[karmicthre]

I think I've posted about this idea here before. I made a small piece of it today and thought I would post up the results.

In all I ended up a fairly strong piece. I made a 2in Dia x 1in disk by using a waxed paper cup and some loctite Metal and Asphalt 5 minute epoxy. I'll let it cure for a day or so before I start smacking it around. But so far it is amazingly hard. even though I only used pea stone instead of the quartz.

In order for me to go forward though I am going to have to find a suppier for maybe a gallon of metal filled eopxy and hardener. I will also need a cure extender and something to lower the viscosity. A shaker table and vacuum pump wouldn't hurt either.

Anyone know any good sources for this stuff? Loctite seems like they might be a bit pricey for the epoxy supplies. Also once I get the formulation and casting quantified a bit more, would anyone be interested in bases cast out of it?

[chuckknigh]

Try looking up the names Moglice and JBWeld. Both are available in large quantities, and both are used for casting stable parts. Not sure about their use as a base, but they definitely can be used to make nuts, etc.

I think their site names are the following, but I haven't checked.

http://www.jbweld.com
http://www.moglice.com

Why use expensive polymers for a base, though? Why not good old fashioned concrete, or similar? Do they have properties that are, in some way, more desirable than concrete?

-- Chuck Knight

[SPEEDRE]

when i was a compression mold maker i used a product from HAPCO. it was an aluminum filled epoxy alloy, very hard, machineable, threadable material. has extenders and retarders avalible in colors, gray, black, white. both air dry and post cure setups avalible in one gallon units, approx. $ 95.00 for a twenty puond unit. some preheating might be nessessary at 125 deg. for 45 min. should be a snap to press bronze bushings for bearing surface. oh, a 1 gal. unit filles approx. 350 cu. in. or just shy of 21 lbs. try HAPCO.COM

[SPEEDRE]

when i was a compression mold maker i used a product from HAPCO. it was an aluminum filled epoxy alloy, very hard, machineable, threadable material. has extenders and retarders avalible in colors, gray, black, white. both air dry and post cure setups avalible in one gallon units, approx. $ 95.00 for a twenty puond unit. some preheating might be nessessary at 125 deg. for 45 min. shoulb be a snap to press bronze bushings for bearing surface. oh, a 1 gal. unit filles approx. 350 cu. in. or just shy of 21 lbs. try HAPCO.COM

[vacpress]

im not an expert - but i really doubt a sinlge resin-cast part used as the base for a CNC machine is a good idea.... there are a few reasons i think.. the main one is cost vs performance compared to other materials.. te other is my belief that poured liquid resin plastics are not dimensionaly stable over time, or in different environments. I think a big casting made of that material would have all kinds of problems with sinks, uneven walls, etc. and then it would all shrink and warp... another similar, probably not that usefull material could be fiberglass enforced bondo... Still. i doubt bondo would make a dimensionally stable base..

i would imagine even MDF would make a more stable base than an epoxy casting, but aluminum would be far better, and maybe even cost a similar amount of $$ - assuming you have the equipment to work with it... but casting alrge resin parts also requires equipment... a vacuum setup is pretty vital, and so is a digital scale.. i have done lots of small castings, in lots of materials... so i do speak from some experience...

concreete is an idea.. possibly as a base slab... make a precision gig that lets you sink hardware into the wet casting, so you can bolt other parts on... that may be cost effective compared to using an all metal base... and also nice and stable... molds maybe could be produced with expanded foam...

i think i have heard of other, more appropriate resin-type plastics, but i bet they cost alot of $$
ideas?

[karmicthre]

The problem is you can't just dump a bunch of resin in a mold and expect repeatable results. You need to get a decent low expansion epoxy, one that has a simmilar coef to steel works fine. You need to wash everything with a solvent. The big thing is, you need a shaker and a vacuume pump for your mold. That way all the agregate is firmly packed. Also the vac will remove most of the problems with voids as long as you are not using too viscous an epoxy. I'd like to do some experimentation, but I lack the $ to setup a proper experiment and my physics classes are taking up too much of my time. If anyone has the time and money to do it please post your results here.

[ESjaavik]

Today a lot of machines are made from quartz(sand) and resin. The ratio of binder and different sieves of quartz is important to get strength and stability. The amount of resin is small as it is a binder "glueing" the quartz grains together. The different sieves are necessary to essentially fill the volume with quartz. Done right, the quartz will be the material that determines the expansion/contraction. For each metre of casting, only a tiny fraction will be the binder between the grains. So any expansion/contraction of resin will have very little influence. The end result will be more or less a stone cast cold in a shape of your desire.

This has been discussed on a German forum Peter's CNC-ecke for those of you that can read the language, here is one thread: http://5128.rapidforum.com/topic=115181924767

It's a quite interesting subject, as the result is thermally and in other ways stable. Also it is good at absorbing vibrations.

Examples: http://www.epucret.de/maschinenbau_anwendungen.html

[svenakela]

> The problem is you can't just dump a bunch of resin in a mold and
> expect repeatable results. You need to get a decent low expansion epoxy, ...

I have to add a bit here.
Yes you could, if the mould itself is stable and precise. Epoxi (or epoxy) is not expanding nor shrinking when its hardening, and it doesn't expand when it gets heated - but it softens. But to make sure you get the strongest piece out of your mould you must have a heat resistant mould that can be placed in an owen, epoxi that is heat treated (it's called "to push it") during the curing face gets a lot stronger and more heat resistant. I've been making sheet metal pressing tools for the car industri in plain epoxi running for years without any fatigue.
Epoxi is a fantastic material, but I think it's not the best price-per-performance-solution for a hobby machine. But if you decide to go for it, be careful with the liquids because they are extremely allergic developing. Good luck!

Cheers,
Sven

[steveg]

http://www.itwpolymercastings.com/
http://www.rockwellautomation.com/an...ymercomposite/

or maybe it's a good idea after all

[steveg]

Karmicthre the product that you might be looking for
http://www.itwresintech.com/pages/grouts.html
CWC 604 machine bond