
jcclark;2415 said:
You don't have to use a hard block on clear to get a straight finish,
if you sand with coarse paper, like 400 grit.
Anything above 600 will basically not straighten but only smooth.
So a soft block with 400 on those curves will get it straight if you
sand it properly, then the finer grits won't change it.
You have to be careful how you sand, not little overlapping strokes
but long strokes to cancel out each other otherwise you'll
create waves that appear like lines from bad bodywork.
I hope that makes sense. It's hard to explain without showing.
Click to expand...

JC I agree the coarser paper works if you're using a softer pad but you can also cut the ripples/waves out with finer paper if you use a flat and stiff block. A plexiglass block with one layer of 1000 or even 1200 will make it as flat as can be.
 
i noticed a big difference in finish work in the early 70's. back when i started there was no hookit or self sticking paper. we used a spray glue on da pads and sanding blocks. the big difference is a piece of 1000 loose on a block will not block flat. it will float into the low spots especially if it is wet. suction will pull it down. now if you use adhesive on the block this will not happen and you will get a truer block if that makes sense. i stat with 600 to cut the highs down then move on to finish paper. i make my own wooden blocks . i hate those damn little rubber blocks. imho they wont block anything.

just my opinion and worth exactly what you paid.............
 
I've been wondering about the rubber blocks to. the seem to flexible.. I do have a durablock that i might try next time, it is much stiffer.
 
Bob Hollinshead;2537 said:
JC I agree the coarser paper works if you're using a softer pad but you can also cut the ripples/waves out with finer paper if you use a flat and stiff block. A plexiglass block with one layer of 1000 or even 1200 will make it as flat as can be.
Click to expand...

I'm going to have to try that, thanks.
 
The durablock is stiffer than rubber but the surface is still too soft to cut the defects out with fine paper. JMO
 
I have started to use some wacky abrasives from Eagle abrasives (kovax in Japan). One type they have is called Tolex. It is 1500-2500 and comes with a very rigid polycarbonate clear "pad"

Some of the other types of abrasives use a backing pad that is softer than a household sponge so I guess it is very important how rigid the pad is. BTW, I don't really use disks and traditional things (paint bicycle frames mostly) but I am really, really liking Eagle products.
 
You must log in or register to reply here.
Back
Top