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

  1. #4881
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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    The shipping is pretty good. it's about $15 from Oregon to British Columbia and that includes handling of customs/duty.



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

    So,

    I was thinking about this again and while rounded aggregate is best in terms of total volume, there is a large downside. With rounded media, you're now more at the whims of fracture propagation. With sharp/jagged media, a fracture shouldn't propagate as far since the fracture should run into a perpendicular surface, unlike with round media.

    The promise behind EG is that you take the innate strength of a compressed aggregate and ensure that you're locking it into place using epoxy. At this point, the youngs modulus for a structure is now mainly based on the strength of the compacted aggregate. So, at this point... you have the mix of aggregate sizes and shapes to take into account. I believe that regardless of the media used at larger sizes, the extraneous volume can be filled with smaller rounded media to take up gaps. But the larger media is what should be assumed as the strength point.

    I also think that a gel coat with reenforcing fibers would make quite a difference in terms of fracture propagation from the surface (perhaps to the point where embedded features could be inlaid closer to edges.

    Mark,

    Did you have a look at the cost/pricing on the media available from the seller at all? I'm only able to get pricing on shipping to myself, but would be interested in hearing what it's like further afield.

    Thanks,


    --
    Scott



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

    Don' t fuss over strength.
    It is extremely hard if not impossible to build a cnc that is rigid enough for milling and then to have it break because it is not strong enough.

    Sven http://www.cnczone.com/forums/diy-cnc-router-table-machines/320812-aluminium-1250x1250x250-router.html


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

    Sven, who said anything about CNC? =0)



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

    Uhm, the url of this website : )

    Sven http://www.cnczone.com/forums/diy-cnc-router-table-machines/320812-aluminium-1250x1250x250-router.html


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

    heh... I was just going by "machine base". A lathe in my case.



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

    Ah, had my own thinking cap on too tight.

    For a lathe strength may have more importance...

    Sven http://www.cnczone.com/forums/diy-cnc-router-table-machines/320812-aluminium-1250x1250x250-router.html


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

    yeah... not killing myself in the process is definitely high up on my list.



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

    I am making samples to find out if it is viable to make a "light weight" machine from EC. In that process I found out something that you should consider when working with epoxy percentages.

    I am trying lean mixes, starting with 5% for a 0.8 mm grain batch of sand.
    That was a bit too wet for my purpose so I decided to try and use 4% for the next batch of 0.5 mm grain.

    It ended up super dry because I forgot that surface area of the aggregate doubles when particle size halves.
    The first batch had 75 grams of epoxy for 1300 grams of 0.8 mm grain sand.
    The second batch should have had about 100 grams of epoxy instead of the 50 grams I used to be slightly leaner....

    Sven http://www.cnczone.com/forums/diy-cnc-router-table-machines/320812-aluminium-1250x1250x250-router.html


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    Default Some Quick thoughts responding to PM's

    Hi Thread,

    I'm dropping in 'cause I got a few PM's. Tenter asked if my aggregate simulator is available. I can make it available if somebody wants to maintain it. It's a pair of linux applications right now that communicate via a named pipe which probably isn't super convenient for most people. It also requires lab measurements of the packing factor which I made for all of my aggregates. The measurement involves vibrating the material under a weighted piston and measuring the volume of the vibrated sample.

    Spherical aggregate is probably more resistant to fracture due to the Griffith equation term for stress intensity increasing with respect to the sharpness of edges. Spherical aggregate also usually achieves a higher packing density. The silicon carbide formula I published is all sharp aggregate and it is plenty strong and of high modulus. Silicon carbide has a higher fracture toughness than quartz.

