Newbie Epoxy-Granite and Aluminum T-Slots


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Thread: Epoxy-Granite and Aluminum T-Slots

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    Default Epoxy-Granite and Aluminum T-Slots

    Hi All

    I'm designing a router/VMC with the idea to work steel. Unfortunately my only option is aluminum t-slots, which is not ideal. At least I have the option to choose some heavy duty t-slots like 80x80mm or 90x90mm

    - My first question is: Since aluminum isn't stiff enough is it a good idea to fill the inner space of every t-slot with epoxy granite.

    - Second; Would you recommend building the machine out of pure epoxy-granite castings. Considering the size I'm concerned about the machine being unmovable .

    - Third. my main concern about the EG filled t-slots is the difference in temperature expansion rates of EG and aluminum. I think that it's possible that the temperature expansion force of the aluminum might exceed the tensile strength of the EG (which of course is limited) and thus form cracks in the EG.

    How do you guys think?

    Thanks a lot in advance.

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  2. #2

    Default Re: Epoxy-Granite and Aluminum T-Slots

    The EG cracking in the profiles because of thermal expansion sounds very unlikely. Filling the profiles is a good idea but probably a machine made out of T-slot stuff will flex way too much to even dream of tooling steel. And if it flexes a lot then the EG might crack because it will be quite thin in the profiles.



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    Default Re: Epoxy-Granite and Aluminum T-Slots

    Quote Originally Posted by PropellerHat View Post
    The EG cracking in the profiles because of thermal expansion sounds very unlikely. Filling the profiles is a good idea but probably a machine made out of T-slot stuff will flex way too much to even dream of tooling steel. And if it flexes a lot then the EG might crack because it will be quite thin in the profiles.
    So according to you filling the profiles with EG would improve things but won't solve the problem? If you say that the EG-filled profiles would bend that means the EG breaking inside, am I right?
    What if I limit the operations only to what's called "iMachining" in solidcam terms?



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    Default Re: Epoxy-Granite and Aluminum T-Slots

    Granite-filled aluminum extrusion sounds like the worst of both worlds. You've got the expense and softness of the aluminum but not its lightness. And you've got the weight of the granite, but in long thin sections that don't have any strength. I don't necessarily see it cracking because of thermal issues, but since it doesn't have much tensile strength in inch-thick bars, I do see it cracking in normal use.

    If you want to build a machine out of aluminum extrusions, that will work - just not for machining steel. If you want to make one out of epoxy-granite, cast it in molds to make thick heavy sections that won't crack. It might be difficult to move, but not impossible, with the right equipment.

    Andrew Werby
    computersculpture.com

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    Default Re: Epoxy-Granite and Aluminum T-Slots

    People use epoxy granite around an aluminum skeleton frame. I.e. The aluminum is the filling, the epoxy granite is the main even.

    I can say from personal experience that, when made right, epoxy granite can be super strong. As other have said, it's also super heavy once it is cast into thick sections. If I was starting again, I would cast it straight onto a base with wheels instead of trying to move it later.

    Aparently, epoxy granite is superior to steel and aluminum for a CNC base because it has better vibration dampening properties. You just have to compensate for it's reduced strength by making it thicker.



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