Tumbler Build - For cleaning plasma cut parts.

Yes. That should make it also easier to fill the voids. I did say "should" !
Can you wash and dry a hand full, see how that end up.
Somehow, i keep thinking that would end up very near to a cast iron frame in weight.
Edit:
I was wrong, it is more than 3 times heavier:
Sand, dry weighs 1 631 kilogram per cubic meter
Steel 7850 kilogram per cubic meter

the thing with E.G. is keeping the resin content low since that is where most of the cost lies. small fillers like sand work well for compacting tight but takes a lot more resin to get the wetting needed to bind it all together well. filling large tubes would be more forgiving since it would not have to be as wet to get the nice casting.

the extra weight would be an added plus since the more weight a machine has the harder it is to get the frame to vibrate. i don't see why the mix could not be modified to add the waste metal from the plasma process.

if you get into the hard core E.G. talks the experts would probably disagree with the idea but i think most of the talks get into to much theory and not enough trial and error to make advancements.

it's not very complicated in material composition and epoxy is pretty forgiving with moisture as well. i would still dry materials before making a batch but it is not the end of the world if you only get 95% of it removed.

i have seen talk of using ultra high fillers like sand blast media but i think that's just a waste and adds extra cost to the process.i think most of the dampening comes from the epoxy honestly. keep the fillers cheap and you still get a material with compressive strength the same as concrete. the mix i did failed at about 3000 PSI which is the same as standard concrete so building the frame from tube keeping the main goal of dealing with rigidity and deflection up the the task of the tube frame on it's own for the most part and adding the E.G. for the assist of extra weight and vibration dampening because that's what it is best at make for a good frame to build the rest on.

Could you do a sketch of what you think a VMC frame would look like from tube? What size tube would I use? Rectangle or Square?

depends on how much foot print you can live with and what kind of travels you are looking for? Z height would be an important part of the needs list.

a fixed bridge is going to be more rigid but the foot print is bigger since the table moves. the typical average VMC is not huge as far as travel goes. the average size VMC might have 24" x 48" of travel on the X and Y axis and maybe 20" from the spindle to the table. so they are not huge on travel but are rock solid because the base is cast iron and weights a several tons with the table usually cast iron as well on the commercial machines.

if you built a gantry mill where the gantry moves you can get a 5' x 10' X and Y axis easy enough but the Z height is going to be tough to get very tall since the higher you go the harder it is to keep things solid.

i think with a welded tube frame the shape of the tube is not that critical, but since it would be filled something rectangular might be better on a longer span. the epoxy does shrink some but it is a very small amount (.001 imperial seems to be where most fall ) i think as long as the tube is thick walled material at least .188 or better things should be pretty solid filled with E.G.

you gain some rigidity from E.G. but i would design the frame to do the bulk of the support. the E,G. makes the frame more like cast iron because the tubes can no longer resonate because of the fill and act more like a cast iron base casting of a VMC.

so the size of the work area is going to be a big factor of what you need to figure out so you can build the machine to suite your needs.

then you get into spindle considerations based on what you want to cut after this. so there are a lot of things to think about first.most commercial VMC usually come standard with a 10,000 rpm spindle. high speed spindles can be good for some things like Aluminum machining since really high speed spindles can let you approach things are really high feed rates. but if you get into the steels you can't run that fast anyways so this is probably why 10,000 is standard and a happy medium on most commercial VMC machines.

I would be happy with 24"x48" (600x1200mm) and I want to machine steel.

I was thinking of the plasma sludge and I think I could strain out the large chunks of steel easily and dry it. I am sure it would add a far bit of weight to the frame, I am happy to give it a try.

I just cant imagine how I would go about making the frame out of tube, would I butt a couple of pieces together and weld them then machine the top and bottom flat?

there was someone over on cnczone that did a linux build i was impressed with the concept. he did a open rib arch design that was E.G. filled that was a moving gantry design i think. i will have to see if i can find it and put a link up for you. he was doing machining on everything it worked that well.

any design that uses the frame work as the mold would work well. it's just a buggers to remove and if you pour and let set and are done with it saves on the cost. materials for a mold add up to extra cost.

i will look for the build i am thinking off though and post a link.