1. The document provides data and specifications for drawing various parts of a DC machine, including the yoke, poles, armature, commutator, and general assembly, using CAD. 2. Fifteen problems are presented that involve drawing different DC machine components based on given dimensions and specifications, such as the pole assembly, armature stamping, and general assembly. 3. Hints and solutions are provided for each problem to guide the CAD drawing of each part based on the given data.

1. 1
Subject: Computer Aided Electrical drawing (CAED)
Subject Code: 10EE65
Syllabus Covered
Part-B
3. Electrical machine assembly drawing using design data or sketches or both
b) DC Machine- sectional views of yoke, field system, armature and commutator
dealt separately.
DC Machine
Introduction:
DC Machines form one of the varieties of electrical equipment and are extensively in use
in various industrial applications like DC voltage generation, electro- plating, metal
extraction, traction, steel industry, paper mills etc. While the performance analysis and
design features have been considered already, given the design data, this chapter deals as
to how to make drawings of parts, sub assembly and general assembly. The input data for
making the CAD drawing may be in the form of wordings, sketches or both.
Te following are the parts of DC machine-
1. Yoke- Housing- Casing
2. Poles- Main Poles- Inter Poles- Compensating Winding
3. Armature and Armature Winding
4. Commutator
5. Brush and Brush Holder
6. Fan
7. Bearing
8. End Shields
9. Lifting lug
The general appearance (Figure-1), a dismantled view (Figure-2), an exploded view
(Figure-3), a general assembly (Figure-4) and a sectional pictorial view (Figure-5) of DC
Machine are given below, to familiarize with the various parts and their relative position
in the machine-assembly.
Yoke and pole with winding constitute stator and armature with winding and commutator
form the rotor. The brush and brush holder assembly is used for supplying or collecting
current from/to the machine. The other structural parts are end shields, bearings, fan, foot
and terminal board. The drawing of active parts is given prominence. However,
knowledge of other parts also, will greatly help in assuming data require for completion
of drawing.

2. 2
Figure-1, General Appearance
Figure-2, Dismantled Machine
Figure-3, Exploded View
Figure-4, General Assembly

3. 3
Figure-5, Sectional Pictorial View
Figure-6, Details of Pole

4. 4
Pole and Yoke Assembly:
The pole is made up steel laminations of 1.2 mm thick as shown in Figure-6. The
laminations are assembled to the required length and then riveted to form a solid core.
The central hole is the driven with steel rod. The longitudinal holes in axial view are two
in number. The bolts are driven through yoke, pole and then to the central rod. The yoke
is shown in Figure-7. If the dimensions are given for pole/yoke, the CAD drawings can
be made.
Figure-7, Details of Yoke
Problem-1
Draw the Pole and Core Assembly of a DC machine with the following data –
Rating: 10 HP, 1500 RPM, 4 Pole, DC Motor
Radius of Pole: 115mm
Pole Length: 210 mm
Pole Width: 76 mm
End Stamping: 5 mm thick
Pole Arc/Pole Pitch = 2/3
Yoke Thickness: 20 mm
Use Suitable bolts for fixing the Pole Brick to the Yoke.
Hints: Prepare a preparatory sketch, using the data-
End plates of 5 mm thick are to be shown.
(This is to prevent the bulging of stamping)
Using commands, prepare the drawing. For solution see Figure-8 .

5. 5
Preparatory sketch for Problem-1
Figure-8, CAD drawing for Problem-1

6. 6
Problem - 2
Draw the pole and yoke assembly of the DC machine with the following details-
Pole radius = 345, Pole arc = 210,
Pole Height = 145, Pole width = 127
Yoke Inside Diameter = 345
Yoke thickness = 55
4 Nos. of rivet, 12 mm diameter
2 Nos. of Bolts, M20
All dimensions are in mm.
Preparatory sketch for Problem- 2
Figure-9, CAD drawing for Problem-2

7. 7
Problem-3
The isometric view of a Pole of a DC Machine is shown in the figure. The isometric view
of the Bobbin with field winding is also shown. Assemble the units and show half
sectional elevation of the assembly and the plan.

