I've seen cement as the pilars of a big Tricept type parallel machine. They use special type of concret with epoxi or similar aditives.
I've heard of similar termal expansion coefficientes for steel an concret, and of the good vibration absorbing properties of concret. I think that the aditives, can help both on the tensile strength and on the vibration disipation part too. Just my two cents, Javier On Mon, Nov 14, 2011 at 5:20 AM, Dave <e...@dc9.tzo.com> wrote: > Concrete is fine for compression loads. You can mix 5000 psi concrete > pretty easily. However it has very poor tensile strength. They say > 10-15% of the compressive strength. Fiberglass has a much higher > tensile strength. > That is why concrete has to be pre-stressed to be used for tensile > applications. > > If it was a great material for machine frames, the machine makers would > be using it. My lathe has a bunch of it in the base- the block is > about 3feet wide - 12 feet long and 14-16" tall. But I think they put > it in the base to > brace the structural steel frame and take the "ring" out of the frame so > it would be difficult for it to resonate. > > Dave > > > On 11/13/2011 10:50 PM, Jack Coats wrote: >> It was Lucien I. Yoeman that patented this back during WW1, not WW2, >> for shell turning. >> http://xa.yimg.com/kq/groups/13335163/1942903983/name/MM++lathe+How+to+Build21a.pdf >> has a picture of the lathe and team that built it. I found his >> patents on patents.google.com >> some time ago. Good but not overly enlightening reading. >> >> No reason not to use this technique to build just about any machinery >> that could use a very stable >> base (lathe, mill, laser cutter, plasma cutter, etc) >> >> The cement is great because it doesn't take rocket science to get a >> stable base that hold >> together. >> >> A friend sells chemical additives for putting in concrete to change >> it's properties >> but for most projects a simple 1,2,3 mix or sacked concrete mix works >> well. To make the >> concrete stronger, use less water, rather than more. >> >> My suggestion is to build one (or more) as an experiment. Most of >> what is needed doesn't >> need steel reinforcing, but putting it is doesn't hurt. A local >> manufacturer makes steps for >> fire stairs, he puts in bolts and leaves the threads exposed about an >> inch. He uses stainless >> steel to ensure they don't rust. So if you want to cast in some >> attachments for long term use, >> stainless is a good option. If it is just for use for a 'few years' >> galvanized or cement covered >> is OK. ... Just my thoughts. >> >> >>> <> ... Jack >>> >> Whatever you do, work at it with all your heart... Colossians 3:23 >> >> On Sun, Nov 13, 2011 at 8:46 PM, Chris Reynolds >> <c_reynolds2...@yahoo.com> wrote: >> >>> I belong to that group, there is some interesting information there. I was >>> under the impression that during WWII using concrete in casting large >>> machine parts was used because of lack of raw materials, and fairly common. >>> I've always thought it would be fun to experiment with this technique, not >>> only for a lathe but for a mill as well. >>> >>> >>> Chris >>> >>> >>> >>>> There is a yahoo group re-developing making a lathe from concrete. >>>> They are baseing their stuff on a guy that made lathes for turning >>>> large projectiles for the Navy. He had a couple of patents. >>>> Basically he had a jig to hold his metal pieces that define the >>>> critical dimensions. He poured the lathe, waited a couple of days, >>>> un-did the forms. installed the jig and some metal pieces, then >>>> poured a low temp metal alloy he developed (formula is lost) that >>>> didn't shrink or expand when cooled to hold the metal pieces in place >>>> in the concrete. >>>> >>>> Anyway, email me directly if you want to get the link to the group (I >>>> just don't have it at hand or I would put it here). >>>> >>>> ... 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