[ckelloug]

Larry,

The upper size limit is somewhat arbitrary. Quartz #4 is weak enough to break with finger pressure. I think quartz larger than #4 will be worse in strength following the basic textbook trend for fracture toughness as particles get larger. I could not break the #4 aluminum oxide walter sent me with finger pressure. Once the rocks get much bigger than number 4, I suspect that it will be difficult to mix without pretty large scale equipment and that this will affect us more than strength considerations.

I've done a lot of thinking about aggregate for home use and this is what I've realized might be unclear about the subject:

A single component mixture of angular grained sand has about 45% empty space in it at maximum reasonable compaction. This means that 40%-50% epoxy by volume has to be used to get a void free solid!

For perfectly graded mixtures of angular aggregate with a given number of components, the following table shows the minimum empty space possible in the mixture which governs the minimum amount of epoxy that must be used to fill the voids. For actual gradings, these numbers are worse. (From the paper by gupta et al., we know that more epoxy than the amount of empty space is required to obtain maximum strength in the part.)
<PRE>
Number of Components and Empty Space in a Perfectly Graded Mixture of Angular Aggregate using equation 1.68 in de Larrard's book
# of Mixture components | %empty space
i=1, pmin=0.451000
i=2, pmin=0.250910
i=3, pmin=0.159661
i=4, pmin=0.111375
i=5, pmin=0.082987
i=6, pmin=0.064943
i=7, pmin=0.052769
i=8, pmin=0.044158
i=9, pmin=0.037832
</PRE>

The predicted empty space for the mixture Walter used in the gorgeous part in <A href="http://www.cnczone.com/forums/showpost.php?p=328458&postcount=1893"> post 1893</A> was around 12% which allowed him to use about 20% epoxy by volume as I understand it.

So to answer Larry's question, you can use any source of local materials if you can roughly follow the grading outlined in <A href="http://www.cnczone.com/forums/showpost.php?p=320419&postcount=1824">post 1824 </A>.

In the context of de Larrard's Compressible Packing Model, there is no such thing as a premium filler, only fillers that are more expensive. Each of the aggregate grades has a job to do and must be present in roughly the correct proportion. A mixture of 80% "premium filler" and 20% epoxy will not perform like a mixture of 10% "premium filler" 70% "non-premium filler" and 20% epoxy.

It's quite possible that there is a sandblast sand that is easily available that could serve as basic raw material though I have not worked hard at identifying one. The best candidate I have seen is DuPont Starblast Ultra. It has to be the Ultra grade though as the other grade's distribution is not really what we might like.

One must obtain aggregate from somewhere and for best results, aggregate on the right grading curve seems to work better according to Walter and the models. In buying either graded aggregate mixed to follow the curve approximately or sieved aggregate designed to follow the curve exactly, one has to remember that it is the grading that you are paying for, not the material. While both may be silicon dioxide, only the graded one will pack to high filler density according to the model.

Like I said before, the greatest gain to be had is in using approximately equal parts of two components of different sizes rather than using just one component. Finally, masochists could always call up http://www.dualmfg.com/ or http://www.retsch.com/ or http://www.ascscientific.com and order himself/herself a set of small sieves and sieve it themselves.

Gotta mow the lawn and hammer drill concrete out in the 100 degree sun.

--Cameron

[greybeard]

Hi Phil, and welcome.
Cameron has probably given you some leads on suppliers, which is just as well as I've been a bit slow of late.
The resin I will be using is from Tomps - www.tomps.com - who are only a few mile from where I am, so I can pick the stuff up personally. It's a fairly low viscosity resin anyway, so for the moment it will do.
My own development will concentrate on using spin casting as a method of producing sub assemblies, and to that end I need to finish a particle separator.
This will enable me(in theory, at least) to first find out what's in the cheap aggregate I've bought from the local supplier(Wickes builders merchants), and then adjust it to get as close as possible to the multi-component mix a la De Larrand.
By using spin casting, I hope to avoid the necessity of including de-airing agents and using vibrators, both being a function of the set up.
PM me if you'd like more details, but it's going to be a slow development - too many other interruptions.

Regards
John

[ckelloug]

John,

I looked at the tomps website about epoxy and I think I've found the manufacturer's datasheet. (I looked closely at the image on the tomps website and googled for DX020 which appeared to be the formulation's manufacturer part number).

Datasheet:
http://www.atlaspolymers.co.uk/Produ...eets/DX020.htm

Atlas Polymer's epoxy page is at:

http://atlaspolymers.co.uk/products....roduct_group=2.


<B>To Craig and others hunting for materials:</B>
I've done a bit of rudimentary analysis and here in the U.S. It looks like one could possibly get the optimal mix delivered for around $1.20-$1.50 per pound to most places in the U.S. That's $.50 a pound for material and about $.70 a pound for shipping and packaging.

