Grinder plans

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Kevin McGovern, Mar 20, 2017.

  1. mike-E

    mike-E

    400
    Mar 2, 2013
    on the updated plans it appears the the pivot is going to swing almost 180 degrees. it only has to move a few degrees past 90(maybe 5)to lock in place.
     
  2. Kevin McGovern

    Kevin McGovern

    Jul 31, 2015
    but to be all the way off tension, doesnt it need to swing the other way as well? We ran a motion model, and it took that swing to get the most travel to unlock. On the AR customs grinder it is about 180 degrees as well.
     
  3. mike-E

    mike-E

    400
    Mar 2, 2013
    https://youtu.be/j69fe-b9aNA look at his pivot track. it might be 100 degrees. the most throw you will get is starting with the spring pointed straight away from the fixed point on the arm. you dont want to do it that way because of how far you will have to pull the handle. your starting point is good, but i dont know why your motion model would have you swing that far to lock/unlock. all it has to do is go a little "over center". the center would be both pivot points and the fixed position in a straight line. also place the spring mounting point as far out as possible on the circle.
     
  4. mike-E

    mike-E

    400
    Mar 2, 2013
  5. mike-E

    mike-E

    400
    Mar 2, 2013
  6. Kevin McGovern

    Kevin McGovern

    Jul 31, 2015
    He has a longer distance between the pivot and travel pins. So more of a toggle action than mine which is a a circular travel. Is my design an issue? There is plenty of meat there, so I'm not worried about strength. So looking at his design, mine is pretty much the same, except since he has a longer distance between the pins (the end of the shock and the cam center) I need more rotation to get the amount of travel I want. Make sense?
     
    Last edited: Mar 22, 2017
  7. mike-E

    mike-E

    400
    Mar 2, 2013
    yes , that makes sense. it's just going to be difficult to move your handle that far. these things kind of ''snap'' in and out of the lock position. if you notice the handles they use with those heavy springs are 8-10'' long for leverage. mine is about the same but im compressing the spring a lot farther. if you use that design you might end up changing the pin position on the handle side so you can extend the handle.
     
  8. Kevin McGovern

    Kevin McGovern

    Jul 31, 2015
    right now it's 12.5" of force to move it, maximum. So I assume it will be less then increase as it hits the highest point then drop into locked/ unlocked position. I am also putting a 3.5" rotating handle at the end of the "lollipop" shaped lever so i can grab/ move it easier.
     
  9. kuraki

    kuraki Fimbulvetr Knifeworks

    Jun 17, 2016
    You're killing me Smallz :( :p
     
  10. mike-E

    mike-E

    400
    Mar 2, 2013
    12.5''? as in inch/lbs? wow!!! i would have guessed much more than that. i might change the stroke length on my set up to swing that far around.
     
  11. Kevin McGovern

    Kevin McGovern

    Jul 31, 2015
    Yes, sorry. 12.5 pounds max force. I'm taking my guy's word for it. He was all "tangent" this and "sine/ cosine" that. had the whole thing calculated out, impressive drawings on the whiteboard in our design center and everything. He has me convinced anyway.
     
    Last edited: Mar 22, 2017
  12. Drew Riley

    Drew Riley Riley Knife and Tool Knifemaker / Craftsman / Service Provider

    Oct 17, 2007
    I thought my ears were itching!
    Just now getting a chance to check this thread out.

    To answer a couple of questions (which I probably already did in my incessant ramblings in my 10 hour long videos :D):

    I use a 100lb spring, though honestly it could probably even be bumped up to 120 or so if I had the notion. If everything is lined up and moving freely, you'd be surprised how much leverage you have to engage/disengage the OCC.
    My stop pin arc, is at 120 degrees. However I laid mine out, this seemed like a good general arc path to get me past center, but still get me enough clearance in the down position withouth going TOO far down.

    I didn't really do any load calculations at any point, I just tried to keep the spring relatively close to 90 degrees to the tracking arm (in the locked position) while trying to keep it as far from the pivot as I could within my design limitations, in order to maximize the force it would apply to the belt. At least it seemed to make sense at the time.
     
  13. Kevin McGovern

    Kevin McGovern

    Jul 31, 2015
    thanks for commenting, and for the background!
     
  14. Tin.Man

    Tin.Man

    868
    Sep 5, 2010
    Think cast tooling jig(aluminum) at 1/2" would be strong enough for this application if I used ez loks for the threaded inserts? I get that it's not as strong as 6061 but still 18000 ksi should be plenty for a belt sander and jig plate is always dead nuts straight and flat. .005 anyways
     
  15. Drew Riley

    Drew Riley Riley Knife and Tool Knifemaker / Craftsman / Service Provider

    Oct 17, 2007
    I imagine it would be just fine, but perhaps unnecessary for this application. I think 1/2" 6061 plate is more than flat enough. It's what I used on my grinder build, and I had zero issues.
     
  16. kuraki

    kuraki Fimbulvetr Knifeworks

    Jun 17, 2016
    Cast mic 6 plate will work fine.
     
  17. Kevin McGovern

    Kevin McGovern

    Jul 31, 2015
    Did some more tweaking of the plans. Here is a motion render of the revised cam over action.


    [youtube]OBrPwuSMSug[/youtube]
     
  18. mike-E

    mike-E

    400
    Mar 2, 2013
    now that looks like it will work excellent.
     
  19. Kevin McGovern

    Kevin McGovern

    Jul 31, 2015
    Thanks. I took your advice and added a stem to the cam on the other side to give enough cam action to be able to shorten the 180° pin track to 90°

    Sent from my ASUS_Z01BDC using Tapatalk
     
  20. mike-E

    mike-E

    400
    Mar 2, 2013
    and it looks like you'll still get about 1 - 1 1/2'' of ''lift'' at the wheel. that will be plenty.
     

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