Pfaff 939 Guide

ADJUSTMENT MANUAL
296-12-18 595/002
Justieranleitung engl. 01.13
939 U
3704
-2/02
-2/03
This Adjustment Manual is valid for machines
from the following serial numbers onwards:
# 2 660 862

The reprinting, copying or translation of PFAFF Service Manuals, whether in whole or in part,
is only permitted with our previous authorization and with written reference to the source.
PFAFF Industriesysteme
und Maschinen AG
Hans-Geiger-Str. 12 - IG Nord
D-67661 Kaiserslautern

Index
Contents ..................................................................................Page
1Adjustment ........................................................................................................................... 5
1.01 Tools, gauges and other accessories for adjusting ................................................................ 5
1.02 Abbreviations ......................................................................................................................... 5
1.03 Explanation of the symbols.................................................................................................... 5
1.04 Check and adjustment aid...................................................................................................... 6
1.05 Adjusting the basic machine .................................................................................................. 7
1.05.01 Balancing weight.................................................................................................................... 7
1.05.02 Centering the needle in the needle hole (in sewing direction)............................................... 8
1.05.03 Parallel guiding of the needle bar........................................................................................... 9
1.05.04 Locking lever ........................................................................................................................ 10
1.05.05 Zero stitch and zigzag stitch scale........................................................................................ 11
1.05.06 Centering the needle in the needle hole (crosswise to sewing direction)........................... 12
1.05.07 Zigzag stitch width ............................................................................................................... 13
1.05.08 Multi-stitch movement (only on the PFAFF 939U) ............................................................... 14
1.05.09 Zigzag stitch movement (only on the PFAFF 3704-2/..)........................................................ 15
1.05.10 Needle penetration symmetry - left, centre and right (only on the PFAFF 3704-2/..)........... 16
1.05.11 Zigzag movement (only on the 939U) .................................................................................. 17
1.05.12 Target positioning sensor (only on the 939U) ...................................................................... 18
1.05.13 Needle position adjustment lever ........................................................................................19
1.05.14 Adjustment wheels for differential feed (only on the PFAFF 939U) ..................................... 20
1.05.15 Zeroing the differentiatio (only on the PFAFF 939 U) ........................................................... 21
1.05.16 Differential feed synchronisation (only on the PFAFF 3704-2/..)........................................... 22
1.05.17 Position of the stitch length adjustment wheel (on the PFAFF 939 U) ................................ 23
1.05.18 Position of the stitch length adjustment wheel (on the PFAFF 3704-2/..)............................ 24
1.05.19 Zeroing the main feed (rear feed dog) on the PFAFF 939 U................................................. 25
1.05.20 Zeroing the main feed (rear feed dog) on the PFAFF 3704-2/.. ............................................ 26
1.05.21 Zeroing the differential feed (front feed dog) on the PFAFF 939 U ...................................... 27
1.05.22 Zeroing the differential feed (front feed dog) on the PFAFF 3704-2/.................................... 28
1.05.23 Torsion spring of the reverse feed lever (on the PFAFF 939 U)............................................ 29
1.05.24 Torsion spring of the reverse feed lever (on the PFAFF 3704-2/..) ....................................... 30
1.05.25 Torsion spring of the differentiation regulating shaft (on the PFAFF 939 U)......................... 31
1.05.26 Torsion spring of the differentiation regulating shaft (on the PFAFF 3704-2/..) .................... 32
1.05.27 Feeding motion of the main and differential feeds .............................................................. 33
1.05.28 Lifting stroke of the main and differential feed dogs............................................................ 34
1.05.29 Height of the main and differential feed dogs...................................................................... 35
1.05.30 Drive belt in the gearbox housing ........................................................................................ 36
1.05.31 Hook bearing bracket .......................................................................................................... 37

