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IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Epoxy-Granite machine bases (was Polymer concrete frame?)
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  1. #4921
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    Jun 2009
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    33

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

    Just a word of caution, on a lathe with the door opening to the right, if you open the door to take a look while the coolant is running it will splash out .
    Also it will be shooting right at the door and frame joint , if the door opens to the left it overlaps the joint.

  2. #4922
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    Feb 2004
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    304

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

    Thanks for the tip Danilom.

    Is my question just too stupid to ask here? Maybe someone can simply point me to a couple of relevant posts, I don't have time to read all 4900 of them in this thread..

    Kevin

  3. #4923
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    Jul 2016
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    6

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

    Hi everyone
    I made a test with the following formula:


    I used a pneumatic vibrator for 4/5 minutes but the sample result is not as expected




    I know i didn't using enough demoulding agent but this is not the most difficult point to reoslve.

    Do you think my formula is wrong? Maybe I should use 12% epoxy?

  4. #4924
    Join Date
    May 2007
    Posts
    68
    Hi All

    Gee its been a while since I Posted in here!
    I have started a thread at another place on building a new DIY CNC Mill Using Mineral castings, (Epoxy and aggregate concrete)

    All the molds are laser cut steel plate as are many of the non critical machine components, over 160 DXF part files were needed.
    When I picked up the laser cutting order the pallet weighed 350kg

    The machine itself will be very rigid and heavy, I drew in a high speed spindle however it could also take an NT 30 or 40 spindle for heavy cuts on steel.

    It will be quite a long journey to document, if you find it interesting keep an eye on the link.
    I have documented the crossmember it will be cast first, the mold is assembled. a few tweaks and it is ready.

    https://www.model-engineer.co.uk/forums/postings.asp?th=139042


    Happy to answer any questions if I can.

    Regards
    John

    Click image for larger version. 

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    Last edited by JohnMcNamara; 11-16-2018 at 03:06 PM.

  5. #4925
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    Feb 2004
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    304

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

    Quote Originally Posted by danilom View Post
    Just a word of caution, on a lathe with the door opening to the right, if you open the door to take a look while the coolant is running it will splash out .
    Also it will be shooting right at the door and frame joint , if the door opens to the left it overlaps the joint.
    Well thanks to your comment I changed it up a little to allow for two doors, so thanks for that. The left door should still block coolant slinging off of the chuck if the right door is opened. I ended up using about 800lb of epoxy, sand, and large river rocks to take up some volume, and It cuts great. I'm working on bending polycarbonate for the doors to finish sealing it up, and plumbing flood coolant. I'm also working on high pressure thru-coolant. Coolant dripping from the left door will drain back into the enclosure when the door is opened. There's no DIY lathe build section here, so not sure if I'll post a build thread. At this point it's about 90% complete.
    Kevin

  6. #4926
    Join Date
    Jun 2010
    Posts
    4252

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

    Very neat looking.
    But no tailstock? I find the lack of one to be a small problem at times.

    Cheers
    Roger

  7. #4927
    Join Date
    Aug 2016
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    132

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

    Quote Originally Posted by kevincnc View Post
    There's no DIY lathe build section here, so not sure if I'll post a build thread. At this point it's about 90% complete.
    Kevin
    Plenty of lathes have been posted in this section: https://www.cnczone.com/forums/verti...e-project-log/

    Please do start a build thread.

  8. #4928
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    Jul 2018
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    6248

