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Thread: Concrete VMC

  1. #61
    Member hanermo's Avatar
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    Default Re: Concrete VMC

    I disagree.
    So do all major industrial manufacturers of specialist epoxies.
    Hysol (locktite) 3478 is one example.

    Rated strength in crush is 1000 kg / cm2.
    So my 2200 mm long rails, 2 of, 35 mm wide, have a 3.5 x 220 x 2 x 1000 = 770.000 kg crush rating. Each.
    == 1.5 Million kg.

    Quote Originally Posted by peteeng View Post
    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




  2. #62
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    Default Re: Concrete VMC

    Every one thanks for the responses. Im not a math guy so there is no calculation behind my design or component choose. I reduced weight of the column a little its now on 280kg of concrete.
    I added a drawing with some dimensions on it so you guys can have an idea of the size. Most all concrete builded cnc mills i can find online are just solid chunks im not trying to a chief a ultra high end milling machine its still a hobby machine.
    And in any way it will be way more rigid then my current mill.

    Im trying to avoid epoxy granite because i don't want to wash 700 kg of gravel. I did a test mold 2 years ago with epoxy and wash only 7 kg of gravel was a lot of work.

    Today first batch of bolts and nuts came in to make all the anker points in the base and column.

    About the height off the machine bed, im a tall guy (195) so i don't mind if my work space is high. I will try to aim this build on 100cm to 105cm now.

    Stef












  3. #63
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    Default Re: Concrete VMC

    Damm i start to doubt now, I found some info about SILIMIX 282 which seems affordable compared to the UHPC which is also pretty expensive. And it looks like then i don't have to wash all my gravel.
    Like i said i did some test in the past with Epoxy granite and it was quite easy to make something with it.

    stef

    Concrete VMC-img_20190404_205721-jpg

    Attached Thumbnails Attached Thumbnails Concrete VMC-img_20190404_205721-jpg  


  4. #64
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    Default Re: Concrete VMC

    IMO UHPC is much easier to work with. First of all you don't need to vibrate it - that alone is a huge advantage. Just throw everything in a cement mixer then pour.
    You should be able to find washed gravel pretty easily. Or you can use the Silimix with the UHPC cement, but it's probably more expensive.



  5. #65
    Member jono5axe's Avatar
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    Default Re: Concrete VMC

    Quote Originally Posted by jackjr-123 View Post
    Why should we care about the flexural/tensile strength in a machine tool?
    The strength (UTS) will allow it to hold fasteners/inserts better, and allows for less material used for the same strength.

    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.
    10kg? and the rest! One liter of concrete volume will weigh approx 5kg. I am not saying to make hollow sections. I am just saying that maybe it doesn't need to be a huge monolithic block of material. A 50mm thick slab & sides with cross webs is not "hollow sections". The higher strength of the epoxy conc allows for less material. And I am saying that looking at old cast iron constructed machine bases and/or other polymer concrete constructed machine bases may give further insights.

    Jonathon Clarke
    www.solpont.com


  6. #66
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    Default Re: Concrete VMC

    Quote Originally Posted by stef110 View Post

    Im trying to avoid epoxy granite because i don't want to wash 700 kg of gravel. I did a test mold 2 years ago with epoxy and wash only 7 kg of gravel was a lot of work.

    Stef

    You should be able to buy pre-washed aggregate. I can buy pre-washed aggregate (supposedly 300 million year old greywacke) from local suppliers. Landscape suppliers I think they are. You just need to make sure that you select a very old, stable and hard stone type. You may be able to buy granite agregate, it was available here, but I was happy with the greywacke. Sand (silica sand) is available pre-washed, but is normally requiring to be dryed out as it is supplied with a lot of water still in it. We spread it out on a sheet of ply for a couple of days to dry it. For the aggregate I can buy pre-washed in different sizes (6mm, 12mm, 20mm and up) and then blend the mix to suit the size of the features in the mold. The greywacke that I buy is generally used for roading construction here in NZ

