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Thread: Concrete VMC

  1. #41
    Member RotarySMP's Avatar
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    Default Re: Concrete VMC

    Forger the o-ring. It is common in industry and also building to thread holes into the top matching plate, and use screws to get the gantry aligned and then inject an epoxy grout into the gap. Just seal the edges with silicon before injecting.
    Mark

    Regards,
    Mark


  2. #42
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    Default Re: Concrete VMC

    I recall someone doing something like this, possibly in the huge thread. They cast tubes in so they could inject the epoxy from above. Wax 1 surface, square with the set screws and inject. I don't recall if he drilled for alignment pins after. That is if you ever plan to pull them apart, saves time for reassembly.



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    Default Re: Concrete VMC

    Here is a nice video showing using epoxy grout for aligning the column to the base.



    He has a few other videos on building a concrete VMC.

    Best
    Jacob



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    Default Re: Concrete VMC

    Quote Originally Posted by stef110 View Post
    I am struggling a bit how to make the connection between the column and the base. I will cast in steel plates so i can bolt the column down to the base. the surfaces of those plates will be machined after the casting but that will never be 100% right so i need to be able to tram the column.
    what i am thinking about is put some big gub screws on each corner so i can adjust the gap between the plates to level it out. and after hat eject the gape between with some epoxy. when going for this option i think i don't need to machine those plates at all after casting.

    Those plates right now are 220x300mm each so they are really big.
    i think i have to mill in an grove and put in a big rubber open o ring around the edge. and then inject the epoxy on one side until it is completely filed.

    How do you guys think of this method?

    stef
    I think it's a good method. One thing that you could do is machine a shallow pocket in the plates to accept a filling of epoxy or maybe even a filling of squeezed in silicone glue to give some damping and some extra holding power. This way you might be able to take it apart if you ever needed to.
    The areas of the plates around the bolts would be as flat as possible and then you would align the column using shim stock to get it dialed in and tightly bolted. Then fill the pocket with epoxy or some kind of adhesive damping material. Or this might not be necessary if there are enough bolts and the surface area under the bolt areas is sufficient for the stiffness required.



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    Default Re: Concrete VMC

    Any news to the mill?



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    Default

    Very nice. Can you please share the 3D drawing . Thanks
    My email :hoangthangbk51@gmail.com
    Thanks



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    Default Re: Concrete VMC

    A very good start and now ?

    Any kind of news of the built ? Heard nothing new for a long time



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    Default Re: Concrete VMC

    Hey guys its been an long while since my last post, In the mean time nothing happens on the mill because of other things that needed to be done.
    Last week i visited a guy how was selling a diy concrete mill, after seeing his amazing build i started to look at my own designs again and i would like to restart this project.

    I want to try to reduce some of the costs of this build now, by skipping the flat milling of the steel blocks that will be in the casting. I want to try to use self leveling epoxy now to get my rails flat.
    Since the collum will be adjustable before final mounting those steel plates don't need to be machined after casting.

    I redraw-ed my base design, and would like to show you for some input from you guys. If i look to some different designs that are out on the internet. I see different ways on the steel mounting blocks.
    Some machines have the steel blocks on top of the concrete and some have the blocks half in the concrete. Will there be any difference? I now drawed a lot of m16 bolts in the blocks to fuse them with the concrete. I want to tap blind holes in the steel and tighly screw the bolts in and then spot weld them so they won't get lose. Will this be enough or is more the better?

    I have to ask this question also with the concrete factory but would it be wise to put some steel rebar in the concrete and connect all the steel blocks together with this rebar?

    Dimension of the base are now 1080x650x200mm (LxWxH)
    The steel frame under the base is now drawed with 100x100x5 steel tubes. Im thinking i will also poor those with concrete when its done.

    stef









  9. #49
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    Default Re: Concrete VMC

    Great to see you back in the saddle. Look forward to seeing your progress. It is a really cool machine you are making.
    Mark

    Regards,
    Mark


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    Default Re: Concrete VMC

    I doubt you will be happy with using "self leveling" epoxy to create the flat surfaces for the mill. Epoxy has a stiffness of less than 4000MPa and steel has 200000MPa. By the time you pull up bolts to their correct tension you will squish the epoxy. Epoxy is used as to "set" surfaces together to take up small gap areas and to create a loadpath across small gaps. Very much like using loctite on screws. A machined flat surface to the manufactures specs is always the best way to go. Cheers Peter s



  11. #51
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    Default Re: Concrete VMC

    Did some more design work last week, the base is pretty much in its final stage now. Steel will be ordered soon and i have contacted Myuhpc for more information about how to use there concrete.
    The idea is now to mount the mill enclosure base tough the base.
    For mounting the concrete base to the steel frame i will make 6 steel mounting pads from 60x100mm steel how stick out a little from the concrete. Do you guys those 6 pads will be sufficient to carry the weight of the whole machine approx 1200kg?

    I now started on designing the column. There will be an pneumatic counter weight in the back of the column with a 2:1 reduction to the head. Im still doubting on how to make the mill head. My idea now is to also make that from an concrete casting or would you guys recommend a steel milling head?
    About the leveling epoxy i will first see how the casting will come out in my design the steel bars are high enough to be re machined after casting.

    Stef










  12. #52
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    Default Re: Concrete VMC

    Wow, I lilke this video too.



  13. #53
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    Default Re: Concrete VMC

    I would suggest that you consider polymer concrete rather than cement concrete. Epoxy concrete will be stronger and give you a nicer surface. Epoxy or polyester concrete/granite (also known as engineering stone) can be machined, ie for bed-ways (or for kitchen benchtops which is an everyday thing). Cement concrete is not very dimensionally stable due to it containing water. Epoxy concrete will be more stable, and even polyester resin should probably be ok, as if the aggregate mix is correct (not excess resin) then the aggregate matrix cannot shrink on cure (polyester has shrinkage on cure). Polyester is cheaper than epoxy. Polymer resin concrete will hold the fasteners/inserts better. You can also add fibres to polymer concrete if you want it stronger again.

