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  • Choosing bolt sizes

    Discussion in 'The main mechanical design forum' started by rpchristian, Oct 29, 2012.

    1. rpchristian

      rpchristian New Member

      Jul 2012
      Likes Received:
      Hello there,

      I'm making a lathe fixture to hold 6 pieces of 2mm, 100mm OD, circular steel plate, stacked together. The purpose is for turning out centre holes in the plates to 21mm ID. The fixture is simple: a block of alu bored out to take the plates, and a steel lid to hold everything in place. (The lid will also function as a drill jig for other holes.) I need to choose bolts to hold the lid in place: I can use either M6 or M8. It's not at all critical in this case, but I wonder how I would go about choosing bolts correctly, assuming that I could calculate the loads on the plate. And is there a rule of thumb for how deep the bolts should go?

      Many thanks,

    3. ankurbanthia

      ankurbanthia Member

      Oct 2012
      Likes Received:
      Of course there is no such rule as to which size of bolt must be used in your case.
      For holding 6 pieces in a fixture so that they do not rotate while machining, you need to see the coefficient of friction between the same and then see what force between them will keep them from rotating, just like a multiple plate clutch. The total force will determine the size of bolt to be used.

      Ankur Banthia

    4. tonycro

      tonycro Well-Known Member

      Nov 2011
      Likes Received:

      also the depth rule of thumb, 2x diameter ideally and 1.5x as a minimum


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