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darryl
01-24-2012, 11:40 PM
I can't believe I got to page 53 on that near 400 pages long thread on CNCZone. Has anybody here simmered all those ideas down and come up with a project? Small, large, whatever-

Seems to me that smaller machinery would benefit as much as larger stuff- a base for a tool grinder for instance, or possibly a sub-base for a router table. Maybe some components for a table-top gantry type milling machine-

Just wondering if anyone has done anything with this method of construction. Even if just decorative doodads using any of the variety of filler materials- quartz sand, aquarium gravel, turkey grit, swarf from the grinder or sander, machinings, etc.

Shewus yer pitchers-

RTPBurnsville
01-25-2012, 08:02 AM
I have read a good portion of that thread. It would be nice if there was a condensed version as trying to find something one read several days back is a huge pain.

Would really like to give it a try as it has to be much better than the import castings of unknown quality.

Robert

JoeLee
01-25-2012, 11:19 AM
This is the only thing I ever did with granite and cement.
Red granite chips and white portland cement. It was the messiest job I've ever done. It came out pretty nice.

JL..................

http://i911.photobucket.com/albums/ac317/JoeLee09/Terrazzo%20Table/Image007.jpg
http://i911.photobucket.com/albums/ac317/JoeLee09/Terrazzo%20Table/Image008.jpg

dian
01-26-2012, 01:45 PM
iv read it all. the problem with this community is that they academically dicuss forever, without much real wolrd output. in particullar they are obcessed with vibrating and degassing. typically a guy wanting to make a epoxy casting starts out with fabricating a vibrating table and gathering components for degassing of the mixture. most of the time they get stuck, because you never hear of them again.

http://www.usinages.com/conception-fabrication-f22/fabrication-une-fraiseuse-granite-epoxy-t15107-195.html

http://www.model-engineer.co.uk/forums/postings.asp?th=51617&p=2

http://bbs.homeshopmachinist.net/showthread.php?t=41608&page=6&highlight=dian

Mcgyver
01-26-2012, 03:06 PM
This is the only thing I ever did with granite and cement.


Joe those look good

For someone just tuning it, be aware the concrete used in machine tools is a mix of granite and epoxy. Cement isn't appropriate as moves over time, especially during the first year or two while it cures.



I can't believe I got to page 53 on that near 400 pages long thread on CNCZone. Has anybody here simmered all those ideas down and come up with a project? Small, large, whatever-

its something. As the second poster to it, I still stick by that early post :). It's the boundary layer properties between the granite and epoxy that make it excellent at absorbing vibration. But its not very stiff - it has a low Young's modulus. I wonder if many of those pursing it sort of suppress that because it's so appealing to think of making anything without need to get a welder or stress relieve things.

there has to be law of diminishing returns on fretting the mix too much - I say just do it and you'll get lots of surface area between granite and epoxy - fill a void in a casting or fabrication and be ready to pop the cork.

EddyCurr
01-26-2012, 03:16 PM
This is the only thing I ever did with granite and cement.

It came out pretty nice.I'll say.

A large format surface table cleverly disguised as a piece of living room
furniture.

Nicely done.

.

Duffy
01-26-2012, 04:15 PM
Darryl, one thought about "epoxy granite." Granite was almost certainly chosen because it has a wide range of colour availability, not because it is necessarily the "best" or only aggregate. Since you are not going for beauty, (although UGLY is not mandatory:), ) I suggest you consider other aggregates. Marble comes to mind, since you can buy bags of it at any garden centre. Also, "garden lime" is usually crushed and unscreened marble. This would be an advantage, since the variety of aggregate sizes goes a long way to maximize final compressive strength of the finished lump.

ckelloug
01-26-2012, 05:05 PM
Hi Guys,

I was the generator of about 60% of the information on the CNCzone thread via my own lab work. I've got it figured out what needs to be done and what should go into the final mix that I'll recommend on that thread. Unfortunately, paying work has inserted itself between me and the last few steps of getting it done. I hope to complete the formula I set out to produce during 2012.

Granite has a high quartz content which is good for thermal expansion. Pure quartz is somewhat better and there are noises at a few large quartz vendors that they sell to Polymer Concrete people (E/G).

The modulus of good commercial E/G is about 4.4million psi. The flexural modulus of ad-hoc E/G made by folks on the thread as I measured it is around 2.2 million PSI which is equal to pine. I've produced some in the 4 million psi modulus range but I was cheating and using silicon carbide at the time.

