5_threads and fasteners

7/31/2019 5_Threads and Fasteners

1/126

Copyright 2010 by K. Plantenberg

Restricted use onl

Chapter 5Threads and Fasteners

Topics

Exercises


2/126


Restricted use onl

Threads & Fasteners: Topics

Summary5.1) Fasteners

5.2) Screw Thread Definitions

5.3) Types of Thread5.4) Manufacturing Screw Threads

5.5) Drawing Screw Threads

5.6) Unified Threads5.7) Metric Threads

5.8) Drawing Bolts

5.9) Bolt and Screw Clearances


3/126


Restricted use onl

Threads & Fasteners: Exercises

Exercise 5-1: Screw thread featuresExercise 5-2: Unified national thread note

components

Exercise 5-3: Unified national thread noteExercise 5-4: Metric thread note components

Exercise 5-5: Metric thread tables

Exercise 5-6: Fastener tables and clearanceholes


4/126


Restricted use onl

Threads and Fasteners

Summary


5/126


Restricted use onl

Summary

What will we learn in Chapter 5? How to represent fasteners and threads on

an engineering drawing.

How to calculate bolt and screw clearanceholes.

Key points Threads are represented by thread symbols,

not by a realistic drawing.


6/126


Restricted use onl


5.1) Fasteners


7/126Copyright 2010 by K. Plantenberg

Restricted use onl

Fasteners

Fasteners include: bolts and nuts (threaded)

set screws (threaded)

washers keys

pins

Fasteners are not a permanent meansof assembly such as welding oradhesives.



Restricted use onl

Fasteners

Fasteners and threaded features mustbe specified on your engineeringdrawing.

Threaded features: Threads are specified ina thread note.

General Fasteners: Purchasing information

must be given to allow the fastener to be

ordered correctly.



Restricted use onl


5.2) Screw Thread Definitions



Restricted use onl

Thread Definitions

Screw Thread:A ridge of uniform sectionin the form of a helix.


11/126


Restricted use onl

Thread Definitions

External Thread: External threads are onthe outside of a member.

A chamfer on the end of the screw threadmakes it easier to engage the nut.

Chamfer


12/126


Restricted use onl

Thread Definitions

External Thread:

An external thread is cut using a die or alathe.


13/126


Restricted use onl

Thread Definitions

Internal Thread: Internal threads are onthe inside of a member.

An internal thread is cut using a tap.


14/126


Restricted use onl

Thread Definitions

Major DIA (D): The largest diameter (Forboth internal and external threads).

Minor DIA (d): The smallest diameter.

Depth of thread: (D-d)/2

Pitch DIA (dP): The diameter at which aline cuts the spaces and threads equally.


15/126


Restricted use onl

Exercise 5-1

Screw thread features

Skip to next part of the exercise


16/126

8

Identify the Major,Minor & Pitchdiameters and the Thread Depth.


7

1 2

3

4 5

6

109

8


17/126

8

Identify the Major,Minor & Pitchdiameters and the Thread Depth.

1 2

3

4

Minor

109

Thread Depth

MajorP


18/126



19/126

Identify the Crest, Rootand Side.


1 2

3

4

109

8Minor

Thread Depth

MajorP


20/126

Identify the Crest, Rootand Side.

1 2

Crest

Root

10Side

8Minor

Thread Depth

MajorP


21/126


Restricted use onl

Thread Definitions

Pitch (P): The distance from a point on ascrew thread to a corresponding point on

the next thread (in/Threads).

Angle of Thread (A): The angle betweenthe threads.


22/126


Restricted use onl

Thread Definitions

Screw Axis: The longitudinal centerline.

Lead: The distance a screw thread

advances axially in one turn.


23/126

Identify the Pitch, Screw Axisand Thread Angle.

1 2

10

Crest

Root

Side

8Minor

Thread Depth

MajorP


24/126

Identify the Pitch, Screw Axisand Thread Angle.

