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