[greybeard]

Let me explain myself..

.........You do have to observe Cameron's sizing formula, of course, but anything you have is a good starting point. It's all about matching components. Not about matching the right components. ........

Absolutely agree Walter, and that's the direction I'm hoping to take.
To that end I'm still going with the idea that we need to know what sizes and in what proportion we've got in our various purchases.

I did a search of the patents on particle size separation/analysis and found one based on the principle of using an air stream to do the separation.
Based on their design I've produced the following sketch, and am putting together the materials over this weekend.
I've tried to keep to the idea that it needs to be very simple to build so that anyone can copy it.
It does have various inadequacies (like me) but it should manage the separation ok.

I've found simply poking the tips of a cheap micrometer into a small heap of dried sand produces quite consistent results on measurement of particle diameter, so that's what I plan to do for measuring the sizes.
This will then give me where to place the collecting divisions (insted of the corrugated plastic in the diagram) for the second run, when I'm trying to get the recipe separation.

I hope this all makes some sort of sense. Any questions of detail please ask.

John

[Xerxes]

Forgive me that I have read only random posts from here but I'd like to ensure couple of points I have in mind:

1) Has anyone tried througly cleaning stones/sand before mixing? Dust or dirt on surface of particles will reduce adhesion and weaken the composite.

2) Has anyone compared different brand epoxies? In my experience, some poor quality epoxies are gummy and better ones get seeimly hard as glass.

Also accurate mixing ratio is very important for epoxies. If I recall correctly a TUT university course called "Composites", less than 1% error is preferred.

[greybeard]

Forgive me that I have read only random posts from here but I'd like to ensure couple of points I have in mind:

1) Has anyone tried thoroughly cleaning stones/sand before mixing? Dust or dirt on surface of particles will reduce adhesion and weaken the composite.

2) Has anyone compared different brand epoxies? In my experience, some poor quality epoxies are gummy and better ones get seeimly hard as glass.

Also accurate mixing ratio is very important for epoxies. If I recall correctly a TUT university course called "Composites", less than 1% error is preferred.

Welcome Xerxes, and I can understand your reading method, even with it's drawbacks.

Washing has been suggested. I washed my stone/sand as a matter of course to remove all the clay which is present in commercial ballast - my starting point.
The use of both methanol and also isopropanol have been suggested as a way of "activating" the surface of the aggregate, a slightly different direction of thought, but I'm sure you will understand that most of these criteria have been taken on board by everyone.
I think those who are doing practical tests are already using solvent free epoxies, chosen for several reasons, ie zero VOC's and low to zero shrinkage. This choice should in itself avoid poor quality epoxies.

Regards
John

[Xerxes]

Good!
I would think that some mechanical dust removal method could be more effective. Perhaps something like ultrasonic cleaning.

[alexccmeister]

Why not just get stones/pebbles/sand sold by aquarium shops? Fish lovers use these to line their fishtank base. I am going that route once I get my base mold setup before doing the final pour. They sell them in bags and generally are cleaned and dried.

The methods suggested here seems a bit PhD for most DIYers. Sorry guys. Thats the feeling i get from reading here.

[walter]

Xerxes, very good points. We dove deep into chemical and other properties and some new readers may be missing on this most basic info.

- Clean dry aggregate is an absolute must. If it's wet- dry it in the oven. I didn't pay attention to this because my quartz comes lab clean.

- Not all epoxies are created equal. As DAK333 pointed out, good adhesion may not equal good binding. Also make sure your epoxy is solvent free. Here's more on this topic http://www.cnczone.com/forums/showpo...19&postcount=7
Our Shopmaninc epoxy was thoroughly checked by Cameron, who called everyone in US to make sure it's the right product. Cameron- I thank you for that.

- Accurate epoxy/hardener ratio is not optional. If it says 100 part epoxy/ 50 part hardener- do exactly as it says. Not 99/51 and not 101/49. Also check if it's by volume or by weight. Very important.

- Aquarium shop aggregate is not dry and rarely clean. I tested it here http://www.cnczone.com/forums/showpo...postcount=1324
Their sand was nice but very expensive, approx 5 time the price I'm paying at my fancy aggregate dealer. Their gravel was awful- expensive, wet, dirty and not quartz. Very soft. Your mileage may vary so please check before you buy.


Cheers!

[ckelloug]

On the topic of Epoxy verification, I called the lead apps engineer for epoxy at Reichhold who makes the epoxy that goes into the uscomposites/shopmaninc 635 epoxy. His response was that he didn't have a better one to recommend and that the one we've chose should do well.

While some of this sounds rather high tech and is, the problem is that I for one would like to know that we made good epoxy granite with at least vaguely characterized strength and modulus. Anybody can put rocks and epoxy in a box, the question is whether the mixture will work well enough to use for structural parts in a machine.

