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  1. #1
    Join Date
    Apr 2018
    Posts
    69

    Epoxy granite base

    Hi All,

    First excuse me for my bad English.

    I'm almost done designing my router.
    I want to move to practical implementation. Most things are bought. I'm left with a router bed and I have a question about that.
    I thought the router bed was made of welded steel profiles. But I have concerns about welding. As a result of the internal stresses obtained during welding, there will be distortions in the structure. And they will change over time.
    If there are no welds, it remains a bolted structure - but it complicates things a lot.
    Please advise people who have worked with epoxy granite.
    Can I replace the steel structure with a epoxy granite structure?


    Please to see attached photos for sizes.
    Will it be strong enough at these sizes?


    Z axis: 52kg. Y axis: 57kg Total Y+Z axis:about 110 kg.
    I do not have enough epoxy granite data to do simulations in solidworks.


    My epoxy resin data (without fillers):
    compressive strength: 60 N/mm2 (after 28 days, 23 Degrees Celsius)
    flexural strength: 30 N/mm2 (after 28 days, 23 Degrees Celsius)
    density: 1.4kg/l


    The epoxy structure will be reinforced with 10mm diameter steel rods (rebar - inside into epoxy granite).
    I can make thicker walls of construction, but the weight gets very big. However, my goal is to transport and lift this bed by several people. It is currently 150 kg (without the two profiles of 50x50mm calibrated steel. They will be dismantled).

  2. #2
    Join Date
    Jul 2018
    Posts
    6248

    Re: Epoxy granite base

    Hi Ivan - The epoxy at 1400kg/m3 tells me its full of thixotrops (thickeners) you need a very thin epoxy with a density of about 1000kg/m3 use Prime 27 from gurit its very thin and easy to use. There's lots on EG in threads here...you won't need the rebar Peter

  3. #3
    Join Date
    Apr 2018
    Posts
    69

    Re: Epoxy granite base

    Thank you for advise peteeng !
    I read the datasheet of Prime 27. This resin has much better mechanical properties: flexural strength 113MPa (113N/mm2) vs 60N/mm2 (my epoxy). Thanks again.

    What do you think about the thickness of the walls and columns? Are they sufficient?
    Beside with wood I plan to work and with aluminumSpindle is for metal work and it is heavy (diameter 110mm, 3KW, 380V).

  4. #4
    Join Date
    Apr 2018
    Posts
    69

    Re: Epoxy granite base

    Because it is difficult to delivery Prime 27, I found a replacement in Bulgaria:
    biresin cr82 (hand lamination, viscosity 740 mPa.s, density 1150kg/m3)
    biresin cr83 (infusion, viscosity 155 mPa.s, density 1150kg/m3)

  5. #5
    Join Date
    Jul 2018
    Posts
    6248

    Re: Epoxy granite base

    Hi Ivan - Use the CR83. Hard to comment on the walls and columns unless engineering is done. But being a casting I think you will find that shape complex to mould. Maybe simplify it to two sides and a middle? I looked up Biresin very good Sika product. For simulation I expect your low modulus will be 22Gpa and your hihj value will be 32Gpa. Instead of using granite or sand look for some aluminium powder. Its the same density and stiffness as granite but once cast you can machine it with std tools. Thread it etc. 1mm aluminium powder is readily available in australia and costs about 15 euro per kg which is cheaper then some sands....Peter

  6. #6
    Join Date
    Apr 2018
    Posts
    69

    Re: Epoxy granite base

    Thanks again Peter for your help
    In Bulgaria aluminum powder costs 20 euro per kg. 100 kg powder - 2000 euro. Too expensive.
    Aluminum oxide (99,96% Al2O3) is at the same price as a quartz sand - 3.5 euro per kg.
    Can I use aluminum oxide?

