[turpija]

idea is to test epoxy granite mix and process with small part and if succesfull, to make something usefull ...

so first i have to make a mold, simple wooden pieces glued together, like this


then cut em in desired shape with cnc


then i fixed some defects and rough parts with wood bondo and paint it with some primer
as the epoxy will stick to primer and wood without problem i had to use some type of release agent, and after some testing the easiest was to lay a thin layer of regular silicone ... you can use your finger to smear it over the surface as i have
and here you can see actual steel plate that would be embedded in epoxy with some aluminum legs


all mixed and finished
after some small tests i figured out that optimal ratio for my aggregate was about 52% small gravel (different sized, 0,5mm-4mm), 36% fine sand, and 12% epoxy
you get rather dry-ish mix that is not actually pourable, but have to compact it manually
here you also see two screws protruding that would later be removed for mounting of top pieces on steel plate, interesting part is that epoxy doesn't stick to duct-tape, so i made cylindrical part with it


after few days i removed the mould, or tear it appart actually, and this is silicone that enabled fairly easy removal of part


the top side ...


machining legs so they are flat ...


here is all assembled and coated top with one layer of clear epoxy, just to make it shiny really


as this test proved to be a success, i'm proceeding into bigger challenges. but i'll start new thread for it

and one note, making mould from single piece is a bad idea, you have to cut and tear it open, few sides connected with screw is far better approach, but hey

[aarggh]

Nice job! I'm quite interested in epoxy for machine builds. I notice you have a bunch of test pieces in the background, how well did the epoxy hold up in tests? I've always imagined the forces in machining steel to be strong enough to be detrimental to gravel/epoxy builds, so I'm very curious to see how it goes.

cheers, Ian

[turpija]

those small pieces are various ratios of epoxy to gravel and sand, and some are too dry so when you brake em you can clearly see that break line is around stones from gravel, and others (with sufficient epoxy) breaks the stones in half and not around...

and for machine build, i don't think it is stronger than steel (or cast iron) but it's vibration dampening properies is why it's used in machines, and for small machine (like i'm building) there would not be big forces involved in machining so it should work, and beside that, it's fairly easy to work with it, and you get huge mass, which will hopefully help when machining ... and casting metal is not practical for home environment

[chevydyl]

pretty good "test" EG is pretty intriguing, i hope to build my machine in the same manner, with a base plate big enough to bolt the Y axis rails and screw along with the column, that way there is no machining to be done to the mounting points as the plate would be blanchard ground, it might be awhole lot cheaper to have mounting pads and then do machining afterwards but i dont have a mill yet and would have to bring it to a shop to have that done.

[RotarySMP]

Have you thought of making a simple pneumatic vibrator to compact the mix. If you search hobby metal casting alloyavenue.com for "vibrator you will see a few.

[aarggh]

Have you thought of making a simple pneumatic vibrator to compact the mix. If you search hobby metal casting alloyavenue.com for "vibrator you will see a few.

Using a vibrator for concreting works well because your dealing with large quantities of concrete usually sliding down sides of formwork when the air is displaced, but given the working area and grain size of a project like this, would that not cause separation of the mix to a degree? Larger heavier ones would tend to sink with smaller ones moving to the top?

cheers, Ian

[turpija]

and epoxy granite mix is much dryer than regular concrete ... i've tried vibrating with regular motor with eccentric weight, and if mix is relatively wet it works, but when it's dry it separate into groups and does not fill the mould correctly (don't know how to describe it better), it leaves pretty big gaps, looks like cracked dry earth actually

[xrdcarbon]

that's very cool test