[johnohara]

This thread is meant to provide a practicum for the application of Epoxy Granite (Mineral Casting, Polymer Concrete).

From test samples to filled bases to large scale machines to precision gantrys to metrology tables and more, all photos, videos, links and comments are welcome.

Please assign appropriate copyright notices where necessary.

To learn more about the theorectical use and application of Epoxy Granite, I highly recommend reading the thread entitled "Epoxy-Granite machine bases."

Once you have increased your understanding and are ready to give it a try, please feel free to share your work here.

~John

[johnohara]

The first post in this thread should rightfully pay homage to walter, lgalla, ckelloug, greybeard, jhudler, brunog, martinW, Geof, and the many others who continue to make the original Epoxy-Granite thread so interesting.

Thank You.

[lgalla]

Here is a good link from WilliamD
http://www.cnczone.com/forums/showthread.php?t=33434
Larry

[johnohara]

Page 2 of this article describes using concrete for the lathe bed.

http://www.vintageprojects.com/machi...urretLathe.pdf

~John

[johnohara]

5 grades of Al2 O3. Nice stuff to work with. I prefer it to the silica.

I remember seeing very high precision systems at the last IMTS show that looked just like this.

Al2O3 has a Mohs hardness of 9.

1. The resolution of the cast is very nice.

2. From the side.

3. Close-up 1 from the side.

4. Close-up 2 from the side.

5. The bottom showing bug holes.

6. Better close-up. Shows density of material.

~John

[johnohara]

This mineral is a joy to work with.

1. Latest cast piece includes sharp edges.

2. Close-up of the mixture. Still using 5 different sizes from mesh 30 to sub-micron. Changing the percentages as I go.

3. Close-up of letters in the plastic bowl. The lines are .50mm wide. What appears to be a bug-hole is actually particles.

4. Close-up from the side. This piece is untouched. No sanding or polishing. I hand-vibrated it.

5. Bottom view.

Dental vibration table is on order -- due in a few days.

~John

[rowbare]

Wow those samples are really looking good. Have you tried taking a hammer to them yet?

I like your approach, there is something to be said for intelligently iterating through a set of options. While the other thread has done a great job of determining what should be possible you are doing a great job of showing what is possible.

kudos

bob

[johnohara]

rowbare:

They're still curing. It takes patience to not touch them too soon (fingerprints).

I took some of the silica samples to my friend's granite shop and had the guys cut it. It scorches the same as quartz countertops -- very hard.

Al Ox has a Mohs hardness of 9 and may be what the grinding wheels are made from. He has big diamond saws which might be needed. I'm going throw a belt sander on the top and then polish them at 3000 grit. I'm interested in how much air is still in there.

Both pieces are already waterproof. It rolls right off and dries with simple dabbing from one sheet of paper towel.

I don't think I'm going back to silica. This latest piece used 10% epoxy and probably could have been less.


1. Recycled glass just for fun.

2. Beer bottles I'm told.

~John

[johnohara]

Happy St. Patrick's Day !

Got a chance to stop by my friend's granite place. I was interested in seeing what was below the surface of AlOx sample 1 (the hockey puck).

First we hit the top with a belt sander. This stuff is hard. Harder than working with Mohs 7 granite that's for sure. It took time.

Then we polished it using a water polisher at grit 800 / 1200 / 3000.

Overall, the compaction is good. We know the surface resolution is okay. Lack of good vibration still yields microscopic bug holes. But it's close.

1. Top view, sanded and polished. The white discoloration is actually where it needed to be sanded further. I stopped because the belt was beginning to burn and smell.

2. Up close. You can see the bug holes. The aggregate seems evenly dispersed which is good. Note the sparkle. Part of the mix.

This piece is 10% epoxy by weight. I tried another at 7-8% but it's too difficult to work with without vibration. I don't recommend it. I'm staying with 10%. Seems to work best.

~John

[johnohara]

This is the 7-8% piece I mentioned in the previous post.

