[BrendaEM]

The stiffness aside...

It's interesting that EG tends to quell vibration because the epoxy represents a dampener and the granite or aggragrate represents a suspended mass--in that each piece of aggregate is a weight suspended by a dampened spring, the epoxy.

I noticed somewhere in this thread that EG seems to do very well overall dampening, but the first initial one-shot event, it doesn't seem to do as well as metal. Could it be that it's not stiff enough to transmit enough of the shock through a heavy enough area?

I wonder where the line lies between stiffness and dampening. Adding glass fibers might make a stiffer part, to better control the the first bang, but it might make the EG part ring more. They might find one day, that adding chopped fiberglass might be good, but only if it's not too long.

It woulds seem that the weight of the aggregate would affect how well the EG dampens as well as the flexibility of the epoxy. Epoxy really isn't all that flexible, but compared to aluminum oxide, it is.

If would seem that the expansion characteristics of the filler, as well as the epoxy would affect the stability. It seems that insulators tend to be stable, like glass, they make telescope mirrors with, and often metals tends to be quite lively, perhaps except for Inconel.

It would be interesting to do different tests with different hardness epoxies to find what's good to dampen the vibration that a milling machine creates.

There might be other aggregates that are heavier, that might work better than others too. Aluminum oxide is quite hard, and stable, but I wonder if there is anything else that's more dense.

[It reminds me of Sorbothane, which is made of durometer/firmness to specifically target a specific frequency.]

Sorry to be so long. You all have me thinking about this stuff, and my cat and roomate don't seem get enthused about epoxy granite : )

[ckelloug]

The stiffness aside...

It's interesting that EG tends to quell vibration because the epoxy represents a dampener and the granite or aggragrate represents a suspended mass--in that each piece of aggregate is a weight suspended by a dampened spring, the epoxy.

I noticed somewhere in this thread that EG seems to do very well overall dampening, but the first initial one-shot event, it doesn't seem to do as well as metal. Could it be that it's not stiff enough to transmit enough of the shock through a heavy enough area?

If I remember correctly about the published test you were talking about, there was a footnote that pointed out that they tested samples of equal size rather than equal "stiffness". Because the "stiffness" of the E/G sample was smaller at the same sized piece of the metals, it deflected more.

I wonder where the line lies between stiffness and dampening. Adding glass fibers might make a stiffer part, to better control the the first bang, but it might make the EG part ring more. They might find one day, that adding chopped fiberglass might be good, but only if it's not too long.

It woulds seem that the weight of the aggregate would affect how well the EG dampens as well as the flexibility of the epoxy. Epoxy really isn't all that flexible, but compared to aluminum oxide, it is.

If would seem that the expansion characteristics of the filler, as well as the epoxy would affect the stability. It seems that insulators tend to be stable, like glass, they make telescope mirrors with, and often metals tends to be quite lively, perhaps except for Inconel.

Glass or carbon fibers in the mix might make the structure more rigid but they will require a different aggregate formulation as they substantially affect the way the aggregate packs in the mixture.

The weight of the E/G material does help damping very much due to simple F=ma effects. Published E/G numbers suggest it isn't awful in thermal expansion due to the large filler content but polymers in general have awful thermal expansion characteristics.

It would be interesting to do different tests with different hardness epoxies to find what's good to dampen the vibration that a milling machine creates.

There might be other aggregates that are heavier, that might work better than others too. Aluminum oxide is quite hard, and stable, but I wonder if there is anything else that's more dense.

Yes, one could probably make a model that helped predict this. Precisely, it's the compressive and tensile moduli rather than the hardness that affect this. I suspect that as filler loading goes up, damping probably goes down. I also predict that this effect will be easier to control from the perspective of percent filler than epoxy type as there are very few epoxies with low enough viscosity to make E/G easy.

[It reminds me of Sorbothane, which is made of durometer/firmness to specifically target a specific frequency.]

