Regarding shaking to get wetting and remove trapped air. I recently cast
some parts for a glass blowing glory hole in a refractory castable. The
recommended water/castable mix ratio leaves it very stiff but I used a
needle scaler to apply vibration and it transformed it. Without the
vibration the stiff mix is very difficult to compact but when vibrated
it consolidates very well. I cast in layers about an inch thick and
placed a wooden block on the mix then used the needle scaler on the
block and worked the block over the whole surface until most bubbles had
surfaced and the mix compacted.

Ed Huntress wrote:

"Richard Nienhuis" wrote in message
. com...

I've been looking around the net for information on how epoxy/granite
machine bases are formulated. So far I have come up with very little.
I'm going to attempt to make a smallish mill with a somewhat homebrew
epoxy formula. If anyone knows anything about these sorts of things
feel free to speak up.

For the base material I'm using the folowing formula:

First I will use quartz rock etched with a moderately strong HCL
solution.
The stones will consist of 1/2 to 1 inch stones.
For fine filler I will try a mix of 90% quartz sand and 10% carbon
fiber.
All the agregates will be soaked in silane and dried before being used
as filler.

For the mold I will use varnished wood. The steel dovetails will be
set directly into the epoxy plum.

Some problems I have a
Where can I get 2 or 3 gallons of epoxy and enough hardener?
I need to find some cheap ground dovetails.

I am probably going to need to make a couple small test batches. If I
cure the epoxy under heat and vacuume is there anything I can use to
seal it to reduce water uptake?

Anything else anyone can think of?


If you can get your hands on a copy of the June, 2000 issue of Machine Shop
Guide, we ran an article on the subject there ("Cast Polymer Machine Tool
Bases"). It isn't as technical as you may like but there's lots of basic
background info, including the names of the three US companies that make the
bases on contract.

There are a few other points: The epoxy you want for this job is not the
laminating or repair epoxies made for boats. You don't need their adhesion
quality and you don't want their high exothermic rates. I don't have a
source to send you to but look for *industrial* sources of casting epoxies,
not laminating epoxies such as WEST System or System 3. You'll save a bunch
of money, besides.

Your idea for the aggregate sounds reasonable. They use multi-graded
aggregates of granite or quartz in the commercial jobs, with one builder
stating they grade their aggregates from near-dust to pieces roughly 1/2-in.
on a side.

If you're looking for a cheap but effective way to do this job, you may want
to consider using some form of concrete for the mass of material, possibly
with an epoxy/aggregate structure on top of it. Oh, and don't try using it
for a headstock. The thermal conduction is too low and you may run into
serious thermal distortion problems. Another point: commercial polymer bases
are built on shake tables. I've never handled a stone-filled epoxy mix
myself but it sounds like you have to shake it pretty good, more than you'd
want to try shaking regular concrete, to get good wetting.

Good luck. I used to write about concrete and polymer bases but it was many
years ago, when Studer was the only one using epoxy. The article I refer to
above was written by Frederick Mason. He's pretty thorough on his research.

Ed Huntress