The amount of engineering needed to make the base of a machine which is big solid blocks that are supported by the floor is a lot lower than the amount of engineering required to make a hollow E/G router gantry beam of minimum weight with specified deflection characteristics.

The strength and stiffness characteristics of E/G are governed primarily by the aggregate to epoxy ratio. For the very strongest material, this must be as high as possible while still maintaining enough epoxy to keep the the material together. The strength of the aggregate, the strength of the aggregate epoxy bond are also critical along with getting the air out etc that don't get accounted for in the theory.

In general, the optimal mix can be made by mixing various sizes of sand to follow a simple equal percentage logarithmic grading curve. As wide a range of sizes as possible helps keep the packing density high. Small (micron sized) aggregate make the wetting of the mixture with epoxy more difficult. Bonding and wetting agents will reduce these problems. Air bubbles must be avoided too, especially ones involving air surrounding each aggregate particle. Deairing agents and vaccum mixing and degassing are the solutions to the air problem. Finally, the entire mixture has to be compacted. Vibration and 1 psi of pressure are considered the technique for maximum compaction by De Larrard's book on mixture proportioning. More compaction might be available with hydraulic or pneumatic cylinder based systems reasonably available in the home shop. Finally, according to the model, nano-additives such as silica fume, carbon black or Nanoresins nanopox or BYK nanobyk can get between the 88% packing density of the mixed sands we've been studying and 92% without resorting to unreasonable compaction techniques. Furthermore, nano-additives have the additional nice property of pinning dislocations in the epoxy lattice causing a nonlinear increase in modulus and strength.


In short, very complicated means have been used to show that epoxy granite reduces to: Pick strong aggregate, follow the logarithmic grading curve, compact with vibration and pressure, and get the air out. These goals can be assisted by bonding agents, deairing agents, surfactants, and vacuum. If you care about the ultimate strength of the material, these steps are all important. If you just want to fill a weldment, anything will work.

Regards all,

Cameron

[Xerxes]

Has anyone tried to get a sample of commercially made polymer concrete from some company that does such castings? Its strength properties could be characterized and used as reference to home made equivalents. I believe companies would be happy to send a piece of material for quality evaluation :-)

[Zumba]

I believe Walter received a few samples from a European company. Reportedly very dense and rock hard.

As for specs, search google for "Anocast". I found a PDF file that has some info such as a young's modulus of 5250 ksi, half that of aluminum (which may be a stretch for homemade composite).

[walter]

That's right. Here's the link: http://www.cnczone.com/forums/showth...30155&page=115

We also started indexing this thread, lots of good info there: http://www.cnczone.com/forums/showthread.php?t=38800


And here's some good news: I will finally be able to test my E/G against real granite. I just got caught dumpster diving behind the granite shop.
_

[greybeard]

If I'm spin casting a thick walled tube of E/G, there will be a "compacting" force on the mix.
You can assume my set up vibrates like h**l as well !
Can I calculate how it equates to the other method of having a weight pressing down during vibration, with a vacuum applied as well ?
If so, can someone give me a formula/method to compare the two.
Obviously there will be some assumptions and approximations to make, but it might be informative to be able to compare the two methods numerically.

John

[walter]

The not-quite usable hypothetical trial formula is by volume:

10.71 part by volume #6 Agsco Brown Aluminum Oxide
10.71 part by volume #4 Unsieved Agsco Quartz
10.71 part by volume #2 Unsieved Agsco Quartz
10.71 part by volume #2/0 Unsieved Agsco Quartz
10.71 part by volume 3M G800 Zeeospheres
25.00 part by volume 3M G200 Zeeospheres
5.355 parts by volume Cabosil TS-530 silyated silica fume
13.39 parts Nanoresins Nanopox F-640 for 5.335 parts 20nm SiO2.

Cameron,

I tested part of this formula and it works pretty well. Actually, it works great.
Your grading algorithms do a beautiful job and you should really patent this thing.

I'm doing the very final batch, this time with BYK chemicals, and I'm using your formula as a base for everything. I don't have nanosand or TS530 silica fume. I don't even have G200 zeoospheres. All I've got is M5 thickening silica fume, which will be used in test later today- I couldn't find the right one, I ran out of time, and I'm going to test this M5 crap (just in case).

My point is, your grading stuff works great. The mix behaves beautifully, just like it should. It mixes with ease in uncompacted state and turns rock solid in compacted state. Just like my primitive 3 component mix pictured in post #1719.

