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IndustryArena Forum > MetalWorking Machines > CNC "do-it-yourself" > Granite build, stuck in my design, please help!
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  1. #21
    Join Date
    Jul 2018
    Posts
    6248

    Re: Granite build, stuck in my design, please help!

    Hi Moonshot - Coming along fine. Just a thought since you have gone down the "solid" construction line think about aluminium. Will look the same as the granite machine but you can have the parts machined so you get all the features very accurately. Will be exceptionally stiff and you will know the stiffness. Granite ranges from 50-100GPa stiffness and you will not know the stiffness of the slabs you get Al=70GPa. I appreciate granite is damper but a very stiff machine does not need damping (broad statement machines do need damping) keep at it. Peter

  2. #22
    Join Date
    Feb 2021
    Posts
    19

    Re: Granite build, stuck in my design, please help!

    Hi, thanks for the input. I had not considered making the machine from solid aluminum. Alas, I already have the granite slabs ready for cutting. I'm currently looking around at different threaded inserts for the granite, and I'm sure drilling and tapping would have been much easier in solid aluminum.

    I haven't seen a solid aluminum machine and frankly the thought hadn't even occurred to me. I'd love to see an example.

    Some things I'm happy about with the granite is their precision surfaces, and low expansion with changes in temperature.

    Honestly I should look around locally for the costs on precision machining just to get an idea, but I was kind of put off by some people's experiences with high costs and then the machining precision is only as good as the machine that does it. I saw one example where they got the machining done but it had a valley midway through its travels.

    Quote Originally Posted by peteeng View Post
    Hi Moonshot - Coming along fine. Just a thought since you have gone down the "solid" construction line think about aluminium. Will look the same as the granite machine but you can have the parts machined so you get all the features very accurately. Will be exceptionally stiff and you will know the stiffness. Granite ranges from 50-100GPa stiffness and you will not know the stiffness of the slabs you get Al=70GPa. I appreciate granite is damper but a very stiff machine does not need damping (broad statement machines do need damping) keep at it. Peter

  3. #23
    Join Date
    Nov 2020
    Posts
    361

    Re: Granite build, stuck in my design, please help!

    Quote Originally Posted by MoonShot View Post
    Honestly I should look around locally for the costs on precision machining just to get an idea, but I was kind of put off by some people's experiences with high costs and then the machining precision is only as good as the machine that does it. I saw one example where they got the machining done but it had a valley midway through its travels.
    upload some files to xometry, I could not find anything that's cheaper locally. and the prices are instant, no need to wait for manual quotes.

  4. #24
    Join Date
    Feb 2021
    Posts
    19

    Re: Granite build, stuck in my design, please help!

    I had forgotten about Xometry, I had seen mention of it but never tried it, so thanks for this, "Oh Yahhhh!" moment!

    I'll use the automatic quote generator when I finalize my mounting plates. I'm glad I've been trying to keep the machining simple, since I had expected to machine them myself on my low quality kit CNC. I was going to build the plates with aluminum so my kit CNC could handle it, then use the new CNC to make the same plates from steel. Honestly it had seemed like an extra step I didn't want to take and I'm excited to see if Xometry can produce the steel plates for me at a reasonable price.


    Quote Originally Posted by ardenum View Post
    upload some files to xometry, I could not find anything that's cheaper locally. and the prices are instant, no need to wait for manual quotes.

  5. #25
    Join Date
    Jul 2014
    Posts
    215

    Re: Granite build, stuck in my design, please help!

    MoonShot, have you thought about bonding an Aluminum plate about 1 inch thick to the granite base. This would be easy to machine and make mounting the rails and gantry towers easier to mount. But the bond between the granite and aluminum would really make the base a good solid support. And you may need to lap the aluminum after careful bonding to make sure it is really flat. you could also just bolt the aluminum in several places with a low hysteresis visco elastic sheet between the aluminum and granite base. This would damp a lot of vibrations. Are you going for high accuracy here. Is that the main reason for the uprights and gantry being granite. CMM's are usually made that way, but they are not stiff enough for CNC machining. So you could go with steel for the gantry supports and then make an EG beam for the gantry. The machine look small enough you could make an EG gantry beam for low cost.

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