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Thread: Working a hardened file.

  1. #1
    Join Date
    Jul 2014
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    Default Working a hardened file.

    I recently got into knife making. And as a beginner, I want to avoid annealing or forging anything right now. So to start, it's common to cut out a shape from a file. Normally done with an angle grinder. I find this annoying to do for lack of a better term.

    I would like to mill out a shape on my Bridgeport. I have never had to machine a file before, and I do not want to destroy an exspensive carbide endmill when I could easily ask if someone here has done this before.

    So... anyone here machined a hardened file before? Or have any reason why this will not work?

  2. #2
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    No to machining...grinding for hard stuff.
    It's work, it ain't easy.. if it was everyone would make their own.

    Smart money says buy the steel guage stock machine it while soft, then heat treat and finish it.

  3. #3
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    An old file would be much too brittle to use as a knife, and too hard to mill well, even with carbide tooling. If you cannot contemplate annealing first, you may as well give up now.

  4. #4
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    The file will eat the end mill. You will have to grind it to shape. You can use a bench grinder, angle grinder, belt grinder, or combination of these or other grinding equipment. Use a 6" or 8" diam. by 1/2" to 1" wide 8s or 9s Scotchbrite wheel for finishing. You can drill holes for the handle scale rivets or screws with a solid carbide spade drill. If you want to save yourself a lot of work, you can have the outline cut with a laser or water jet.

    Tool steel can be bought in the annealed state for a very reasonable price. I prefer S7, but 01, A2, and D2 are readily available. A2 and D2 are air hardening and will be too hard to cut with anything but carbide if you get them hot while cutting. S7 and 01 are more forgiving. S7 machines nicely and holds a sharp edge a long time after heat treat. You can machine all these with HSS or carbide if you keep the heat out of them.
    Last edited by Toolguy; 02-12-2019 at 03:27 PM.

  5. #5
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    I've never milled a file with a solid carbide. But I've drill a couple of files and some other hardened parts with carbide tipped drills. It's a flame fest with glowing chips of steel flying all over the place. Check YouTube for "hard milling metal" and "hard turning metal" for examples of the fireworks.

    Assuming you only want to cut the outline shape I'd say go ahead and just align the end mill so it has nice long approaches into the cut to avoid shocking the carbide. But before I did that I think I'd grind away the teeth as well first to avoid a pattern of dimples in the vise jaws.

    And how are you going to profile the blade? It'll be too thin and oddly shaped to hold in any sort of vise and mill the profile. At least I'm guessing that this hard milling requires a fair amount of pressure to make the cut. So you're back to some sort of grinding and water dipping again.

    I did a couple of knives from files way back. But they were small size wood working knives so not long blades. Think smaller compact skinning knives for size. I used the bench and angle grinders and very frequent water dipping. And the risk of burning the edge is always just a millisecond away. You're 110% right that it's a long slow and very annoying process.

    The whole time I was doing the grinding I was thinking that it would be SO MUCH EASIER with a heat treating forge of some sort. A couple of years later I'm seeing all sorts of small forges based around using one or two common propane torches. Google and YT search for "coffee can forge" and "soup can forge".

    I've collected some plaster of paris and vermiculite and sand and just need to get off my keester and make a soup can forge. The idea is to allow me to harden small tooling items made from drill rod or smaller ground flat stock which will fit into the 1.25 x 4" chamber of a soup can forge. And if this works out well next would be a slightly bigger coffee can forge using some 8" heating duct as the outer ring to form a 1.5 x 7 inch chamber with open ends which get closed off with firebricks as needed so I can heat and harden somewhat larger items and heat up short sections of bar stock that will fit and bend or forge the heated bits. I'm thinking I should be able to run this second larger forge with two of the stronger high temperature swirl tip commercial torches.

    Yeah, making the forges is more work. But if you've done even one ground blade and kept the edge hard I think you'll agree that it's less time and frustration.

    And frankly I really can't see using the mill for any more than just the outline. Figuring out how to hold the blank for profiling the cross section would be a lot of work too. Although I'm now thinking held by the tang in the mill vise and the head tilted a bit and with a slide up and lock in place set of braces for the back side of the cut. But there's a lot of energy going into that milling too. So you are looking at flood coolant or at least a steady hand squirt bottle and a real mess spraying all over the place or all the hardness will go away again in the thinner sections at least.

  6. #6
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    There's another issue as well. Files are brittle hard. So unless you temper them before working on them I'm also thinking that the shock of the end mill against the file is quite possibly going to cause it to shatter. The good news is that an hour in a toaster oven will draw the file back to a straw brown to slightly deeper brown and give the file some ductility. I'd suggest that such tempering before any milling would be essential.

  7. #7
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    take your file to any welding shop, find the old guy, ask him to anneal the file. after you make the knife, take it back to the old guy and have him harden it. then temper it in your home oven.

  8. #8
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    If it was easy, everybody would be making knives. Oh, wait, they are!

  9. #9
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    I concur with Toolguy, bite the bullet and get some flat stock like 01. I made knives with my son, and simply made a small enclosure of firebrick as a kiln and heated it with Mapp torches. Worked fine for the hardening. Plunged into a loaf tin full of oil.

    My son's best work:

  10. #10
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    Aug 2018
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    Tai Tokerau - NZ
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    @BCRIDER
    I would steer clear of Plaster of Paris as a refactory or even insulative.
    My recipe is Portland cement (calcium aluminate cement if you can find it), powdered bentonite clay, sand and perlite at a 3:4:3:4 ratio. Packed into form, dried, then baked out slowly.
    This has so far stood up to direct impngement of an oil burner flame for quite some time.

    If you can find comercial refractory locally, that would be even better, and for a little furnace like that, not expensive.

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