sharp/dull blade drawing Hock A2 small map
Finest abrasives.
Microbevels front and back.
Use a jig.
Copyright (c) 2002-15, Brent Beach

Test Summary

Hock's A2 Cryo replacement plane blade.

A2 (Air cooled) steel has been touted as a superior steel for edge tools for some time. For example, Lee Valley says that their A2 blades are "tougher and more wear resistant than high-carbon steel as well as being able to hold a keen edge up to five times as long". In my earlier tests of A2 irons, these claims have not been proven. Far from being tougher, A2 blades have proven to be fragile, even with larger included angles [see the tests of Lee Valley and Shepherd irons, for example].

The Hock A2 Cryo iron appears to be free of the fragility problem. While not holding an edge 5 times longer, the Hock blades are more wear resistant than High carbon steel blades.

Pro: Very durable iron that retains a good edge. This is probably as good as you can do short of using High Speed Steel blades.
Con A little harder to sharpen. However, you can't get a more durable blade unless you work a little harder sharpening it.

The Tests

August 2004. During this test I was attempting to achieve one other goal - find a way to deduce the shape of the front and back wear bevels. [See an extended version of this test here.] I did not use my standard sharpening procedure with this blade. The blade comes with a primary angle of about 25 degrees. I honed a secondary bevel at 29 degrees using 15u (15 micron) abrasive paper, with a 2.4 degree back bevel (standard so far). Rather than use wooden slips for the 5u and 0.5u abrasive, I used both abrasives at the same 29 degree angle.
February 2005. Again a slightly non-standard sharpening sequence, this time using a Norton translucent Arkansas stone for the final microbevel.

Primary angle at 25 degrees, first microbevel at 29 degrees using 3M 15 micron abrasive, second microbevel at 31.5 degrees using the Norton translucent Arkansas stone.

The Results

All images are of the front bevel at 200X magnification.
As delivered. as delivered
Freshly sharpened.
Aug 2004: After the 0.5u paper at 29 degrees.

There are only two bevels visible in this picture. The bright area on the right is the factory bevel. The dark area on the left is the secondary bevel, at 29 degrees using 15u, then 5u, then 0.5u abrasive paper.

The scratches in this area are left over from the higher grits. Had I spent (a lot) more time with the 0.5u paper I would have eventually removed these scratches. My usual procedure, in which I increase the angle with each grit, concentrates the new grits at the edge and is able to remove all evidence of scratches from higher grits.

5 micron
Feb 2005: After the Norton translucent Arkansas stone.

There are 4 zones on this image. The rightmost zone is the primary bevel at 25 degrees. The next zone is the 15 micron first microbevel at 29 degrees. It originally ran right to the edge.

The third zone, the bright area next, is a combination of the 15 micron scratches and the Arkansas stone scratches. It is between the first and second microbevels.

The fourth zone, running right to the edge, is the second microbevel at 31.5 degrees.

I added the dark line with a carbide scribe before taking the picture to help me locate the exact part of the front bevel.

norton translucent arkansas
After 100 passes along 4 foot douglas-fir board.
Aug 2004.

Very narrow wear bevel, about 4 pixels wide, with good edge quality.

100 passes
Feb 2005.

100 passes
After 200 passes.
Aug 2004.

The wear bevel is about 7 pixels wide, the edge is still smooth.

200 passes
Feb 2005.

Again, a good edge with a wear bevel that is about 7 pixels wide.

200 passes

LINKS

Check out my jig page for a simple jig you can make in your shop, along with a sharpening set up using sheet abrasives, that reliably produces excellent edges, for all types of irons.

Blade Testing Page

Back to the Blade testing home page.

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