What grit sandpaper for smooth finish?
05-06-2003, 11:10 PM
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What grit sandpaper for smooth finish?
I need to sand the ridge off of my fibergalss cowl and am wondering how fine does the grit need to be to end up with a smooth finish? I have 600 grit on my bench.
Frank
Frank
05-07-2003, 01:17 PM
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What grit sandpaper for smooth finish?
Frank,
I started off using my Dremel™ tool and a stone wheel to grind the biggest part of the ridge down on my Goldberg 300 FG cowl. When it was about level I went to 220 grit on a sanding board to get it flush. When all was flush (running my fingers across the ridge I could not feel it at all) I switched to 300 for a few passes, then 600 dry.
When it felt very smooth I primed it, then started off with 600 wet. Primed again and 600 wet. In my case I primed AGAIN and 600 wet, then 1000 wet. I did it as many times as it took to get the pinholes filled and smooth.
Then I painted it. If you are using a metallic paint you should not color sand directly on the metallic paint, you need to clear coat it first. If you don't it can mess up the finish and you will need to put another coat or two of metallic before clear coating it. I know.
After clear coating 5 light coats I switched to 1500, then auto polish. I was soooo happy with the finish, just to find out I had to open up a bigger hole for the needle valvle. Next time I do one I will TOTALLY fit it out, with all cutting and drilling, THEN paint and finish. hehehe. Still looks good though.
I started off using my Dremel™ tool and a stone wheel to grind the biggest part of the ridge down on my Goldberg 300 FG cowl. When it was about level I went to 220 grit on a sanding board to get it flush. When all was flush (running my fingers across the ridge I could not feel it at all) I switched to 300 for a few passes, then 600 dry.
When it felt very smooth I primed it, then started off with 600 wet. Primed again and 600 wet. In my case I primed AGAIN and 600 wet, then 1000 wet. I did it as many times as it took to get the pinholes filled and smooth.
Then I painted it. If you are using a metallic paint you should not color sand directly on the metallic paint, you need to clear coat it first. If you don't it can mess up the finish and you will need to put another coat or two of metallic before clear coating it. I know.
After clear coating 5 light coats I switched to 1500, then auto polish. I was soooo happy with the finish, just to find out I had to open up a bigger hole for the needle valvle. Next time I do one I will TOTALLY fit it out, with all cutting and drilling, THEN paint and finish. hehehe. Still looks good though.
05-07-2003, 05:55 PM
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What grit sandpaper for smooth finish?
Mike is probably correct. I am thinking I put WAY too much effort into a cowl for this size plane, and for the very minimal difference in appearance it probably made.
In retrospect I could have used the extra time I spent and put it toward finishing the plane and working on my flying skills. Ah, well, there is always next time.
In retrospect I could have used the extra time I spent and put it toward finishing the plane and working on my flying skills. Ah, well, there is always next time.
05-07-2003, 07:40 PM
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What grit sandpaper for smooth finish?
Thanks for the replies!
I finished with 600 wet, and the results are pretty darn good. There's still a bit of a "step" where the pieces don't mate just right, but I'm not worried enough about that to try and fix it. I figure the odds of me doing a low slow knife edge pass and someone saying "Nice plane . . . except for that line on the cowl" are pretty slim.
My biggest concern was that I would end up with a rough spot on an otherwise glassy finish.
Frank
I finished with 600 wet, and the results are pretty darn good. There's still a bit of a "step" where the pieces don't mate just right, but I'm not worried enough about that to try and fix it. I figure the odds of me doing a low slow knife edge pass and someone saying "Nice plane . . . except for that line on the cowl" are pretty slim.
My biggest concern was that I would end up with a rough spot on an otherwise glassy finish.
Frank
05-08-2003, 05:28 PM
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What grit sandpaper for smooth finish?
Frankenthumb - A lot of people don't understand the process of sanding. There's shaping and finishing. The process that Post Hole described is exactly right. You shape (removing ridges is shaping) using coarse paper, files, wood/razor planes, dremel tools, etc.
Then you go to progressively finer grits. A lot of guys make the mistake of starting out with a fine grit paper which actually causes problems. It's easy to make a part flat if you use coarse paper, but if you use fine paper, you can actually make it less flat if you sand with it for too long.
After the initial shaping you start stepping up with successively finer grits to remove the scratches from the previous grit. I've seen people switch from 80 to 400 grit in one shot and sat there sanding and sanding and never got the scratches out. A lot of work for little result.
For paint prep, 600 paper is good. For polishing, you can get paper up to 12,000 grit, but 1000-1600 will work if you also have a good polishing compound. I have some 12,000 so I know it exists. It came with a motorcycle windshield polishing kit. I only use it to polish clear wind screens on plastic models and that's about it.
Then you go to progressively finer grits. A lot of guys make the mistake of starting out with a fine grit paper which actually causes problems. It's easy to make a part flat if you use coarse paper, but if you use fine paper, you can actually make it less flat if you sand with it for too long.
After the initial shaping you start stepping up with successively finer grits to remove the scratches from the previous grit. I've seen people switch from 80 to 400 grit in one shot and sat there sanding and sanding and never got the scratches out. A lot of work for little result.
For paint prep, 600 paper is good. For polishing, you can get paper up to 12,000 grit, but 1000-1600 will work if you also have a good polishing compound. I have some 12,000 so I know it exists. It came with a motorcycle windshield polishing kit. I only use it to polish clear wind screens on plastic models and that's about it.
