[PiotrCz]

Hi,

I would like to share with you my new project

Number of axis: 3
Field Work: 150x150x100 (he he, in millimetres, of course).
Material: epoxy resin + sand + some aluminium
Motors: a small 0.5-1Nm
Driver: A USB integrated
Purpose: Wax, plastic, plastics
Spindle: 100W
Mills: ER11 mainly 3.175mm diameter

No surprise - except maybe two things that I want to try:
a) integrated stepper motors with ball screws
b) the mill's structure it is going to be made out of epoxy resin and sand - yes, yes - as ~Walter did and his followers.

Since I like the theoretical preparations, I started to study topics in the forum, and then I read a little bit about the sphere packing (the article on wiki is obligatory for every one), how to set the optimum sand balls in three or more dimensions, etc. All in all I found even more than I expected. Generally, three types of aggregates I will comply (with three sizes - each is approximately the diameter of ~ 0.64x of the previous ). I think I should be able to obtain in the 'garage environment' up to 74% - 80% of the packing (one fraction gives you up to0.74 assuming an ideal density and conditions), using only a vibrating table without the pressure pump.

For those who like the slides & powerpoint, I found a great scientific paper http://www2.latech.edu/~jkanno/packing.pdf - I recommend to you read it.
That is a general idea:



It is going to be my fourth cnc machine. I made those below:
1) made ​​of metal (for one frame of colleagues) Metal cnc-heavy-metal
2) the ready frame Proxxon cnc-proxxon-mf-70-upgrade
3) aluminum frame minimill-cnc

So time for a little bit different material fourth frame. I have a little bit of the experience with casting resins so far - I am a hobby figures maker. During the weekend I tested a couple of things...

Parts for the vibrating table - an old cutting board, motor, speed control, spring (already cut into four)


Resin and sand in two gradations


Bucket and stirs


Casting mold plywood test


'Improved' stirring - patent pending note I is not a mixer for pizza, but I hope it will be good enough


Well, The form itself, I used a nivea cream as a separator


How it was done- it can be seen on youtube - sorry for Polish language (I added English captions) - it's a hobby and fun ... [youtube] [ame=http://www.youtube.com/watch?v=8vDjuiIig5g]EpoxyGranite 1 - first attempt - YouTube[/ame] [/ youtube]

Resin


After removing it from the mold, surprisingly it went smoothly - nivea cream worked well




Attempts to break it


And bit more effective smashing




Couple of the novice's conclusions:
1) It went well, it was surprisingly hard and rigid - of course, it was possible to destroy it with a hammer - but it required a few strong knocks with a hammer.
2) The cast perfectly recreated crumpled foil - I wonder why sometimes cast is shiny, sometimes dull?
3) As you can see there is a bit of bubbles - they are small - the bricks' smallest dimension is about 1 inches thick.
4) Generally, at first glance, it is suitable for cnc ... rigid, heavy and strong.

Test 1 completed. It's time to test 2 Number of 200g of resin

I hope you like it .

Best regards, Piotr

[PiotrCz]

As previously promised I cast another 200g of resin mixed with black dye (addative to the concrete). Black dye acted as an extra filler - it has dust consistency.


Close-up, of course, It was broken again using the hammer ...


So how it looks after breaking - less bubbles than yesterday - I think it's because of the dye ... but I'm not sure , yesterday was colder - it was around 1C in my garage - brrr. pretty cold winter - but it has that advantage that it extends the resin's cure time.



And two cups of resin, one cast at atmospheric pressure, the second in hypertension in pressure pot ... guess which one... below).



And here the close-up the resin's filling in a cup (those little scratches, are made with a screwdriver) - is not bad ...


Close-up of resin -2-3mm thickness is difficult to break by hand



The cast on the left (with fewer quantity of bubbles) was casted using extra pressure, the theory is proven ... but ...

but ... I figure out that my air pressure chamber leaks - after two hours was 2atm, in the morning was close to 0 (and in the begining I pumped to 4atm) ... so the test is only half good - I need to seal the chamber and try again.




