Electronics > Mechanical & Automation Engineering

Very High Grit Sandpaper Application Question

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bostonman:
Recently I was shopping for spare sanding pads for my palm sander and saw the variety of grit numbers.

Last year I built a bookcase and used 220 (or maybe 400) between coats along with a final sanding. That sandpaper was very smooth and provided a very glass like feel on the wood.

I'm curious, when the grit number gets up to 1000 or higher, does it actually do much? Seems like a liquid polish would be more suited rather than the possibility of a hard particle getting between the sanding pad and scratching something.

Kleinstein:
For wood the much finer grids than 220 are rarely used, mainly for oiled surfaces of hard wood up to maybe 400.
Besides the grid also the glue used can make a difference to the feeling and finish. Epoxy glued is usually sharper, more grip, but also trends to cause deeper scratces than natural thermoplasic glue.

The realy fine ones are a thing for the final touch before high gloss paint/varnish and for polishing metall or plastics.
The liquid polish can be easier to produce and avoid scratches. The finest "paper" (actually plastic film) I remember using was 6000 grid, but this is alerady rare and paste may be more common then.

Bud:
Working on minor car finish scratches need 2000-4000 grit before polishing with paste. Same for knife blades, but may need to start with lower grit, depending on blade condition.

bostonman:

--- Quote ---I remember using was 6000 grid
--- End quote ---

Wow. I thought 800 or 1000 was smooth.


--- Quote ---Working on minor car finish scratches need 2000-4000 grit before polishing with paste.
--- End quote ---

Good point. Anytime I hear "sandpaper" I think it's going to scratch (in this case) paint on a car whereas a liquid polish is the necessary solution.

Someone at an old job built a hobby radio and made the knobs on a lathe. If I remember correctly, he used fine grit sandpaper, wet I think, and then a liquid polish. It was smooth and looked like chrome.

That was the first time I ever heard of very fine grit a high grit number sandpaper; but I don't remember the number he stated.

Bud:
1000 grit will eat car clear coat in no time. Better to start with 2000 and then go up. Fairly deep scratches will take you forever if only to use polishing paste. Also, using sandpaper on some sort of a supporting block (wood or plastic or foam one) gives beter control over the job. Polishing paste is messy, you lose visibility of where you go, and typically it is used with electric polishing tools and fairly large polish pads (2-6 inch) so it goes over large areas. Polishing paste is used as final touch.

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