    For which ever concrete you choose, you should select a type of aggregate stone that is very old and stable, not just any old aggregate that the concrete company is using that day.

    Looking at you cad renderings of the base and column, they appear to be completely solid lumps of concrete. I would suggest considering using polymer resin concrete and not making the parts completely solid, rather say 50mm thick main sections with support webs etc, similar to if it was a cast iron design.

    If you really want to avoid machining, you might be able to come up with some idea how to mold the bedways off the machined steel ones that you have already set up? But in my experience that type of exercise is very time consuming.

    Regarding joining the parts, just think about it the same as if it were steel / aluminium / cast iron - use shims and bolt it or epoxy grout it (epoxy grout has sand or similar load bearing particles in it). But you need to consider the relatively reduced strength and hardness of the concrete when designing the joint / bearing areas.

    Jonathon Clarke
    www.solpont.com


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    Default Re: Concrete VMC

    Thanks for you reply jono,
    UHPC is not an ordinary concrete, they already use it to build machines bases, here is an example of a company how made machine parts with it: https://www.sudholt-wasemann.de/mach...e-of-uhpc.html

    The parts i drawed are mostly massive im trying to make the column a bit hollow now but its easier to just make an massive casting and the extra weight will only be good to absorb vibrations right?
    I have a question about the height of the machine bed is there any giving recommend height for that? On my current machine the bed is around 110cm above the ground.

    stef

    stef



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    Default Re: Concrete VMC

    Quote Originally Posted by stef110 View Post
    Thanks for you reply jono,
    UHPC is not an ordinary concrete, they already use it to build machines bases, here is an example of a company how made machine parts with it: https://www.sudholt-wasemann.de/mach...e-of-uhpc.html

    The parts i drawed are mostly massive im trying to make the column a bit hollow now but its easier to just make an massive casting and the extra weight will only be good to absorb vibrations right?
    I have a question about the height of the machine bed is there any giving recommend height for that? On my current machine the bed is around 110cm above the ground.

    stef

    stef

    How do you like the table at 110cm? My larger vmcs (fadals) have table height around 85cm.



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    Default Re: Concrete VMC

    Quote Originally Posted by stef110 View Post
    Thanks for you reply jono,
    The parts i drawed are mostly massive im trying to make the column a bit hollow now but its easier to just make an massive casting and the extra weight will only be good to absorb vibrations right?
    To simplify things, there are 3 important factors that determine resonance / vibration of a structure:
    1. Stiffness - increasing stiffness increases the natural frequency.
    2. Mass - increasing mass decreases the natural frequency.
    3. Damping - damping is generally a property of the material

    Increasing mass lowers the natural frequency of a structure. Lowering the natural frequency is generally bad. The ideal machine tool has natural frequencies that are above any frequency it will actually encounter in use.
    Increasing mass can increase stiffness, e.g. by increasing the thickness of a section. Increasing stiffness is good. However, you can actually To increase stiffness it is usually much more effective to increase the size of a section. Stiffness mostly comes from placing mass as far as possible from the neutral axis.

    The ideal is to increase stiffness while lowering mass, and retain damping.

    Where you do not have a particular size constraint, you are much better off making a bigger hollow column than a small solid column of the same mass.

    Just throwing extra weight on does not absorb vibrations. You may actually increase the chance of a machine tool vibrating if you lower the natural frequency into the operating range of the machine tool.



  17. #57
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    Default Re: Concrete VMC

    Quote Originally Posted by stef110 View Post
    Thanks for you reply jono,
    UHPC is not an ordinary concrete, they already use it to build machines bases, here is an example of a company how made machine parts with it: https://www.sudholt-wasemann.de/mach...e-of-uhpc.html
    Yes what you say is correct, but uhpc is still a cement concrete with water and what I posted is also correct. 15 MPa is not that impressive. Re solid sections, if you look at other video of concrete / polymer concrete bases being manufactured there are many that are not completely solid (but rather more like an old school cast iron sand cast machine base).

    Jonathon Clarke
    www.solpont.com


  18. #58
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    Default Re: Concrete VMC

    It is possible that that Sudholt-Wasemann Nanodur®-concrete E45 has a water-based polymer additive. But all uhpc does not necessarily have that. All uhpc is not equal.


    Jonathon Clarke
    www.solpont.com


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    Default Re: Concrete VMC

    Quote Originally Posted by jono5axe View Post
    15 MPa is not that impressive. Re solid sections, if you look at other video of concrete / polymer concrete bases being manufactured there are many that are not completely solid (but rather more like an old school cast iron sand cast machine base).
    Why should we care about the flexural/tensile strength in a machine tool?

    I also don't understand why you suggest making hollow sections. The 10kg saved won't change anything except making the mold more complex.

    Last edited by jackjr-123; 04-03-2019 at 07:11 AM.


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    Default Re: Concrete VMC

    Quote Originally Posted by jackjr-123 View Post
    I also don't understand why you suggest making hollow sections. The 10kg saved won't change anything except making the mold more complex.
    Generally, you want a higher natural frequency of your structure. Higher natural frequencies result in smaller amplitude dynamic deflections, faster response, and is easier to damp out. In a very general case, a spring mass will naturally resonate at F=sqrt(k/m). So if you increase the mass, you reduce the natural frequency.

    Having said that, while I've seen studies that investigate what happens when you make a machine with big hollow sections, I've never seen the comparison to the same design with the hollow sections filled in. The natural frequency will go down with such a solution, but the static stiffness will go up...



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