Conclusions:
1) dye works
2) the pressure chamber (pressure pot) is promising
3) vibrations are important - these samples vibrate only two minutes max ... because the engine in my vibrating table just flown away... .

Now I am waiting for used mixer bought on ebay and better vibrating table in order to make more samples.


Stay tuned! BTW anybody any thoughts?

BR, P.

[rybov]

Piotr,

Interesting experimentation. I am also experimenting with epoxy granite casting at the moment.

Will you share your mix?

What I have found is that the mixing is a bit of a problem, when your have a low percentage of epoxy. Still trying to locate a very low-viscosity epoxy.

Vibrating is very effective. Much more than I would have tought. Even with a very thick EG mixture.

Look forward to follow this thread.

/Jacob

[LN-JET]

rybov; I have good experience with the R&G L1100 resin + 294 hardener.
Viscosity is low, and the very slow hardener gives you many hours of work time, and no problems with exothermic reactions even in large quantyties.

Regards

Lars

[the4thseal]

Post cure heating of casting is a plus as well.

[PiotrCz]

Hello all readers,

rybov - I used Epidian 6011 + hardener z-1. Resin characteristic (in Polish) -> http://www.ciech.com/PL/Produkty/Pro...idian_6011.pdf

the4thsea - indeed - samples after heating have more 'stone' sound. Still resin need around 7 days to be cured completely.

The good news is that my new (but used) vibrating table has arrived today, so I will be able to do more testing.

Regards, P.

[rowbare]

Did you calculate what your epoxy percentage is? How much do the finished parts that you made with the 200g of resin weigh?

I think you might want to add some larger sized aggregate as well. If you read through the thread It looks as though using 4 or 5 sizes leads to better packing density.

bob

[rybov]

LN-JET, PiotrCz: Thanks for the recommendations for epoxies. This is very helpful, but I think I need to brush up on my Polish. That datasheet did not make a lot of sense to me :-)

the4thseal: I have heard about the post curing, but never tried it. As Piotr mentions just storing the casting at room temperature for a week does certainly change the resin compared to just curing for 24 hours. I am sure the is a lot of difference from one epoxy formulation to the next, but for how long do you heat cure the part and at what temperature? The biggest problem for me will probably be finding an oven that is large enough.

Thanks
Jacob

[the4thseal]

You may be able to use a light box made out of plywood and insulation and lightbulbs, and thermonitor. The temperature you need to reach is not that terribly high, if I remember correctly it's between 200 and 375°.

[kkester1963]

For a temp in that range, a large cardboard box with a hot plate in the bottom would work. I have done quick and dirty one time smokers using that method at 250 for 10 hours. No reason it couldn't go longer.


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[rybov]

the4thseal, kkester1963: Thank you for your help. I talked to the supplier of a new epoxy I try, BASF. They confirmed the post curing heat treatment is a good idea as long as it is held under the glass phase temperature of the epoxy.

I will go ahaed and build myself a hot box :-)

PiotrCz: Sorry for hi-jacking the thread, I look forward to follow your build.

/Jacob

[rocketflier]

Stay tuned! BTW anybody any thoughts?

BR, P.

Pouring a thin stream into the mold gives air a better chance to evacuate the epoxy. Don't move it around, just into 1 spot, then in the mold it will flow across (from one of the videos on mold making).

Vibration is pretty simple with an offset weight. You can take a solid pulley and drill out material in one area. Better is to mount the pulley on it's own axle so the motor's bearings don't take the hit from the shaking.

If you simply drape a stretchy material in the mold rather than try to line the mold, the weight of the epoxy should stretch it out avoiding the telegraphed wrinkles. Learned that from my above ground pool liner,..

(this thread page has some links to what I'm talking about in vibration tables)
http://www.cnczone.com/forums/epoxy_...frame-383.html