Sorry to be so long. You all have me thinking about this stuff, and my cat and roomate don't seem get enthused about epoxy granite : )

Vibration in the simplest case is modeled by a second order differential equation. If you know the mass of the particles and the moduli of the springs connecting them, you can build a model. I'll have to think about the damping characteristics. Different aggregate designs and filler loadings will produce different effects.


Finally, you're welcome to post your musings here. I suspect from personal experience that most of the people who want to hear about E/G and how it works are already here so lets party. They sure aren't out in public where I live. . .

--Cameron

[BrendaEM]

Thanks Camron,

After reading your posts, interferometry, or a modal simulation pops into my mind, because a better machine could be made if you knew how it was going to vibrate...and FEM pops into my mind because a better machine could be made if we knew how it was going to heat up.

[Modal study of the Space Shuttle tail

It seems that someone could make something pretty GOOD, pretty easily with EG. Okay, it takes careful preparation, and experimentation to make it right, but it's not as hard as casting the part from iron.

Walter, I'm amazed that you made a part so large that's not scrap.

I've not thought about: Different cutting speeds might produce different frequencies, some of which might be tolerated by the machine better than other's...and the thickness of the sections of the machine might affect how they expand and contract.

[AustinT]

I want to play!

Hi I recently discovered this post and it took a couple of days ot catch up. I am fascinated at the possibilities of E/G I just ordered a gallon of the 635 epoxy. Camron's formula looks good but im going to try something a little different at first just because i have some available aggregate. We have a ready mix company and have a supply of aggregate. The aggregate is roughly 90 percent quartz. It works out great because we never have a problem getting good breaks. I have access to crushed or round rock quartz rock and sand. We put our oversize through a crusher to knock it down to a more usable size. The rock wears out the high manganese crusher dies quickly and it is not uncommon to shim the crusher everyday so it can continue to make a usable product. To start I think I will just try using our mix design for PC . I will also start off with the uncrushed rock. Ill post some pics and results when I get it done. I also have some extra load cells and I can make a machine to test the results. If all goes well I could do some test cylinders as well

Thanks for all of the good reading

Daniel

[greybeard]

Cameron - starting from Bob B's mention of babbit metal bearings prompts me to wonder what the surface wear properties of the E/G mix might be.
I'm working on a design for a diy linear recirculating ball bearing, and I think casting the body in E/G might be nice.
As the design has about 30 balls carrying about 5kg in total, I wondered if my spun surface of quartz in resin might not stand up pretty well.
Any thoughts ?

Regards
John

[ckelloug]

John,

The 1975 book of proceedings talks about putting corundum into the epoxy to increase the surface wear properties. In general E/Q ought to be pretty good without or without corundum, I think although small aggregate will have more surface exposed and work better. PM me with your address, John and I'll postal mail you xeroxes of the four or five pages of data from the de Larrard book.

--Cameron

[ckelloug]

Austin T,

Have fun. Compressive strength will be interesting but keep in mind due to many of the uses for E/G that tension will more often be the limiting factor. The mix designs that I've posted are designed to minimize the amount of epoxy used to hopefully maximize the strength. It will be interesting to see how your portland cement aggregate design works. Francois de Larrard from the french government department of roads and bridges has shown that Fuller's formula provides an 8% lower filler density than optimal. If you don't plan to use the absolute minimum epoxy for maximum stiffness, the last few percent won't matter but a single size of anything won't get a packing density beyond 65% for crushed and 71% for round. (Round aggregate will pack to a higher density than crushed).

Smaller aggregates have a higher fracture toughness and should make a stronger material according to the materials science I've been trying to apply although they make the bonding more difficult without additives.

In general, most aggregate designs will produce a solid product but the design Walter used was calculated for for 88% fill and from what he says, it seemed to do well with deairing additive for making a void free product. Because of the tensile loadings for many E/G applications, one must be careful about voids as they provide flaws from which lower the strength of the material.

I'd like to compare notes with you. I am working on acquiring the right instruments and equipment to do a very scientific study of the effects of the additives, aggregate designs, and aggregate compositions. I'm guessing I'll be able to start doing lab work in October.

