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Thread: CNC machine made out of granite

  1. #21
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    Default Re: CNC machine made out of granite

    Something i forgot to ask you..
    What bolts diameter and inserts you used to joint granite pieces together ?



  2. #22

    Default Re: CNC machine made out of granite

    Any updates on this build lately? I really like what you did and hope to do the same one day!



  3. #23
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    Default Re: CNC machine made out of granite

    I am working my way towards building one:

    1. Engine hoists are inexpensive for moving plates. Think ahead and allow for slings to slip and the occasional dropped item (don't be under it; jump AWAY if it starts to fall).

    2. fox3d posts occasional YouTube videos on this and associated projects, recommended!

    3. Planning to extend the sides and Y rails beyond the bed to regain Y travel lost to the Y sliders length.

    4. Surplus granite countertop material is inexpensive (Craigslist, remainders, cutouts free in dumpsters at places that sell granite countertops). If used for the bed would cost precision (won't be very flat).

    5. Hard to find economical 5cm granite countertop; 2cm and 3cm are widely available (where I live). Perhaps epoxy lamination or basing machine size on the available surface plates.

    6. Wet cutting controls dust and extends blade life. Best to use a GFCI or wet saw. Diamond blades are available for skilsaws. The Evolution DISCCUT1 has a 4" cut depth; stories about injuries and deaths due to kickback so appropriate care and precautions! Planning to add water blade cooling and always use a GFCI.

    7. Suggest goggles and a ($40) half-mask P95 or P100 respirator when grinding granite. Look up silicosis; sharp particles cause scarring of lung tissue. Scars don't breathe well.



  4. #24
    Member peteeng's Avatar
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    Default Re: CNC machine made out of granite

    Hi Gaemon - You say granite is stiffer and stronger than steel. This is not true. At best it maybe as stiff as aluminium but I can't find any references that quote it above 60GPa stiffness. commonly are at 30GPa. Steel is 200GPa. Mild steel is 250MPa yield and it would be hard to find a granite with compressive strength above 200MPa. Its tensile is very weak <25MPa. Its benefits are : its very damp, low thermal expansion, relatively dense similar to aluminium and being hard wears very well in say surface plate applications.

    For machine design you need to think of it more in terms of a less stiff aluminium.

    Now if you make epoxy granite you can make stuff that's stiffer then granite by using alumina grit or silicon carbide grit. Alumina is 300GPa stiffness and SiC is 400GPa stiffness. If you achieve 50% grit fraction by volume which is about their bulk density and since particles are about 50% efficient in transferring strain through a matrix vs long fibres being 100% then if you use alumina you get 300x0.5x0.5=75GPa stiffness which is stiffer than aluminium same for SiC much stiffer than aluminium., So if you make epoxy/grit parts use these grits. Normal sand is SiO and is only 70GPa so its tough to get past 20Gpa with it. Sand is worn granite so has similar elastic properties to granite... For my next project I am casting parts using steel fibres and epoxy and alumina and epoxy.....Cheers Peter S

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  5. #25
    Member awerby's Avatar
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    Default Re: CNC machine made out of granite

    Quote Originally Posted by MrScott View Post
    I am working my way towards building one:

    1. Engine hoists are inexpensive for moving plates. Think ahead and allow for slings to slip and the occasional dropped item (don't be under it; jump AWAY if it starts to fall).

    [An engine hoist is optimized for lifting engines out of cars; it's not a very good general material-handling solution. It's easy to overbalance, and won't lift anything very high.Rent a forklift with a boom arm to handle large pieces of granite; you'll be glad you did. Granite slabs are usually gripped by a pinch-release mechanism, which is a lot easier than cargo slings.

    4. Surplus granite countertop material is inexpensive (Craigslist, remainders, cutouts free in dumpsters at places that sell granite countertops). If used for the bed would cost precision (won't be very flat).

    [Polished granite slabs are plenty flat enough for a machine bed, but countertop cutoffs are going to be long and narrow - not the usual proportions you want in a machine bed.]

    5. Hard to find economical 5cm granite countertop; 2cm and 3cm are widely available (where I live). Perhaps epoxy lamination or basing machine size on the available surface plates.

    6. Wet cutting controls dust and extends blade life. Best to use a GFCI or wet saw. Diamond blades are available for skilsaws. The Evolution DISCCUT1 has a 4" cut depth; stories about injuries and deaths due to kickback so appropriate care and precautions! Planning to add water blade cooling and always use a GFCI.

    [I haven't heard about injuries or deaths from kick-back of diamond-bladed stone saws; that's much more common with wood saws.]

    7. Suggest goggles and a ($40) half-mask P95 or P100 respirator when grinding granite. Look up silicosis; sharp particles cause scarring of lung tissue. Scars don't breathe well.
    [This is true; you want to do any granite cutting with plenty of water coolant, and clean up thoroughly afterwards to avoid residual dust.]

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


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