My DIY riving knife. Should it be shaped like a fin?

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  • JamieRI
    Forum Newbie
    • Feb 2020
    • 11
    • Rhode Island
    • BT3000

    My DIY riving knife. Should it be shaped like a fin?

    The BT3000 I bought had no blade guard. I made an 0.079 riving knife out of an old Craftsman blade using the attached pattern by cutting it with a grinder. It is very flat and sturdy.

    Click image for larger version

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    Click image for larger version

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    Click image for larger version

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    That is what I made above.

    It is not shaped like the fin in the example below. Is there a difference in performance? Is the large squared off back end of the riving knife better or worse than a curved back that makes it look like a fin? It looks bulky to me, as I cut it from a pattern used for a blade guard.
    From Wikipedia:

    So, do I carve my riving knife to look like a shark fin?
    thanks!
    Jamie

    If bored:
    My old Craftsman saw bought in college only had a blade guard that hung out the back and I took it off back then and never used any protection these past 40 years. As I am teaching my son to use tools, I revisited safety and watched https://www.youtube.com/watch?v=u7sRrC2Jpp4 "Kickback on Camera! and then this https://www.youtube.com/watch?v=8f8VWwtaudU "MUST WATCH! How table saw kickback injuries occur, and how to STOP them!" and that is all I needed! I haven't turned on my BT3000 yet!
    Attached Files
    Last edited by JamieRI; 04-29-2020, 07:12 PM. Reason: The pictures I pasted into the original post disappeared. I won't use ^V anymore!
  • LCHIEN
    Internet Fact Checker
    • Dec 2002
    • 20914
    • Katy, TX, USA.
    • BT3000 vintage 1999

    #2
    Looks good to me.

    As far as function goes, I don't think there's any real difference between square back and shark fin.
    Last edited by LCHIEN; 04-30-2020, 01:03 AM.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

    Comment

    • capncarl
      Veteran Member
      • Jan 2007
      • 3564
      • Leesburg Georgia USA
      • SawStop CTS

      #3
      As I understand a riving knife, it’s purpose is to provide something to prevent the wood from closing up on the spinning blade, (clamping) and causing a kickback. I question how much thinner than the blade be before they fail to be effective? I suppose that the additional height over of the knife vrs. what thickness wood the normally be cutting would have the purpose of keeping wood from somehow climbing onto the back of the blade and knocking the users teeth out.
      I agree with Lchien.
      My problem with riven knives is most do not move with the angle of the blade as it is adjusted. When it is removed it is useless metal clutter.

      Comment

      • Jim Frye
        Veteran Member
        • Dec 2002
        • 1051
        • Maumee, OH, USA.
        • Ryobi BT3000 & BT3100

        #4
        I made one from the blade guard from the BT3100. I just disassembled the guard leaving just the blade and cut it down ti thee same height as the blade. It works fine. On the BT3Ks, the guard mounts on the locker bracket so ti moves with the blade.
        Jim Frye
        The Nut in the Cellar.
        ”Sawdust Is Man Glitter”

        Comment

        • JamieRI
          Forum Newbie
          • Feb 2020
          • 11
          • Rhode Island
          • BT3000

          #5
          My photos disappeared from my first post. I think I pasted them at full resolution using ^V and that is not how it works for this forum software. I uploaded them using the Image button this time.

          So, my question about fin shape vs rectangular shape is still on my mind. Are those fin-shaped riving knives like that for a reason? I can cut mine down to match if so.

          thanks
          Jamie


          Comment

          • DrakePandor
            Forum Newbie
            • Apr 2018
            • 11
            • BT3000

            #6
            The riving knife as you have it is fine as long as the thickness is consistent, the main shaping decision is to have it fairly close to the blade at all heights. The back portion being shaped like a shark fin would be to save material costs and aesthetics.
            Last edited by DrakePandor; 04-30-2020, 04:20 PM.

            Comment

            • Pappy
              The Full Monte
              • Dec 2002
              • 10453
              • San Marcos, TX, USA.
              • BT3000 (x2)

              #7
              Just an uneducated observation/opinion. With the squared off back on the splitter the kerf will stay open longer and I don't know if that makes any difference. On the down side it creates more drag as the kerf tries to close on it.
              Don, aka Pappy,

              Wise men talk because they have something to say,
              Fools because they have to say something.
              Plato

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