--Cameron

[AustinT]

Austin T,


I'd like to compare notes with you. I am working on acquiring the right instruments and equipment to do a very scientific study of the effects of the additives, aggregate designs, and aggregate compositions. I'm guessing I'll be able to start doing lab work in October.

--Cameron

Sounds good to me Cameron. Ill keep everybody posted. My first attempt using the Portland concrete mix design is just to see how well the sample does with no changes other than the epoxy. I have plenty of test breaks I can compare to. After this I would also like to use the optimal formula. Once we have it all figured out I could change out screens at the plant and wash out a pile of material to the correct specs. I really think this material will work great. Usually our breaks hit the 4000 psi mark in 7 days. 28 day breaks go around 5500 psi. If we use water reducer breaks are over 6000 psi and have been as high as 7500 psi .
I just got an email saying my epoxy has shipped out. I bought the 635 from Us composites. A gallon was around 60 dollars. Where is the 30 dollar/ gallon epoxy?
Thanks
Daniel

[ger21]

A gallon was around 60 dollars. Where is the 30 dollar/ gallon epoxy?
Thanks
Daniel

Buy 5 gallons and your close. 5+2.5 hardener = 7.5 gallons for $244, or $32.50/gallon. Buy 10 gallons and your under $30 gallon.

[BrendaEM]

Perhaps like conventional concrete, perhaps the portland mix would have less tensile strength, but as in concrete, it would have good compressive strength.

Perhaps your machine design could take that into account.

[lgalla]

Previous posts have questioned epoxy bearing surfaces.
Epoxy can be mixed with graphite or teflon to make a wear resistant bearing or machine ways.Nuts can also be cast.This is ways beyond my knowledge but an interesting subject.http://www.epoxyproducts.com/2_fillers.html
Source:Add 5+ ounces of graphite per quart of epoxy (15% by volume - other sources suggest 10% which is about 6 tablespoons per quart of epoxy) for a slicker, less frictional surface with improved wear resistance and durability. Improves temperature conductivity, electrical conductivity and reduces friction. Sometimes used on boat bottoms that get pulled up on beaches/rocks. Use on rudders and centerboards, and bottoms of dry sailed racing boats. Also sometimes used in seams on teak decks for traditional 'black seam' look. When mixed with epoxy turns the epoxy a very dark, somewhat shiny gray/black. Leaves 'pencil' dust when sanded. Priced cheaper than other suppliers.


1 pound unit - $14 (about 1 quart volume)

---- ORDER NOW via link to online storefront (section 5 - thickeners/fillers) ----


Teflon Powder:

Add 5+ ounces of Teflon per quart of epoxy (15% by volume) for a slicker, less frictional surface. Epoxy actually get slicker as it weathers or when sanded. Not as messy as graphite above. White powder.


half pound unit - $30 (about 1 pint volume)

www.moglice.com
Larry

[greybeard]

OK, so this is where I show my engineering ignorance.
Should a bearing surface designed to have steel balls rolling along it, as in a drawslide design, have a low friction surface(which might promote slippage) or a medium/high friction surface to avoid the same ?
Rolling friction being lower than sliding friction, I assume the latter case would be the way to go, if I'm thinking of using E/G as a surface for the balls to circulate around. I've assumed already that the quartz loaded surface in my spin cast bearing is going to be wear resistant enough as well as hard enough not to deform with the sort of loading I have in mind.

John

[martinw]

_
_
Very first and unofficial picture of my mineral casting. Cameron's Formula, all natural color, no pigments, 150lbs with motor. It's straight out of the mold, still has some plastic and artifacts on it- I just vacuumed it for now.





:
_

Dear Walter,

I have been away, and returned to see your totally (as we say over this side of the pond) "gob-smacking" machine. I am gasping with admiration.

Utterly brilliant.

We are not worthy...

Best wishes,

Martin

[walter]

Thanks Martin! Good to see you back!