    I am not sure how to link to a specific post but hopefully you can see what I use here: https://www.cnczone.com/forums/cnc-w...neering-4.html

    Jonathon Clarke
    www.solpont.com


  7. #67
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    Default Re: Concrete VMC

    Today i recived a bag of silimix 282 and some epoxy and did a small test with it. Made a mix with 10% epoxy it mixed well and i think its even a little to wet.
    Tomorrow i will try to get it out of the mold and then try a 8% mix and try to get lower and lower with it.
    Also putted 2 thread inserts in it to see how it gone look like.

    stef













  8. #68
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    Default Re: Concrete VMC

    Started today on machine the steel inserts that arrived this week. Also made 3 test casts now with 3 different epoxy amounts.

    stef















  9. #69
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    Default

    This may not matter much, but strength and stiffness are not necessarily proportional. Epoxy stiffness (not necessarily industrial strength epoxy):
    https://netcomposites.com/guide-tools/guide/resin-systems/strength-stiffness/

    Stiffness of epoxy from chart is 3.5gpa which is ~508ksi, compared To 10700ksi for aluminum or ~30000ksi for steel.

    Therefore, regardless of strength, a layer of epoxy will be 21 times more flexible than an equivalent layer of aluminum and 59 times more flexible than steel. Given a thin enough layer of epoxy, this may not have a significant impact on rail mounting. But, a 500lbf bolt preload over a 1in^2 of .25" thick epoxy will cause ~.0002" of deflection in the epoxy layer.

    Quote Originally Posted by hanermo View Post
    I disagree.
    So do all major industrial manufacturers of specialist epoxies.
    Hysol (locktite) 3478 is one example.

    Rated strength in crush is 1000 kg / cm2.
    So my 2200 mm long rails, 2 of, 35 mm wide, have a 3.5 x 220 x 2 x 1000 = 770.000 kg crush rating. Each.
    == 1.5 Million kg.




  10. #70
    Member jono5axe's Avatar
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    Default Re: Concrete VMC

    Quote Originally Posted by ice_2k4 View Post
    This may not matter much, but strength and stiffness are not necessarily proportional. Epoxy stiffness (not necessarily industrial strength epoxy):
    https://netcomposites.com/guide-tool...gth-stiffness/

    Stiffness of epoxy from chart is 3.5gpa which is ~508ksi, compared To 10700ksi for aluminum or ~30000ksi for steel.

    Therefore, regardless of strength, a layer of epoxy will be 21 times more flexible than an equivalent layer of aluminum and 59 times more flexible than steel. Given a thin enough layer of epoxy, this may not have a significant impact on rail mounting. But, a 500lbf bolt preload over a 1in^2 of .25" thick epoxy will cause ~.0002" of deflection in the epoxy layer.
    The consideration is not of epoxy resin in isolation but rather of the finished composite material, in this case the aggregate and binder combination.

    The reason to use epoxy is because it has better performance than cement (and water) over a number of factors in such an application.

    Re similix / aggregate and cost thereof, I pay approx $30 per cubic meter for different grades (sizes) of washed aggregate, so considerably more cost effective. I also believe that polyester could be used in this situation as the shrinkage is controlled by the aggregates inability to shrink. Polyester is half the cost of epoxy. Testing samples will determine the suitability.

    Jonathon Clarke
    www.solpont.com


  11. #71
    Member jono5axe's Avatar
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    Default Re: Concrete VMC

    Quote Originally Posted by stef110 View Post
    Started today on machine the steel inserts that arrived this week. Also made 3 test casts now with 3 different epoxy amounts.

    stef
    That stuff all looks pretty damn awesome, (I don't think it really matters what you use for the concrete material, those inserts/mountings look bombproof)

    Jonathon Clarke
    www.solpont.com


  12. #72
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    Default Re: Concrete VMC

    Today finished the rest of the steel inserts. Next step making the mold.
    Today i bought some MDF sheet with a ready to paint plastic sheet on it. to see how my release agent reacts on this surface i made a small test bar again also with 10% epoxy mix.

    stef







  13. #73
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    Default Re: Concrete VMC

