Why does a metal file last longer than sandpaper?

[Tetsuaiga]

I was thinking if say aluminium oxide is harder than hardened steel, why doesnt it last as long?

I'm thinking it's because a file/rasps shape means it cuts, whereas sandpaper is more like a scrape so more wear right on its tips? The rasp's tips aren't engaged as much as the sandpaper tip.

 

[transatlantic]

Isn't it that the grits on sand paper fall off as opposed to wear down?

 

[Sheffield Tony]

I assume because the hardened steel stays attached to the file, but the grit on abrasive paper comes off, then helps to blunt what is left attached ?

I've mentioned before that our school woodwork teacher taught that it was a mistake to go back from abrasives to edge tools because of this; any embedded grit from the abrasive dulls the tool.

 

[Phil Pascoe]

Aaahh... back in the days you got told off for calling glasspaper sandpaper?

 

[Sheffield Tony]

Aaahh... back in the days you got told off for calling glasspaper sandpaper?

Yep. That would be right

 

[Tetsuaiga]

It could be that the sandpaper falls off I suppose. But it still becomes dull from wear without all coming off its backing, I suppose that may be the more exposed grits fall off first leaving a smoother surface.

 

[MattRoberts]

I always thought it was the adhesive that fails on the sandpaper..?

 

[Robbo3]

Aaahh... back in the days you got told off for calling glasspaper sandpaper?

... and when we smashed glass between two towels & used the bits as scrapers.
But what would I know. I got chucked out of woodwork for being so bad. The teacher couldn't believe someone could be as incompetent as me.

 

[Phil Pascoe]

I didn't go that far, but when I was working if I ever had to replace a broken window I went through the shards and kept the pieces with gentle, regular curves for that purpose.