Axis Pitch

Angle

Crest

Root

Side

8Minor

Thread Depth

MajorP


25/126


Restricted use onl

Thread Definitions

Right Handed Thread:Advances whenturned CW. (Threads are assumed RH

unless specified otherwise.)

Left Handed Thread:Advances whenturned CCW.


26/126


Restricted use onl

Application Question 5-1

Name an example of a left handed thread.

Left peddle of a bike


27/126


Restricted use onl


5.3) Types of Thread


28/126


29/126


Restricted use onl

Types of Thread

Thread form choice depends on; what it will be used for

length of engagement

load etc


30/126


Restricted use onl

Types of Thread (Form)

Thread Name Figure Uses

Unified screw

thread

General use.

ISO metric

screw thread

General use.

Square Ideal thread

for powertransmission.


31/126


Restricted use onl

Types of Thread (Form)

Thread Name Figure Uses

ACME Stronger than

square thread.

Buttress Designed to

handle heavy

forces in onedirection.

(Truck jack)


32/126


Restricted use onl


5.4) Manufacturing ScrewThreads


33/126


Restricted use onl

Manufacturing Threads

Internal Threads First a tap drill hole is cut with a twist drill.

The tap drill hole

is a little biggerthan the minor

diameter. Why?


34/126


Restricted use onl


Internal ThreadsThen the threads are cut using a tap.

The tap drill hole

is longer than the

length of the

threads. Why?

Incomplete

threads


35/126


Restricted use onl


Internal ThreadsChamfers are sometimes cut to allow for

easy engagement.


36/126


Restricted use onl


External ThreadsYou start with a shaft the same size as the

major diameter.


37/126


38/126


39/126


Restricted use onl

Drawing Screw Threads

There are three methods ofrepresenting screw threads on adrawing.

Detailed Schematic

Simplified

Screw thread representation present in

this chapter is in accordance with the

ASME Y14.6-2001 standard.


40/126


Restricted use onl

Detailed Representation

A detailedrepresentation is a closeapproximation of the appearance of an

actual screw thread.


41/126


Restricted use onl

Detailed Representation

Pros and Cons?Pro: Looks good and clearly represents a thread.

Con: Takes a long time to draw.


42/126


Restricted use onl

Schematic Representation

The schematicrepresentation usesstaggered lines to represent the thread

roots and crests.


43/126


Restricted use onl

Schematic Representation

Pros and Cons?Pro: Nearly as effective as the detailed

representation and easier to draw.

Con: Still takes some time to draw.


44/126


45/126


Restricted use onl

Simplified Representation

The simplifiedrepresentation uses visibleand hidden lines to represent the major

and minor diameters.


46/126


Restricted use onl

Simplified Representation

Pros and Cons?Pro: Simple and fast to draw.

Con: Doesnt look like a thread.


47/126


Restricted use onl

Simplified Internal Threads


48/126


Restricted use onl

Simplified Internal Threads


49/126


Restricted use onl

Drawing Screw Threads

Thread tables in the appendix can beused to look up value for the;

Pitch

Minor diameter Tap drill diameter

If screw thread tables are not available,the minor diameter can be approximated

as 75% of the major diameter.


50/126


Restricted use onl


5.6) Unified Threads


51/126


Restricted use onl

Unified Threads (inch)

After drawing a thread, we need to identifythe size and thread form in a thread note.

Thread Note


52/126


Restricted use onl

Unified Thread Note Components


53/126


Restricted use onl


Major Diameter: The largest diameter.Threads per inch: Number of threads per

inch for a particular diameter.

Equal to one over the pitch (1/P).


54/126


Restricted use onl


Thread Form and Series: The shape ofthe thread cut.

UNC = Unified National coarse.

For general use.

UNF = Unified National fine.

Used when high degree of tightness is required.

UNEF = Unified National extra fine.

Used when length of engagement is limited(Example: Sheet metal).


55/126


Restricted use onl


Thread Class: Closeness of fit betweenthe two mating threaded parts.

1 = Generous tolerance. For rapid assemblyand disassembly.

