Design documents guidelines

What design document can you attach?

When posting a new machining job request you should attach at least one design document to specify your requested part(s) dimensions.

This document can be a sketch, drawing, CAD model, photo, or anything else. If you have a fancy CAD model of your part, that's great, you can upload the file as an attachment. Otherwise, you can also simply draw a hand sketch of your part(s) dimensions.

What information should your design documents include?

It really depends on the part(s) you need. For a simple part, the dimensions should suffice. However, for anything more advanced, you may want to consider the following.

Typical dimensions and parameters on a 2D drawing:
  • Any parallel outside and inside dimensions (e.g. length. width, height, etc.)
  • Hole and bore diameter & location
  • Tapping hole thread size and depth
  • Tolerances (See below)
  • Material (See below)
  • Surface finish (See below)
Tolerance

No machine can hold dimension perfectly precise to the nominal value, hence it can be important to also specify the acceptable degrees of variation.

  • Understand what dimension is critical for your assembly. Can you allow any inaccuracies in Form, Location or Orientation?
  • Do not over-dimension or over-tolerance your design. Only include the maximum allowable lower and/or upper deviation if necessary.
  • The standard tolerance of any dimension in CNC machining is ± 0.125 mm. However, if your part requires very high precision, tolerance down to ± 0.025 mm is achievable by some machines.
Material

You can request any material you need for your part. Metal is one of the more popular type of materials used in machining due to its material property. Here are a few common options:

  • As-machined - no finishing process, no added cost, but tool marking may be visible
  • Aluminum - relatively light weight, protection against corrosion
  • Alloy Steel - hard & tough and provides wear resistance
  • Mid Steel - lower cost, good mechanical properties
  • Stainless Steel - high strength and ductility, excellent wear and corrosion resistance

Another type of material commonly used in machining is Plastics.

  • ABS - common, lightweight, excellent impact strength
  • Nylon - good mechanical properties and excellent chemical resistance
  • Polycarbonate - can be coloured, excellent impact strength and thermal resistant properties.
Surface Finish

Surface finish, sometimes also known as surface texture, is the characterizing of a surface's quality or conformance to expectations. Typical surface finish for machined metal parts include:

  • Anodized - layer of anodization can help protect against scratching and corrosion, can be dyed in different colours during te process.
  • Brushed - Brushed parts have a uniform, parallel grain surface texture to smooth our the exterior of a part.
  • Sand Blasted - for uniform matte texture
  • Plated - It can improve the durability and corrosion resistance of the part.
  • Polished - Smooth, non-texture, glossy finish. Often used for decorative part.
  • Power coated - similar to paint but provides greater durability