[ckelloug]

Hi all,

I've come to the conclusion that I will have to buy a small materials testing machine to extract flexural strength and flexural modulus data from my planned series of tests and due to the expense of the machine, I am starting to wonder if there is a commercialization opportunity.

Would anybody be interested in casting 5 samples 3/8 thick ,half inch wide and 7 1/2 inches long and having an ASTM D-790 flexural strength/modulus test done on them? I am also curious whether our readership would be willing to pay for such tests and if so, what would folks be willing to pay. The going rate for such tests from PTLI is $250 for a ten sample test to determine flexural modulus and flexural strength.

If I were to offer a subscription deal of $100 per year for all the tests that an individual needs to test and optimize his/her material, and $20 for a sample mold with test results posted to the thread, would I get any takers? If not, what would folks consider an acceptable price? I'm willing to do this for well below the going rate seeing all the contributors around the world who have posted and helped the process, I would however like to recover the capital expenses for the testing machine.

Secondly, we know from the thread that additives are important to making E/G work well. Unfortunately, many additives require precise measurements and some additives like nanoclays etc. initially require violent high shear mixing which is likely impossible in the home shop without expensive special purpose equipment. Some additives are also difficult or impossible to acquire personally. I am currently considering the purchase of an ultrasonic cavitator to facilitate the use of nano-additives and wonder if others would like to take advantage of it. Were I to offer pre-measured quantities of a tested mixture of bonding, deairing, and nano-reinforcement additives at a cost that works out to $10-$20 per E/G machine part would I have any takers? If not, what price would folks feel was reasonable?

Finally, when my research is complete would anybody be interested in purchasing a complete kit of deairing, bonding and nano-reinforement agents, epoxy, hardener, and aggregate mixed to the optimal specification that came with a couple sets of strength tests and full directions? Also, for the kit, would folks care what the aggregate material was? Quartz is inexpensive but corundum (aluminum oxide) is a tiny bit more expensive but theoretically stronger and stiffer.

Regardless of the answers to these questions, I'll keep posting results here, answering questions, and keep an active role. The work that has been done here is property of the community and I'm glad to have been a part.

I am not interested in making a large profit on the items I'm considering offering, I'm just interested in offering items that make E/G easier, stronger, and more successful for the folks who are interested in doing it themselves while not having to personally absorb over $10,000 in capital costs. If I ever profit significantly from E/G, it will be by selling finished parts to those not interested in making the parts themselves, not those who have helped create the recipe.

I still have a ways to go before I could offer kits or additives although I could potentially offer testing by September if there is interest. This posting isn't soliciting preorders or commitment, I'm just checking to see if anyone would be willing to pay a nominal below market rate fee for materials and services that each of us individually would likely not be able to acquire on his/her own.

Regards all,
Cameron

[lerman]

It appears that the apparatus consists of a support at each end, a means of gradually applying force in the center, a means of measuring the force, and a means of measuring the deflection.

A small hydraulic cylinder with a digital pressure gauge should work for applying the force. A hand pump should be fine. A cheap digital scale from a vernier caliper should work for measuring the deflection.

Ideally, you would want a computer hooked to this so you could gather the data and plot the results.

I don't have a copy of ASTM D-790, but from what I've seen: http://www.ides.com/property_descriptions/ASTMD790.asp it appears that there are two procedures with differing rates of strain specified. Is that important? Since we apply stress and measure strain, how is this normally done?

Ken

[ckelloug]

Ken,

ASTM D790 does specify strain rate. Most plastic like materials are somewhat sensitive to strain rate.

A testing machine actually applies strain via a constantly increasing displacement via a hydraulic or screw based mechanism and then measures stress via a load cell which is in turn measuring strain in a metal load cell of known geometry. The crosshead feed rate prescribed in D-790 is specific to each sample geometry to keep strain rates constant at .01 inches/inch minute in method A or .10 inches/inch minute if method B is used.

It would be possible to build a semi-accurate strength testing jig ignoring strain rate. A nice intro to doing this based on hydraulic principles is available at Richard Nakka's model rocket site. http://members.aol.com/riccnakk/hydlc.html This was posted on this thread eons ago.