One factor that hasn't been discussed lately is the more epoxy you have in the mix, the more exothermic the cure and the greater the shrinkage problems in precision parts.

Regards all,

Cameron

[VetteNut72]

I am really excited about the prospects for user created cold casting and what it can bring to the DIY guy. Here is a thought on using E/G for an X/Y axis slide. I'm thinking about using UHMW for the mold, more on that later.

This is what I hope to cast in E/G for the X/Y slide support.


And building the components onto the support. These 20mm slides and bearings are fairly inexpensive. I plan on filling the slide rails with E/G.








Craig

[harryn]

VetteNut72 - those are interesting drawings - similar to the commercial Frelon type slide bearings from Pacific Bearings. Just be careful with the center of gravity hanging too far out into space - there are some very detailed app notes on that subject in their documentation.

[VetteNut72]

Here is some more on the X/Y slide support. I'm going to use two ballnuts on each axis. The flanges are tied together by threaded shafts that float in the support and should help to force a compressive load at each axis.


Quick thoughts on a E/G base. The Y axis ballshaft mounts, as well as the motor mount will be cast into the base.


Here's a better look at the X/Y slide that sits in the base. Still a few more things to work out.




Designing the mold for the X/Y support and the base are next.

Craig

[VetteNut72]

harryn - Yes, very similar. They are Drylin bearings from IGUS.

Craig

[walter]

VetteNut72,

Looking good! I really like that big fat E/G base.

Now you need to be careful here, E/G is very weak in tension and should not be used for small gizmos, motor mounts, etc. Any screwing is done via deeply embedded metal members:




Vendor who sells polymer concrete mini mill bases did the motor mounts/hardware in polymer concrete and is now 10 months behind with his product, going through major redesign- a lesson for all of us.

[ckelloug]

VetteNut72,

That stuff is looking awesome! What kind of CAD software are you using? As for walter's comment about tension, you shouldn't count on more than 1 or 2 ksi tensile strength. Compressive strength could be as high as 16ksi according to some old values in the literature.


Walter,

How is your machine doing?

[walter]

Cameron,

Didn't we have some kind of E/G thickness guidelines, like 6 times the steel or something like that? I remember you and Andrew doing the math for this.

As for my machine, pretty slow going; Currently working on heavy duty supports. And my camera died, can you imagine that? Well, maybe it's just the battery that is faulty.. Anyway. There are 3 last good pictures, the rest is from cellphone camera- I apologize for the poor quality.

#1- design of mating parts

#2- 1144 stress proof bars, class 8 screws

#3- complete mating surfaces (reverse cast)

#4- support bars installed

#5- working out strategy

#6- preliminary result


This is the 8th time I tried to post this message, is server down again? I can't preview, the Zone page reload took more than 25 min; Maybe I clogged the server? Too many pictures??
I'm just going to avoid the Zone on weekends, I can't take this.
_

[ckelloug]

Walter,

Despite the fights I've had with Andrew here for reasons I don't understand, he is probably better qualified to answer your question on how E/G compares to steel or aluminum than I am. From a quick comparison of the tensile strengths, aluminum at 30ksi tensile strength used in a beam is about 15 times stronger than E/G used in a beam at 2ksi flexural strength.

I did the following calculations back in May:

Here are some rules of thumb for 100 lbs load plus beam weight. These
calculations use 2e6 psi for flexural modulus at safety factor of 6 for
simply supported beams i.e. beams that are supported with both ends
sitting on something. They also assume 2ksi for flexural strength.

The material you were using came out to better than 1 ksi flexural strength which means it might have made something near 2ksi like the material in the calculations.


These figures apply only to carrying the load, not to deflection.

0-12 inches: 2inch x 2inch beam sufficient
0-24 inches: 2.5inch x 2.5inch beam sufficient
0-48 inches: 3inch x 3inch beam sufficient
0-96 inches: 5inch x 5inch beam sufficient
0-192 inches 13inch x 13inch beam sufficient


For simply supported beams considering deflection:

For Unreinforced E/Q considering the weight of the beam plus
100 lbs at .0001 deflection

12 inch long: 4inch x 4inch beam required
24 inch long: 8inch by 8 inch beam required!
48 inch long: 25inch inch x 25 inch beam required!!!
96 inch long: Unachievable
192 inch long: Unachievable


For Unreinforced E/Q considering weight of the beam plus 100 lbs at
.001 deflection

12 inch long: 2.5inch x 2.5inch required
24 inch long: 4inch by 4 inch required
48 inch long: 8.5 inch x 8.5 inch required !
96 inch long: 30inch x30inch required!!
192 inch long: Unachievable

Best of luck Walter, it looks like you're making lots of progress. I just pulled the wire for my workshop so I too am making progress.

Regards all,

Cameron

[AustinT]

Hey I have some news on a epoxy beam.

