Planning a CNC Program - 3: The Part and the Tools
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
The part drawing or blueprint is the basis for the NC program. For the work piece to be machined, the drawing should be dimensioned in such a way that a programmer can convert the dimensions directly into a program without requiring additional computations. For example it helps a great deal to have the part dimensioned with ordinates (not shown in this blueprint)

Developing a plan for each operation on the part allows the planning of the sequence of tools and the operations that each tool will perform before writing the program. A well thought out program plan will avoid the use of extra tooling, using the same tool at different times in the program, or having the tools programmed in the wrong order.

Planning for fixtures and holding devices should be early in the planning process. This ensures adequate lead time for the purchase or construction of the needed holding equipment.

A standard machine vise or lathe chuck should be used wherever possible to avoid the need for special fixturing. Close attention should be paid to clamp locations in order to program around their location. The main purpose of clamping is to hold the work piece firmly against the locating surfaces and to resist the cutting forces acting upon it.

CNC machines are very versatile and are able to perform various operations in one work setup. A work holding device should be designed so that it can be used to hold a group of work pieces having similar features without the need for significant changes.

Decide ahead of time what tools will be required to do the machining and if they are available. Make sure the tools required are inventoried, can be purchased quickly, or can be fabricated in time.

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label: CNC programs, planning, machine slection, fixtures and tools, simple programs