  7. #7
    Join Date
    Jul 2018
    Posts
    6248

    Re: Epoxy granite base

    Hi Ivan - Al oxide is a ceramic and you will have to grind it. If you want to std machine the material after casting it will have to be a metal powder. Are you imbedding steel or aluminium in the casting for post machining? get a quote from the australian company to freight Al powder to you. Maybe cheaper than you think. Euro buys 1.6 aussie dollars. Peter

    Al oxide has a modulus of 200GPa whereas quartz is about 80GPa so I'd use the Al2O3 to make it stiffer.

    https://www.azom.com/properties.aspx?ArticleID=52

    https://www.crystran.co.uk/optical-m...z-crystal-sio2

    But remember if you have to grind anything you cast it will be V expensive! Peter

  8. #8
    Join Date
    Jul 2018
    Posts
    6248

    Re: Epoxy granite base

    Hi Ivan and others - My interest in polymer-rock parts is their stiffness. Being a designer I need to know its stiffness to design the part. You mention Al2O3 which is of interest because its as stiff as steel which is nearly 3x stiffer then silica (or normal sand). Looking at the published figures for commercially available EG we see that they are about 30-36GPa which is about half that of aluminium. I converted the anocast figures to volume ratios. SiO is 82% and Ep is 18% by volume. Using rule of mixtures 70x.82= 57GPa is the top achievable stiffness. Round shapes are about 0.5% efficient in transferring load through a matrix. Long fibers are 100%. So if the SiO is 50% efficient then 70*0.82*0.5= 29GPa. Which is close to the other figures. I think the published 36GPa is a bit high (unless they calculated this from the compression test). Now if you use Al2O3 then you start with 215*0.8*0.5= 86GPa which is stiffer then aluminium. I think the 0.8 packing factor is a bit high but 0.65 is good so 215*0.65*0.5= 70Gpa which is same as aluminium. So I'd go with the Al2O3!! In processing fibreglass and carbon fibre we rarely get above 55% by volume. In an autoclave at 6bar we can get CF to 0.6 vol fraction. So I expect the actual packing factors to be lower than theory in our Ep/Granite. But clearly the Al2O3 is stiffer then the SiO... Peter

  9. #9
    Join Date
    Apr 2018
    Posts
    69

    Re: Epoxy granite base

    Quote Originally Posted by peteeng View Post
    .... If you want to std machine the material after casting it will have to be a metal powder. Are you imbedding steel or aluminium in the casting for post machining? ....
    Hi Peter,
    I will not std machine after casting.
    Into the mold preliminarily will be inserted holes, threaded bushing, bolts etc.
    After installation (and leveling) of the solid calibrated steel profiles 50x50mm (on which are linear guides), they will be processed with hand scraper https://www.grainger.com/product/SAN...-Scraper-5HME5 and precision machinist bridge straight edge to achieve flatness.
    Thanks for taking the time to research Al2O3. I plan to use it.
    Have a nice evening Peter !

  10. #10
    Join Date
    Jul 2018
    Posts
    6248

    Re: Epoxy granite base

    Hi Ivan - No problem. It helps me clarify my thoughts on my mill build. I wrote a spreadsheet maybe helpful. I'm using metal fibres but they're a bit springy in the mould so don't pack as tight as I'd like. The Al2O3 gets to the stiffness target I want (on paper) so maybe that's the pathway.... Peter

  11. #11
    Join Date
    Apr 2018
    Posts
    69

    Re: Epoxy granite base

    Ok Peter. Thanks for spreadsheet !

    P.S. I'm following with interest your posts in other topics here.

  12. #12
    Join Date
    Jul 2018
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    6248

    Re: Epoxy granite base

    Hi All - I've upgraded the sand excel sheet to include material stiffness. Al2O3 at6 300Gpa is the stiffest additive I can find to make whatever we are going to call it now. Epoxy Thingy. The only stiffer material is high modulus carbon fibre and thats a bit pricey. Cheers Peter

    edit - I mean commercially available stuff. There are carbon nano tubes and fullerenes and graphene to play with if you can get it. Carbyne for instance has a stiffness of 33TPa can't even think how big that is. 33000GPa, staggering...
    Attached Thumbnails Attached Thumbnails carbon.JPG  
    Attached Files Attached Files

  13. #13
    Join Date
    Jul 2018
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    6248

    Re: Epoxy granite base

    Hi All - I tracked down some alumina grit used for sandblasting can get 0.2 or 0.5mm or 1mm or 1.2mm for $4.40/kg in 25kg lots sounds good. Epoxy is about $22/kg so the mixture is $8.50AUD per kg so its quite a good cost for a great material. 1kg is 339mls or 1litre weighs 2.55kg . Cheers Peter

  14. #14
    Join Date
    Apr 2018
    Posts
    69

    Re: Epoxy granite base

    Really very low cost for aluminum grit !
    Thanks for new Excel sheet Peter.

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