JUKI MF-7900 Series User manual

2
INSTRUCTION MANUAL
MF-7900(D)/UT55,56,57
No.01
70002031

i
CONTENTS
!. SPECIFICATIONS ..........................................................................................................1
@. AT THE BEGINNING......................................................................................................1
#. INSTALLING THE ACCESSORIES ...............................................................................2
1. Installing the presser lifting cylinder ............................................................................................ 2
2. Installing the air regulator .............................................................................................................. 2
3. Installation and setting SC-921...................................................................................................... 3
(1) Installing the SC-921 on the table ( Table-mount type ) ............................................................................3
(2) Installing the SC-921 on the table ( Semi-submerged type ) ....................................................................3
(3) Connecting the cords...................................................................................................................................4
(4) Setting procedure of the machine head .....................................................................................................5
(5) Setting the lower stop position of the needle bar .....................................................................................6
$. AIR PIPING DRAWING ..................................................................................................7
1. Piping of the thread trimmer device (UT57).................................................................................. 7
2. Piping of the thread trimmer device (UT55).................................................................................. 8
3. Piping drawing for air blow (UT56)................................................................................................ 9
4. Adjusting the air regulator ............................................................................................................. 9
%. THREADING THE MACHINE HEAD ...........................................................................10
^. ADJUSTING THE LOOPER THREAD TRIMMER MECHANISM................................11
1. Adjusting the thread trimmer air cylinder....................................................................................11
2. Adjusting the Lower knife ............................................................................................................ 12
3. Adjusting the position of clamp pressure adjusting spring ..................................................... 12
4. Adjusting the knife engagement and the knife pressure adjusting spring ............................. 12
5. Adjusting the pressure of clamp spring ..................................................................................... 12
6. Initial position of the looper thread trimmer mechanism.......................................................... 13
7. Adjusting the stopper ................................................................................................................... 13
8. Adjusting the height of the lower knife....................................................................................... 13
9. Adjusting the lower knife holder guide....................................................................................... 13
10. Adjusting the longitudinal position of the blade point of lower knife...................................... 14
11. Adjusting the thread trimmer sensor.......................................................................................... 14
12. Adjusting the speed of looper thread trimmer ........................................................................... 14
&. ADJUSTING THE THREAD RELEASE MECHANISM................................................15
1. Adjusting the disk-rise ................................................................................................................. 15
2. Adjusting the thread release hook .............................................................................................. 15
*. ADJUSTING THE TOP COVERING THREAD TRIMMER MECHANISM....................16
1. Adjusting the engagement of knives .......................................................................................... 16
2. Adjusting the pressure of clamp spring ..................................................................................... 16
3. Adjusting the position of the blade point of moving knife........................................................ 16
4. Adjusting the speed of moving knife .......................................................................................... 17
(. ADJUSTING THE AIR-BLOW WIPER (UT56).............................................................18
1. Installing the air-blow wiper......................................................................................................... 18
2. Adjusting the air-blow wiper ........................................................................................................ 18
). ADJUSTING THE NEEDLE THREAD WIPER (UT55) ................................................19
1. Adjusting the clamp spring.......................................................................................................... 19
2. Installing the needle thread wiper ............................................................................................... 19
_. MAINTENANCE ...........................................................................................................20
1. Cleaning the motor fan ................................................................................................................. 20

– 1 –
!. SPECIFICATIONS
Model name High-speed, cylinder-bed coverstitch machine Semi-dry head, high-speed, cylinder-bed
coverstitch machine
Model MF-7900 series MF-7900D series
Stitch type ISO standard 406, 407, 602, and 605
Example of application Hemming and covering for knits and general knitted fabrics
Sewing speed Max. 6,500 sti/min (at the time of intermittent operation)
V-belt type
Max. 6,000 sti/min (at the time of intermittent operation)
Direct-drive type
Speed of stitch at the delivery:
4,500 sti/min (at the time of intermittent operation)
Max. 5,000 sti/min (at the time of intermittent operation)
V-belt type
Max. 5,000 sti/min (at the time of intermittent operation)
Direct-drive type
Speed of stitch at the delivery:
4,000 sti/min (at the time of intermittent operation)
Needle gauge 3-needle .....5.6 mm and 6.4 mm
2-needle .....3.2 mm, 4.0 mm and 4.8 mm
Differential feed ratio 1 : 0.9 to 1 : 1.8 (stitch length : less than 2.5 mm)
(1 : 0.6 to 1 :1 .1, when the differential link hinge screw is changed)
Micro-differential feed adjustment mechanism is provided. (Micro-adjustment)
Stitch length 0.9 mm to 3.6 mm (can be adjusted up to 4.5 mm)
Needle UY128GAS #9S to #14S (standard #10S) UY128GAS #9S to #12S (standard #10S)
Needle bar stroke 31mm (33 mm when the eccentric pin is changed over)
Dimensions (Height) 450 x (Width) 456 x (Length) 299
Weight 45 kg (With pneumatic type thread trimmer) , 42 kg
Lift of presser foot 8 mm (needle gauge : 5.6 mm without top covering), and 5 mm (with top covering)
Micro-lifter mechanism is provided.
Feed adjustment
method
Main feed............... dial type stitch pitch adjustment method
Differential feed ..... lever adjustment method (micro-adjustment mechanism is provided.)
Looper mechanism Spherical rod drive method
Lubricating system Forced lubrication method by gear pump
Lubricating oil JUKI GENUINE OIL 18
Oil reservoir capacity Oil gauge lower line : 600 cc to upper line : 900 cc
Installation Table-mount type, Semi-submerged type
Noise - Equivalent continuous emission sound pressure level
(LpA) at the workstation:
A-weighted value of 79.5 dB; (Includes KpA = 2.5 dB);
according to ISO 10821- C.6.2 -ISO 11204 GR2 at
4,500 sti/min.
- Equivalent continuous emission sound pressure level
(LpA) at the workstation:
A-weighted value of 76.5 dB; (Includes KpA = 2.5 dB);
according to ISO 10821- C.6.2 -ISO 11204 GR2 at
4,000 sti/min.
Remove xed band 1for transportation before setting
up the sewing machine.
@. AT THE BEGINNING
1

