6.1 Introduction
Tim A. Bacon
Knowing how to create a reliable work plan is essential to success in the machining field. Planning requires critical thinking and problem-solving skills which are highly sought-after machinist traits. In fact, the US Department of Labor, on their O*NET OnLine site (2024), ranks critical thinking as the second most important worker-required skill.
A job plan is a written sequence of general steps to take when making a part. Writing the plan down forces the machinist to think through the complete process before starting. The best way to learn about job planning is to go through the process, especially when you have a part to make. This chapter will look at building a bench block to illustrate the process of making a job plan. As you read, make note of how decisions are made and documented. The written plan must be easy to follow when making the part. With the information provided in this chapter, you will be able to replicate the process and write your own job plan.
| Project Planning For | |||||
| 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 | |
Note: A table showing project planning for a bench block.
A bench block is a tool that is used when working with hand tools such as drills and taps. It will assist in keeping the drill and tap perpendicular to the part that is being worked on. A machinist can also use it to hold small round cylindrical parts when working on them. This use is a type of workholding. Bench blocks are useful tools, and every machinist should have one. You can buy them, but making one helps students build necessary skills, and doing so is a common assignment because of the many skills needed to build it.
The Role of Job Planning in Machining
Job planning is a best practice because it saves time and effort when making a part. It is also an expectation in the workplace because it saves the employer time and money.
One way job planning saves an employer money is by reducing the material used to make a part. A clear plan limits errors and therefore, waste. In machining, material is typically removed by physically cutting or grinding. This removal of material is referred to as subtractive manufacturing. Once material has been removed, it cannot be replaced. A job plan helps the machinist use only the supplies needed and do the job correctly from the start.
Some benefits of having a job plan are:
- Keeping the project on track.
- Less effort is needed to make a part because problems have been solved during planning.
- Critical features have been identified prior to starting the part.
- Materials are conserved due to reduced waste which saves costs in producing the part.
When the part’s complexity increases, so does the equipment it is made on. CNC machines are commonly used when large numbers of complex parts with tight tolerances are required. A mistake at one of these workstations can be costly. So always be thinking of how you might plan a job and determine if a written plan is needed. Considering a work plan may increase efficiency and reduce waste. But, even when a plan is not necessary, considering the steps to be taken may result in the machinist identifying a more productive or cost-saving process.
Developing a job plan is often vital to ensuring the successful machining of a part. Job planning involves creating an organized approach to machining operations.
The basic elements of job planning are:
- Examine the technical drawing
- Identify the tools needed to create the features
- Select the appropriate material
- Choose a machine that the work will be done on
- Identify how the part will be held while being worked on
As noted in step one above, job planning begins by examining the technical drawing of a part. The features that need to be made will become apparent. The next section introduces technical drawings and how to read them.
Attributions
- Figure 6.1: Bench block: ready to use by Kirill Ignatyev is released under CC BY-NC 2.0
- Figure 6.2: Dry drilling of titanium – MITIS SineHoling technology by Cosme2c is released under CC BY-SA 3.0
Subtractive manufacturing is various material removal processes that start with solid blocks, bars, rods of plastic, metal, or other materials that are shaped by removing material through cutting, boring, drilling, and grinding.