Mini lathe spindle mounted on bearings in 2-1/2 in. AL schedule 80 pipe
Not sure if I am going to drive with DC motor or stepper. Right now I have a #25 60-tooth sprocket to use with stepper. Bearings are 6206-rs. Will see about casting block around spindle. Trying to decide between fiber reinforced concrete or epoxy granite.
Aluminum is easy to pour. You could use that. Be like Dave Gingery.
@Paul_Frederick Yeah, but I really wanted to go with more mass than that. Besides, I wanted to test out new materials to play with.
Epoxy. Way cooler 
And when you want to work it, it won’t destroy your tools.
@David_Kirtley
Fiber reinforced concrete is nothing new to me. I’m not a big fan of it either. I poured concrete for 10 years in the union so I’ve seen a lot of the stuff. I’ve busted a lot of concrete up too. Some fiber. Fiber is better than nothing, but not much better. If you’re really going to use concrete I’d suggest you plan on some kind of steel reinforcing. Steel is the real deal. Fiber is a waste of time. I’d take a couple strands of ty wire over fiber any day. In theory fiber sounds like a good idea. But I’ve never been impressed with its real world performance personally. I think some college boy dreamed it up to get around building codes. You want some texture on the steel you use, so the concrete can grip it. I’ve busted up machine pads that just had some chicken wire nailed to the slab. Even that can be pretty tough. Tougher than I’d give it credit for being before working on it. Tougher than fiber concrete ever is, way tougher.
For what you want to do you probably want some kind of special concrete too. You know the kind without any aggregate in it. What you probably want is a high performance patching mix. Some of that stuff is pretty amazing. Too amazing in fact. Be very wary of products that claim to be fast setting. I’ve seen some of it setup so fast I couldn’t even mix it.
It ain’t just me either, no one could mix it! We ended up mixing it in the hole we wanted to fill. Almost lost a trowel doing that too. But that particular mix was just crazy. I think it was called Octoconcrete? On the bag it said it was 8 times stronger than concrete, and setup 8 times faster too. I sure can vouch for the fast setup time. Sometimes outrageous claims are remarkably true.
I have enough bearings and pipe to make at least 5 more to experiment with. For prototypes, I am using cheap ABEC1 bearings. At about $2 each, I don’t really worry too much about them. If I find a solution I like, I will put the tapered roller bearings I have into it. I will probably put 1/4 in spines on the tubing to lock into mix. Once I find what I like, I have some 20mm supported rails I can mount to another block for a bed.
Options I am considering:
Plain cheap crack resistant big box store mix + 3mm braided dyneema reinforcing. Possibly with a 2oz twill glass wrap to keep it together and seal the concrete.
Countertop mix of AR glass, plasticiser, and aggregate with an epoxy seal
Molded glass/epoxy shell with pour in grout filler. Could also include some unidirectional carbon fiber that I have “just because”
Pea gravel, sand, chopped strand, and fumed silica with an epoxy binder. Would be fun to play with but maybe not as the epoxy I have is pretty hot mix for that much volume.
@David_Kirtley
Stranger things have been known to happen. You know to oil the form right? You don’t have to, but it helps.
Head on over to http://cnczone.com and look up the discussions on “epoxy granite” and “polymer concrete”.
http://www.cnczone.com/forums/epoxy-granite/30155-epoxy-granite-machine-bases-polymer-concrete-frame.html is a good start.
From the reading, a proper mix of various sizes of aggregate is key if you’re looking for the best damping in your structure. Maximize the aggregate fill factor, which also reduces the volume of epoxy you use. Slower cure is another key, produces less thermal expansion and distortion. Overall, I’d stick (heh) with epoxy.
@Mark_Fuller
Whenever I read CNCzone I get the impression that nothing works but Gecko drives and Mach3 software. That kind of lowers the veracity of the site for me.
I just ignore those guys still living in the Windoze XP/Pentium II era.
It’s a great site, with boundless amounts of information and informative people.
I’ve read though most of the cnczone epoxy granite form and i must say i have plans to follow that route when i go to make a machine that can handle much heavier work. the key is to get a good mixture of agragget and to shake the mold vacuum would also be a huge help. be sure to plan out your fasteners and embed them into the mold since i doubt your going to do much drilling or tapping once its set 
In my opinion, the only definite advantage of epoxy over cement as a binder is cure time. If the mix is properly designed, It doesn’t really make much difference what the binder is. The entire load is carried by the aggregate. Yes, it dampens vibrations a bit better but there are other ways to handle that. It is more chemically resistant but you can put a coating of epoxy over cement based concrete as well.
I think the big concern over concrete is shrink and the fact that concrete can take a very long time to FULLY cure. It may be hard enough after a day or two but the reaction is far from complete.
Yes, it can take some time but as far as the shrinkage, it is not really the issue that people make it out to be. It is like saying that a brick wall will shrink because the mortar cures. Cement by itself will shrink. No argument. The lime hydrates and the structure changes. Aggregate doesn’t shrink. A properly designed mix will be supported by the aggregate and not the cement. The cement cannot squeeze and shrink the aggregate.
@David_Kirtley
Well concrete expands, and contracts due to changes in temperature. That is why control, and expansion joints are put into concrete. I still see slabs crack where they are not supposed to anyways.
Water is the big killer for concrete because it doesn’t expand and contract at the same rate as the concrete and water will actually expand when freezing. By itself, concrete has a lower coefficient of linear expansion than steel or cast iron.
