6.8 Application
Tim A. Bacon
Reading the drawing
When looking at the technical drawing, specific information such as tolerances, and finish requirements will help determine the process used to create the part. It is important to note that tolerance can be viewed subjectively. A person cutting blocks of material to be supplied to a machine shop may usually have +/-.06 for tolerance. So, a job requiring a tolerance of +/-.01 would require extra attention and effort to achieve. At another shop, machinists may routinely make parts that are +/-.001. To them, a +/-.01 is nothing to worry about.
The drawing will typically state the type of material required for the part. A machinist could choose the material if it was for a fixture to be used on a job. (This is the case for the bench block exercise.) Some customers may provide the material that is to be used for the job. This may happen because the material is expensive. When the material is provided, there isn’t any extra material in case a mistake happens. If this is the situation, it is allowable for the machinist to again choose a piece of material to make a first part, provided that it is clearly marked as a setup part. The part must say “set up” or NCM (non-conforming material) on all sides and be visible at all times. Remember, ensure you have the correct material before starting. Whenever you are unsure, ask, and take notes so you don’t have to ask again.
Making a part for the first time, even for a Journeyman Machinist, is a learning process. Making mistakes is part of the learning process. If a mistake is made, try to save the part by repairing it. This task will rely on and improve problem solving abilities. Learning from the choices made will also aid in future decisions.
| Project planning for bench block
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| Sequence | Feature | Holding | Machine | Tooling | Notes |
|---|---|---|---|---|---|
| 1 | Grind | Magnetic Chuck | Surface grinder | Minimal material removal | |
| 2 | Spot drill | Vice with parallels | Vertical mill | Add step to square up stock | |
| 3 | Drill | Vice with parallels | Vertical Mill | ||
| 4 | Bore | Vice with parallels | Vertical Mill | Adjustable boring head | |
| 5 | Groove | Vice with parallels | Vertical Mill | Flat end mill | Tilt head to 45 deg |
| 6 | Counter bore | Vice with parallels | Vertical Mill | Flat end mill | Rotary table |
| 7 | Profile | Through holes with fixture in three jaw | Vertical Mill | Flat end mill | Rotary table |
| 8 | Knurl | Through holes with fixture in three jaw | Lathe | Pinch knurl tool | |
| 9 | Turn | Through holes with fixture in three jaw | Lathe | Turning tool | |
| 1.5 | Square up stock | Vice | Vertical Mill | Face mill | |
| option | Counter bore | Three jaw chuck or form jaws | Lathe | Boring bar | |
| option | Profile | Through holes with fixture in three jaw | Lathe | Turning tool | |
Here are the steps to create an individualized project plan:
- Create a spreadsheet for the different features that need to be cut.