I mixed the entire gallon at once and added extra zeeospheres. Here's the rundown (this time by volume/I screwed up last time and gave you everything by weight):

1 part #6 Agsco Brown Aluminum Oxide
1 part #4 Agsco Quartz
1 part #2 Agsco Quartz
1 part #2/0 Agsco Quartz
1 part G850 Zeeospheres
2 parts G800 Zeeospheres

The gallon pictured below has very special properties. You can mix it with a fork, like the finest chicken noodle soup. At 5" deep you barely feel the thing. But put it on a shaker for 20 seconds and it's rock solid. Unstirrable. Simply awesome. Thanks for the hard work.
_

[ckelloug]

Walter,

Glad that this mix is working well for you. I don't know if the M5 silica fume will or won't cause a problem. I'm going to suspect it won't but it's a guess. I did want to tell you that I ran a better simulation of you mix from <A href="http://www.cnczone.com/forums/showpost.php?p=312253&postcount=1639"> Post 1639</A> and you had essentially gotten to a mix with a very similar density on your own. My prediction is that your mix from that post should compact down to about 88% with reasonable compaction. My research indicates that an optimum mixture of unsieved aggregate will only achieve about 89% without silica fume and nanosand so you got awfully close to optimal. The only real difference between the optimum mix of unsieved aggregate and yours is that the optimal mix of unsieved quartz will be slightly less likely to segregate. The optimal mix of sieved quartz will have a few percent higher density and be even less likely to segregate under heavy vibration.

Congratulations!!! :cheers:

--Cameron

[walter]

I'm beginning to really like math! :cheers:

Here's something I've been mulling over lately.

Long time ago someone posted pics of his E/G column design. I thought it was pretty cool and should be used in some kind of DIY milling machine. The one that can actually mill some metal

Let's say you build a plywood mold, for both column and table, insert some rail mounting gear and pour the entire thing. I mean, it's $0.80/lb - you can make it a 100lbs machine, you can make it 500lbs machine. Or a 1000lbs machine. The beauty of simplicity.

No structural issues really.. You can make it as thick as it needs to be, right? Need thicker stronger base? Just add another bag of sand. Or 5 bags of sand. How hard is that? Or insert some heavy gauge steel junk, if you don't trust it. For $800 you could make a 1000lbs bench top monster..

Or am I just seeing things? lol
_

[walter]

_
Could you guys advice me on mold release agents (and how to use them effectively). Ease of use and good surface finish preferred.

Could any of these be used? http://www.uscomposites.com/moldrelease.html

Thanks!

[lgalla]

Walter,I have used PVA or poly vinyl alcohol as a release agent after 4 coats of one of the waxes.The problem is it is so thin it is difficult to spray with out runs.The good thing about it is it is water soluble.On difficult releases water on the partline will work its way down and assist in release.PVA is a good agent but difficult to get a good finish.Generally wax and PVA are used on new molds to break in and to guaranty release.
Those Parafilm look good not needing spray equipment.Can't say I have used them.
Never use silicone based releases.They work but nothing will ever stick to the part.Sanding does not remove "silycone"
Just a few questions.Does you mold have draft?No I don't mean:cheers: Is it a take apart box?A few details may help in the choice of a release.
Larry

[walter]

Thank you Larry, your advice is always appreciated!

The mould is one time throw-away type. My parts are going "in" so there's no room for error- it has to go right the first time and no skimping on supplies. The mould has a U shape, like a flower box (I'm still working on it, some parts are missing). Open top, center cavity for ballscrew, poured from top. Sharp edges, entire pour at one go.

I found this in E/G tips&tricks: "Use a wax based release that is brushed on. Apply a coat, let dry, buff with a soft rag, then repeat two to four more times.."

What do you think?
_

[lgalla]

Walter,I will just babble on abit about molds.
If your U has no draft,that is 2or3degrees angled outward release is more difficult.If the box has straight sides and is screwed together,the part will release or the sides will knock off easily.If the mold is collapsible the joints must be well sealed as the epoxy will leak through the joints.
Melamine is a good cheap mold box if you do not need a smooth surface.
Remember the good old days of the first posts.The German guys had release problems as the vibration compactation "sanded away"the mold release.
An excellent laminate similar to Formica is Nevemar ARP.It has an aluminium oxide coating,Mohs hardness of 9.Steel wool will not mar the glossy surface.This product maybe necessary if doing the vibro thing but needs to be laminated to a substrate.I ass um e your parts are aligned to the mold first and encapsulated with E/G.I also assume surface plate is not an issue in this case.
The brush on wax is release wax in solvents to make waxing easier.Ordinary mold wax is better.The solvent based is for molds that are broken in.
This is my first nopunpost.Can I hold back?
Larry

[lgalla]

Heads-up Nevada E/Gusers.The wind chill factor in Vegas is 104F.Your slow epoxy is 5 minute epoxy.I thought wind chill factor was only for Canada.Eh,like 20below in the wind feels like 40 below.Strange,after the global warming concerts it is too hott all over the world.A+,epoxy will cure much faster.
Larry

[walter]

No draft Larry, it has to look sporty.

I'll just screw the sides to the bottom, wax it good and I'll go for it. I understand there can be problems.
I appreciate the comments.