CNC Multimachine Specification

Cartesian Precision Motion Construction Set – 3 axis motion systems for precision machining.

The basic design is for a precision motion system (down to ½ thousandth of an inch with zero backlash) based on a modular design of structural holding table, drive, and structural precision rail system for linear motion. Further, this precision motion system is extensible, or scalable – via a mechanism for attaching consecutive motion system members to extend the length of the precision motion system.

• Force requirements are 1000 pounds of downward pressure in drilling operations
• Force requirements are 1000 pounds of sideways pressure in milling operations
• Table workpiece holding requirements are up to 500 lb workpieces
• Basic size of precision motion module is 9 by 18 inches for the rail and table
• These modules can be added linearly to accommodate any length of machine, such as a lathe with a 6' bed
• The componentized structure of each motion axis should include: (1) precision drive: precision drive system such as a ball lead screw; (2) Rail system: rail/slide system to provide both precision and structural holding strength of the motion system while under the stresses caused by machining operations; (3) Reinforcement - a reinforcing component placed on the rail/slide system may be used whenever the motion system is scaled, which may be necessary to accommodate the additional strain associated with increased machine size
• Structural scaling may be obtained via addition of a strengthening module to the motion assembly. To accommodate this, a block with a large section modulus may be bolted or otherwise fastened to the surface of the rail/precision drive assembly. Typically, a workpiece-holding table is attached to the rail/precision drive assembly. In the case of machine scaling, an intermediate reinforcing piece may have to be used.
• Module can be arranged horizontally (lathe for holding chuck and tailpiece, or table of a mill) or vertically (such as the holder for the drilling head on a drill)
• Module is attached to a monolithic, concrete block to provide mass and structure to counteract vibrations
• Modules can be stacked one upon the other. This is clear for the x and y axes, but this is also the case for z motion, where the x and y axes can be attached to the z via a right-angle bracket
• These modules are operated manually with a turning wheel, but the turning can readily be retrofitted with stepper motors or servos for CNC control
• Modular rotary axis of motion is also a module in this design - for rotary precision motion

Design for Fabrication: Simplicity and Modularity

• Simplicity and modularity are the keys to keeping the fabrication costs of this precision motion system as low as possible. For this reason, a structural block of concrete is used as a base for the machine (horizontal or vertical). Modularity stipulates that once the design for a single axis is obtained, it can be used on the other axes – thereby simpifying both design time and reducing fabrication time as the same pieces need to be fabricated.
• Design for fabrication should be employed to simplify fabrication procedures, reducing cost
• The design should be such that the precision motion element is an off-shelf device such as a lead screw, but the structural rail holding system should consist of stock steel or metal. Stepper motors may be bought.
• Design assumes that in order to reduce material costs, stock steel can be machined, hardened, and precision ground. It is assumed that the fabricator of this machine has access to a surface grinder, milling machine, and a heat treating system such as an induction furnace that can be used to harden materials as needed.
• Modular reinforcement for scaling linear axes
• Assumes stock steel, case hardened and surface-ground to precision
• Assumes surface grinder and mill are used in its construction up to a 4' working bed
• Can be used to make a mill or lathe
• hydraulic motor drive, flow control for speed control
• Interchangeable heads
• Indexing head is also motor head