Index
Contents ..................................................................................Page
1.05.32 Hook lubrication ................................................................................................................... 38
1.05.33 Pre-adjusting the needle height ........................................................................................... 39
1.05.34 Needle rise, hook-to-needle clearance and bobbin case positioning-finger ......................... 40
1.05.35 Final adjustment of the needle height ................................................................................. 41
1.05.36 Bobbin case opener position ............................................................................................... 42
1.05.37 Bobbin case opener motion................................................................................................. 43
1.05.38 Presser foot to needle plate clearance / Presser foot pressure........................................... 44
1.05.39 Thread diverter pin ............................................................................................................... 45
1.05.40 Limiting the knee lever stroke ............................................................................................. 46
1.05.41 Knee lever play..................................................................................................................... 47
1.05.42 Bobbin winder...................................................................................................................... 48
1.05.43 Stitch condensation (only on the PFAFF 3704-2/02) ............................................................ 49
1.05.44 Switching to reverse feed (only on the PFAFF 3704-2/03) ................................................... 50
1.05.45 Thread puller (only on the PFAFF 3704-2/02) ....................................................................... 51
1.06 Adjusting the thread trimmer -900/24 ............................................................................. 52
1.06.01 Axial position of the control cam ........................................................................................ 52
1.06.02 Preliminary adjustment of the control cam.......................................................................... 53
1.06.03 Position of the thread catcher and cutting test .................................................................... 54
1.06.04 Readjustment of the control cam ....................................................................................... 55
1.06.05 Needle thread tension release ............................................................................................ 56
2Switch diagrams ................................................................................................................ 57

Justierung
5
1 Adjustment
On the PFAFF 939 U and 3704 do not use a screw clamp on the needle bar!
The special coating of the needle bar could be damaged.
Please observe all notes from Chapter 1 Safety of the instruction manual! In
particular care must be taken to see that all protective devices are refitted
properly after adjustment, see Chapter 1.06 Danger warnings of the instruction
manual!
If not otherwise stated, the machine must be disconnected from the electrical
power supply.
Danger of injury due to unintentional starting of the machine!
Notes on adjustment
All following adjustments are based on a fully assembled machine and may only be carried
out by expert staff trained for this purpose. Machine covers, which have to be removed and
replaced to carry out checks and adjustments, are not mentioned in the text.
The order of the following chapters corresponds to the most logical work sequence for ma-
chines which have to be completely adjusted. If only specific individual work steps are
carried out, both the preceding and following chapters must be observed.
Screws, nuts indicated in brackets ( ) are fastenings for machine parts, which must be loose-
ned before adjustment and tightened again afterwards.
1.01 Tools, gauges and other accessories for adjusting
●1 set of screwdrivers with blade widths from 2 to 10 mm
●1 set of wrenches with jaw widths from 7 to 14 mm
●1 set of Allan keys from 1.5 to 6 mm
●1 metal rule, (Part No. 08-880 218-00)
●Feed dog adjustment gauge, part no. 91-119 995-05
●1 adjustment pin (5 mm dia.), Part No.. 13-030 341-05
●Hook bearing adjustment gauge, part no. 91-119 996-05
1.02 Abbreviations
TDC = top dead center
BDC = bottom dead center
1.03 Explanation of the symbols
In this adjustment manual, symbols emphasize operations to be carried out or important in-
formation. The symbols used have the following meaning:
Note, information
Service, repair, adjustment, maintenance
(work to be carried out by qualified staff only)

Justierung
6
Fig. 1 - 01
4
2
5
1
3
1.04 Check and adjustment aid
By blocking with holes 1 - 5 the required needle bar positions can be fixed ex-
actly.
●Turn the balance wheel until the needle bar has approximately reached the required posi-
tion.
●Place the 5 mm blocking pin in the appropriate hole and put pressure on it.
●Turn the balance wheel forwards and backwards a little until the blocking pin moves into
the slot in the crank behind the bearing plate, thus blocking the machine.
Hole 1 = 2.0 mm after the bottom dead center of the needle bar (2.0 past tdc)
Hole 2 = Top dead center of the needle bar (tdc)
Hole 3 = 0.25 mm after the top dead center of the needle bar (0.25 past bdc)
Hole 4 = 1.0 mm after the top dead center of the needle bar (1.0 mm past tdc)
Hole 5 = 4 mm after the bottom dead center of the needle bar (4.0 past bdc)

Justierung
7
Fig. 1 - 02
1
2
1.05 Adjusting the basic machine
1.05.01 Balancing weight
●Bring the needle bar to b.d.c.
●Adjust the balance weight 1 (screw 2) in accordance with the requirement.
Requirement
With the needle bar at bdc the largest eccentricity of the balancing weight 1 must be
pointing upwards.

