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Thread: Mini mill riser blocks

  1. #61
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    Quote Originally Posted by peekaboobus View Post
    I think the common sense "more the merrier" rings true here. It really doesn't matter if it has high strengh-to-weight ratio or high second moment of area... it is still inferior to a single piece of material right? You want your mill to be as rigid as possible right? Then why compromise?
    Maybe:
    it's not a compromise if it's properly designed or over-engineered, it doesn't require a P.E.;
    cost, always a factor, even in the "real world" and more so here;
    availability of materials and lack of local suppliers.

    If hollow parts are generally inferior, why are so many machine parts cast?
    Answer, so we don't waste time and money machining away unneeded material, save on weight and transportation costs as well.

  2. #62
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    Quote Originally Posted by Rosco-P View Post
    Maybe:
    it's not a compromise if it's properly designed or over-engineered, it doesn't require a P.E.;
    cost, always a factor, even in the "real world" and more so here;
    availability of materials and lack of local suppliers.

    If hollow parts are generally inferior, why are so many machine parts cast?
    Answer, so we don't waste time and money machining away unneeded material, save on weight and transportation costs as well.
    A piece like that is under compression, torsion and bending. It cannot possibly be more over-engineered than a solid piece of material. Mass is not a concern so there is no need to remove material to achieve a strength-to-weight ratio.

    You want hollow or heavily machined away parts often to save weight. Thsoe applications might call for it. But again, as stated, this application benefits from rigidity. You can't beat rigidity of having a filled dumb block of material as is given the space allowed. A solid piece is the most rigid structure you can possibly achieve in that design space. Its weight cannot be a source for its failure like a cantilever, so in this case you want bigger the better.

    Saving time machining is by doing what he did, which is a solid block. Clearly this is superior than hollow stuff you're suggesting.

  3. #63
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    I made a riser out of 2 pieces of 1018 steel. The bottom piece could be used alone for a 2" rise, and longer bolts, or to add another 2" top block.

    The top block for another 2" of rise is tapped for mounting the mill, and 4 countersunk holes to bolt to the bottom piece.

    The top block also has 2 tapped holes for the chip protector to mount to.

    Now the mill Z height is 4" taller for a 4th axis, which is my next project.

    I went the solid route for a sturdier base, and also because I had the material.
    Larry

  4. #64
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    If the discussion is about making due with what you have, then yes, using a solid block of steel would work. The question really is about squaring up the block precisely and then tramming the mill. If this discussion is about finding a solution to the lack of Z space, either use collets or graduate to a bigger mill.

  5. #65
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    Quote Originally Posted by Kd0afk View Post
    It's 4" tall. Little machine shop and others seem to think anything taller would run into strength issues with the bolts. I think it could go taller with the right setup.
    Why would there be any strength issues with longer bolts??

    --Doozer

  6. #66
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    Quote Originally Posted by Doozer View Post
    Why would there be any strength issues with longer bolts??

    --Doozer
    Bolts stretch as a percentage of the length. A 4 inch long bolt torqued to 25 ft-lb will stretch further than a 1 inch long one. When extra stress is applied, the longer one will have more give.


    Dan
    Measure twice. Cut once. Weld. Repeat.
    ( Welding solves many problems.)

  7. #67
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    You are not thinking quite right.
    Longer bolts exhibit more strain per same given unit of stress compared to shorter bolts.
    Plainly said, they do stretch more.
    But if you torque the bolts to the same value,
    both long and short bolts will have the same amount of clamping force.
    The fact that the longer bolts stretched more to achieve that same clamping force
    does not mean they are any less strong.
    "When extra stress is applied", presuming you mean to the joint,
    the joint will hold the same, no mater what length bolts are used.
    In fact, I prefer to design bolted joints with as long of bolts as possible.
    The extra stored energy in the bolts assure they stay tight, especially in
    conditions of varying temperature or with vibration. Short bolts always
    tend to loosen themselves first. Basic engineering.

    -Doozer

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