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

    Hi Guys - I'm very interested in this epoxy granite stuff. But I'm perplexed why we need to use a mixture of sizes if small spherical particles are available. If they are round (any size) they will theoretically pack at about 91% volume of a solid material (see image attached) Using rules of mixtures and granite Granite E~70GPa and epoxy E=3.5GPa then neglect epoxy E mixture = 0.8*70= 56GPa. None of the texts I have read have tested any of the mixtures at this value they are about half of this at best so they are only getting 40% packing by volume?? I've been involved in composites for many years and with carbon fibres or glass fibres (which are round and smooth logs) we rarely get above 60% by volume packing so lets call 60% the top practical value. The graded approach to packing means to me that the viscosity of the epoxy is preventing consolidation of the mixture. If the viscosity was low enough like water for instance then the particles would naturally pack to a very high level. Many of the epoxies I see in this thread are laminating or thickened epoxies providing no hope of consolidation as they are thickened systems. To have any chance of success to achieve a high packing factor the resin needs to be an infusion grade one (ie no thixotropes) or you need to use a very very slow hardener and increase the temp of the resin to about +40degs C and then it will be like water but you will have a short gel time. You should be able to pack a mould dry and pour epoxy in and it will soak up like a sponge until full?? I'm about to do some tests with a ceramic short fibre and vacuum infuse it for machine parts and I expect to get over 50% packing by volume. I'll keep you posted..... Just putting some thoughts out there There are acrylic PMMA resins that are nearly water viscosity and have infinite gel time until raised to 80-90deg C then they kick off. Plus acrylics have very low shrinkage like epoxies, that maybe the way to go.. Peter

    https://www.turntex.com/ or cactus juice

    please note the vacuum process used in this site is used to remove water from the timber and air from the timber voids so the resin can infiltrate it. The voids in sand for instance are big enough that surface tension and capillary flow do not factor in so if you pour water onto sand it infiltrates immediately this is what we should see in our mould full of granite particles or any other large particle?

    Edit - corrected 80% to 91% image attached has 81% which is incorrect...

  9. #4929
    Join Date
    Aug 2009
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    230

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

    But I'm perplexed why we need to use a mixture of sizes if small spherical particles are available.
    I've been keeping an eye on this for a while... but I'm no expert, so take the following with appropriate quantities of salt...

    My understanding is that the sizes are supposed to be different enough from each other than the smaller particles fill in the voids left by the next size up... in theory getting to much higher packing density than a single size alone would yield.

    I'm about to do some tests with a ceramic short fibre and vacuum infuse it for machine parts and I expect to get over 50% packing by volume. I'll keep you posted.....
    Please do! And if you have any good links for where to get materials for this online; please do post them.

    __________________________________________________ ______________________

    Any idea what the thermal expansion properties of Cactus Juice is? Ideally we'd pick materials for the frame, aggregate, and binder resin that all had the same properties, thermo-dimensionally.

  10. #4930
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Britt - My diagram shows that a single size can achieve 91% pack by volume with a single size particle, hard to expect to get better. If you say the "large" particle has a diameter of 1 then the smaller diameter to fit in is 0.15x the big one. That will take you to a very big packing factor in a two size system. I don't think people are getting to a good packing factor because of the high epoxy viscosity. We do not use other resins because they shrink and will change shape eg polyesters shrink 8-9% by volume. These can be used as they are cheaper but you would have to post cure them completely to stabilise and shrink them, then machine out the deformation. typical post cure of polyesters is 80degC for 8hrs so it's not a tough one but the post machining of EG is!

    Spherical packing is probably less than 91% but not by much.

    epoxy is about (45-65)x10-6 m/m/K Granite is about 8, PMMA (cactus juice) is about 50 -100 granite is about 8, aluminium is 24 and steel is about 13. Plastics have high expansions.

    https://en.wikipedia.org/wiki/Poly(methyl_methacrylate)

    I'd expect similar results with short glass fibres used in plastic injection moulding. The fibre has a modulus of 70GPa they are about 2mm long and in automotive plastics they run at 30% addition by weight as they have to be able to be injected into small sizes. I'd have to convert that to volume ratio. But glass fibres are made from sand and sand is made by wearing down granite so it's the same thing really. Sand is probably cheaper then the fibres.

    By the way glass, granite and aluminum have the same elastic properties so if there is a machinist nearby that makes heaps of Al swarf use that. You can also buy aluminium powder. Then you can machine it easily after it cures vs trying to machine the granite! Cheers Peter

  11. #4931
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    Sep 2018
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    6

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

    Is anybody try to use low viscosity epoxy like DOW DER3271 or Hexion Epikote 05102 bisphenol A and with difunctional reactive dilluent. The viscosity about 200-400mPas. Mixture with 8% by weight it no problem. But stiffness is not good after 3 days. The test bar is "liquid" like strong rubber. The displacement test show after 1 hour 20micro, after 3h-25, after 8h-40, after 24h- 60
    Ordinary resin is 7000-10000mPas. And 8% its impossible, lowest i test is 12%. But stiffness is better after 24hour
    What is the best resin for EG ?

