For the “Shop Made Tool Swap - 2015: Hand Planes and Spokeshaves”, I decided to make two planes (one to keep, one to swap) including the blades. I started with a 1/8” thick 2.5” wide precision ground flat bar of A2 tool steel that I happened to have on hand. After some requests for more information, I decided to start this tutorial blog for making them.
You can buy tool steel pretty cheap from MSC:
Other sources of tool steel include Online Metals, Jantz, McMaster Carr, and Grainger. Be sure to buy the precision ground variety to avoid flattening hassles later. Blade thickness is up to you… most are between 3/32 and 1/4” for wood-bodied planes, I believe. Tool steel bars come in an “annealed” state, which means it’s soft enough to machine. We’ll heat treat it later.
These are the two most common steel types for plane blades. O1 is easier to sharpen and can hold a delicate steep (25 deg or less) edge without chipping, but the edge wears quickly so sharpening is needed more often. A2 will hold an edge a fair bit longer than O1, but is harder to sharpen and can have large carbides that tend to fracture on a steep edge… most sources recommend a 30 deg or higher bevel for A2.
I started by cutting the blades out of the A2 stock with an angle grinder and thin metal cut-off wheel:
I just winged it on the blade length… as long as they’re tall enough to protrude from the plane body and wedge, they’ll be adjustable with a mallet and work fine. I then sanded the rough edges square-ish on a stationary belt sander using a miter gauge.
To grind the bevel, I used my slow-speed 8” bench grinder and freehand ground to the squared edge I made earlier, leaving about a 1/32” edge thickness to prevent thin steel from burning/warping in the kiln:
I dipped the blades in water from time to time to cool them between grinding sessions. The angle is somewhere between 25 and 30 degrees, we’ll see if the A2 can hold up to this steeper angle… if not I’ll grind it back a little after heat treatment.
I then lapped both sides of the blade flat-ish, as this is much easier in the soft annealed state than after heat treating. I used this grinding jig on my stationary 9” grinding wheel for the bulk of it, then sandpaper on granite for the rest:
This step could probably be avoided if you were careful not to bend/warp the precision-ground stock when angle grinding.
Next up is heat treatment. Most tool steels shouldn’t be exposed to oxygen during the hardening, or the carbon atoms will react with it and burn away. This is called “decarburization” and can pit or even ruin tool steel in bad cases. To prevent this I first apply two coats of ATP-641 anti scale coating, a product used commonly for hobby knife making:
I just paint it on with an acid/glue brush, wait a few hours, then re-coat. This is a thin clay product that prevents oxygen from contacting the steel while heating.
For hardening, I use my Father’s digital kiln that’s normally for jewelry work (precious metal clay, enamels, etc). It is possible to harden with a torch, but you can’t get the “soak” times at the hardening temperatures that the steel alloy’s elements need to go into full solution in the steel. A2 and O1 tend to benefit from this soak more than simpler steels like 1095, as they have many small quantities of rare earth elements that take time to distribute.
Here are the hardening steps for each steel type, which I came up with as an average of many separate internet resources (and review from knife form experts for the O1 steps):
O1 Tool Steel:
preheating: 1250 deg F, keep blade in kiln while warming, hold for 10 minutes
hardening: 1475 deg F, hold for 10-15 minutes
quenching: canola oil warmed to 125 deg F, agitate rapidly up and down (NOT side to side), keep going until bubbles stop and piece is hand warm
tempering: 375 deg F, hold for 2 hours minimum, cool with water, repeat for second temper at 375-400 deg F
A2 Tool Steel:
preheating: 1400 deg F, keep blade in kiln while warming, hold for 10 minutes
hardening: 1750 deg F, hold for 10-15 minutes
quenching: cool in still air to 150 F (able to hold in bare hand) before tempering
tempering: 400 deg F for RC 60, hold for 2 hours minimum
For A2, “quenching” just means taking it out of the kiln and leaving it in room-temperature air for a while. This is easier than dunking in preheated oil for O1. I actually do the tempering in a kitchen oven, as the kiln takes forever to cool down after hardening. I generally get lazy tempering and just do 400 deg F for an hour for both steels without bothering with a second cycle.
Here is the kiln and blades after removal:
Notice how the coating pops off during the quench:
After the kitchen oven tempering, you can see the yellow color of the steel below the remaining coating:
This color change indicates tempering hardness, hopefully I got it somewhere around RC60.
Now comes lapping the blades again to remove the coating and make sure they didn’t warp during heat treatment. This step took forever and I’m still not completely done:
I’m using a Veritas lapping plate here with grit powder, but it is extremely slow and labor intensive. Wish I had a big coarse diamond stone for this.
Next up I’ll work on etching a logo and actually make the wooden plane bodies.
-- Allen, Colorado (Instagram @bobasaurus_woodworking)