Talk:Lathe Build: Difference between revisions

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== Spec ==


What are the needs?
*Length, diameter of object?
*Tolerances, including surface finish?
*Manual or CNC?
*Material to be turned?
*etc
*RPM range?
== Danger ==
20HP at low rpm involves HUGE forces. This is going to be seriously dangerous because many of the possible failures would be catastrophic and faster than a human operator can react. Much smaller lathes cause fatal accidents from time to time. Breakage of the tool support or failure of the workholding would quite likely lead to big bits of metal flying about. Extreme caution is justified.
The proposed XY table is not intended to support anywhere near the max load that the hydraulics can apply. Most cast iron will fail fast (shatter).
A much smaller version may be a rewarding use of time to prove the design at reduced scale, cost, risk of failure, and danger of fatal or crippling injury.
== Materials, Rigidity ==
Pro lathes are usually made of the fewest thickest possible pieces of cast iron, for rigidity and damping. If mild steel box and sheet, bolted or welded, was good enough then I would expect to see examples out there. If it's easy and cheaper and the Chinese won't do it then it probably doesn't work. I'm not saying that I'm sure it won't work, but I think it won't work at all well, unless it's small and made of very thick stock. If any machine tool is insufficiently rigid then the cutting edge chatters on the work piece, giving a bad finish, rapid heating of the tool, and rapid tool failure. Also, cutting forces cause the machine to elastically distort, quickly introducing very large errors. 
Without defining the spec, I'm not sure what to advise. The only materials that I'm aware of for machine tool frames are
*Aluminium alloy, on small cheap low precision or soft material tools
*Cast Iron, on most machines. Well proven.
*Synthetic or real Granite, on super precision moderate mechanical load machinery
Synthetic granite is made from ~80% granite powder with an epoxy binder, and has ~9x better damping than cast iron but much lower tensile strength. I'd like to experiment with machine tools made from a synthetic granite modified with chopped strand carbon fibre, but that's an unproven material. [[User:Leo.dearden|Leo.dearden]]

Latest revision as of 20:49, 22 November 2009

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