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2 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Machining Design Guidelines Turning Design Guidelines
Issue XI, May 2015
3 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
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4 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
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Welcome to another issue of the DFM Guidebook. We highly appreciate your feedback for our previous issues. Please continue sending us your comments, suggestions and ideas for subsequent issues.
This week, our DFM experts provide you an interesting summary of important design guidelines for Turning Process.
Turning is the most important machining process and can produce a wide variety of parts. Primarily, turning is used to produce parts cylindrical in shape by a single point cutting tool on lathes. In turning operation, design the part for easy fixturing and secure holding. A large, solid mounting surface with parallel clamping surfaces should be provided to assure a secure setup. Avoid designs that require sharp corners and sharp points in cutting tools because these make the tools more subject to breakage. It is preferable to avoid interrupted cuts, if possible, because they tend to shorten tool life In this edition, we focus on manufacturability guidelines for turning covering specific guidelines like Blind Hole Relief, Keyways, Long - Slender Turned Parts, Minimum Internal Corner Radius, OD Profile Relief and Symmetrical Axial Slots. If you have any feedback or questions on DFM guidebook, please write to us at [email protected] Happy reading!
Rahul Rajadhyaksha Senior Product Manager Geometric Limited
5 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Contents
Blind Hole Relief ...................................................................................................... 6
Keyways .................................................................................................................. 7
Long - Slender Turned Parts .................................................................................... 9
Minimum Internal Corner Radius ......................................................................... 10
Outer Diameter Profile Relief ............................................................................... 11
Symmetrical Axial Slots ......................................................................................... 12
6 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Blind Hole Relief
Provide tool relief for the bottoms of blind bored holes.
Tool relief at the end of a bored hole will simplify the operation of honing, boring, reaming, and
grinding and reduce costs. The minimum amount of relief is expressed as a percent of the
diameter of the pre-bored.
It is recommended that relief at the end of bored hole should be greater than or equal to 3% of
the diameter of bored hole.
7 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Keyways
The most commonly used type of keys are woodruff, round-end machine and square-end
machine. Out of the three, square-end machine key is most difficult and costly to generate.
For generating radiused keyways, end milling cutter or a slotting cutter has to be used and can be
done much faster compared to other processes. To suit a cutting tool, blind axial keyways should
be radiused at the end.
It is recommended to use radiused keyways at the end of a key-slot. Radiused keyways need to be
milled with end milling cutters, so that the rounded end or ends of the key may fit the ends of the
keyway. The cutters diameter should always be equal to the width of the key.
A blind keyway that is square at the end is very difficult to achieve by milling process.
8 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Keyways should be radiused at the end to suit the cutting tool.
If the end of keyway is radiused in such a way that it could be cut by a slotting cutter it will
improve the speed of machining keyways.
9 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Long - Slender Turned Parts
The axial-length of the part should be proportional to parts minimum diameter to avoid
deflection towards center direction.
For long-slender part, it is recommended to center drill the free end and use a dead or live center
in the tailstock to support it. Without support, the work piece would bend and displace away
from the tool. Also, it may loosen the grip of chuck jaws on work piece and cause injuries or
accidents.
However a very long slender part, even if supported by tail stock, may deflect toward the center.
Where possible, turned parts should be designed such that a tail stock support is not required.
This is done by designing the part to be stubby rather than long with a high aspect ratio. It is
recommended that, ratio of total length of part to its minimum diameter should be less than or
equal to 8.
10 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Minimum Internal Corner Radius
It is recommended to avoid sharp internal corners and provide large inside radius so that a tool
with large nose radius can enter easily. A tool with large radius is less prone to breakage. A turn-
down surface at right angles to an un-machined (cast) surface might lead to burrs. The minimum
radius on internal corners of a turned part determines the cutting inserts that can be used.
It is always recommended to use cutting inserts with larger radii.
11 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Outer Diameter Profile Relief
Profile relief on the outer diameter of a turned part helps in smooth turn-machining of part.
The turned contour should allow easy tracing with a minimum number of changes of stylus and
cutting tool. Grooves with parallel or steep sidewalls are not feasible in one operation.
Contours inclined upto an angle of 58 from the axis of the part are feasible for a cutting tool (and
stylus). Following image shows feasible contours when they are perpendicular to the axis.
12 A DEFINITIVE GUIDE TO DESIGN FOR MANUFACTURING SUCCESS
Symmetrical Axial Slots
The width of axial slots and keyways on turned parts should be symmetrical about the turn axis. If
width of axial slots and keyways is not symmetrical about the turn axis, then the part will face
problems while coupling with other turn parts.
It is recommended to design axial slots and keyways such that they are symmetrical about the
turn axis. This guideline identifies whether the width of axial slots and keyways is symmetrical
about the turn axis or not, a condition which is likely a result of an error during modeling.