2 = Normal production

3 = High accuracy


56/126


Restricted use onl


External or Internal Threads A = External threads

B = Internal threads

Right handed or left handed thread RH = Right handed (right handed threads

are assumed if not stated.)

LH

= Left handed


57/126


Restricted use onl


Depth of thread: The thread depth isgiven at the end of the thread note and

indicates the thread depth forinternal

threads This is not the tap drill depth.


58/126


Restricted use onl


Thread class is assumed to be 2.Threads are assumed to be RH.

May be left off if

assumptions hold.


59/126


Restricted use onl

Exercise 5-2

Unified National thread note

components


60/126


Restricted use onl

Exercise 5-2

Identify the different components of thefollowing Unified National thread note.

1/4 20 UNC 2A RH

1/4

20

UNC

2

A

RH

.25 inch Major DIA

20 threads per inch (P = 1/20 = .05)

Thread form & series UN Coarse

Thread Class

Normal ProductionExternal Threads

Right Handed Threads


61/126


62/126


Restricted use onl

Exercise 5-3

Unified National thread note


63/126


64/126


65/126


Restricted use onl

Exercise 5-3

Write the thread note for a #10 finethread. (See Appendix B)

10 32 UNF


66/126


Restricted use onl

Exercise 5-3


Is the major diameter 10 inches? No

10 32 UNF


67/126


68/126


Restricted use onl

Exercise 5-3


Is the major diameter 10 inches? 0.190

10 32 UNF


69/126


Restricted use onl

Exercise 5-3


What is the minor diameter?

10 32 UNF


70/126


71/126


Restricted use onl

Exercise 5-3


What is the minor diameter?

10 32 UNFD 1.0825P=0.190 1.0825/32 =

0.156


72/126


Restricted use onl


5.7) Metric Threads

M i Th d


73/126


Restricted use onl

Metric Threads

The metric thread note can contain apitch diametertolerance.

What is the pitch diameter? Lets see.

Pi h Di


74/126


Restricted use onl

Pitch Diameter

The pitch diametercuts the threads at apoint where the distance of the spaces

equal the distance of the threads.

M i Th d N C


75/126


Restricted use onl

Metric Thread Note Components

M t i Th d N t C t


76/126


Restricted use onl

Metric Thread Note Components


77/126

M t i Th d


78/126


Restricted use onl

Metric Threads

Major Diameter: The largest diameterPitch: (P) Millimeters per thread.

M t i Th d


79/126


Restricted use onl

Metric Threads

Tolerance Class: It describes thelooseness or tightness of fit between the

internal and external threads.Number = Tolerance grade

Letter = Tolerance position

M t i Th d


80/126


Restricted use onl

Metric Threads

Tolerance Class: Tolerance Grade: Smaller numbers indicate

a tighter fit.

Tolerance Position: Specifies the amount of

allowance.

Upper case letters = internal threads

Lower case letters = external threads.

M t i Th d


81/126


Restricted use onl

Metric Threads

Tolerance Class: Two classes of metricthread fits are generally used.

6H/6g = General purpose

6H/5g6g = Closer fit. A tolerance class of 6H/6g is assumed if it is

not specified.


82/126

M t i Th d


83/126


Restricted use onl

Metric Threads

Depth of thread: It indicates the threaddepth for internal threads, not the tap drill

depth.

Metric Thread Note


84/126

Copyright 2010 by K. PlantenbergRestricted use onl

Metric Thread Note

A tolerance class of6H/6g is assumed.Threads are assumed to be RH.

May be left off if

assumptions hold.


85/126


Exercise 5-4

Metric thread note components

Exercise 5 4


86/126


Exercise 5-4

Identify the different components of thefollowing metric thread notes.

M10 x 1.5 4h6h RH

M10

1.5

4h

6h

Int. or Ext.