    There probably isn't a need to go to silicon carbide if you have cheap quartz available but it is the aggregate I characterized and did the work with. Since silicon carbide is available as an abrasive, the gradings tend to be accurate whereas with easily commercially available quartz, it is more difficult to match a grading curve made by simulation. My results for silicon carbide showed higher modulus and strength than the quartz formulas I worked with but rotary SMP is right that a machine designed heavy enough to work is unlikely to be anywhere near the loadings where the strength matters much. If you design the machine to be stiff enough to work well, it will be plenty strong. Also, Silicon carbide EG can be machined or ground with boron nitride inserts or grinding wheels however it will wear them out quick: much better to make your molds accurate.

    I believe the formula I published is near the maximum achievable modulus with relatively cheap materials however it isn't necessarily optimized for maximum practicality.

    I will reiterate the offer from earlier in the thread that I can test flexural modulus and strength of samples that are made to the size spec I published long ago. PM me if you have samples to test. I'm really busy so it may take me awhile to answer. I'm really impressed with the work that's gone on on this thread and I wish I had time to pay as much attention as I used to.



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

    Cameron, is there a standard "box" that's common all over the place that can be used as a mold for the test pieces? That's probably the easiest for folks to send test samples.



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

    Hi Konobi,

    I have a very small test machine so the sizes I can handle are limited. The test I can do is ASTM D-790 flexural strength and modulus. This isn't as definitive as compressive stength and modulus or tensile strength and modulus but those require a test machine 10 times as expensive and it was well out of my hope of ever acquiring one. I can't find the test specification right now for more details. The size spec for the sample I can test is 7.5 x 3/8 x 1/2 inches. If folks can make a plate 1/2 thick by 7.5 long and 5 inches wide, I can diamond saw the 5 samples required for the test out of this piece.

    Happy 2016
    --Cameron



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    Default

    Quote Originally Posted by lgalla View Post
    Dave,we are not building machines to produce Hubbel mirrors in climate controlled rooms with passport ackess.We are not running 24/7.I must agree with your post 100%.The engineers manage to convince the shop guys or the hands on machinist that their ideas are no good.I have experience where we the shop guys saved the engineers asses.Lets say engineering wanted 10% ep0xy.The shop guys know this was impossible so we tip the scales a little at 15 % and things worked out OK.When invintory asks of the 5 %,We had a spill.The number crunchers can prove our designs are poo and can stop us from persuing new ideas.I am guilty of listening to the number crunchers and stopped thinking about new ideas.Hats off to you for.forging on
    Larry
    Composite Arrogance

    Epoxy soup + Larry.



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

    Hi Gang,

    While looking for something totally different, I came across this excellent open access paper on polymer concrete.
    http://dx.doi.org/10.4236/wjet.2013.13009

    I think anybody who is interested in theory will like it.

    Regards,

    Cameron



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

    Hey guys

    I got a quarz mixture called sillimix 282 but unsure about type of resin to buy ?
    I also want to introduse a dark black effect to it hope someone can help

    Thanks



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

    Well, I finally read this entire thread. Much of my reading was late at night and bleary eye-d, so I probably forgot lots of it. What a wealth of information! On the subject of vibration, has anyone tried speakers? I was also considering a orbital palm sander screwed directly to the mold. Any thoughts?



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

    Quote Originally Posted by richardmg9 View Post
    Well, I finally read this entire thread. Much of my reading was late at night and bleary eye-d, so I probably forgot lots of it. What a wealth of information! On the subject of vibration, has anyone tried speakers? I was also considering a orbital palm sander screwed directly to the mold. Any thoughts?
    Heh, putting the bed to bed with a little Crystal Method!




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

    1600


    Sent from my iPhone using Tapatalk



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

    Who is that suplier?



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

    You need pretty violent vibration. I used a 3 phase concrete vibrator which weighed about 15kg to compact the M/G I used on the head support for my mill and it still took a fairly long time to compact. Also I still had some air bubbles. To do the vibrating accoustically, you would need to borrow the The Who's PA system.

    If you have a nearly ideal packing density, this stuff is really still. An orbital sander won't impress it at all.
    Mark

    Regards,
    Mark


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