Cracked Spine

[Ed Tipton]

In my knifemaking experiences, I have had a few problems involving blades cracking during the quench. I don't consider it to be a big problem...it doesn't happen that often...but when it does happen, the cracks tend to occur on the back or spine of the blade rather than on the edge. I am unsure as to why this happens but I am wondering if it is a flaw in my technique, or is this a problem that others have noticed as well. A blade cracking on the spine seems counter-intuitive to me as I would expect them to occur more frequently on or near the edge. I leave about .030-.040" edge material prior to the HT, but I have also noticed that this seems to occur more often when the blade has been clayed. This also seems counter-intuitive to me...so evidently, there is a "hole" in my knowledge base that I need to fill!

[Robert Mayo]

That's interesting Ed what type of steel are you using, are you claying the spine as well and what type of quench? I have used water and oil and managed to crack and break lots of blades mostly experimenting but have never only cracked the spine yet.

Bob

[Ed Tipton]

Robert Mayo...Most of my knives are made with 1080 and occassionally I'll throw in a 5160. Most of the time, I try quenching in oil with both types of steel, but sometimes the 1080 will not harden in the oil and I have to go to quenching with water. With water being the more severe quench, that's where the cracks have occurred. I have never had a blade crack during the quench when it's been quenched in oil. Whenever I use the clay, I apply it only to the spine and never to the edge. As stated, it has not been a big problem, but it's just something that I don't quite understand what's going on, and why the cracks are happening on the spine of the blade.

[Robert Mayo]

Ed i meant do you put the clay on the actual spine on top as well as the top side of the blade.
I still cannot understand why you have cracked spines especialy in water as the blades generaly curve up which will cause the edge to tear.

Bob