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+-- Thread: A 20 Minute Mini Heat Treating Forge (/showthread.php?tid=7267975)
A 20 Minute Mini Heat Treating Forge - jteneyck - 04-18-2016
We have a TroyBilt chipper/shredder that my wife uses every year to make a lot of mulch for our landscaping. Some years she'll make 30 to 40 big garbage cans full. That much wood going through it causes the shredder blades and chipper knife to wear pretty quickly.
The chipper knife is no longer available as a replacement part, so I make new ones every 4 or 5 years from some A2 bar stock that I get from McMaster Carr. I made two of them while I still worked in a lab where I had access to all sorts of high temperature furnaces. But now that I'm retired my furnace connection is gone.
I bought a piece of steel during the Winter because I knew the knife was shot and I needed to make a new one. It's pretty easy to fabricate a new knife. It's a standard 1/4" x 1-1/4" bar with a 45° beveled edge and three counter sunk holes. I actually cut the beveled edge with a hacksaw, then rough ground it smooth but not quite to a sharp edge. I drilled and countersunk the holes easily enough on the drill press, using the old knife as a template. OK, but now how am I going to harden it?
I tried just heating it with a Mapp Gas torch. Nadda. Couldn't get it to turn much color at all. That was a bit of a surprise. OK, I need a forge. I remembered I had a little SS boiler I had taken out of a dead coffee maker. After finding it I cut a hole in the side near the bottom into which I inserted a piece of 1" iron pipe. I drilled some holes near the top for some steel rods to support the knife and then wrapped the hole thing with some high temperature blanket insulation. A hair dryer provide the combustion air to super heat the charcoal fuel.
And here it is in action:
Holy cow the thing worked great, so well that I had to pull the hair dryer back away from the pipe inlet to slow it down. The photos are after maybe 15 minutes and just before I decided it had been heated to what I guessed was the right color for hardening. I pulled the knife out and let it cool in still air until I could handle it with gloves. My file danced off it so it definitely hardened. It's in the oven now annealing.
That was fun.
John
Re: A 20 Minute Mini Heat Treating Forge - blackhat - 04-18-2016
Now to scavenge up an old bathroom fan and give the hair dryer back.
Re: A 20 Minute Mini Heat Treating Forge - daddo - 04-19-2016
To set the hardness and even it out, do you bring it up a second time to around 520* then cool it slowly?
Re: A 20 Minute Mini Heat Treating Forge - jteneyck - 04-19-2016
Yes, although I used 450F. That should give me something around 60 Rc hardness. It's all guesswork about what the correct annealing temp. should be. It's the age old quandry of wanting it to be hard enough not to dull/wear too fast, but not so brittle that it breaks. The two I made before never broke so I my annealing temp. must have been high enough.
Here's what the new blade looked like after I sharpened it this morning compared to the old worn out one.
Because the knife is mounted on the rotating disk of the shredder assembly the branch that you put into the chipper chute gets pulled to the outside end of the blade, so most of the cutting and wear occurs there. You can see how much the old blade is worn compared to the new one.
It took quite awhile to hone the blade this morning so I think it's plenty hard. We'll see how long this one lasts.
John
Re: A 20 Minute Mini Heat Treating Forge - CLETUS - 04-19-2016
For some reason I can't see the pics in the first post. But I see the second set.
Re: A 20 Minute Mini Heat Treating Forge - daddo - 04-19-2016
CLETUS said:
For some reason I can't see the pics in the first post. But I see the second set.
I can't see any of them!
They're simple jpg files from google.
Re: A 20 Minute Mini Heat Treating Forge - jteneyck - 04-19-2016
Really? I see them all. Anyone else having problems seeing them? I posted these from Google Photos, using the advise someone here recently posted to resolve a problem linking photos from that site. Maybe it doesn't work 100%?
John
Re: A 20 Minute Mini Heat Treating Forge - Wild Turkey - 04-19-2016
I can't see them either.
Re: A 20 Minute Mini Heat Treating Forge - daddo - 04-19-2016
Must be a problem with a link or activex filtering or a tracking blocker?
Re: A 20 Minute Mini Heat Treating Forge - crokett™ - 04-19-2016
daddo said:
Must be a problem with a link or activex filtering or a tracking blocker?
I can't see them either. He may not have them marked as public.