8. 8
Hints: Make the preparatory sketch after carefully studying the pole and bobbin with
winding. Sharp corners are to be drawn with ‘fillet’ command. Bobbin edges will be seen
in the plan. The winding will not be seen in plan and hence shown in dotted line.
Figure-10, CAD drawing for Problem-3

9. 9
Problem-4
Draw the Armature stamping of a DC Machine with the following dimensions-
Rotor Outside Diameter = 110 mm
Rotor Shaft diameter = 25 mm
Number of armature slots = 32
Slot Dimension = 4 mm x 20 mm
Show the key way in the stamping.
Hints: Armature core is made up of thin stampings which are blanked out from 0.5 mm
thick cold rolled non grain oriented (CRNGO) steel sheet. The slots are made using
cropping tools.
Draw the centre lines. Draw the OD and ID of the stamping. To draw the slot, consider
the angle subtended by one slot pitch at the centre, viz, 360/32 = 11.25 0
. Draw the slot
with respect to centre line with the given dimensions. Retain the arc as shown in the
enlarged slot diagram. Then using polar array form the stamping with 32 slots distributed
over 3600
.Draw the key way in rotor ID.
In this design, the armature core will be directly assembled on the shaft.
Figure-11, CAD drawing for Problem-4

10. 10
Problem-5
Armature diameter = 380 mm
No. of Slots = 36
Slot Dimension = 15 mm x 35 mm
Stamping Inside Diameter = 250mm
DC Machine Diameter = 80 mm
Draw the armature stamping. Furnish comment on providing spider/ hub
Hints: The method of drawing is similar to steps given in problem-4. Here, it is to be
observed that the core behind the slot is very less. This is the case with DC Machines
having large number of poles. The core is assembled on an intermediate piece, known as
spider or hub. The ID of spider or hub will sit on the shaft and the stamping will sit on the
OD. To arrest the radial displacement, suitable arrangement like thin circular, dove- tail
or rectangular bar can be used. Provide suitable grooves for this purpose.
Figure-12, CAD drawing for Problem-5

11. 11
Two types of intermediate supports for holding the core on the shaft are given in Figure-
13 and Figure-14. Problem-6 illustrates an example where the armature core is directly
mounted on shaft. Problem-7 and Problem-8 deal with spider and hub assembled
armature core, respectively.
Figure-13, Armature Core and Hub assembly
Figure-14, Spider

12. 12
Problem-6
Draw the assembly of stampings to form the armature core on the shaft. The details are
given below-
OD of the stamping = 230 mm
ID of the stamping = 50 mm
Slot size = 8mm x 22 mm
No. of slots = 32
Armature core length = 170 mm
6 nos. of vent holes of 20 mm dia, on pitch circle dia of 110 mm
Key way dimensions = 14 mm x 9 mm
Assume suitable collar on one side of the shaft and groove on the other side of the core
for fixing the core axially.
Hints: Armature is resting against a raised collar on the shaft on the left hand side. On the
right hand side a groove is made in the shaft. In this groove two semi circular washers are
inserted. If necessary the washers are tag welded to the shaft. This arrangement ensures
arrest of axial movement of the core. The key on the shadt ensures arresting of radial
movement.
Figure-15, CAD drawing for Problem-6

13. 13
Problem-7
The profile of a stamping is given in the figure above. (key way = 22x14 mm)
OD = 380 mm dia
ID = 250 mm dia
36 slots of dimension 15 mm x 35 mm
The shaft dia. of the machine is 80 mm
Using the stamping, draw the longitudinal half sectional view of core with spider
assembly
Figure-16, CAD drawing for Problem-7

