Grinding a blade before or after heat treating?

I also use my thumbs, and keep constant contact with the blade. My blade tip rests on my specially manicured thumb nail. I do very little grinding on hardened blades on the wheel, all slack belt. Using gloves is more dangerous in my opinion, I want complete unmodivied control of the blade at all times, this requires the most sensitivity left in my hands. I keep the blades cool, diping them in an LOC and water mix that I like very well to cool the blades. Soap or LOC keeps the grit from laying on the surface of the water. I use only fresh belts on hardened steel, this reduces the potential for overheating.

As a side light: Rex did some experiments trying to over heat un hardened blades, found it impossible to damage the steel from the heat generated by friction on the belt grinder.
 
Very interesting Ed. I am curious, were these grinding test results using 52100 or a different steel? I'm glad someone has done some testing on that subject. I am curious to see the results of doing so on an unhardened stainless like ATS-34 or a HSS like M2. Very interesting indeed.

-Jason
 
Hello Jason: Good question, I should have included the type of steel, it was 52100. Rex burned it to a black color, way too hot to handle, then did some photomicrographs and found no change in the steel. It would be pretty hard to reach heats that could alter the steel by grinding by hand.
 
Excellent, thank you Ed. You should convince Rex to try out those other steels in the same test. :cool: I'm really curious to see what happens, especially after later heat treatments.

-Jason
 
Ed: Thanks for the info. I'm not surprised with those results for non-air hardening steels. And, there have been many, including Bob Loveless, who have stated that reaching a dull orange heat during rough grinding is not a problem for 154-CM (air hardening), providing you perform a stress relief as part of the hardening cycle.

Given a choice, I will always take dead soft, annealed steel as my choice for a material condition prior to heat treat. The more heat put to the steel during grinding, the more internal stress that has to come out during HT, and, if nothing else, the warpage will be less in a blade that hasn't seen much heat before HT.

I agree with you on using fresh belts. Why smear/stress the grains when you can use a new belt and do the job cleanly?

To me, the only advantage to allowing steel to get hot while grinding is so the maker can go faster.

I just checked my reference material on surface grinding hardened steel. Surface grinding can produce temperatures between 2000-3000F at the interface of the wheel/workpiece. If straw color is observed at the surface after grinding, the steel has been heated in the 400-450F range, and THERE IS ABOUT A 30% CHANGE THAT MICROCRACKING HAS OCCURRED. For a bluish color, the chance of cracking goes up to about 70%. These are cracks you can't see, and, in the case of a (thin) knife's edge, cracks that you probably can't grind out.

I grind barehand, too, but, I suspect that even when we don't burn our thumbs, there is considerably more heat than we suspect

Although surface grinding is more severe than belts, the message remains the same. AVOID THE HEAT!

RJ Martin
 
Thanx Ed, I'll stay tuned for that. My gratitude in advance to Rex if he takes you up on it.

-Jason
 
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