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Thread: Epoxy-Granite machine bases (was Polymer concrete frame?)

  1. #61
    Member greybeard's Avatar
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    Whatever size you choose for the biggest "pebble", make the next size 1/5 the size/diameter.
    If you consider the pebbles as perfect spheres, the smaller one will just fit in the gap in a tetrahedral packing.
    (Well I've got to start with some assumptions, haven't I.)

    I can't see how to calculate the third size, so tomorrow I'll try a practical approach.

    John

    Edit - By the way, if you consider shaking up a dry mix, then sucking in the epoxy with a vacuum, the dry shaking will separate the sizes, with the biggest ones coming to the top !!

    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.


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    Registered lgalla's Avatar
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    Hey Guys
    Has everyone lost interest?I have not.We were getting some where.
    Now we know the aggregates are a commody product,you can get locally at building supply or landscaping places,cheap.If 80 to 90% fill is obtainable,we have a very low cost damping material.On premixed epoxy grouts,I don't know,but it is better than nothing.
    Our aggregate mix could be playsand [appears to be clean and fine& smooth]builders sand or sharp sand and pea gravel.3 grades mixed should be enough.Interestingly I found on the web E/G has better properties for damping than solid granite.I think the 90% ratio is hard to acheive for the home guys.The big companyies with huge vibrating tables can get these ratios,but the main reason would be for low cost.
    Previous posts have said this was for us woodrouter guys not milling machines.Not true!I dont know much about milling machines etc,but if your coloum is filled with E/G it will provide damping.Vibrations are reduced or eliminated by combining different materials in a structure.Each material has a different resonance and combining two or more materials will tend to cancel unwanted vibrations.With or E/G we have 3 different aggregate sizes + epoxy +the machine base material steel or aluinium,resonating at different frequencyies tending to cancell one another.Result less chatter.I am not proclaiming to be an expert on the subject,I am sure it is new techonolgy.My knowledge pertains to "fake granite counter tops"which is simmilar except we had much lower ratios.We had to mix in a vacuum and do the shaking thing.
    Posts have helped me to new ideas.I want to build a6'X12' router table and have studied the Zone for many months.I don't see how anyone could have a steel tube machine.I must ring like a bell.I am long winded,hope you don't mind long posts.Lets try to keep this thread alive.Post questions or answers.
    Larry
    Granite chip sweeper



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    I hope you guys keep working on this! We have been working on epoxy-granite mill bases for a small mill that we are developing (and will be releasing to market soon...we hope!). There are many tricky aspects to it, but the final results are worth it. Through many months of research and testing we have managed to create a small machine with the vibration damping and rigidity of a much larger machine. With knowledge, careful design and planning--a similar machine is within your reach. Don't be discouraged by the unknown.

    I hope I can answer any questions about this process. I will try and write up a tutorial on making your own. For now, I will just leave you with some pictures of one of our prototypes that served as a development test bed. Sadly, it has been cannibalized for the benefit of newer prototypes, but it was a great machine and is a good goal for those up for a challenge.


    Good Luck!
    Matt

    Attached Thumbnails Attached Thumbnails Epoxy-Granite machine bases (was Polymer concrete frame?)-img_1917-jpg   Epoxy-Granite machine bases (was Polymer concrete frame?)-img_1918-jpg   Epoxy-Granite machine bases (was Polymer concrete frame?)-img_1924-jpg  


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    Hi Matt

    WOW!!! What is the price range that you shoot for? When are you going to come out with it? BTW what is the percentage of granite in your machine?
    Thanks...



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    Member greybeard's Avatar
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    Matt - I presume that anchor points for the track/rail etc are cast in situ ?
    Or do you cast metal lengths in place ? Fairly obvious problem with future alignment there.
    Is the general approach to design in "modules" that are bolted/keyed together, or to try to get as much as possible in a single block ?

    Larry - I've sent pm via zone.

    Regards
    John

    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.


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    Member RotarySMP's Avatar
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    Larry, according to Nucky and Thomas's post on the german forum, there is a big difference in consistancy between 8% and 12%. At 12% they had epoxy pooling.

