121.2.3 - Manual Machining

Manual Mill Order of Operations

Milling Order of Operations

When performing almost every machining operation and cutting almost every feature into a part, a strategy of rough → finish is used:
- Roughing cuts quickly remove excess material, getting the workpiece close to its final shape.
- Finishing cuts refine the part for precision and a smooth finish. Together, they ensure efficient machining with accurate and quality results.
Order of Operations in the context of machining defines the sequence and relationship between steps in which different tools are used to cut specific features into a block to result in a desired, finished part shape
- A common, generic order of operations for milling parts is:
  1. Face Top of Part
  2. Profile Outside of Part
  3. Cut Inside Features
Certain scenarios dictate non-standard order of operations be used. For example:
- Thin Walls. For thin walls, which can vibrate or deflect due to the forces during milling, using fixtures or slower feeds might help, or milling them later to ensure more material support.
- Partial-Diameter Holes/Arcs. Machining partial-diameter hole/arc features - especially small ones - may requiring drilling/holemaking first then machining afterwards.
- Edge Features. Milling features too close to the edge or another feature can lead to breakouts or deformations. Oftentimes it is beneficial to save critical or delicate features for last.

Holemaking Order of Operations

There are many ways to make a hole in a part using a milling machine, but generally they follow a similar order of operations to milling features:
1. Spotting accurately marks the location of the center of a hole and also creates and entry and alignment point for hole roughing tools. Spotting can be accomplished with tools such as:
  - Spot Drills provide a conical start for a hole, which helps in aligning subsequent drilling operations, increasing accuracy and minimizing tool wander.
  - Center Drills are typically used to start holes for lathe work, but can also be used in mill holemaking
2. Hole Roughing rapidly and efficiently removes the bulk of material from a hole, but often leaves the hole imprecise and out-of-round. Hole roughing tools include:
  - Drills come in all shapes, sizes, materials, and configurations, and are the most common hole roughing tools used. Drills remove hole material via cutting, turning the entire inside of a hole into chips
  - Hole Saws are ideal for roughing large-diameter holes, and work by only cutting the outside of a hole, rather than cutting all of the hole interior material.
  - Annular Cutters are similar to hole saws in that they cut a hole's outer edge, leaving a solid core in the center.
3. Hole Finishing achieves the final desired dimension, shape, and surface finish of the hole, but typically requires most of the hole material to be removed prior (via hole roughing tools). Hole finishing tools include:
  - Reamers refine and slightly enlarge pre-drilled holes, ensuring high accuracy and a smooth finish. Reamers are available in precise increments and typically are fixed; only able to cut a single diameter of hole (though; adjustable reamers do exist).
  - Boring Tools are good options to finish larger diameter holes, where the material cost of large, individual reamers would be prohibitively expensive. Boring tools are edjustable and create holes of varying diameters.
  - (Internal) Threading Tools - the most common of which are taps - create threads in a hole to allow joining/fastening of multiple components to one another.
  - Broaching Tools cut specific, non-round shapes or profiles in a hole, and can be used to create features such as keyways or splines, as well as to create unique hole shapes (square, hexagon, etc.).

2.3✔ CHECKPOINT

Plan D6 Order of Operations

With instructor guidance/supervision, discuss & demonstrate the following understanding/competencies:
- Write down all operations needed to make the features on your D6 Dice, including details like workholding setup, part orientation, feature locations, tooling, cut width/depth, speeds/feeds, etc.
- Walk-through all your operations, and reorganize them as needed until you feel that you have the optimal order of operations to make your part

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