14. 14
Problem-8
Draw suitable HUB and CORE assembly to accommodate the following requirements-
Stamping OD = 407 mm
Stamping ID = 240 mm
Core packets = 3 of 27 mm thickness
‘H’ piece = 2 of 9 mm thickness
Shaft diameter = 54 mm
Figure-17, H piece, which is assembled in between two core packets as spacers
Hints:
It is to be noted that the steel hub consists of two parts.
The left hand part is seated on the shaft on key way.
After the assembly of core packet and H plates are over, the smaller clamp is placed and
the bolts are holding the unit securely
Platform is provided on the clamps to support winding overhang.
Figure-18, CAD drawing for Problem-8

15. 15
Problem-9
The stamping of DC Machine armature has an OD of 240mm and ID of 74 mm.
Vent holes = 6 Nos. 20 mm dia on a PCD of 120 mm.
The core packet thickness = 36, 42, 36,36,36,42 mm respectively.
5 nos. of ‘H’ pieces of thickness of 12 mm are provided in between the core packets, for
cooling.
The commutator dimensions are given below-
On segments, 150 mm dia
On riser, 200 mm dia
Axial length,95 mm, Riser width, 12 mm
Commutator ID = 50 mm
Distance between core and commutator surfaces, 54 mm
Draw the longitudinal view showing the above details.
Hints:
The problem consists of two parts –
i) Placement of core
ii) Placement of commutator
Better to draw the stamping drawing for guidance purpose
Projection in the elevation is derived from thereof and the core packets and H pieces are
assembled.
Draw the commutator profile with given dimension at the given distance.
The collar and grooves are not shown in the figure.
This sub-assembly helps to decide the shaft diameters and tolerances at the appropriate
locations.
Figure-19, CAD drawing for Problem-9

16. 16
Problem-10
Draw the commutator in half sectional elevation and half sectional end view. Assume
suitable fillets for sharp corners. Mica insulation thickness = 1 mm.
Assemble the given parts-
 Copper segment
 End clamps or jaws
 Screwed cylindrical nut
Figure-20, Dimensions of components of the commutator

17. 17
Figure-21, CAD drawing for Problem-10
Problem-11
The parts of a commutator are shown in the Figure-22, along with dimensions.
Draw half sectional end view and half sectional elevation of the assembled commutator.
Figure-22, Parts of commutator

18. 18
Figure-23, CAD drawing for Problem-11
Problem-12
The details of an armature and commutator of a DC Machine are as follows –
Armature diameter = 410 mm, Shaft diameter = 90mm, Armature core length = 250mm,
Number of ventilating ducts (H Piece) =2, Width =10 mm, Axial holes in the armature
core = 8 numbers of 15 mm diameter,
Number of armature slots = 48,
Winding overhang on either side of armature =108mm, 144 mm respectively
Diameter of Commutator = 270 mm, Number of commutator segments = 144, Total
length of commutator = 150 mm.
The Armature core is positioned by two cast iron flanges, which also acts as winding
over-hang support. One flange is butting on the shoulder on the shaft. The other is
secured by means of a ring nut screwed to the shaft. This prevents axial movement of
armature. The armature is keyed to the shaft to prevent radial movement. Draw the half
sectional longitudinal view of the armature, showing the winding over hang, ventilating
ducts, over-hang and end plates. Show the commutator without sectioning.

19. 19
Figure-24, Hints for drawing of Overhang
Figure-25, CAD drawing for Problem-12

