Wet/Dry Sandpaper and how you know it's done with

[Bevel]

Ok guys, make sure you're sitting down for a pretty dumb question.

Basically, when sanding a blade, how do you determine you need a new piece of paper.
On low grits like 80 it's not too bad as it feels more like 400 but on higher grits like 1000+ it's not as easy to know it's not really doing anything anymore.

Anyone have any rules of thumb so to speak.

 

[RayClem]

W/D abrasives use silicon carbide as the abrasive material. SiC is a friable material. That means that over time, the particles break down into ever-smaller particles. If you are trying to remove a lot of material, that break-down can be detrimental. If you are trying to polish a blade, the longer you continue to use the sheet, the finer the polish.

Thus, you should replace your sheet when it is no longer accomplishing the task you intended.

 

[bluesman 7]

but on higher grits like 1000+ it's not as easy to know it's not really doing anything anymore.

I agree. On the high grits, especially if you're using them wet, it gets hard to tell the more used part of the sheet from the less used. I usually feel the sheet with my finger tips and look for a change in friction or bite.

I saw a demo by a high end kitchen knife maker, where he was finishing an etched damascus knife, and he had torn his high grit paper into postage stamp size pieces and was using them wet with his finger tips. I started doing this with 600 grit and up and I like it. It seems to make it easier to tell when each piece is done, and when you pick up a new piece it is really new.

 

[stone and strop]

I agree. On the high grits, especially if you're using them wet, it gets hard to tell the more used part of the sheet from the less used. I usually feel the sheet with my finger tips and look for a change in friction or bite.

I saw a demo by a high end kitchen knife maker, where he was finishing an etched damascus knife, and he had torn his high grit paper into postage stamp size pieces and was using them wet with his finger tips. I started doing this with 600 grit and up and I like it. It seems to make it easier to tell when each piece is done, and when you pick up a new piece it is really new.

This is what I do as well.

 

[eKretz]

Same here. I have been cutting my abrasive sheets into single use pieces ever since I can remember. Using wet is good with fine paper as it helps wash the swarf away. Another tip - if you do use them dry, you can clean them out with compressed air and they will start cutting better again. Very fine grit stuff loads up with swarf rapidly, so clean frequently!

 

[Bevel]

All good advice thanks guys.
I do sometimes flick low grit paper with my finger on the non-abrasive side to clear the paper if sanding wood.
On metal I don't think that does much good though.

I've been sanding a blade and it's extremely slow progress using 150.
I've made good progress on one side but have to be careful on the side that has etching, I'm using 320 for that.

 

[eKretz]

Yeah on metal a compressor and a good high velocity small jet airgun cleans it out well. Nothing much else will do it as well that I've found.

 

[Bevel]

Cheers.
I have the other side almost clear of patina and need to go up through the grits but on this side there's a real danger of permanently damaging the "The Celebrated" stamp as it's quite faded as it is.
The rest of the etching is reasonable but I'm in a bit of a dilemma on how to proceed with this.
Any thoughts?