With regards to the mixture: Too many fine particles and it produces little rat turds of epoxy and fine particles and it doesn't come together. Too few fine particles and the modulus is lousy. The wrong particle size ranges are also bad for the modulus.

Primary Diamines like Isophorone Diamine appear well suited to being used as the hardener. Thin Epoxy With Reactive Dilutants such as Hexion 813 with Cresyl Glycidyl Ether is preferred by me although harder to get. The thin epoxy from uscomposites.com, which is Reichhold 37-127 with 37-606 hardener can also be used although it's performance is not that good.

Bottom line is that most anything that you can throw together will be acceptable for parts where stiffness and strength aren't critical. For design stiffness/strength purposes with ad-hoc mixtures, consider the E/G to be well-approximated by white pine.

Hope this helps.

Regards all,

Cameron

JoeLee
01-26-2012, 05:59 PM
I know that you have to use epoxy if you use crushed glass as the glass is too smooth and won't stay imbedded in cement. I ground the table top down with diamond polishing pads, working my way up to 600 grit, and water. Messy...........


JL.................

wierdscience
01-26-2012, 08:56 PM
I've wondered about using Quartz,around here are several companies that specialize in Quartz sand and pebbles,everything from 120 mesh up to 3/16" mesh.

the4thseal
01-27-2012, 01:15 AM
I fallowed the cnc zone from the beginning and still to this day. I have contributed from time to time. I guess i missed the perfection of it along the way. 60% hhhmmmm I guess i will have to reread :)' If you could post your perfected formula that would be great. I keep having a hard time finding it. It is such a huge thread.
I would like to file it away for future use. I went down a different , parallel but different path.

dian
01-27-2012, 01:28 AM
what did you do?

WCPenney
01-27-2012, 12:11 PM
Why go through all of the expense of using epoxy when regular old High strength Quickcrete would probably work just fine? I worked with a couple of masons that have made some pretty stable and strong ornamental pieces.

A sheet of plywood, small jug of mold release, a good rubberized paint (bed liner), a fist full of lags, some stainless wire, and a dildo on a stick. Yes... yes I did just say dildo and I'll probably get away with it :D

Most of the way surfaces and sliding parts would be steel or cast iron attached via embedded lags and shims to correct for minor distortion during curing anyway. A good radius on all corners would prevent chipping. A little experimentation might yield some good rules of thumb for embedded parts.

I've thought about discarding the base to my Mini Mill and doing something as above with a machined Y axis and the column bolted to a concrete mass. It couldn't possibly be any worse than it is now.

Mcgyver
01-27-2012, 01:46 PM
Why go through all of the expense of using epoxy when regular old High strength Quickcrete would probably work just fine? I worked with a couple of masons that have made some pretty stable and strong ornamental pieces.


again, cement is not stable. takes years to cure and it moves around. when you say stable, what does that mean? the patio still looks flat? a machine element moving around a couple thou will ruin accuracy.

The Artful Bodger
01-27-2012, 02:31 PM
Concrete seems to be fairly stable around here although I have heard that just up the road, near Christchurch, entire buildings are prone to rattle and dance around the place.:cool:

Concrete moves, yes, but how much movement in a casting that is 1 meter/yard long? Would there every be as much movement as I could measure with home shop tools?

noah katz
01-27-2012, 05:14 PM
How about regular concrete and going heavy on the rebar near the outer surfaces to increase stiffness.

Or get really fancy and triangulate and weld the rebar, for even more stiffness and I'd guess a big improvement in stability.

Mcgyver
01-27-2012, 06:15 PM
Concrete seems to be fairly stable around here although I have heard that just up the road, near Christchurch, entire buildings are prone to rattle and dance around the place.:cool:

Concrete moves, yes, but how much movement in a casting that is 1 meter/yard long? Would there every be as much movement as I could measure with home shop tools?

on this subject we must differential between cement and concrete. Epoxy granite is a concrete, what you're talking about is a concrete made with cement. What Hardingle calls Harcrete is epoxy granite for example, its a concrete but there is no cement to be found.

I would bet that the movement would be detectable by home shop equipment for a 1 meter length of cement concrete.... but I can't quantify it. How much does a machine tool need to be out on an axis to defeat the purpose? We know bridges and buildings flex but the concern is isn't deflection from load; its well known that it moves about while curing and takes years to fully cure. This tidbit combined with the fact the machine tool builders spend the premium for the epoxy is what I'm going with....If I'm wrong so the rest of industry who doesn't use cement because its not stable.

