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  1. #1
    We are hard turning some circular knives (60 HRC), and are struggling to get a clean sharp edge, see attached pictures. We tried many different speeds, feeds, and depth of cuts. As well as using different CBN and ceramic cutting tips (V style, 0.8 rad), but whatever we do we canít get the edge to clean up and not have any burrs.

    Have you got any suggestions on how we can get a clean sharp edge? Is there a tool or method we are missing? We are using a Doosan Lynx CNC lathe.



  2. #2
    Welcome to the forum
    Solution is grinding, rough out the taper leaving enough to grind the cutting edge.

  3. #3
    Yer thanks, but we want too hard turn it all. Not two processes.

  4. #4
    I assumed that, but it won't work, it's always going to fracture on the edge.

  5. #5
    Sorry but we know it can be done, I've seen it done with my own eyes at a local tooling shop. Machining from blank to form a perfect sharp knife with a great edge all on the CNC lathe. However they wont tell us how's its done in terms of all the variables.

  6. #6
    When you find the method, please post.
    Try YouTube

  7. #7
    The solution will be related to the side force exerted by the cutter in order to cut the material being low enough not to buckle the sharp edge.
    Do the materials science to calculate that and talk to cutting tool suppliers to identify the required product.
    If I had worked out the solution to this and was using it commercially I wouldn't share it, I have solutions for several frequently asked questions on machining forum sites (but not this one), because I spent time and effort developing and working them out and because they now they give me a commercial advantage in manufacturing some products, I don't share them.
    Ask if they will sell you the solution ;-)
    You think that's too expensive? You're not a Model Engineer are you? :D

  8. #8
    You might need to enlighten me a little bit here..... but the images you posted look remarkably like they have been ground..... I am toolmaker by trade. I think you will find that support is your answer. I doubt anyone can give you a 100% answer unless they are involved in something very similar because processes have to be developed and you often have to throw the rule book and think outside the box.

    I guess the tool shop wont tool them because they used to make them for the poster :0)
    Last edited by spluppit; 07-11-2019 at 11:44 PM.

  9. #9
    I suppose the answer would vary depending on how many thousands of blades you are producing. My approach would be to turn as fine an edge as you can without causing deformation and then refine the edge faces with an abrasive stone attached to a shank. There again, I tend to look for the QAN solution.

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