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    Lightbulb CNC machine made out of granite

    Hey, I just finished my solid granite cnc machine and i would like to share results and process of making it.
    Looks like its working really well. It can cut 1200mm/min 25mm deep and 20% tool engagement with amazing finish.

    I thought about epoxy granite but it would be messy and i would need something flat as a reference base. and some other problems related to casting.
    so i just directly went with 600x900x100mm granite surface plate which looks like its cheaper and already flat.

    tools used to build it where:
    - makita cordless drill
    - bosh drill press
    - ozito drop saw
    - drills, and bits.
    - dial indicator 1 micron precision

    because i went with cheapest chinese linear rails and ball screws precision is with in 25 microns over the whole surface.

    I haven't seen anyone doing anything like it. so i thought it might be a good reference for someone else to use.

    videos on the youtube from newest down:







    I hope you will like it

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    Default

    You made great machine!



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    Default

    its not fully made of granite?



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    Default Re: CNC machine made out of granite

    Really nice job! Don't have time to fully watch the videos at this time but will definitely back and check them out. Very interested to see how it all goes together. I do have one question though. Do you foresee any future stress crack problems with the granite gantry? Just my first thought.



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    Default Re: CNC machine made out of granite

    one of the coolest builds ive seen



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    Default Re: CNC machine made out of granite

    520052, this is my main concern. but on the other hand I won't be hogging cubic meters/min on this machine.
    I wanted to do this machine by myself at my workshop. if i would choose any other material i would need some engineering shop to ground flat 1 meter long gantry. And it doesn't matter if it is steel aluminium or something else. it has to be ground flat.
    this would cost a fortune, in addition i will have to wait for them to find time to do this.
    making it out of granite i skipped this problem because granite is already incredibly flat. as i checked it was as flat as my surface plate.

    gantry is 190mm tall 50mm thick and 1030mm long. so it is quite solid piece of stone. I had an accident where i dropped one of the sides on the concrete floor. for the split second i thought it will shatter but nothing happen. so this give me a bit more confidence.
    on the other hand spindle is mounted to the z axis through rails and than this is mounted to the gantry through the rails.So this should distribute the force quite uniformly.
    anyway i'm still a bit worried about it. but if it crack i will make replacement out of epoxy-granite. even cracked i still can use it as my new gantry face for the mold.

    ITCO, base is granite, side walls are granite, gantry its granite, everything else is not.

    smlua, bzen, thanks guys, i'm glad you like it



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    Default Re: CNC machine made out of granite

    Did you drill the granite for attachment to the rails, or just glue them on? How did you get everything squared up - just counted on everything being sawed perfectly square, or was there a way to adjust things? How much does that gantry weigh, and is it able to change directions easily?

    Andrew Werby
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    Default Re: CNC machine made out of granite

    Fox,

    I love it and think it is great. The shear mass of the thing with the flatness of a surface plate. I think your idea is genius!! I just wondered about the gantry as it was my first thought. Epoxy-granite would probably be more forgiving but I understand why you went the way you did. Let us know how it works out over time, I might just steal your idea if I ever decide to do a build.



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    Default Re: CNC machine made out of granite

    awerby,

    i drilled granite and used inserts, check my first video, one picture is worth 1000 words
    Its kinda hard to explain how i squared everything. i think it will be in the first video as well
    once you have surface plate you can reference all the measurements from there.

    gantry weight:
    just a stone about 60 pounds.
    with everything on it about 100-120 pounds.

    it doesn't have any problems with changing directions and it runs 3000 mm/min 120 inch/min
    i could push it faster but its fast enough for my needs.


    520052,

    i will let you know how its going. at the moment i'm a bit terrified of it, im testing feeds and speeds and its scary how fast i can go with it.
    i have to learn everything from scratch.



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    Default Re: CNC machine made out of granite

    Quote Originally Posted by fox3d View Post
    520052, this is my main concern. but on the other hand I won't be hogging cubic meters/min on this machine.
    I wanted to do this machine by myself at my workshop. if i would choose any other material i would need some engineering shop to ground flat 1 meter long gantry. And it doesn't matter if it is steel aluminium or something else. it has to be ground flat.
    this would cost a fortune, in addition i will have to wait for them to find time to do this.
    making it out of granite i skipped this problem because granite is already incredibly flat. as i checked it was as flat as my surface plate.

    gantry is 190mm tall 50mm thick and 1030mm long. so it is quite solid piece of stone. I had an accident where i dropped one of the sides on the concrete floor. for the split second i thought it will shatter but nothing happen. so this give me a bit more confidence.
    on the other hand spindle is mounted to the z axis through rails and than this is mounted to the gantry through the rails.So this should distribute the force quite uniformly.
    anyway i'm still a bit worried about it. but if it crack i will make replacement out of epoxy-granite. even cracked i still can use it as my new gantry face for the mold.

    ITCO, base is granite, side walls are granite, gantry its granite, everything else is not.

    smlua, bzen, thanks guys, i'm glad you like it
    I think you'll be ok. Granite is stronger and stiffer than steel. It would be the material of choice for all machines if it wasn't so expensive and hard to shape (compared to cast iron). Datron's uber expensive precision machines are made of granite and epoxy granite with a similar design to yours. Not a bad company to copy....

    I want to use a granite surface plate as the base for my epoxy granite gantry. As you said, it's an inexpensive but high precision flat surface with superior properties to iron, steel or aluminum. It cost a fortune in resin to make my gantry. Real granite is cheaper for the base.

    I think more people would use granite surface plates if they weren't so heavy. I had to buy a shop crane for it. There is no way I could move a 500lb slab of granite by hand.

    I doubt there is anything you could cut with that spindle that would cause enough force to snap a few inches of solid granite. It's really strong stuff.



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    Default Re: CNC machine made out of granite

    Where did you source your granite from?



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    Default Re: CNC machine made out of granite

    Quote Originally Posted by jgwentworth96 View Post
    Where did you source your granite from?
    Granite is easy to source although it gets expensive and hard to move in larger sizes. When I was researching sources for my build, I found that granite surface plates are cheapest when ordered direct from Grizzly. They are cheaper there than buying a used one off eBay once you factor in freight costs (which are typically around $400 with your average eBay seller).

    I am using a Grizzly 24" x 36" granite surface plate to mount my moving table on.

    If I was building an all granite gantry bridge, the Grizzly 12" x 18" x 3" surface plates would make excellent (and very precise) risers for less than $50 a piece. Great value when you see how much people charge for very poor quality paper thin aluminum gantry plates.

    Finding a long narrow and precise piece of granite for the gantry beam is more difficult if cost is a factor. I searched for a while and I found a few used 8" x 48" granite parallels on eBay for around $500 but it was slim pickings. They do come up though.

    There is also Craigslist where there is a steady supply of leftover granite from kitchen installs. You'd have to scrape it flat yourself though.

    Ultimately, while I decided to use real granite in the base, I used an epoxy granite / carbon fiber mix for the gantry bridge. I couldn't shake the thought that the joint between granite riser and granite gantry beam would be a limiting factor so I designed a one-piece gantry.

    For a while at the start, I was tempted to buy an old broken granite CMM machine off eBay to convert. They are a great source of ready made granite machine bases as they already have a granite table and gantry bridge that is tapped for rails and precision flat as it comes.

    Basically, granite is used anywhere where precision movement or measurement is needed so there is always plenty of used granite machines if you know what to search for.



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