Lathe Build

Auger

Ben,

So here's my plan right now. Use a hydrauilic fixture with 20 hp that can be fixed to a table readily. This is what I have already on LifeTrac - a stiff auger mechanism:

Bill of Materials

Here is the bill of materials:

Bill of Materials

Lathe

Is it possible to convert the auger to a lathe? Sure. Take a chuck from here.

Add a slide from Enco. See review

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.

Comments

• The entire system is non-optimized. It is a generalized system that optimized interchangeability of parts, not performance. Performance can be optimized by further interchangeability. This is not a finished product, but an item that works for intended applications of milling motor couplers and boring steam engine cylinders.
• 20HP is max. It can be run from 1-20 hp.A 20 HP accident is no more fatal than a 1 HP and accident when it comes to machine vs. delicate human.
• XY table is absolutely too weak, but it is sufficient and cheap. Other suggestions are welcome.
• Marcin has significant experience regarding failure modes and behavior characteristics of hyraulics. Not an issue.

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 there would probably be examples out there (If it's easy and cheaper and the Chinese won't do it then it probably doesn't work). There are substantial risks that the lathe will work poorly or not at all unless it is 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, it is difficult to design. Materials for machine tool frames include

• 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. Leo.dearden)