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Fred's Bubble Jig

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by David6789, Oct 16, 2019.

  1. David6789


    Feb 14, 2019
    Hey guys so I just ordered a bubble Jig. Bevels are definitely an area I am hoping to improve upon and thought this jig may help.

    Anyone else use the Bubble Jig?

    I saw the videos Fred created but They are pretty old and was looking for some more and updated info.

    In the video Fred starts out with a 10 degree wedge (to develop the edge) and he doesn't make it clear if he grinds 10 degrees all the way to the center line before moving onto 4 degrees and then to 3 degrees. And how far do you grind with the 4 and 3 degree settings?

    I am just looking for more detailed info please.
  2. seanj

    seanj Gold Member Gold Member

    Mar 1, 2010
    I use his Bubble jig all the time. I don't go all the way to the center line with 10 degrees. All you're doing is establishing an edge at the beginning. So three or four passes on each side should be sufficient. Just make sure you do the same number of passes on each side.

    Then next you want to select the angle that suits how you want the blade to be. For me that usually means selecting an angle that is closest to the finished angle that I want the blade to be. If you are grinding pre-heat treat you want to leave an edge that is roughly a dime in thickness. If you are grinding post-heat treat it doesn't really matter. Though I will usually leave an edge on the lower grit belts and that edge will diminish as I use finer and finer grits.

    Thus the way I do it is a bit different than Fred. Fred works his way up to the final angle he wants a bit at a time. Which is probably a better practice than the way I do it. He is the developer after all :)
    His way does give you better control of the outcome if you aren't sure how far up the blade you want to progress. You can then see visually what looks the most pleasing to you.

    You can also decide what angle you want by using a calculator. Here's the one I use. http://dcknives.com/public/grind_angle.php
    It's fairly self-explanatory. And will give you a starting point.

    With some experience you will understand better how to select the angles you want. But that's how I do it.
  3. Hengelo_77

    Hengelo_77 Basic Member Basic Member

    Mar 2, 2006
    I use a bubble jig and think it is a big help.
    Don't worry about angles to much.
    Start at 10 and decrease untill you have what you want. The next blade I don't go back to 10, I just leave at at around 5.

    A dime thick edge is very thick! I outscource HT and go as thin as 0,25mm pre HT, no problems
  4. Randydb

    Randydb Basic Member Basic Member

    Sep 27, 2014
    I've used it to do 8 knives now....it certainly worked very nicely for me.
  5. Branson1369


    Feb 17, 2019
    Anyone using the bubble jig on forged blades or only stock removal?
  6. lanternnate


    Nov 5, 2016
    I use it on forged blades as well. You just need your ricaso area to be relatively flat and parallel. That means being careful about that at the anvil if going brute de forge or just carefully grinding that area flat after. On a forged blade I lay the as forged bevel against the disc (I grind fully with a disc grinder right now) and set the bubble to that. If the bevels aren’t the same angle off the anvil I use whichever is the more acute angle and take advantage of the jig to get them to a matching angle. That allows me to initially clean the bevel at that angle. If the grind line isn’t where I want at the end of that, I then just check what angle block I’m currently close to and start working down from there.
    Branson1369 likes this.
  7. kuraki

    kuraki Fimbulvetr Knifeworks

    Jun 17, 2016
    I continue to use my bubble jig for grinding swedges. I don't use it for bevels anymore but I did when I was learning and it helped me build muscle memory to do it completely freehand. Swedges and false edges though are just too short for me to feel when I'm making good contact, so I keep mine for that.
    seanj likes this.

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