20. 20
Problem-13
Draw the General Assembly of a DC Machine in end view. The machine has the
following data-
Rating: 18.5 kW, 4 Pole, 220 v, 1500 rpm
Armature diameter = 0.18 m
Core length = 0.2 m
36 slots of dimension 8mm x 24 mm
Shaft diameter = 55 mm
Pole arc/ Pole pitch = 0.6666
Pole height = 65 mm
Pole width = 60 mm
Yoke Thickness = 35 mm
Air gap between stator and rotor = 2 mm
i)The armature is directly resting on the shaft.
ii)10 Nos. of ventilating holes, on a PCD of 96mm
Hints:
Draw pole with yoke sub-assembly.
Also show the field winding with suitable depth and height.
Take polar array to show all the 4 poles.
Delete the poles in the bottom half.
Use M10 bolts for fixing.
Use zoom window and zoom all wherever necessary.
Take up armature stamping drawing.
Draw the slot profile of 6x24 mm dimension, confining the details within an angular
arc of 10 0
(i.e.360/ 36) on a radius of 180 mm.
Take polar array to show all 36 slots.
Delete the slots in the bottom half.
On the shaft, show half key way, for a key of 16mmx10mm.
Concentrate on the un-sectioned bottom half of the drawing.
Half of END SHIELD will be seen.
The wire mesh opening is for ventilation.
End shield is attached to the yoke through bolts.
Show the FOOT and the bracket butting the housing.

21. 21
Figure-26, CAD drawing for Problem-13
Problem – 14
Draw the half sectional end view of a 1000kW,500 V,1250 rpm, 6 Pole DC shunt
generator with the following data-
Diameter of armature = 750mm
Length = 278 mm
No. of slots = 86
Size of slot = 11.1x 52.4 mm
Depth of iron behind slot = 92.6 mm
Air gap length between Stator & Rotor = 5 mm

22. 22
Main Pole – Breadth=177.5 mm,
Height = 240 mm
Central Rod = 50 mm dia
Pole Arc/Pole Pitch = 0.7
Inter Pole – Breadth = 46.3 mm
Height = 237 mm
Air Gap = 8 mm
Thickness of Yoke = 75 mm
Length of yoke = 400 mm
Shaft dia = 90 mm
Commutator –
No. of Segments = 344
Diameter of Commutator = 560 mm
Length of Commutator = 123.5 mm
Segment Pitch = 5.1 mm
No. of Brushes/Spindle = 3.
Hints:
Draw the main pole arc, choosing dia at pole periphery as 760mm and subtending an
angle of 42 deg., complete pole profile.
Draw the inter pole at the mid of pole pitch.
Draw the field windings (assume the depth and height of the winding).
Polar array- get all 6 sets of poles, then delete the bottom half poles, retaining only the
poles seen in top half.
Draw the armature stamping, slots, and the semicircular holes at the inner diameter, to
facilitate assembling the same on to the spider.
Choose reasonable thicknesses so as to complete the half spider (6 No. of spokes
selected)
Complete the lower end shield and foot.
Show title, scale and dimensions.

23. 23
Figure-27, CAD drawing for Problem-14
Problem-15
Draw the half sectional end view and half sectional elevation, showing the General
Assembly of the DC Generator, rated as 30 kW, 4 Pole, 1200 rpm
Shaft radius = 35 mm,
Armature radius = 110 mm,
Armature core length = 210 mm,
Inner radius of the yoke = 168 mm,
Outer radius of yoke = 195 mm,
• Pole width = 65 mm, pole height = 66 mm, Pole arc/ pole pitch = 2/3, Steel rod in
the main pole = 40 x 40 mm,
• Inter pole dimension = 20 x 52 mm,
• No. of armature slots = 32,
• slot dimension = 8 x 22 mm,
• Vent holes = 6 of 10 mm dia,
• Axle height = 200 mm

24. 24
• Commutator dia = 110 mm
• Commutator length = 90 mm
Hints:
Assume data not given
Make a preparatory sketch.
Almost all details of active materials are given
The dimensions of fan, end shield, over hang length, supporting bracket, have to be
assumed.
Figure-28, CAD drawing for Problem-15
Referances:
1. Performance and Design of Direct Current Machines, AE Clayton and NN
Hancock, CBS Publishers and distributors, 2002
2. Electrical Engineering Drawing, KL Narang, Satya Prakashan, New Delhi,2001
3. Electrical Drafting, SF Devalapur, Eastern Book Promoters, Belgaum, 2006
4. CAD for Electrical Engineers, MS Indira, VD Sankarlal, D Beula, Fillip
Learning- Elsevier, 2013
5. Materials from Google.com
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