    Matt, We really approeciate when a professional contributes. Cosidering how many companies world wide are making mineral cast machine bases, it is suprising how little information has leaked out to the hobby guys.

    I'll try to summarize the specific questions which have come up.

    How are you doing the deaerating?
    Do you use a mix of vibration table and tamping.
    Do you also use vaccum during the vibration phase?
    Do you have any guidance on Frequency and amplitude of the shaker?
    Does the alignment os the vibration (vertical, horizontal) make aa significant difference?
    Do you gel coat? The guys on the german web site are not experimenting with a sand/epoxy gel coat as the use of mould releasing agent alone got sanded away causing bits of the mould to stick.
    What mould release agents do you recommend?
    As stated above, the theory would indicate aggregate sizes in 1/5 diameter steps for best filing. Does this correspond to experience?
    Is rounded aggregate better than sharp edged?
    How do you do the expoxy/aggregate mixing?

    Regards,
    Mark


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    things puzzling me that I'd add to the Q list....

    Epoxy on its own has low rigidity, what then is the effect of aggregate size on the elasticity of the finished mix? for example 3" stone might produce a different rigidity than sand or 3" + 2" + 1". - any engineer advice/info on how aggregate size affects vibration dampening and rigidity?

    i think that based on the 6:1 difference in modulus of elasticity that a steel fabrication filled with EG is best. then again rigidity depends on the cross section as well. while the steel or CI might be more rigid, maybe the solid EG structure, while having a low modulus, overall is more rigid because of its greater cross section than say a casting or steel walled fabrication. anyone thought about an engineered answer to this? what are the aggregate sizes used by industry. are we making it too complicated, ie just go for 1" crushed granite throughout?

    Finally, as the void to be filled decreases as volume %, flow and viscosity will be come an issue won't it? the more you fill the void, the more surface area of granite you have, the tougher it will be to get the epoxy to flow throughout. any way to control or predict this or alter the viscosity?

    The point assumes the granite is in place in the structure and the epoxy is added vs mixing it as a batch and then pouring - which is the right way to go? considerations?



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    Registered lgalla's Avatar
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    Mcgyver I have to agree, there must be a limit to how large a rock you can use.
    I did not understand the last part.Are you talking about filling the coloum with stones and pouring in epoxy?The epoxy is mixed and the fillers are added and then poured in place.
    On aggregate sizing and type go to Google.....machine design polymer castings....Lots of answers there.
    Larry



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    Registered lgalla's Avatar
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    Also try Google search.......moldmaking technology secrets to hard milling



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    Quote Originally Posted by lgalla View Post
    I did not understand the last part.Are you talking about filling the coloum with stones and pouring in epoxy?The epoxy is mixed and the fillers are added and then poured in place.Larry
    Larry,

    Yes I'd envisioned a normalized steel fabrication filled with aggregate and then polymer poured in as oppose to the polymer/granite being mixed and then poured. When i posted that, I envisioned (rightly or wrongly) a largish (maybe 1"-2") size aggregate, if this was the right size to use then mixing first would seem to me messy, extra work and of limited benefit. This may make no sense to someone thinking a 4*8 router out of 2" tubing, I'm thinking more along the lines of a small but massive machine for metal, filling a much more boxy shaped cavity...maybe welded from 6 or 8" column steel with the total machine being less than a couple of feet in each direction.

    This idea of pouring the polymer with granite in place may be a bad one, don't know, its just how how it occured to me to do it.

    on the other hand, if sand is the right size, it would of course have to be premixed, else you'd have a puddle of polymer on top.

    Maybe a more succinct way of expressing the question is,

    -what is the effect of aggregate size on the strength of the material?
    -what sizes of aggregates are commonly used for various applications?
    - for a give size(s) of aggregates, what are the techniques & concerns so far as mixing and pouring goes

    Mike



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    Registered the4thseal's Avatar
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    I am thinking about doing some experiments to get some shop truth.
    I am thinking about putting the aggregate in all of its sizes into the mold and then using a vacuum to pull the epoxy through the mold, much in the way you do with composite fabrication. It works in that and the molds are much more complicated. I am going to make a test and will let you know how it goes. I will be using a combination or granite and steel fibers.