  12. #4932
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Obvian - both of these systems use diluents to reduce the viscosity. Diluents generally reduce physical properties and also the resin shrinks as some of the diluent desorbs from the resin over time. You need to check the datasheets for the shrinkage. Better off using 100% solids resins so shrinkage is very very small. I don;t think there is a best resin for EG. There are many many to choose from and it depends what is available in your area. I'd go with an 100% solids epoxy that is intended for infusion. These have low viscosity and V low shrinkage. Another path is to use tooling grade polyester resins. These are duplex systems that use polyester because its cheap and a thermoplastic resin filler. When the polyester exotherms it cooks the thermoplastic which expands to counter the PE shrinking (the resin then goes white. If it does not go white then you have to post cure it) . The issue is it comes as a filled system usually with ATH (alumina trihydride) which does not help you much. I used to buy the tooling resin unfilled as it was much thinner then epoxy and it was excellent but the importers do not bring in the unfilled system anymore into australia. You maybe able to get it where you are. Polylite tooling resin via Riechhold.

    I think the "best" is probably PMMA if you look for cactus juice resin but you will need an oven to kick it off. https://www.turntex.com/ or cactus juice.

    The two things you are battling when you create a close packed system is 1) air and 2) water vapour. Both can be removed under vacuum and then the resin can infiltrate very easily as these are not there to stop it.

    The infusion epoxy I use has a viscosity of 240 mPas so is quite low. Its the R118 from ATL Composites Peter

  13. #4933
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Obvian - I looked up the polylite viscosity its 120MPas so is really low if you can get it. I've attached an image of some tooling board I used to make for a customer. Its glass microspheres and polylite. Its density is 500kg/m3. Its white as it has "cooked" itself correctly. The felt image is a geotextile block I made using epoxy and a geotextile felt (polyester felt). The glass block is quadaxial glass stack. Its quite stiff at 22GPa and 1800kg/m3. I regularly had to make large chunks of fibreglass for electrical tests and structural tests. Look up G10 material its very similar. If I can make slabs of glass spheres or fibres 100mm thick say 1m x1m or bigger or thicker then I think its straight forward to make a sand block or granite block to any size or shape. By the way the white block is over 10 years old and has not changed shape as far as I can tell. I made several blocks using vinyl ester resin and they warped about 3mm quite early in their lives. In developing these sort of materials I infused sawdust, solid timber, MDF and other stuff in the search for a cheap filler that made a solid block yet was easy to machine. Infusing rocks would be easy but if you use the polylite you could just pour it in its so thin. If you can infuse I would use glass fibre vs rocks. Its easy to machine, takes threads directly and is very strong,. For instance the FG block tests at 350MPa tension and 750MPa flexure which is much better then most mild steels. Chop strand mat is quite cheap so you could use that and get very good strength and stiffness. Probably better then published granite and epoxy figures. But it has to be infused as the vacuum applies 10 tonne /sqm and compacts the fibres into about 50% fibre volume (packing efficiency or 50% bulk volume) The vacuum also removes the air so the resin can wet and flow very easily compared to in ambient conditions. Cheers Peter

    edit - I added the Prime 27 datasheet as its an internationally available resin.

  14. #4934
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Obivan and others out there - To pursue the issue of wetting the "granite" and creating a dense structure. Adam Bender https://www.adambender.info/post/201...e-frame-how-to did good work in finding that the graded mixture was not as good as a simple sand mixture. To discuss further.The published bulk density of dry sand is about 1700kg/m3. Granite is about 2700kg/m3. 1700/2700= 63% solid ratio. Adam used 80% sand and 20% epoxy by weight so lets convert that to a volume ratio. (0.8/2700)=0.000296m3 and (0.2/1100=0.000182m3) most epoxies are around the 1100kg/m3 mark. Now 0.000296/0.000478=0.63 or 63% wow good guess . So I expect to get better then 63% volume ratio is tough. With infused fibreglass laminates its tough to get past 50-55% and about 60% volume for carbon as they are thinner fibes.