Justierung
8
Fig. 1 - 03
2
1
3
1.05.02 Centering the needle in the needle hole (in sewing direction)
Requirement
With the zigzag setting at "0" and the needle position set at "middle" the needle must
enter the center of the needle hole as viewed in the direction of sewing.
●Bring the needle bar to b.d.c.
●Adjust the eccentric pin 1 (nut 2 and screw 3) in accordance with the requirement.

Justierung
9
Fig. 1 - 04
1
3
4
2
5
1
3
4
6
2
5
1.05.03 Parallel guiding of the needle bar
Requirement
Guide bar 5 must be parallel to the needle bar.
●Bring the needle bar to tdc (hole 2).
●Loosen screws 1,2 and nut 3.
●The largest eccentricity of pin 4 must be facing downwards.
●Bring the groove on guide bar 5 into a position in which it rests against eccentric pin 4,
turn eccentric pin 4 in accordance with the requirement and tighten nut 3.
●Push guide bar 5 downwards and then upwards as far as possible. Bushing 6 must not
move laterally during this movement (readjust eccentric pin 4 if necessary).
●Move guide bar 5 until it rests against eccentric pin 4 and tighten screws 1 and 2.

Justierung
10
0
1
2
6
5
3
4
Fig. 1 - 05
1
3
2
4
1.05.04 Locking lever
Requirement
The zigzag stitch adjustment lever 3 must be able to be locked in any position.
●Loosen screw 2.
●Press locking lever 1 against the zigzag stitch adjustment lever 3.
●Turn pivot pin 4 as far as possible to the left.
●Release locking lever 1.
●Locking lever 1 must be parallel to the zigzag stitch adjustment lever 3.
●Tighten screw 2.

Justierung
11
Fig. 1 - 06
1
23
4
5
6
7
7
1.05.05 Zero stitch and zigzag stitch scale
Requirement
With the zigzag stitch set at "0":
1. the needle bar must not move laterally when the balancewheel is turned and
2. the marking "0" on scale 1 must be at marking 2.
●Set the needle position adjustment lever 4 to "middle" and loosen screws 5 and 6.
●Run the machine slowly and turn the zigzag stitch adjustment lever 3 to the right until the
needle bar no longer moves laterally.
●Turn the machine off. Move screw 5 to the right until it touches and then tighten it.
●Loosen screws 7 and move scale 1 in accordance with requirement 2.
●Tighten screws 7.
Screw 6 remains loose for the following adjustment.

Justierung
12
Fig. 1 - 07
1
2
1.05.06 Centering the needle in the needle hole (crosswise to sewing direction)
Requirement
With the zigzag stitch set at "0" and the needle position setting at "middle" the needle
must enter the center of the needle hole as seen across the direction of sewing.
●Adjust the eccentric pin 1 (nut 2) in accordance with the requirement.

Justierung
13
Fig. 1 - 08
4
1
2
3
1.05.07 Zigzag stitch width
Requirement
At the largest zigzag stitch setting, marking 1 must be at the largest zigzag value on
scale 2.
●Turn the zigzag stitch adjustment lever 3 in accordance with the requirement.
●Move screw 4 upwards until it touches and then tighten it.
If the machine is equipped with a needle plate with a smaller hole than is mar-
ked on the scale, the zigzag limit must be set according to the needle hole
width on the needle plate.