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    Quote Originally Posted by Mcgyver View Post
    .... I'm thinking more along the lines of a small but massive machine for metal, filling a much more boxy shaped cavity...maybe welded from 6 or 8" column steel with the total machine being less than a couple of feet in each direction....
    To some extent you are talking apples and oranges here. This idea depends on the steel for the structural properties and the aggregate/binder fill for the vibration damping properties. You are not worried too much about the mechanical strength of the aggregate/binder fill so you can tolerate very large voids between the aggregate that get filled with the binder.

    In the technique being developed by the German chaps you are concerned about the mechanical strength of the epoxy concrete so you do need to worry about having a range of aggregate sizes so that you have a minimal volume that is filled by the epoxy binder.

    I think the steel structure filled with something to damp vibration is feasible on a DIY level. I don't think the full epoxy concrete approach is feasible for DIY. If you look at the German pictures they appear to have steel ways with bolts screwed in the back side and mounted in their mold. It would seem the bolts are acting to anchor the steel ways in the epoxy concrete. Some of the other links also mention making highly accurate molds for casting the epoxy concrete to tight tolerances and they also mention that it cannot be worked once cured; all threaded attachments have to be cast in situ. This means that for epoxy concrete you need to make an accurate mold or some form of structure to hold and locate the attachment points, etc, which is then discarded after the epoxy concrete structure is cast. This is fine if you are doing production because the mold is reused many times; this point is also mentioned in some of the links. For DIY it seems to me to make more sense to build your steel structure, use large section tubing, get it stress relieved if necessary, do all the attachment of guideways etc on a structure that can be drilled and tapped anywhere and then fill the structure to take out the vibration.



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    Gold Member BobWarfield's Avatar
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    Great thread. I have been interested even in the idea of filling the castings of my existing Asian mill to increase rigidity since reading Bamberg's thesis "Principles of Rapid Machine Design." Lots of good data there on using concrete to dampen fabricated steel frames on machine tools.

    You can Google for it, or the last link I had was:

    http://www.mech.utah.edu/~bamberg/re...e%20Design.pdf

    Best,

    BW



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    A very interesting thread! I have been thinking about polymer concrete machine after I saw some Datron router videos. At least some of their high speed routers are based on polymer concrete.

    See your self. They are very impressive

    http://video.google.com/videosearch?q=datron



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    Just saw a show on TV where they were installing "composite" counter tops similar to this threads subject material(s). The aggregate of choice was broken glass. Glass is silicone? What is granite? They finished it quite nicely.

    DZASTR


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    Quote Originally Posted by RICHARD ZASTROW View Post
    ..... What is granite? ...
    Almost everything.

    I stole this:

    Granite primarily consists of orthoclase and plagioclase feldspars, quartz, hornblende, muscovite and/or biotite micas, and minor accessory minerals such as magnetite, garnet, zircon and apatite. Rarely, a pyroxene is present. Very rarely, iron-rich olivine, fayalite, occurs.



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    Both glass & granite are approx. 72% silcon. If your E/G mix is 90% aggregate, wouldn't that make your mix about the same?

    DZASTR


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    I have been following this thread for some time now, as it is of particular interest to me. I intend to use this method to construct my machine base, possibly the gantry as well but thinking about carbon fibre. I came across this book online, might be of some use to some of you. Page 52 advises aggregate sizes 10, 5,3 mm and by weight 16.0 : 10.0 : 9.0 : 19.5 : 45.5

    I am having trouble posting the link, will get it to you as soon as possable



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    This is the sort of thing I am thinking of at the moment

    Attached Thumbnails Attached Thumbnails Epoxy-Granite machine bases (was Polymer concrete frame?)-millweb-jpg  


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Epoxy-Granite machine bases (was Polymer concrete frame?)

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