    If you are using a graded mix you can pack this into a known volume container on a scale. Fill with water and the water weight will represent the available volume. Then you can convert that to the epoxy needed to fill the space. To take this further if we have a solid volume of 60% then the modulus using the rule of mixtures is 0.6x70Gpa = 42Mpa (aluminium is 69GPa) . This is the top value you can achieve with this mix no matter what the rock size. Round rocks (sand or aggregate are not 100 % efficient in strain transfer so the modulus is less then the 42MPa. Some say 0.5x but say 0.75 so 32GPa which is in agreement to published data. Some data is as low as 20GPa. Infused fibreglass laminates range from 20-30Gpa so as good as granite. Cheers Peter S

    edit - I found this in another EG thread. So 74% is maximum spherical packing. So 60 % is close and you don't want the bits touching too much anyway as they do need epoxy in between them. So going from 70% pack back to weight ratios.

    30% is epoxy so 300 litres is 330kg and 70% granite is 700 litres so is 700x2.7= 1890kg so the density is 2220kg/m3 and the resin ratio is 330/2220= 14.8% so if your adding under 15% I expect you will be a bit dry.... cheers
    Attached Thumbnails Attached Thumbnails sphere packing.jpg  

  15. #4935
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi All - Made the first chunk of Tetrium today. All went well. Now to do some machining tests. Will keep yuz posted. Release it tomorrow then post cure it then do some drilling and milling tests. Peter

  16. #4936
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    Sep 2014
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Following with interest!

  17. #4937
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi all and sundry- Released first block of Tetrium. It's not as dense as I hoped for, turned out same density as aluminium. If so using rule of mixtures its the same stiffness as aluminium. So now I've used up the sample fibres I'll buy some more fibres and make some larger blocks for testing. Need to get some tested to establish exact modulus for design purposes. So need to work on packing it a bit better and making a part for in service testing. May make new columns for Scoot or start a redesign on Maximus!! Cheers Peter

    edit - Later today I post cured the block then I drilled a hole in it. Drilled very nicely, soft swarf, Material sounds and feels crisp not buttery. So will send to a friend for some milling trials and comments. I'll have a go at it on my router as well.

  18. #4938
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi All and sundry - I've ordered 25kg of fibre so anyone who wants a slab for something, Z axis blank, full gantry etc speak up so I can figure out how to do it. This will make about 35kg of Tetrium so I'll need to do something with it!! Peter

    edit I faced the casting today in my router. It machined very well. Scoot struggles with aluminium as its not very stiff yet it fly through this like it was plastic. So now I have to test it to figure out its exact modulus and strength. So I've spoken to the University that usually does my mechanical testing and they are figuring out a cost. Plus they are figuring out how to do a damping test (zeta) . I really want to know these two values. Cheers Peter

  19. #4939
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    Sep 2018
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    hi peter and all.
    What is resin 100% solid for infusion? What are they based on ? why do they have low viscosity
    What resin uses in industrial commercial mixing like Rampf , Schneeberger, Studer?
    https://www.rampf-group.com/en/produ...neral-casting/

  20. #4940
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Obvian -
    1) a 100% solids resin has no solvents in them
    2) Generally all mineral castings suitable for machines are made from epoxy as it has very low shrinkage (.25%) ie it has no solvents that leach out over time eg polyester and vinyl ester resins shrink 8-9% by length as the excess styrene leaches out
    3) They have low viscosity because the manufacturer has not added any thickening agents (thixotropes) and they have selected a thin base epoxy. Epoxy resin can be water thin or like chewing gum depends on a few things
    4) The companies you mention, They are probably epoxy if you look at their MSDS it will tell you.

    cheers Peter

    Obvian - to cut the story short use Prime 27 (or a competitors equivalent) from Gurit available all over the planet. Use the fast hardener will give you over an hour to mix and pour. To figure out your weight ratio put your mineral mix into a known volume container (weigh container), tamp it down. Put it on scales now you know the weight of the solids. Now fill the container with water. Prime 27 has a density of 1070kg/m3 so is same as water. So now you can calculate the required resin ratio by weight. I don't agree with the graded approach just use good clean sand. The graded approach comes about because of the thick nature of concrete so you have to use large lumps. With Prime 27 you could pack a container or mould with the solids and just pour the resin in. cheers

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