Mcgyver
01-27-2012, 06:22 PM
Or get really fancy and triangulate and weld the rebar, for even more stiffness and I'd guess a big improvement in stability.

re bar gives concrete extra strength (ie it won't break) in tension, can't see it doing much of to stop the movement while it cures unless you added a large %.....but in thinking fabrication you've got to what I always thought is the value of this stuff for the diy machine maker; filling heavy fabrications. Steel gives the strength and the epoxy granite the vibration reducing ability. I think you'd want to stress relieve the fabrication first though

The Artful Bodger
01-27-2012, 06:45 PM
I imagine a practical method for a home shopper to make a concrete machine would be to first weld up the basic machine in skeleton form ensuring that critical parts have thick enough metal to allow post machining. This skeleton machine would then be boxed up in formwork material of choice then filled with the concrete/cement/resin mix or whatever.

It would be quite a challenge to cast a hollow headstock for a gear head lathe this way but I think a more traditional back geared headstock would be achievable.

Small 'castings' would be much more difficult than large ones, I think.


Hmmmm, I wonder what would be a likely candidate for trying this method of construction?:rolleyes:

darryl
01-27-2012, 09:11 PM
I would like to try a sharpening machine, personally. The vibration-dampening ability of E/G would seem to make this an ideal use. I have not strayed from my ideal of including a steel framework within the mix as well.

One thing I have been thinking about lately is making the mold, or at least lining the mold with plastic laminate. All corners would be sealed before the pour, of course, and the laminate becomes a permanent part of the structure. I have been considering adding a layer of heavy fiberglass to the inside of the laminate, allowing it to set up an appropriate time before continuing with the pour of E/G (or E/Q). The laminate is mostly cosmetic, but does add some freedom from air diffusing out of the mold structure and into the E/Q mix. The fiberglass would act to strengthen the structure, while the E/Q would add weight and damping. I've also been thinking about making the reinforcing framework with fiberglass.

You almost cannot avoid having some threaded steel fasteners molded in, so these can be fastened in place with bolts through the laminate and glass cloth layer. Then bundles of pre-soaked glass 'rope' could be strung around the fasteners and made into the framework, which is subsequently surrounded by the E/Q mix. Maybe you would tamp in part of the mix first, then add the glass rope, then more mix- this might make it easier to lay the rope straight so it gives maximum tensional support for the filler.

In any event, a reinforcing framework gets included within the casting. The choice of laminate is a personal thing, for color and texture, and gives a wide range of options as to what you want the final thing to look like.

Elninio
01-28-2012, 01:00 PM
can epoxy granite be machined? i think i saw that somewhere

JoeLee
01-28-2012, 06:02 PM
The epoxy can be machined but the granite can not. It would have to be ground with diamond abrasive pads. So if you had granite chips in the epoxy the entire surface would have to be ground with the diamond pads and water which works best.


JL................

darryl
01-28-2012, 06:03 PM
Yes it can be machined, but this is territory where you are pretty much defeating the advantages of using it. If it is used as a filler for steel columns, etc, it shouldn't need any machining at all. If it's used as a base, either alone or cast around a framework, you would make all the visible sides inside a mold so it comes out in net shape. If you have need of fastening points, these should be included in the mold and not added afterwards. You can drill it, but why make it difficult and expensive for yourself- if there are to be holes, then you would include cores for those holes in the casting before pouring.

If the machining was required to correct a twist or to level a surface, then you wouldn't have prepared the mold correctly to begin with. One significant advantage of the molding process is to be able to eliminate the need for subsequent machining.

noah katz
01-29-2012, 06:57 PM
I was thinking that if triangulated, the shape would be determined by the high tensile/compressive stiffness of the rebar.


re bar gives concrete extra strength (ie it won't break) in tension, can't see it doing much of to stop the movement while it cures unless you added a large %.....but in thinking fabrication you've got to what I always thought is the value of this stuff for the diy machine maker; filling heavy fabrications. Steel gives the strength and the epoxy granite the vibration reducing ability. I think you'd want to stress relieve the fabrication first though

darryl
01-29-2012, 08:52 PM
Triangulated works for me. I've always figured that if you can keep the compressive and tensive forces aligned with the direction of the framework members, you will have the most resistance to twisting. I'm a little rusty with this now, but if you compare a triangular box with a cube, you should find that the cube is more flexible if you apply a twisting force to any side. I need to study this again for long sections of four sided vs three sided box beams. I think the cube benefits most from the addition of the last side, whereas the five sided box would be inherently stiffer without one of its sides. If the triangular box was four sided, that probably is the stiffest shape possible when using simple flat sides. A person could nest several of these shapes together for a bed structure, for instance. It would be crucial for the corners of this shape to be well fastened together.

