O1 v. A2 (one more time)

For our “high carbon” steel blades, HOCK TOOLS uses AISI (American Iron and Steel Institute) O1, a simple high carbon tool steel with very little added to the iron/steel alloy other than 1.1% manganese. That pinch of Mn allows the steel to harden with an oil quench (the “O” in O1 stands for Oil.) Oil removes heat more slowly than water, reducing the thermal shock that occurs when orange-hot steel is plunged into water. Reducing that thermal shock minimizes the risk of cracking or distortion in the hardened piece. With an alloy as simple as O1, containing so few alloying elements, the hardened grain structure is as fine as possible which allows honing to the sharpest possible edge.

O1 at 1000x magnification, the carbides are too small to see

AISI A2 differs from O1 with the addition of 5% chromium and 1.1% molybdenum, allowing it to quench in still air (“A” for Air.) While “stainless” amounts of chromium (12% or more) make tool steel “gummy” and hard to sharpen, the modest amount of chromium in A2 improves its toughness and abrasion resistance, but imparts only a slight measure of corrosion resistance (like high carbon steel, it will rust and appropriate preventative care must be taken.) But there is a trade off. During heat treatment the chromium addition combines with some of the carbon in the alloy to form chromium carbides – tough, hard particles dispersed through the steel. These carbides are the primary contributors to A2’s celebrated edge retention. However, during heat treatment, the chromium carbides can grow quite large – large enough to affect your ability to hone the edge as close to zero-radius as you may want. And these carbides are held in place with less strength than the rest of the steel matrix which can allow them to pop out under the stress of honing or cutting leaving a small gap in the edge. To strengthen the edge we recommend a larger bevel angle for A2 than we would use for O1. For a bench plane iron, try your A2 blade at about 30° or 33°. A chisel or block plane blade can be even steeper; try 35° or so and see if edge retention is improved.

A2 at 1000x magnification with some of the carbides in yellow

A2 is one of the steels that respond well to cryogenic treatment. This extreme cold treatment (-320°F) essentially finishes the original quench, increasing the steel’s toughness without any decrease in hardness. You get increased wear resistance without any increase in brittleness so a cryogenically treated blade will hold its edge longer. You can keep working instead of sharpening. A2 is a great steel that offers a real improvement in edge retention. O1, on the other hand, is still preferred by many for its relative ease of sharpening and its ability to get sharper.

Who you callin’ “Ol Bastard”?!

I have a sample of the “Ol Bastard Jig Sharp Scraper” and find it a clever solution to the problem of keeping a paint and flooring scraper sharp. The scraper is a well-designed, ergonomic version of the paint scraper that I used to prep a house for paint.

The Ol Bastard at work

That seemingly endless job included frequent resharpening of the scraper blade, a necessary task that helps keep the job from being truly endless. This is the good part about this innovative tool. It is integrated with a sharpening fixture that files the edge without removing it from the handle.

The scraper slides on the rod for quick, accurate sharpening on the captive file

The scraper handle has a groove (white plastic in photo above) that rides the rod in the sharpening fixture which holds a file. The angle of the edge to the file is proscribed and the edge is filed sharp with a few quick strokes. Clever.

This scraper won’t replace your #12 or your hand/card scrapers for furniture work. But when you’re stuck prepping for paint or refinishing a floor, this tool combo should keep things moving along.

Lots more info at Ol Bastard’s website.

Of Thick and Thin

I’d like to explore the prevailing belief that thicker plane blades are always superior to thinner ones. While it may seem like an intuitive truth, consider that the cantilevered portion of a bevel-down blade remains the same for thicker blades. It’s just moved farther away from the ramp on a larger, thicker cantilever. If the last fraction of an inch of the blade is flexing, adding to the thickness fails to modify the offending portion. That last, flexible fraction is still in play.There are some real advantages to thicker blades: when hollow ground, they are much easier to hold securely on a stone for honing — the edge and heel of the bevel register with positive, tactile feedback; many woodworkers like the feel of a plane with additional weight; and some additional mass and rigidity adds to the overall stability of the plane/blade system. But thicker for its own sake is overrated and may require modifications to the plane and breaker that are unnecessary. If the plane is properly fettled — the blade making good contact with the ramp, the cap iron* and lever cap both doing their jobs — a standard thickness blade will function as intended.

Thicker blades in bevel-up bench planes add needed support across the width of the mouth. The low bed angle employed in most bevel-up smoothers and jack planes creates a very thin wedge at the mouth that can be a bit fragile and a beefier iron helps that thin wedge resist deflection and possible fracture.

*While this may be a bit off topic, the illustration shows how a cap iron (chip breaker) contributes to a plane’s performance by adding pre-load stress and rigidity right down at the thinnest, most flexible part of the blade.

(The illustration is by Martha Garstang Hill from The Perfect Edge, the Ultimate Guide to Sharpening for Woodworkers.)

Seconds, please.

Plane Kit Bargains!

We’ve accumulated a number of Plane Kit parts that I can’t sell as “Firsts” — they have minor checks or sap pockets that won’t effect their performance but make them look… less than perfect. So we’re offering them as “Seconds” for a substantial discount. Go here for more info.

AND we still have a few of our old-style kits available. They’re maple bodies with jarrah soles. More info here, if you’re interested.

— Ron