[RotarySMP]

Don't forget that the same weight of cast iron (which would be a thinner section) would also fail that sledge hammer test.

A sample which would pass that test would not be representitive of the desired properties of a machine part (100% epoxy would pass the test, but would not be rigid). For machine structures all you are looking for is rigidity and damping (and thermal, chemical stablity etc).

The beauty of polymer cement is that strength can be acheived by simply adding wall thickness to a feature to acheive the required strength. With Cast iron, that is very differcult as you need near uniform wall thickness of features in a pour.

The rigidity is in the aggregate. Try to add a mix of aggregate sizes up to about 1/5 the smallest feature size.

[harryn]

Hi - I was curious - did you find any methods to make the surface "self level" so it did not have to be flipped over from a flat plate ? I am imagining here that if it were a liquid and given enough time, would flow out - sort of like honey - but maybe that is not at all where this material is.

BTW - good luck with your new baby. My youngest (now 9) was born early as well. That is a lot of work, and it was touch and go for a long time.

[lgalla]

Harryn,Yes epoxy can self level to I beleive .005.This is neet or unfilled epoxy as a surface poured on the epoxy granite.Epoxy surface plates are covered in polymer concrete frame.Sorry don't remember post's #.Check www.precisionepoxy.com for ESP
Larry

[davo727]

Hey williamD- Are you hitting the unbreakable one with a full size long handle 8 lb sledge? Thanks, Dave

[Mussel Kar]

Wow! I thought I was one of the few who used poly concrete. I use several tons per year and have a few small tidbits to add. For internal threads I use standard concrete anchors, the type that are used by drilling into the concrete and epoxying in (sim to the ones that failed on the "big dig" project). Only difference is that I have precise holes in the mold where these anchor points are bolted in. They come in a lot of standard thread sizes and are fairly inexpensive. Regular past wax works fine for a release agent. Vibrating is something I do not really need yet but here is an observation. A concrete vibrator does not seem to do little more then burrowing a hole into the mix. If you gently move the filled mold back and forth you will see the mix also slowly move back and forth and it will settle nicely. Move it a whole lot faster and the viscosity prevents if from setteling any faster. Vacuum seems the best way to go, but not for me right now. Another trick I sometimes use is to take a propane tourch and quickly play it back and forth over the surface to pop the air bubbles. I think the heat helps a bit, but I also think the CO2 is the bigger factor.
I'll post some pics later this eve when I get to my shop.

[kentavv]

Epoxi (or, epoxy as some write it) is extremely allergy developing! Gloves is a must!!!

Just as a side comment... I know I guy who built a composite plane - one of the many Long-Ez like variates. He consistently applied chemical cream to his hands and then put on gloves (a belt and suspenders guy). So far so good... but he would wipe his glove covered hands occasionally on his pants. Before the plane was complete he became allergic to the epoxy. To this day, over a decade later, if he enters a room where composite work is being done he breaks out, apparently just from the smell. Pretty amazing really. BTW: He struggle through and did finish the plane.

[WilliamD]

I know it's been awhile, but time for an update.

I've actually been following the main polymer concrete thread this whole time, as well as other CNC related projects, but I figured it was time to come back to this one.

I bought a good vacuum pump for some veneering I'm starting in woodworking, which will also work for vacuum pressing my epoxy granite molds. So I have the vacuum setup, as well as a container to vacuum the air out of.

So I used the same sand as last time, but being a complete newby as this, i have some observations and need advice.

First, I tested the vacuum out on some marshmallows. They did the classic thing of expanding really large, then when the vacuum was released, completly collapsed on them selves.

So next, I tried it with a mix of epoxy granite. I had a thin set epoxy with a 15 minute pot life hardener. I did 20% by volume epoxy, which had a good wet consistency.

I then pulled a vauum on it. It did the same thing as the marshmallows, which I did not expect at all. The tupperware was about 1" full of sand and epoxy mix. It was about 3 inches tall with full vacuum. The bowl was only 4 inches tall, so I was afraid the vacuum would suck up the mixture. Oh, and I'll have video of this pretty soon, with some pics. Just playing around for the moment.

So I even tried to use my random orbital sander to vibrate it a bit, but it didn't seem to have an effect. When looking at the sides of the container, I could see air bubbles everywhere, but they were just suspended there.

So I let it run for maybe 2 minutes, then released the vacuum. It did shrink down considerably, but also created this large crater in the middle. I think I released the vauum too fast. I need to build a resovoir for it. The mixture did pull away from the sides, like it had shrunk. Kind of hard to explain. The video will do a bit better.

But I haven't seem much about vacuum pressing the mix on the other thread. So I want to get any ideas and advice on this thread, for anyone that would like to go this route.