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A rack of Hock blades being removed from the furnace at Edwards Heat Treating Service. The Perfect Edge; The Ultimate Guide to Sharpening for Woodworkers , page 26, Popular Woodworking Books.

At Sharp & to The Point, we toggle our Q&A Issues between Ron Hock, who answers metal related questions, and Isaac Fisher, who answers woodworker related questions. This question about a well sharpened chisel's edge chipping and breaking down is right up Ron's alley.

Q: I have a chisel that won’t hold its edge. It gets wicked sharp, but the edge seems to chip and break down with hard use. What’s up with that?

A: It sounds like the steel may have been overheated during the hardening process.  

Most chisels are made from simple water-hardening high-carbon steel – traditionally AISI W1 or similar. It hardens by heating to 1450° to 1500° F (788° to 815° C) then quenching in water. (Other steel alloys may be quenched in oil or air.) The blade is then tempered at a lower temperature, say 325° F. 

Overheating above 1500° F during the hardening process causes the formation of large grains in the steel. The blade will seem properly hardened – a Rockwell hardness test will even confirm it. But those large grains are fragile. They’re not stuck together as well as they should be had the part been kept below 1500°. Hence your crumbling edge problem.

The only test for this condition that I’m aware of is a destructive one: you must break the part and do a visual study of the internal steel. Properly hardened steel will have grains that are so small they look matte gray, almost like gray primer paint.

Steel that’s been overheated, on the other hand, will have visibly large, sparkly grains.

It’s possible that the blade could be rehabilitated by having it heat treated over again, but without knowing the exact alloy it would be a bit of a crap shoot.

Above: this sample was overheated and quenched then broken. The area shown is about 1/8” across. Notice the very large grains.

Above: this sample was heated properly and quenched then broken. The area shown is about 1/8” across. Notice the very fine grains.

People Profile: Bill Carter

Bill Was Struck by Cupid’s Arrow, But it Was the Bow that Got Him.

An interview with Bill Carter by Linda at Hock Tools.

I had the pleasure of meeting up with Bill and Sarah Carter at the European Woodworking Show last September. The weather was bracing in the barn to which Bill Carter Woodworker Planemaker and Hock Tools were assigned. The Carters off in a corner, Hock Tools in a booth along a wall in one of the two barns built in the 13th century by the Knights Templar at Cressing Temple.

Bill’s table-top was filled with his planes, both small wooden handplanes and many of his now signature (pun accidental) metal mitre planes. Bill and Sarah hardly had a moment to breathe; so many woodworkers and well-wishers flocked to their tiny corner in that rare, medieval barn.

It’s difficult at tool shows for vendors to get a chance to visit one another. Yet, I stole a moment to visit Bill and Sarah, dashing over when I saw an opportunity to say hello. It seemed to me that Bill had more planes to offer than during the 2015 exhibit. he’s made hundreds over the last 30 years. And, finally, I took better notice of Bill’s use of the Cupid’s Bow motif. As I reviewed the table, the Cupid’s Bow motif become increasingly obvious to me, and more varied as Bill worked it differently into different homages to 18th and 19th century British handplanes. 

To read the interview with Bill Carter, click on the marking knife below: