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grinding techniques

Discussion in 'Shop Talk' started by Anton, Jul 22, 2015.

  1. So it was only a question of time for me to get a myself a real belt grinder and I finally got it. Still waiting for belts to arrive thought, so I started to explore theory. Basically I'm trying to find any info about proper grinding techniques in regarding to kitchen knives.

    I have 2-3 old kitchen knives that I'm planning to reground, and I also would love to get myself a piece of hardened steel and grind a knife from scratch (basically the same task that Greg has done using his crazy bathroom-grinder setup).

    I tried searching any WIP on youtube, but can't say I was very successful. There's a video of Carter that shows how to grind a knife, but he uses large water-cooled stones, not a grinder. I believe I could more or less follow the same approach, but would need to pay extra attention to blade temperature. On another thread it was said that I could ruin HT if I heat blade over 150 °C or higher, so I guess if I could control temperature with hands.

    Hollow grounds sounds pretty easy in theory (providing you have a big enough wheel), but convex bevels seems to be more time taking, as you'd need to carefully change angle while grinding. So convex sounds pretty complex to me now. And there's one thing that I don't understand at all: how could I ground proper distal taper? Let's assume I have a piece of mono steel. A nice straight piece. Do I need to mark center line on the edge of it and then try to remove more material towards the tip? Not sure how I could control whether I remove the same amount of metal from both sides (the closer we are to the tip, the more it's important to have similar amount of metal removed from both sides).

    I guess each maker has his own secrets and preferred techniques, but if there's some basic info that you can share, then I'd love to read, watch and learn :)
     
  2. Some basic videos:

    hollow ground


    grinding wide bevels
     
  3. I'll try to give my view on it, maybe something is useful for you. I'm no expert though, still learning.

    I think this is one of those things you need to get hands on and get a feeling for, and develop your own technique for.

    I did my first knives without marking the centerlines and I regretted that many times. I think it is possible to do a decent distal taper without marked spine, but it sure helps.

    I think the most important thing to learn and practice on is inspecting your blade and seeing where it needs work. Having a proper flat surface nearby can help. A diamond plate to scratch a little on can also be good to find high or low spots. Use a calliper to check consistent thickness. Maybe set a cutting bevel to see it (but don't make it sharp).

    For convex I go mostly flat until I'm almost there, and then introduce some convexity either on some slightly slack belt or by handrubbing. I've used a 120 grit diamond file to adjust grind manually by drawfiling with it. Could be done on stones too I think.

    Maybe you can find someone willing to heat treat for you? Like an industrial site that heat treats for toolmakers and such might be willing. If you can rough shape your blades in the annealed state it helps alot.
     
  4. That second video had alot of good tips. You may want to consider using a worn belt for making that first steep guidebevel as it can wear your belts alot.

    For handrubbing I would recommend nick wheelers tutorial:
     
  5. CrisAnderson27

    CrisAnderson27 Professional Craftsman

    This. I've never actually seen another person forge, grind, or otherwise shape a knife in person...and I like to think that developing my skills in a semi vacuum has helped me form my own style. I feel strongly enough grounded in that style now, that seeing other makers working would help me gain in efficiency, without effecting the end results. Remember, most often...our methods absolutely have an effect on the appearance of our product.

    That said, go down to your local hardware supply, and pick up some 3-4mm thick wood sheet. Cut some knife blanks out, and grind your knife. Multiple times. You will learn what angles are necessary, you will learn to control grind lines, you will learn how certain ways you would instinctively grind something absolutely WRECK other things. You can develop your own grind...and even though you can't test them, when the time comes that you make them from steel, you'll know precisely what you need to do...because you'll have done it dozens of times for pennies on the dollar of what it would have cost you in steel.

    I was actually going to PM Anton about helping him out by heat treating bar stock...if we can find a feasible way to do it with the distance :).
     
  6. CrisAnderson27

    CrisAnderson27 Professional Craftsman

    20150625_213753.jpg
    This is basswood. Note there is no burned wood, it has a clean feather edge, rounded spine and choil...if this were steel, it would cut like...well, Anton's knife I just finished!

    ;)
     
  7. WarrenB

    WarrenB Contributor

  8. Thanks for all the advices guys! It looks like Russian Post could delay my package with belts any longer so I'm gonna get it tomorrow and finally try to grind something. Love the idea of grinding some wooden knives — great souvenirs IMO (and you could carve/paint any hamon you like. I wanna Chinese dragon shaped hamon).
     
  9. BathonUk

    BathonUk Founding Member

    Hey Anton.

    I just started my journey in to the knife making, but I would like to add few words from me. Grinding convexity in to the knife have one common thing for stones and grinders - pressure points. You need to place your fingers in proper spots. I am just grinding new knife and I think that I have ground good amount of convex. How do I know? I have covered the whole blade with marker.
    [​IMG]

    If I put my fingers on the edge I will grind only this part.

    [​IMG]

    [​IMG]

    Quick repainting and my fingers are going on to the middle of the blade:

    [​IMG]

    [​IMG]

    And now on top:

    [​IMG]

    [​IMG]


    And now on top and the edge. As you can see middle is not touched.

    [​IMG]


    I will let you know about cutting abilities when I finish.
     
  10. The pictures are awesome, Greg, so even such a dumb person as me could get it. Thanks a ton. This is a final grinding being made on a hardened blade, right?


    … but I think you were cheating a little bit there and moved your grinder out of the bathroom.
     
  11. CrisAnderson27

    CrisAnderson27 Professional Craftsman

    Nice Greg!! I also spy a soft backing on your platen!! Is it cork or leather?
     
  12. BathonUk

    BathonUk Founding Member

    You are right Anton that I was cheating. I was hand sanding my blade and I have found few very deep scratches which looked like impossible to remove, so I quickly put my belt grinder on the floor in the main corridor and quickly ground it. Sometimes I am doing that when I am lazy.


    11774784_1179313948750760_1776320557_n.jpg



    Cris I just super glued piece of cork to my platen. Gosh, I wish I had proper grinder. Faster I mean... Mine is doing only 400RPM.
     
  13. CrisAnderson27

    CrisAnderson27 Professional Craftsman

    Nice!! The cork is brilliant. I use a piece of 2oz leather :D.

    On the grinder, I lower mine down quite a bit for doing what you're doing in the video...perhaps 10% speed (340-400rpm), so you're probably not far off in regards to speed for the work you're doing. That said, I also wet grind my blades, so I do have a bit of advantage there :D.
     
  14. BathonUk

    BathonUk Founding Member

    I was afraid to use water and grind wet blades at the beginning because my grinder is not meant to be used this way. However, now I am dipping blade in to the water, quickly wipe excess and put it back to the grinder. Sometimes top part of the blade is whole wet. No problem so far. I understand that you have lowered your speed Cris, but for initial grinding I wish to mame 3003RPM. It took me hours to get in to that stage.
     
  15. CrisAnderson27

    CrisAnderson27 Professional Craftsman

    I bet it did lol! It takes me hours to get to that stage too! I don't ever really run full speed right now though....I doubt I actually even hit 3000 rpm either. One thing to remember, is that you can substitute pressure for rpm very readily. Lean into it, and the 400 rpm will cut like 1500rpm with moderate pressure.

    And you have better control that way also.

    Just some things to think about ;)
     
  16. From what I've read so far, the RPM speed of belt grinders doesn't tell you anything, as with the same RPM actual speed would different on different grinders, depending on belt length, wheel sizes etc. Again, from what I've read, the general recommendations from belts manufacturers seems to be in the 20-30 meters per second range.
     
  17. CrisAnderson27

    CrisAnderson27 Professional Craftsman

    You're right Anton, and my grinder has a 6" drive wheel (approximately 150mm) which increases the belt speed also. But again...more pressure will absolutely substitute for less speed to a large degree. I've found my belts also last longer because the grit is being fractured vs glazed over. Now...that said, when whole heartedly hogging metal pre-heat treat...I use higher speed AND higher pressure. But post heat treat I prefer to lower the speed and raise the applied pressure. Better control, and more aggressive removal without as much heat seems to be the result.
     
  18. Twistington

    Twistington Founding Member

    I'm pretty sure Gregs grinder has a way too small motor for leaning... like a sewing machine or so. :)
     
  19. CrisAnderson27

    CrisAnderson27 Professional Craftsman

    Could be! My 6x42 belt sander for wood did ok. Just gotta get good belts I guess :).
     
  20. BathonUk

    BathonUk Founding Member

    When I push to strong, my belt grinder is giving me weird sounds. When I have experimented with WD-40 on the belt it was even worse. Actualy I can stop my grinder with bare hand:D
     

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