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Computer controlled machining

Group assignment:

  • Complete your lab’s safety training

  • Test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine

Safety

This week, we’re going to start our work with the ShopBot Alpha, a large-scale machine used for a variety of manufacturing tasks. Before you start working with this machine, it’s crucial to understand its features and technical specifications.

It is imperative to consider safety precautions and procedures when interacting with ShopBot Alpha. Please read carefully, understand and follow all posted instructions and warnings, especially those specific to this CNC machine.

Here are a few safety rules that are sure to help.

Before accessing the shopbot, it is imperative to strictly follow the established safety instructions. This includes wearing appropriate personal protective equipment, such as hard hats, safety shoes and gloves. In addition, it is crucial to comply with the safety rules and standard operating procedures in force for the use of equipment and machinery in shopbpt. Any deviation from these instructions may jeopardize your safety and that of others, as well as the smooth running of operations.

the protective equipment we use is as follows

- Surrounded in red are the wood chip protection bezels.
- Surrounded in blue are protective gloves. 
- Surrounded in yellow are the anti-fog helmets.
You can see them in the following image

Tools

Before we move on to the various tests, let’s take a look at the tools we have available for milling on the Shopbot.

We visually inspected different types of cutter and used two of them to carry out our tests. We’re looking at carbide-tipped cutters - Spoilboard Surfacing , V-Carve , End Mills , etc. Each is designed for a specific purpose. Each is designed for a specific purpose and all can be used in a CNC router.

  • 91-000 Carbide tip - Roof panel surfacing

  • Solid carbide cutter, 2 flutes, down-cutting

  • Solid carbide 60-100PLR - Polaris compression

  • Carbide tipped cutter, 2 flutes, V-bottom

  • Solid carbide drill, 2 flutes, 8 facets

Translated with DeepL.com (free version)

The following image shows the characteristics of the various tools.

Alignment

To avoid the milling work coming out of the material to be machined, it is important to ensure that the edges of the material are aligned with the machine axes, especially for large milling jobs.

To achieve this, we follow these steps:

  • Align the work material with the material edges of the hammer, which must be aligned with the machine as it touches an edge of the work table.

  • Check alignment by moving the spindle along the x and y axes and measuring the distance to the edge.

We have found information on calculating feed rate on this website .

Feed rate depends on various factors, including :

  • Machine power and rigidity

  • Rigidity of workpiece support

  • Spindle power

  • Depth and width of cut

  • Cutting tool sharpness

  • Cutter design and type

  • Material to be cut

Feed speed

It’s important to produce chips rather than dust. Chips help to eliminate the heat generated during the cutting process, which increases tool life and improves edge quality.

The feed rate is calculated using the following equation :

Alimentation = N x cpt x RPM

N = number of cutting edges (flutes)

cpt = chip load (chips per tooth) is the amount of material to be removed by each cutter tooth as it rotates and advances through the work. (mm per tooth)

RPM = speed at which the cutter rotates in the spindle (revolutions per minute)