The beam was about a foot long and the cross section dimensions are about 1.75 by 2.5" I just used our standard grout sand mix. Its around 3/8" minus. The sand is washed in a sand screw then I dried it in an oven. I did not use any chemical to help remove air pockets. I also did not vibrate the mold very well. After 5 days cure the beam was placed in a press on two simple supports that were 10" apart. I used a 5k load cell between a hydraulic ram and the beam so I could know the force on the beam. The force was applied midspan. The beam was oriented for the greatest moment of inertia, "bending around the strong axis" . I then slowly applied a load on the beam until faliure. The Beam broke at 2047pounds and made a loud snap when it broke. I ran some numbers and the strength was 2900psi. Upon examination none of the rock pulled out from the mix " The rock broke". Also the beam was full of voids and pockets. I have a video showing the load indicator and the beam being loaded until failure. I also have some pictures of the exact cross sectional dimensions, measured with a caliper. I will post everthing here tomorrow along with the video. What Psi mix do we need?

[goldcoast]

Hello everybody!

Where can i buy aggragates and epoxy-granite stuff in europe?

Thanks Alan

[ckelloug]

AustinT,

Your result is wonderful. This is only the second actual hard test result we have had posted. The first was from Walter who managed to load a beam of similar size to a load of about 500 pounds without it breaking leading to a flexural strength estimated at over 1ksi.

Air voids are a nucleation point for cracks that lead to failure but without measuring the size of the voids, fracture mechanics cannot be used to determine what the critical void size is and whether your voids were a problem.

Finally, we don't have enough numbers on this thread to know what is "enough" I have done my sample calculations with 2ksi strength and 2000ksi flexural modulus which it sounds like your sample exceeds in both respects. Some things will be easier to design as strength and stiffness go up. I personally am trying to find out where the maximums are so as to have full command of the range of properties. E/G like yours that has been demonstrated to be well over 2ksi without a lot of work will be good for most general machine parts. Unless one is micro-optimizing, this says that grout sand mix from the local aggregate plant is going to do a lot better than the half baked mixtures we might concoct.

Commercial E/G in the NIST paper cited long ago on the thread gives flexural strength of 4ksi and a modulus of 4000ksi IIRC.

Finally, can you explain a sand screw and your drying process for the benefit of our audience and me, that would be awesome.

goldcoast,

BYK Chemie is a german company. Look them up on the web. Reichhold who manufactures the epoxy we're buying is international. 37-127 and 37-606 are the material ID's for reichhold. http://www.reichhold.com/company/locations.cfm Huntsman Advanced materials also makes epoxy and I believe they are Dutch. User greybeard on this thread has the best handle on English sources. Calling the sales department at any of these companies and having them direct you to a repackager is probably the best you can do other than just web searching.


Regards all,

Cameron

[walter]

Welcome, Goldcoast!

Did you know that E/G originated from Switzerland?

Fritz Studer first came up with it's Granitan technology in the early 70's and they kept it proprietary until about 4 years ago, now licensing to many companies around the globe. It was a mixture of reactable epoxy resin from Ciba-Geigy, and granite (sometimes gravel). I believe I have the sample of their product, which was sent to me from France (thanks Leif!) ---> http://www.cnczone.com/forums/showth...30155&page=115 A real slice of E/G history..

If you poke around your local library, you will find many gems of Studer's knowledge and aggregate details. That crushed granite idea was pretty neat, it should be easily obtainable and very cheap.

Cheers!

[walter]

Walter, Despite the fights I've had...

Thanks for the great post- I've been meaning to bookmark a link for something like this for a while.


AustinT,

Awesome work, lets have a go at it!


Walter

[ckelloug]

Ceiba-Geigy after untold buyouts is now Huntsman Advanced Materials. The Araldite resins used in 1975 for some of the initial work by B.W. Staynes are still available today from Huntsman.

[lgalla]

If the rocks are breaking as Austin and Walter had experience,perhaps the magic 7%to10% of the commercial guys is only to cut costs and requires expensive machinery to get results.
Austin's results would be higher if the beam was attached to the support and overhanging the end supports.
I would hazard a guess crushed aggregates are a No No as they may be full of fractures
Larry

[walter]

Larry,

I've been wondering about that, too. I think vibration damping test will settle the issue.

And- for whatever it's worth, the epoxy pictured below claims 7.4 ksi tensile and 36 ksi compressive. Consistency and colors of Nivea creme and peanut butter, made by 'Plumber's Weld' people, Goopit.

Colorwise- not a good choice for machine tool (lol).
_

[lgalla]

Walter been wondering too.Is epoxy rock hard or harder than rocks?Rock On!
Color or as Canadian translation;colour,Nivea-peanut does not have the British"sporty look".Not being "sporty"is a problem as"that looks good for my face or good enough to eat does not support"Sporty Look".Perhaps a tblspoon of carboon black will bring back the "Sporty"look.
Larry