Design for cheaper CNC parts

Most of the cost of a machined part is fixed by its design. These guides cover the changes that usually save the most without changing what the part does.

• Internal corner radii for CNC pockets: Why milled pockets cannot have sharp inside corners, which radius to choose for a given depth, and how to handle square parts that must fit.
• How deep can a milled pocket be?: Pocket depth limits for CNC milling, how depth relates to tool diameter, and design alternatives for deep cavities.
• Minimum wall thickness for CNC machining: Minimum wall thickness for machined metal and plastic parts, why thin walls cost more, and how to design stiff lightweight parts instead.
• Choosing hole sizes that are cheap to make: Standard drill sizes, clearance and tap drill sizes, and why odd hole diameters make CNC parts more expensive.
• How deep should a tapped thread be?: Recommended thread engagement for steel and aluminium, tap drill depth, and why deeper threads add cost without strength.
• Reduce setups to cut machining cost: Why every side of a CNC part that needs machining adds cost, and how to arrange features so a part can be made in one or two setups.
• Design around standard stock sizes: How standard plate and bar sizes affect the price of CNC parts, and how small design changes can drop a part into cheaper stock.
• Tolerances: tight only where it matters: How tolerances affect CNC machining cost, which tolerance to use by default, and how to call out critical features on a drawing.
• Surface finish and what it costs: Common Ra surface roughness values for machined parts, which finish to specify by default, and how finishes like anodizing affect dimensions.
• Chamfers or fillets on outside edges?: Why outside edge chamfers are usually cheaper than rounded fillets on CNC parts, and when to use an edge break note instead.

The DrawMyPart tool checks a STEP file for all of these at once and estimates what each change saves.