With the number and kinds of samples and the modulus results I need for the test program to produce commerical E/G material, I personally need calibrated results and the proper test jig so that my tests are comparable with standard tests. Buying a machine (I got a quote of about 6K from Admet and about 20K from Instron) also gives me software to handle the data, a calibrated load cell and a test controller which handles the proper test profile. Finally, calibrated pressure gages and especially transducers are expensive in and of themselves and while a single one of us might be able to build an improvised manual test rig for a few hundred bucks, getting one that produces not only strength but accurate flexural modulus numbers which can be relied upon for design purposes will be difficult.

Regards All,
Cameron

[ckelloug]

BrendaEM,

E/G strength is much higher in compression than tension. Like concrete, when it is used in an unreinforced beam, it will fail in tension. This is why I worry so much about tension. Compressive loadings are preferable to tensile ones which is why for example, it is theoretically stronger to run a bolt all of the way through with large washers and nuts on each end than it is to place an insert into the material and then apply a tensile load against the insert.

greybeard,

I'm not exactly sure what you are proposing and I don't know much about bearing surfaces. My oldschool Bridgeport mill has solid scraped cast iron ways and no linear bearings. I'd assume that it's harder to hold really tight tolerances with rolling parts as it would be with sliding ones but I have no experience at this aspect yet.

lgalla,

That's awesome the post about graphite and teflon in the epoxy. I had thought of teflon but didn't realize it was common practice. Kudos to Bob B. too for mentioning the graphite!

Austin T,

So I take it you have a full sized concrete testing machine? I looked back to BW Staynes' paper in the 1975 proceedings of the concrete society and the Epoxy Concrete mixture (as he called it) had a 16,000 psi compressive strength! I look forward to comparing notes. I guess that means I'll have to start lab work. . .

--Cameron

[AustinT]

BrendaEM,



Austin T,

So I take it you have a full sized concrete testing machine? I looked back to BW Staynes' paper in the 1975 proceedings of the concrete society and the Epoxy Concrete mixture (as he called it) had a 16,000 psi compressive strength! I look forward to comparing notes. I guess that means I'll have to start lab work. . .

--Cameron

Hi, No I dont have a machine. We send test samples in for breaking. About the testing machine. What do we need exactly? Here in two weeks Ill be back in school and will have access to a 60K dollar load frame. I also do all of the load cell work on our plants . What size load cell would be needed if we make our own machine?

[ckelloug]

Hi, No I dont have a machine. We send test samples in for breaking. About the testing machine. What do we need exactly? Here in two weeks Ill be back in school and will have access to a 60K dollar load frame. I also do all of the load cell work on our plants . What size load cell would be needed if we make our own machine?

What load cell and machine you need depends on what we want to do. I'm planning a long series of tests to determine the required additives for bonding, deairing and the strength and flexural modulus effects of nano-additives. Since the formula I've been posting about used relatively small aggregate, I think an adequate analysis can be done using the 3/8 inch thick, 7.5 inch long ASTM D-790 samples which are supported near the ends horizontally while force is applied in the middle . The quote I got from Admet is for a 250lb actuator and load cell which is probably about 8 times the force required to break a 3/8 thick sample with the 6 inches between supports used in the ASTM D790 three point bending test for 3/8 thick samples.

For a compressive test to failure of a 3 inch diameter compressive specimen something like I understand are used for concrete with 16,000psi compressive strength, my back of the enveloping indicates that failure would be at about 113,000 lbs

A homebrew test machine for an ASTM D-790 style flexural where the forces are in the vicinity of 40 lbs is doable and provides data on how the material will perform in a beam. I don't think a compressive test like those done for concrete is something we can achieve on homebrew gear.

Answering your question directly, I'm looking at a system with a 250lb load cell. Other types of tests could require a significantly different approach. If your school has a big load frame, it probably can do a compressive test like is done for concrete and has a big load cell too.

Regards all,

Cameron