RH

Metric Form10 mm Major DIA

Pitch mm/threads

Pitch DIA tolerance

Minor DIA tolerance

External

Right handed threads

Metric Thread Tables


87/126


Metric Thread Tables

Standard screw thread tables areavailable in order to look up the;

Major diameter

Pitch

Tap drill size or Minor diameter

Thread tables are located in Appendix B.


88/126


Exercise 5-5

Metric thread tables


89/126


90/126

Find this page.


91/126

Exercise 5 5


92/126


Exercise 5-5

For a 16 internal metric thread.

Which has the finer thread?

Pitch = 2 Pitch = 1.5

Exercise 5 5


93/126


Exercise 5-5

Write the thread note for a 16 mmdiametercoarse thread.

M16 x 2


94/126



5.8) Drawing Bolts

Drawing Bolts


95/126


Drawing Bolts

D represents the major diameter.

Nuts are drawn in a similar fashion.


96/126



5.9) Bolt and Screw Clearances

Bolt and Screw Clearances


97/126



Bolts and screwsattach one material

with a clearance

hole to another

material with a

threaded hole.



98/126



The size of theclearance hole

depends on;

the major

diameter of the

fastener

and the type of fit

normal close

loose

Table 5-2 (Normal fit clearances)


99/126


Table 5-2 (Normal fit clearances)

Other fits may be found in Appendix B.


100/126


101/126



102/126



Countersink:Countersinks are

angled holes that are

designed to recess

screws with angledheads.

Typically,C1 = D1 + 1/8 (3 mm)

Appendix B gives other

counterbore, countersink

and shaft clearance holes.


103/126


Exercise 5-6

Fastener tables and clearance

holes

Exercise 5-6


104/126


Exercise 5 6

What is the normal fit clearance holediameter for the following nominal bolt

sizes.

Nominalsize Clearancehole

1/4

3/4

9/32

13/16

Exercise 5-6


105/126


Exercise 5 6

A 5/16 - 18 UNC Socket Head CapScrew needs to go through a piece ofmetal in order to screw into a plate below.

The head of the screw should be flushwith the surface.

Exercise 5-6


106/126


Exercise 5 6

5/16 - 18 UNC Socket Head CapScrew

Fill in the following table. Refer to

Appendix B.Head diameter

Height of head

Normal clearance hole dia.CBore dia.

CBore depth


107/126

D = 5/16


108/126

Exercise 5-6


109/126


Exercise 5 6



Appendix B.

Max. Head diameter A = 1.5(5/16)=.469

Max. Height of head H = D = 5/16

Normal clearance hole dia.CBore dia.

CBore depth


110/126

Exercise 5-6


111/126


Exercise 5 6



Appendix B.



Normal clearance hole dia. C = D + 1/32 = 11/32CBore dia. B = 17/32

CBore depth

Exercise 5-6


112/126


Exercise 5 6



Appendix B.



Normal clearance hole dia. C = D + 1/32 = 11/32CBore dia. B = 17/32

CBore depth


113/126


114/126

Exercise 5-6


115/126


Exercise 5 6

M8x1.25 Flat Countersunk Head MetricCap Screw

Major dia.

Head dia.

CSink dia.

Close clearance hole dia.

Exercise 5-6


116/126


e c se 5 6


Major dia. 8

Head dia.

CSink dia.


Exercise 5-6


117/126



Major dia. 8

Head dia.

CSink dia.



118/126

Exercise 5-6


119/126



Major dia. 8

Head dia. A = 17.92

CSink dia.


Exercise 5-6


120/126



Major dia. 8

Head dia. A = 17.92

CSink dia.



121/126

Exercise 5-6


122/126



Major dia. 8

Head dia. A = 17.92

CSink dia. Y = 17.92


Or, Y = A + 3 = 20

Exercise 5-6


123/126



Major dia. 8

Head dia. A = 17.92



Or, Y = A + 3 = 20


124/126

Exercise 5-6


125/126



Major dia. 8

Head dia. A = 17.92


Close clearance hole dia. 8.4

Or, Y = A + 3 = 20


126/126


The End

5_threads and fasteners

Documents