dian
01-31-2012, 03:16 PM
fiberglass is not especially rigid. aramid is better, carbon is best. expensive? compared to what?

ckelloug
01-31-2012, 06:06 PM
Hi Guys,

@Elninio
I've machined some of my experimental Silicon Carbide based polymer concrete with Cubic Boron Nitride TNG322 inserts. This would also work fine on Granite/quartz and probably not be quite as hard on the inserts. Silicon Carbide was really hard on the pair of 60 dollar a piece inserts but worked to machine about 64 square inches flat removing about 1/8 of material on my bridgeport.

There are some suggestions in Alexander Slocums book on precision tool engineering but:
If you want to make stuff with E/G, you typically either want to have made the item in a mold accurate enough that no secondary finishing is necessary or you want to have made the item such that the only important locations are defined by very accurately placed metal inserts embedded in the E/G. The third but least appetizing method is that E/G can be diamond ground or sawed about as easily as stone thus given a large way grinder you could potentially make an accurate E/G anything albeit expensively.

There is a guy on the model engineers workshop forum who has done a beautiful epoxy granite worden tool and cutter grinder. http://www.model-engineer.co.uk/forums/postings.asp?th=51617&p=1

@dian
Epoxy granite is not all that rigid. It's less good than fiberglass and without very expensive heroics, it does not approach aluminum in modulus or come anywhere near it in strength. E/G applications generally work against rebar due to differential thermal expansion and vibration transmission. E/G is good for two things, it can be cold cast to near exact dimension (doesn't shrink like cast iron) and it is a really effective vibration damper. It's also low water absorbtion, generally an electrical insulator, and not decomposed biologically.

The Worden grinder project linked shows how it is good to make items in the home shop that would otherwise involve having to do an iron or aluminum pour. It's also good for home shop projects where accurately placed linear bearings in a sturdy vibration damping framework are adequate and scraping type precision is not required of the surfaces themselves.

E/G is not a solution to all problems machine tool. It is somewhat expensive and difficult to optimize to every type of local materials. It is good because it has very low mold shrinkage, reasonably low thermal expansion, and is completely dimensionally stable after an oven cure. All of these properties are essential when you want to make machine tools that reliably hold .0001 inch type tolerances that don't drift due to material property changes.

Ordinary concrete is not dimensionally stable to the .0001 level and has mold shrinkage issues. The rebar needed to impart non-zero tensile strength transmits vibrations and has a different coefficient of thermal expansion than the concrete. A wood lathe made from ordinary concrete would probably work fine unless a large thermal dimension change caused the spindle to bind etc. A diamond lens turning machine from concrete would probably not hold tolerance well.

@Mcgyver
Having spent a lot of time in the library looking up history of E/G, people have tried polyester resin to make polyester concrete machine tool parts but the bad thermal expansion and water absorbtion were a failure. Epoxy concrete (E/G) was the winner in the precision cold casting of objects.

After a fairly extensive cost analysis, I've concluded that E/G is not popular because it is too expensive for most applications. Machine tools are one of the few areas that need the dimensional stability properties badly enough to warrant the cost. Certain types of electrical enclosures and manholes use E/G because of it's durability when exposed to the environment and it's tendency to remain an insulator even when wet. In most other applications I have examined, Epoxy Polymer Concrete (E/G) was not cost effective.

noah katz
02-01-2012, 03:59 PM
I'm surprised the modulus of E/G is so low; if I'm not mistaken that of granite is about the same as alumium.

What's the resin/granite ratio of E/G?

EVguru
02-01-2012, 04:44 PM
I'm surprised the modulus of E/G is so low; if I'm not mistaken that of granite is about the same as alumium.

The density is about the same, a fact I point out to people who describe Aluminium as 'light'.

Peter.
02-01-2012, 04:53 PM
can epoxy granite be machined? i think i saw that somewhere

I should think you could put a diamond wheel on a Blanchard grinder and grind epoxy granite or normal granite very easily. Diamonds love granite - much nicer to cut than concrete usually though the harder grades can blunt the diamonds. Compare it to cutting grey cast iron (granite) and mild steel (concrete).

One thing that granite has much more of than concrete is tensile strength. I can pop either with a hydraulic burster but the granite holds out much longer and goes with a bigger pop.