[John1987]

Any progress?

[nateman_doo]

see? and people thought I nagged :P
going on 2 years now.

[rocketflier]

If you left click on the person's name, then select 'view profile', you can see their last activity date. June of 2017 in this case.

[phucrobusl]

Epoxy does not dissolve styrofoam. Polyester resin does.

This is true. However it might make sense to use Polyester instead of Epoxy to make granite. It's hella' cheaper! Can live without styrofoam. Replace it with fibreboard structure or PUR foam (which can handle polyester, unlike styrofoam)... I am thinking about making milling machine using Polyester granite. Wonder why everybody uses expensive epoxy. Polyester might be little harder, which makes it kinda brittle. But i guess this can hardly affect thick pieces that are casted for milling machines. Such machines are commonly made using relatively fragile cast iron. They even use plain old concrete to cast such machines!

[skrubol]

This is true. However it might make sense to use Polyester instead of Epoxy to make granite.

From what I've read all polyester resins shrink on curing, whereas some epoxy resins do not. If you're going for anything precise without post cure machining, shrinkage es no bueno.

[CaptainVee]

From what I've read all polyester resins shrink on curing, whereas some epoxy resins do not. If you're going for anything precise without post cure machining, shrinkage es no bueno.

Indeed, polyester shrinks.
So does epoxy, but by very tiny amounts.
A friend of mine built a EG gantry with steel on one side to later connect the rails to.

Even with setting up the cast on a surface plate, the steel was 0.1 to 0.2 mm convex over 600 mm after curing.
That suggests a very small shrinkage indeed, but it required reworking the steel.

[skrubol]

He may have gotten the wrong type of epoxy. Some epoxies have more shrinkage than others. I think I remember reading somewhere on the huge epoxy granite thread on here that VOC's are the thing to look for. Any VOC's will evaporate and cause shrinkage.

[CaptainVee]

This guy knew what he was doing and he had the right kind of epoxy.
And lets be clear, to get this kind of curve the shrinkage is absolutely minute.

All this means is that there is some shrinkage, not a lot, and most may not notice it.

But if you need it to be zero for what you are going to do, test first and adjust your plans if needed.

[RCLOUTIER1]

Is anyone of these guys making a DIY kit yet that you just need to supply your own epoxy/granite? It would be so much easier and cheaper to source the concrete locally.

[eloid]

Nice work Petruscad, it's coming together slowly but surely. Do you have a surface plate large enough to get readings on the other side once you turn it over?

And will you be using the same scraping technique on the EG surface. Or do you have steel mounting rails on the other side?

where did you source your precision flat straight edge?

[masinecc]

Is it possible to get the moulds in Step or IGS files pls ?

[peteeng]

Hi All here - I'll discuss resin shrinkage. There are a few mechanisms to understand but in terms of mineral cast machine parts there are two main ones, then there's thermal expansion/contraction
1) solvent desorption & 2) crystal re-organisation
1) Resins such as polyester and vinylester use styrene as a diluent and a cross linker. The resin is supplied with about 8% more styrene then needed so that in transport and when open to air in the mould the evaporation of the styrene is not enough to leave it short for the required cross linking,. Excess styrene is trapped in the cured resin and over time desorbs from the solid creating large shrinkage 6-8% linear shrinkage is usual. 100% "solids" epoxy has no solvent or diluent in them so these do not suffer from this type of shrinkage
2) Liquids have more space in them then solids plus when the resin molecules cross link they "entangle". Generally this entanglement is volumetrically smaller then when the molecules are floating around in liquid form. So there is a small volume change due to this mechanism. eg in some plastics and concrete the volume change can be an increase in volume. This effect is usually small say less then 0.5% linear shrinkage/growth
3) during cure resins are exothermic ie they get rid of internal energy as the solid form requires less energy then the liquid form. This energy heats up the resin and this heat expands the resin and its formwork. If you have steel for instance it expands at about 13e6m/m/C vs the epoxy at 50m/m/C so the epoxy expands say 4x more then the steel. Normal epoxies can get to 60-100C when cured in mass. Granite and minerals typically used in EG expand around 10m/m/c so have a similar expansion rate to the metal. So the epoxy expands more during initial cure, then as the assembly cools they then shrink differentially and you end up with some distortion. Now this info has to be tempered a little as the epoxy is usually a small amount of the casting so you can volumetrically proportionally calculate all of these effects if you like. If you use resins that are designed for river casting like one I use it takes 2 days to cure so the heat release is over a very long time and the temperature buildup is nearly imperceptible, but it must exist.

The mineral component went through these changes some billion years ago so has had a long time to achieve equilibrium!! Good luck with any EG projects out there, post your stuff always good to know what happening out there. Peter

[petruscad]

Life is a weird thing. Right when you give up all hope, then, and only then progress is made. I hope some of you folks that were following this build are still around on this site. I don't even know if this site is still active, it surely seems deluged by all kinds of adds. These days the cool guys have YouTube channels producing build videos rivaling Hollywood movies.

When I left off the build it was because of me buying a house, moving, screwing my lower back (not due to the project), losing hope and giving up on the project. The XY table sat there on its platform for a few years waiting for my back to mend itself and me getting the courage to contemplate working with heavy objects again. About a year or so ago I decided to finish it, don't remember why any longer. And here is how it looks right now.



And these are some closeups of the head, from the right and left sides. You can see the E-Stop, the double tool release pneumatic cylinder, and the VFD for the belt-driven spindle. The spindle motor is 3 phase, 240V from a treadmill.



The CAT40 spindle is cast into the head itself and cannot be removed. The table is a solid plate of steel that was scraped flat on the bottom to sit on the carriages. The final machining of the table was done by using the mill itself.

The black hand wheels on the saddle and the head are the manual controls. They rotate optical encoders which send the pulses to the electronics which directly control the three stepper motors. The brains is based on the ESP32 microcontroller and is WiFi enabled. The software is a heavily modified FluidNC.

Well, enough details for now. Now you know what happened to the mill !

[Chazaxl]

Welcome back.

[high-side]

How's she cut? Does it perform as you expected it would?

[nateman_doo]

Welcome back! I lol'd at the youtube thing. currently doing some maintenance to my own machine as well.

[kutuprofil]

This might be an old topic, but the information is still valuable. I would like to know which type of epoxy paint was used for the large bed and column made from epoxy granite material. Is this the paint that was used? https://www.galaxypaint.net/epoksi-boya.html