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N8 · 02-11-2003, 01:51 PM

To add more about surface finish:

Surface finish is an absolute measurement. The means to get there (sandpaper, grit sizes, polishing compounds) are only relative - as in there is a variation.

Lets take 600 grit for an example. 600 grit is just an average size assigned to the material. The deviation from average could be small or large. The sanding paper may be labeled 600 grit, but it may have anywhere from 400-800 grit particles on it. Higher quality papers will have a smaller deviation from average.

The material on the sanding paper may be different. Silicon carbide grit will remove material differently than aluminum oxide grit or even diamond grit.

The SHAPE of the particles on the sanding paper will be different. You could have two different pieces of 600 grit sandpaper with silicon carbide on both, but 600 grit is just a size range, it has nothing to do with shape. What if there are silicon carbide pieces on one paper that are more pointy and the other has more rounded grit?

Another issue is the density of the grit on the paper. You could have two pieces of 600 grit sandpaper, but the amount of grit on each piece could be different. The piece with a higher density per square inch will produce a finer, more consistant finish, while the piece of sandpaper with less grit on it will produce a more variable scratch pattern.

The length of time you use the sandpaper will affect the shape of the grit on the paper. It will clog the higher density papers faster than lower density sanding paper. The longer you use the sandpaper, the more rounded the tips of the grit become, altering the shape of the grit.

NOW, consider that all of the above variables are combined. Just think of the different variations in conditions you could come up with for 600 grit sandpaper. You can end up with a surface finish that is TOTALLY different depending on these variables, even if two different people finish up with 600 grit sandpaper.

Now think about operator differences. Even if two people have the exact same 'movement' techniques, exact same sanding paper, one of the two might push very lightly on the paper, the other will push very hard. This pressure difference with produce very different results for surface finish.

Whether you use water or dry sand will also change the surface finish.

There are many many variables that affect what we are doing.

The only measurement that is absolute is the surface finish on the material itself (heatsink, etc.)

For a good read on grit sizes and issues, conversion tables, etc., go here:
http://www.newportglass.com/grit.htm

One word of caution, grit size conversion tables are NOT standardized, so there are some variations to be found from different tables.

02-11-2003, 01:51 PM	#22
N8 Cooling Neophyte Join Date: Sep 2002 Location: Pullman, WA Posts: 91	To add more about surface finish: Surface finish is an absolute measurement. The means to get there (sandpaper, grit sizes, polishing compounds) are only relative - as in there is a variation. Lets take 600 grit for an example. 600 grit is just an average size assigned to the material. The deviation from average could be small or large. The sanding paper may be labeled 600 grit, but it may have anywhere from 400-800 grit particles on it. Higher quality papers will have a smaller deviation from average. The material on the sanding paper may be different. Silicon carbide grit will remove material differently than aluminum oxide grit or even diamond grit. The SHAPE of the particles on the sanding paper will be different. You could have two different pieces of 600 grit sandpaper with silicon carbide on both, but 600 grit is just a size range, it has nothing to do with shape. What if there are silicon carbide pieces on one paper that are more pointy and the other has more rounded grit? Another issue is the density of the grit on the paper. You could have two pieces of 600 grit sandpaper, but the amount of grit on each piece could be different. The piece with a higher density per square inch will produce a finer, more consistant finish, while the piece of sandpaper with less grit on it will produce a more variable scratch pattern. The length of time you use the sandpaper will affect the shape of the grit on the paper. It will clog the higher density papers faster than lower density sanding paper. The longer you use the sandpaper, the more rounded the tips of the grit become, altering the shape of the grit. NOW, consider that all of the above variables are combined. Just think of the different variations in conditions you could come up with for 600 grit sandpaper. You can end up with a surface finish that is TOTALLY different depending on these variables, even if two different people finish up with 600 grit sandpaper. Now think about operator differences. Even if two people have the exact same 'movement' techniques, exact same sanding paper, one of the two might push very lightly on the paper, the other will push very hard. This pressure difference with produce very different results for surface finish. Whether you use water or dry sand will also change the surface finish. There are many many variables that affect what we are doing. The only measurement that is absolute is the surface finish on the material itself (heatsink, etc.) For a good read on grit sizes and issues, conversion tables, etc., go here: http://www.newportglass.com/grit.htm One word of caution, grit size conversion tables are NOT standardized, so there are some variations to be found from different tables.