Comments on my Scarey-sharp grit scale

[blueman]

I got a piece of custom 3/8 inch glass that fits 12 1/3 sheets of 11x9" sandpaper - 6 per side.

The scale I have been using is:

120 150 220 320 400 600 800 1200 1500 2000 2500 3000

I chose the scale based on the assumption that the grits appear (to me at least) to run somewhat logarithmically.

I stopped at 3000 since it seems hard/expensive to find finer grits and its not clear you gain much beyond that.

I started at 120 because based on my limited experience that seems like the coarsest one would want to go without totally chewing up the metal.

Any comments or suggestiong for improvement on the above approach? I am open to changing the grit scale to other common sizes if mine seems wrong.

Thanks

[blueman]

Another related question: Do people add any type of oil, water, or other lubricant when doing the scarey-sharp method or is it best done dry?

[Zz Yzx]

I did a similar trick with 3 separate pieces of 1/2 glass using 1/2 sheets. Works great for me.

My grit schedule goes:

100 150 220 320 400 500 600 1000 1200 1500 2000 2500

My schehule is based more on what I had laying around. Note the gap between 600 - 1000 grit, because I can't for the life of me find 800 CAMI wet-dry paper. Note that grit sizes that start with a "P" (i.e. P800) are a different scale that CAMI. I'll post a comparison chart over on abpw

I've NEVER used the 100, very rarely the 150. Most chisels and plane blades I start at 320. Once it gets past 400-500, it only takes a few mins on the higher grits. You can get the 2500 and 3000 grits at auto body supply shops. If I want to go past 2500 I switch to the microfilms.

I've not used water yet, but I'm planning to as soon as I figure out an way to keep my bench clean.

-Zz

[blueman]

I seem to have found 800 at the same places that stock the rest of the series so I have always assumed the scale was the same since the products were listed together. Can you explain what I may be missing here?

I have been able to find the silicon carbide up to 3000 from the same suppliers as the lower grits.

What is the advantage of microfilms over silicon carbide other than that they seem to go up to much higher grits (10 or 20 thousand)? They seem to be more than 10X expensive though...

What would be the advantage of water over dry sanding? Does swirling around the grit do a better job of making the scratches uniform and/or polishing than dry sanding?

Would oil (e.g., light machine oil or even WD40) be better or worse than water?

[GROVER]

If I understand your system, you are grouping six different grit papers on the same piece of float glass. This seems to me an invitation to allow coarser grits to cross over onto the next finer grit. When I was grinding and polishing a telecope mirror we were instructed to clean up completely after each size grit so as not to contaminate the next finer grit. This mirror polishing may have a lesson here for tool sharpening.

Joe G

[David Nebenzahl]

On 4/4/2010 12:24 PM blueman spake thus:

Here's my take on this aspect of sanding/sharpening: a liquid lubricant is a good thing here, as it tends to "float" the sanding swarf and reduces the possibility of clumping and clogging.

Years ago I had a partner in a woodworking enterprise who was an absolute fanatic about sharpening. He *insisted* that one should never use any liquid when sharpening, because it creates a slurry that would round off the edge of the thing being sharpened.

Now as then, I dismiss this as mostly bullshit. Whatever ill effects of using water or oil are more than compensated for by the benefits. And just intuitively, I seem to get better results sharpening with a lubricant than without.

[dadiOH]

Lose them unless you had to use 120 in which case lose the 150

I personally wouldn't bother with any of these. Why? Because they are pretty much polishing, not sharpening.

YMMV but I would rather spend my time making stuff than going through a

*dozen* - 12, count'em, 12 - grits for a bunch of tools to make a nice shiny edge that is going to start dulling the instant I start using it.

[Jeff Gorman]

"blueman" wrote >> I've not used water yet, but I'm planning to as soon as I figure out

As a matter of possible interest there's an informal list of tried liquids (and soap) at

[Larry Jaques]

Title corrected. There is no "e" in ScarySharp(tm), guys.

On Mon, 5 Apr 2010 08:45:53 +0100, the infamous "Jeff Gorman" scrawled the following:

link.

was what you were after, isn't it? The end of your link was to "page77.html" for some reason.

I've always done sharpening dry and am happy with the result. I both blow and wipe off any swarf during blade checks as I sharpen.

Works for me.

-- In order that people may be happy in their work, these three things are needed: They must be fit for it. They must not do too much of it. And they must have a sense of success in it. -- John Ruskin, Pre-Raphaelitism, 1850

[David Nebenzahl]

On 4/5/2010 7:44 AM Larry Jaques spake thus:

Probably not critical. I just prefer the feel of using a lubricant as opposed to dry. Probably makes little difference in the final result.

[Derek Darling]

Here's an idea I heard about. If you have a bunch of old hard drives lying abut, and who doesn't? take them apart, glue a series of higher-grit to the drive surfaces, then set up the power through a series of switches and tie 'em all down. So now you have all the grits, in order, spinning at easy

12,000 rpm. Sharpening to scary can be just that fast! And cool, if you add in a bunch of unnecessary but cool geek-ware light blue lights etc. DD

[J. Clarke]

Interesting notion. Anybody tried it? You do have to remove the heads, or else fire the drive up with the grit in place and let it fling them across the room (I've seen a fingerprint do that).

[Father Haskell]

For a typical edge, grind at 20 - 25 degrees (exact angle doesn't matter) and hone a 30 - 35 degree microbevel with the finest grit you have. Strop or buff to take off the wire edge, and you're done. I love sharp edges, but I have other things to do with my time.

Most of the work is polishing the back face to a mirror finish prior to the first sharpening. It's nothing to maintain the finish, just don't use the tool as a brick chisel and don't hit it with a coarser grit paper / stone except to repair damage.

[Father Haskell]

I can pare wood dead flat with my chisels. If using a honing fluid rounded off the edges, that would be impossible.

[Derek Darling]

I'm going to try it in about 3 weeks, I work in IT, and the one thing we have in abundance is old hard drives to recycle. I heard another use for old drives;, as source metal to build a Dave Gingery workshop. All that aluminium!

DD

[J. Clarke]

If it's good enough for Japanese swordmakers it's good enough for me.

[blueman]

I would doubt that would work - while the drives spin fast (and most are

7500 or maybe 10000 but few are higher than that), they have very, very little torque. In fact, the only resistance the plattens face is air resistance since even the heads rest on a cushion of air.

So good luck sharpening anything other than a micro/nano chisel at best ;)

If you all you needed was a small DC motor to sharpen, why would anybody be using multi-amp grinding machines?