Hot Time in the Old Town …
With my lab furnace ready for action, I needed a good first project. I have an old Stanley 103 block plane that needed a blade, so I prepared a blank from 1/8″ O-1 tool steel. I rough ground a bevel in the annealed steel to save time later on. I also volunteered to make a run of small plane blades for a project my woodworker’s group is doing — making “itty-bitty” planes — so I prepared two blanks of each size (1/2″ x 1″ x 1/32″, and 3/4″ x 2″ x 1/16″) as a test run. In all I had five pieces ready for firing.
My friend Ron Hock recommends peanut oil for quenching O-1 steel, so I had a gallon of that on hand. A trip to Harbor Freight tools yielded a 16″ long needlenose plier that would serve as tongs, as well as some cheap long-cuff welder’s gloves. I bought a single firebrick and a stainless steel woven mat from Lonnie’s, and created my ‘stilt’ from that. Nothing for it now but to fire the thing up.
I ran the furnace up to 1500°F and let the pieces ‘soak’ at that temp for a good 20 minutes. I then pulled each piece out separately with my ‘tongs’ and quenched in the peanut oil. While the steel rested I shut the furnace off and opened the door to let the internal temp drop, monitoring it with the digital PID readout. Meanwhile I descaled the steel and polished some of it to clean metal, in order to see the color produced in tempering. I also performed the only hardness test available to me, testing the edges of the pieces with a file — which simply skipped off the metal, indicating a dead-hard condition.
After the furnace had cooled considerably, I found I was able to keep the residual heat in the furnace right at 400°F by cracking the door open just so. I loaded the semi-polished steel back onto the stilt platform and monitored the ‘soak’ for almost one hour. At that point the polished steel revealed a uniform ‘straw’ color, typical of a 400°F temper, so out they came. I polished the backs, ground and polished the bevels, and voila! — sharp tools! The Rockwell is theoretically 61-63RC at 400°F, so perhaps a little harder than some would like. We’ll see how they do in use. I’ll have to make 20 or so of each of the small blade sizes for the group project.
The furnace worked perfectly, and exactly as expected. I’m excited about making more plane blades, as well as knife blades and other specialty tools such as Innuit-style crooked knives.
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