10 Ways to Save on CNC Machining

Tip #1: Use a 3:1 ratio of round internal corners

Details: All internal corners should be rounded, not squared, with machined pocket features. Be generous with the radii in pockets of the internal corners. An inside radius of 3:1 (Length to Depth) or less will allow a single tool to smoothly and quickly build the features.

Reason: To cut metal and plastic parts into form, CNC machining utilises spinning tools. An endmill is most widely used to render features such as internal pockets. Since a rounded vertical cut is created by an endmill, the internal corners may not be sharp or squared. Additionally, to allow faster cutting of the feature, the radius on an internal corner should be above a standard endmill scale. This makes it possible for the cut motion to engage an even amount of material irrespective of whether it is a side or corner that holds the cutting movement or feeds continuously quickly.

Tip #2: Stop Deep Pockets
Details: We recommend pieces of lengths of up to 4X their pocket depth as a best practice. Anything greater than that is becoming increasingly more costly to produce. Notice that for optimal machining, the deeper the feature is, the larger the instrument radii, as well as radiused corners, should be per tip # 1. For example, round drills may create holes where endmills should hold closer to a 1:4 ratio at a radius of 1:10 to depth ratio.

Reason: Cutting instruments are made of very hard materials so that during service they stay rigid. This also suggests that materials are fragile, such as carbide. Anything in the instrument that causes flex or vibration may cause it to snap or chip. Parts with deep inner cavities are also time-consuming and costly to produce because to shape the features, the instrument must be slowly stepped down in smaller increments.

Tip #3: Restrict Close Tolerances to Use

Details: Design the process’s General Manufacturing Tolerances as much as possible. Allocate tighter tolerances and GD&T to mission critical characteristics and surfaces only. Try to describe a single date, such as the two sided intersection or the centre of a pit, and then calculate all elsefrom that common reference.

Reason: CNC machining is inherently a very precise process.”Typical distance tolerances are 0.005.” An operator must carefully monitor the process to achieve tighter tolerances, and even make adjustments to the machining code on the fly. In-process inspection (IPI) time is added and machining time is improved.But for measurement, specialised inspection tools can be needed. When creating an online manufacturing quote, you can request an inspection report. Call-outs like surface profile would inherently include a CMM study, adding cost and time to the project, General Dimensioning and Tolerances (GD&T).

Tip #4: Make Thin Walls stretch

Details: For regular features, thin walls should have a minimum width of 1/32″ with twice that, 1/16,” suggested. If very thin walls are needed, the use of other manufacturing methods, such as sheet metal fabrication services, is typically more economical.

Reason: On a flat edge, chatter on a portion looks like rough, scale-like features. Usually, this is induced during cutting by the part shifting or flexing. When machining, handling chatter involves specialised
equipment and slower feed speeds, increasing costs. Designing thin features to be thicker allows the surface more resilient to flex, reducing or removing chatter.

Tip #5: Tapped Holes Maximize
Details: Avoid call-outs with tap depth that are more than 3X the hole diameter. Beyond the tap depth in the cavity, ensure that there is at least 1/32 clearance. For drill tips, this does not provide clearance.
For your modules, use normal thread sizes.

Reason: Both hole-tapping depth and tap size play a cost-effective role. Special tools or risky manufacturing can involve unnecessary tapping, such as full-thru tapping. These can raise costs and the risk of manufacturing scrap. Mechanically, the strength of the hold is not improved by increasing the tap length beyond 3X the diameter of the opening. Most of the work is performed in the first couple of rounds. Normal threads mean standard, heavily commoditized taps. Hundreds of dollars for special purchases and control gauges can be added to custom threads.

Tip #6: Regular Drill Sizes leverage
Details: Hold sizes of hole to standard sizes of fractional, number, or letter drill.

Reason: To cut circular holes equal to their diameter, drill bits are used. Drill bits are not designed to move laterally, unlike an endmill. For an endmill or reamer, circular holes made outside of standard drill sizes will need to be manufactured, adding to component costs.

Tip #7: Using less expensive materials
Details: Use less costly materials in your design where possible. The least costly CNC metal is the aluminium 6061-T6. The less costly machined plastic is usually Acetal (Delrin).

Reason: Softer materials are easier to cut than materials like steel, such as Aluminum 6061-T6. This reduces cycle time during machining and allows regular drills and endmills to be used to cut these materials. Harder materials require more costly instruments which can add to the cost of the project.

Tip #8: Multiple finishes prevented
Details: Where practical, minimise surface finish requirements. This involves part marking, surface smoothing, and finishing services for post-processing.

Reason: During the machining stage, finishes such as lower surface roughness (below 125 Ra), knurling, and other texturing are applied and can increase cycle times. After the component is machined, post-processing finishes like anodizing, chemical conversion coating, or paint are added. Setup and potentially masking are needed for any finish. With multiple finishes, such as chemical conversion and anodizing on the same component, time and cost per part are increased by additional handling steps.

Tip #9: Dynamic Parts Break Up
Details: Break large and complex parts into an assembly where possible. After processing, the use of screws and pins will achieve flush assembly. Weldings are also excellent ways to construct intricate metal shapes by incorporating simpler designs.

Reason: Large components, like those with deep pockets, require extensive removal of material from solid billets, adding time to the machine. Specialized tooling may also be required to produce internal features. It may be substantially easier to produce shallow features.

Tip # 10: Order greater quantities
Details: The ordering of several quantities of the same item helps to produce efficiencies in output and reduce the cost per piece.

Reason: Per service, machining includes CAM programming and setup. There are non-recurring costs, which means that the manufactured first element would be far more costly than any additional components. As volumes rise, setup costs are amortised and direct material costs and machine time are correlated with most parts costs.https://grapcotooling.com/cnc-machining-services/