Milling is typically used to produce parts that are not axially symmetric and DFM guidelines recommend avoiding sharp internal corners inside pockets when it is to be manufactured using milling process. Read the guidebook for important design rules such as Deep Radiused Corners, Sharp Internal Corners, Tool Accessibility, Narrow Regions in Pockets, Side and Bottom Radius, Tool Clearance Check and Angular Milling Faces. To subscribe to Guidebook, please visit http://dfmpro.geometricglobal.com/dfm-guidebook/

2. 2A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Machining Design Guidelines
Milling Rules
Issue IV, Jan 2015

3. 3A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
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4. 4A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Welcome once again to another issue of DFM Guidebook!
Milling is one of the most flexible and well known method of
machining. Due to the high tolerances and surface finishes that milling
can offer, it is ideal for producing parts with precision features and
shapes.
Milling is typically used to produce parts that are not axially symmetric and DFM guidelines
recommend avoiding sharp internal corners inside pockets when it is to be manufactured using
milling process.
In this issue we cover important design guidelines for Milling such as Deep Radiused Corners, Sharp
Internal Corners, Tool Accessibility, Narrow Regions in Pockets, Side and Bottom Radius, Tool
Clearance Check and Angular Milling Faces.
If you missed reading previous issues of DFM Guidebook, please visit our website,
www.dfmpro.com
Rahul Rajadhyaksha
Senior Product Manager
Geometric Limited

5. 5A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Contents
Deep Radiused Corners........................................................................................... 6
Sharp Internal Corners............................................................................................ 7
Tool Accessibility..................................................................................................... 8
Narrow Regions in Pockets ..................................................................................... 9
Side Radius and Bottom Radius ............................................................................ 10
Tool Clearance Check............................................................................................ 11
Angular Milling Faces............................................................................................ 12

6. 6A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Deep Radiused Corners
Flute engagement in the milling operation is important because it directly influence
the forces. When the axial depth of cut is increased, the length of engaged flutes
increases, and the milling forces also increase.
Longer end mills are prone to breakages and chatter, requires longer machining time
and results in increased tool vibrations.
Vibration creates uneven wear on cutting tools and thereby shortens tool life.
Designers should design milling areas such that longer end mills are not required to
machine it.
Example

7. 7A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Sharp Internal Corners
Rounded corners provides number of advantages such as less stress concentration on
part and tool, few operational steps and reduced scrap rate.
Sharp inside corners cannot be produced by milling and require more expensive
machining methods like EDM. When designing a three-edged inside corner, one of the
inside edges should be radiused. It is advised to avoid sharp corners and use fillets and
radii.
If a sharp corner is required for mating clearance, then drilling a separate relief hole
as shown below may serve the purpose.

8. 8A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Tool Accessibility
Features should be accessible to the cutting tool in the preferred machining
orientation.
Example

9. 9A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Narrow Regions in Pockets
It is recommended to avoid features that are too close to each other such that the gap
between them is too narrow to allow milling cutter to pass through them. If narrow
regions are unavoidable, then they should not be very deep.
The size of the milling cutter is constrained by the smallest distance between the faces
of the feature. Small diameter cutters are prone to breakage and chatter. Hence larger
diameter, shorter cutters are generally preferred.
Example

10. 10A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Side Radius and Bottom Radius
Use of standard side radius and bottom radius for milling features will ease
manufacturing of milling features with standard available milling tools. For reducing,
machining cycle time and tool setup cost, it is recommended to avoid non-standard
side radius and bottom radius.
As a general guideline use single standard side radius and single standard bottom
radius.
Example

11. 11A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Tool Clearance Check
Machining Features or slots should be accessible to the cutting tool in the preferred
machining direction and at the same time there should not be any clash between tool
holder and component while machining the feature.
Tool clash with components leads to adverse effect like tool damage, component
damage, and it will be unsafe for machine operator as well.
Example

12. 12A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Angular Milling Faces
Side and bottom faces of milling features separated by bottom fillet should be at 90º
to each other to allow production with an end mill having bottom corner radius.
Machining of angular faces require multi-axis machining, which leads to higher
machining cost.
It is recommended that side and bottom faces of milling features separated by bottom
fillet should be at an angle 90º to each other.
Example