    You would be very disappointed with polyester. It shrinks 8% by volume. Over time your parts would warp and move ask any boat builder about their boat panels shrinking.... Epoxy or PMMA is the best for this application. Are you using PVA for the release? Not PVA glue which should be properly called PVAc Peter



  14. #74
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    Default Re: Concrete VMC

    Today is started fabricating the mold, steel strips are now aligned and bolted to the bottom plate of the mold. Tomorrow i want to place the rest of the inserts.
    Yesterday the silimix arrived next week the epoxy will arrive so next weekend i can hopefully start casting.

    stef







  15. #75
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    Default Re: Concrete VMC

    Sihts about to get real!



  16. #76
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    Default Re: Concrete VMC

    1) Make sure table is stout enough for the weight.
    2) Brace the long sides so they don't bow outward from the pressure
    3) Clay or caulking to radius the joints to help keep epoxy contained within and ease of release.



  17. #77
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    Angry Re: Concrete VMC

    Quote Originally Posted by peteeng View Post
    You would be very disappointed with polyester. It shrinks 8% by volume. Over time your parts would warp and move ask any boat builder about their boat panels shrinking.... Epoxy or PMMA is the best for this application. Are you using PVA for the release? Not PVA glue which should be properly called PVAc Peter
    Peter, you are completely full of it. You seem to be purposely posting misleading information to suit your negative agenda. Someone reading your post would likely assume that polyester composites would shrink by 8% which is obviously complete BS. Maybe resin by itself in a cup, but laminates are half fibre. For polyester laminates, which are for the most part made in a mold or on a surface table, the mold holds the part during cure and laminate shrinkage is toward the mold surface (i.e minor shrinkage of the laminate thickness) and not on the overall dimensions of the part. Polyester parts can be very dimensionally accurate (if allowed to reach significant cure before demolding). Conversely, polyester laminates not constrained in a mold will exhibit shrinkage to some degree. But considering polyester as a concrete binder is very different due to fibre in a laminate being like pushing on the ends of a piece of string (i.e. the fibre is inherently unable to resist shrinkage) whereas aggregate (rock) is uncompressable and therefore very able to resist shrinkage. You need to open you mind a bit, and stop posting your bs..

    PS you say "ask a boat builder".... well that would be me. Marine - transport - industrial. We use polyester / vinylester by the ton(s) every day.

    PPS Low / zero shinkage modified polyester products are available.

    Last edited by jono5axe; 04-19-2019 at 11:52 PM.
    Jonathon Clarke
    www.solpont.com


  18. #78
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    Default Re: Concrete VMC

    Hi Jono - If you read the data sheet for polyester and VE resin it states 8% shrinkage. The resin is supplied with an excess of styrene for transport and other reasons. This excess does not contribute to the polymerisation of the resin so over time desorbs from the solid. The part then shrinks to what ever constraints it has. There is no way to compensate for this. Sure you can fill it with other stuff but the shrinkage is a physical fact. Low shrinkage polyester resins such as tooling resins are duplex systems. They are a combination of polyester resin and a thermoplastic resin. As the resin exotherms the thermoplastic resin expands compensating for the shrinkage. I do not have a negative agenda just dealing with facts. And sure there are a few strategies to compensate for the shrinkage but they only compensate. Over time the part will suffer some dimensional change. Been dealing with that for a long time in the same industries you mention....

    You state that the rocks etc will resist the shrinkage, this means the part will have internal stress. There's heaps of discussion in here about achieving machine parts with no internal stress for good reasons. The machine makers use epoxy by the tonne for good reasons as well. Materials get matched to their application, in this case PE is not a good match. Machine makers want materials that do not change shape over time. Cheers Peter

    Last edited by peteeng; 04-21-2019 at 04:43 PM.


  19. #79
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    Default Re: Concrete VMC

    Still few things to do so i hope i can have this beast casted at the end of next weekend.







  20. #80
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    Default Re: Concrete VMC

    Very impressive build. Thanks for sharing it.

    Regards,
    Mark


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