Justierung
14
Fig. 1 - 09
43
2
1
5
1.05.08 Multi-stitch movement (only on the PFAFF 939U)
Requirement
1. When the needle, at its b.d.c., penetrates on the right-hand side, the recess 5 on the
control cam 3 should be positioned horizontally towards the rear.
2. The lateral movement of the needle bar should have been completed when the needle
penetrates the workpiece (carry out a check with the largest zigzag setting).
●Set the adjustment wheel 1 at multi-stitch.
●Set the zigzag stitch width lever 2 at "largest zigzag width".
●Adjust control cam 3 (screws 4) in accordance with the requirement.

Justierung
15
Fig. 1 - 10
21
5 mm
4
2
5
1
3
1.05.09 Zigzag stitch movement (only on the PFAFF 3704-2/..)
Requirement
When the needle bar, on the right of its throw, is positioned at t.d.c. (adjustment hole "2"),
the needle bar should not move laterally when the zigzag stitch adjustment lever is mo-
ved to and fro.
●Bring the needle bar, on the right of its throw, to t.d.c. and place the adjustment pin in
hole "2" of the bearing plate (locking the machine).
●Turn the zigzag eccentric 1 (screws 2) in accordance with the requirement. Make sure
that he zigzag eccentric 1 is about 5 mm away from the right inner side of the casting
wall.
●Remove the adjustment pin from the bearing plate.

Justierung
16
Fig. 1 - 11
21
1.05.10 Needle penetration symmetry - left, centre and right (only on the PFAFF 3704-2/..)
Requirement
When the zigzag stitch is set at "0", the needle should penetrate in the centre of the
needle hole. With the maximum zigzag stitch set, the needle should penetrate on the left
and right at the same distance from the centre hole.
●Let the needle penetrate in the required zigzag settings using paper.
●Without twisting it adjust zigzag eccentric 1 (screws 2) in accordance with the
requirement.

Justierung
17
2
Fig. 1 - 12
3
4
1
4
2
5
1
3
1.05.11 Zigzag movement (only on the 939U)
Requirement
When the needle bar, moving from its right b.d.c., reaches its t.d.c. (hole 2), it should not
carry out any lateral motion when the zigzag stitch width lever 4 is moved to and fro.
●Set the adjustment wheel 1 at zigzag.
●Adjust the zigzag eccentric 2 (screw 3) in accordance with the requirement.

Justierung
18
Fig. 1 - 13
1
3
2
0,2 - 0,3 mm
1.05.12 Target positioning sensor (only on the 939U)
Requirement
There should be a clearance of 0.2 – 0.3 mm between sensor 1 and control cam 3.
●Adjust sensor 1 (screws 2) in accordance with the requirement.

Justierung
19
Fig. 1 - 14
2
1
4
3
1.05.13 Needle position adjustment lever
●Loosen screws 1 and 2.
●Set the needle position adjustment lever 3 to "middle" and the zigzag stitch adjustment
lever 4 at the largest zigzag stitch.
●Place a piece of paper underneath the presser foot and perforate it to the left and right
with the needle.
●Set the zigzag stitch adjustment lever 4 at "0" and move the needle position adjustment
lever 3 to the right/left until the needle is exactly over the perforations made in the last
step.
●For the left needle-position bring screw 1 to a position where it touches and tighten it and
for the right needle-position do the same with screw 2.
Requirement
The left and right throws of the needle must be the same size at the largest zigzag stitch
setting and at the left or right needle position.

Justierung
20
Fig. 1 - 15
1.05.14 Adjustment wheels for differential feed (only on the PFAFF 939U)
●Loosen screws 1.
●Turn both adjustment wheels 2 until guide pin 3 is in the middle of the connecting link.
The ends of the two toothed racks 4 must be flush with each other.
●Turn both scale rings in accordance with the requirement and tighten screws 1.
Requirement
With guide pin 3 in the middle of the connecting link and the ends of the toothed racks 4
flush with each other, the zero markings on the adjustment wheels 5 must be at marking 6.
4
1
5
2
2
3