1. Top view. Dimensions: 380mm x 250mm 19mm (15" x 10" x 3/4")

2. Top shot with ruler.

3. Workability is affected by epoxy percentage. It's difficult to get the air out without vibro-compaction at 7-8%. The Zanite video shows the workers troweling the cast. But vibration is the key.

Another point. I think the 93% aggregate / 7% resin number is related to polyester resin not epoxy resin. Epoxy resin/hardener seems very happy at 10%. At least with AlOx anyway.

4. Close-up. Did I mention bug holes? The white blotches are thin layers of epoxy over more bug holes.

5. From the side. Shouldn't be difficult to get the precision everybody talks about.

The piece is heavy. Even at this thickness.

[lerman]

Hi John,

1 -- Am I correct that whenever you say 7-8%, you mean by volume?

2 -- Could you post the details of the mixtures you are using? What sizes and how much of each size? What epoxy/hardener?

3 -- It would be great if you could send some samples to ckelloug so that he could measure and tell us the physical properties? (I believe that Cameron has offered to do this?)

Ken

[mredican]

Could someone elaborate on "Al2 O3". Where can you buy it, how is it mixed, and so on? Thanks

[Geof]

Could someone elaborate on "Al2 O3". Where can you buy it, how is it mixed, and so on? Thanks

An alternate name for aluminum oxide is corundum; it is used to make grinding wheels, sanding belts, etc. One bulk source could be a supplier of sandblasting media.


Johnohara; Are you not using vacuum degassing?

[johnohara]

Geof:

I don't own adequate vacuum equipment for industrial degassing. I've based much of this process on the fact that commercial casters seem to rely on vibration rather than degassing (i.e. the Zanite video). The Scott Bader video calls for degassing but the mix is more a slurry with a high epoxy percentage.

Doing is learning and I'm getting better at working with the material. Have you tried to cast anything?

mredican:

Al2 O3 is Aluminum Oxide, aka Corundum. It's used as an abrasive and comes in a large variety of sizes (36 - 1500). It has a Mohs hardness of 9 but more important seems to work better with epoxy than does silica. More expensive tho'. You won't be buying 50lbs for $10.00 that's for sure.

~John

[thehairs]

I am wanting to build a Gingery style lathe and use a mineral cast base. I want to cast right on top of the piece of colr rolled I will be using for the bed way. I'm think of using sheet metal for the sides of the mold and start by using epoxy to glue the sheetmetal to the way and have the way attachments already drilled amd mounted before the pour. now comes the problem. I'm thinking of using waxed foam to form the voids I want in the mineral casting. Would the epoxy eat through the wax and attack the foam. I am also thinking of casting the base with several pours about 1/2 to 3/4 inch thick. do you think doing several thin pours would make getting the air out easier.

Thanks
David H

[keebler303]

With styrenated resins, like polyester or vinylester (standard "fiberglass resin") you have to be careful because the styrene will eat polystyrene foam. Epoxy will not so you should be fine. It would be easy to test a small piece to make sure though.

Matt

[thehairs]

So, it sounds like as long as I use epoxy I won't even have to wax the foam. Have you done any mineral casting? If so what do you think of the casting in layers.

D.Hair

[keebler303]

I work in composites, no mineral casting but some resin casting with other things in them. If you just use the foam, it will be stuck, but you can rip the foam out and you will be left with a fairly clean shape. Wax will make it a PITA to bond to later if that is your intent.

Casting in layers is not recommended because you may not get a good mechanical bond between the layers.

Can epoxies be bonded to cured epoxy?

[thehairs]

OK. What if the layers were about 1 1/2 hours apart. That would still be in the early cure stage. The reason I was wanting to layer the bed is where I could work all the air possible out of the first layer before pouring the second. Sorry to be picking your brain, but this is my first attempt and I hope to get it right thr first time.

David Hair

[keebler303]

I'm not a chemist so I can't say what the effect will be. If you rough up the surface between layers, it should be fine. All the casting I do is vacuum degassed before pouring or while in the mold. In some cases, a propane torch quickly moved over the surface will help to burst the bubbles near the surface.

Matt