– 2 –
1
2
1. Installing the presser lifting cylinder
#. INSTALLING THE ACCESSORIES
WARNING :
To protect against possible personal injury due to abrupt start of the machine, be sure to start the
following work after turning the power off and ascertaining that the motor is at rest.
1) Install presser lifting cylinder asm. 1to the sewing
machine with screws 3, washers 4and spring
washers 7.
2) Tighten screw 3in such manner that a clearance
of 1 to 2 mm is provided between cap 9 at the top
end of presser lifting cylinder asm. 1and presser
lifting lever 2.
If the clearance cannot be adjusted to 1 to 2 mm,
adjust the height of nut 8and cap 9to obtain the
correct clearance between the cap and lever.
3) Adjust the height of screw 5referring to the
Instruction Manual for MF-7900 (^-14. Adjusting
the presser foot lift), and tighten nut 6.
4) Stroke of cylinder asm. 1is 30 mm. Make sure
that presser lifting lever 2comes in contact with
screw 5within the range of cylinder stroke.
1) Install air regulator asm. 1under the table with
wood screws 2.
2. Installing the air regulator
1
2
3
4,7
5
6
1 to 2mm
8
9

– 3 –
* The instructions apply to the case the control box is installed on the table of the MF-7900(D).
To use any other machine head, install the control box on the table referring to the Instruction Manual for the
main body of the relevant sewing machine.
1) Install control box 2on the table with mounting bolt asm. 1supplied with the unit.
At this time, insert the nuts and washers supplied with the unit as illustrated in Figure Aso that the support
plates and the control box 2 are securely xed.
2) Install the control box 2(or the one equipped with a small sized motor unit) on the table. Then, install the
sewing machine head on the table. (Refer to the Instruction Manual for the sewing machine.)
3) Install the mounting plate on the CP-18 panel 5with four tapping screws 4supplied with the unit.
At this time, take care not to allow the cable to be caught under the mounting bracket.
(Install the CP-18 on the table as illustrated in Fig. B.)
4) Install CP-18 panel 5on the table with wood screw 6.
1) Install right and left support plates 7and two
rubber seats 8of the respective support plates.
2) Install control box mounting plate 9on the
control box with four screws !0.
3) Install the parts assembled in Step 2) on the
underside of support plates 7with four screws
!1.
4) Install support plates 7and the control box
2on the table with mounting bolts asm. 1
supplied with the unit. At this time, insert the
nuts and washers supplied with the unit as
illustrated in Figure Aso that the support plates
and the control box 2 are securely xed.
* The steps of procedure from the next one and
beyond are same with those for the table-xed
type machine head.
(1) Installing the SC-921 on the table ( Table-mount type )
3. Installation and setting SC-921
(2) Installing the SC-921 on the table ( Semi-submerged type )
1
2
6
5
Convex
washer
Spring
washer Hexagonal nut
Fig. A
4
6
Fig. B
1
9
!0
7
8
!1
1
2

– 4 –
(3) Connecting the cords
1) Pass cords 1of the thread trimming solenoid,
reverse-stitching solenoid, etc. and the cord from
the motor through hole Ain the table to route them
down under the machine table.
2) Loosen screw Bin cover 2with a screwdriver to
open the cover.
3) Connect 14P code 3coming
from the machine head to
connector 6(CN36).
4) Insert 3P cord 9coming
from the machine head into
connector !0 (CN42).
5) Insert presser foot lifter cord 2P
4into connector 7(CN37).
6) Connect connector 5coming
from the motor to connector 8
(CN30) on the circuit board.
7) Insert pedal sensor cable !1 into connector !2 (CN34).
8) Insert motor fan cord !3 into connector !4.
[Connecting the connector for the operation panel]
Be sure to turn OFF the power before con-
necting the connector.
Be sure to securely insert the respective connectors after checking the inserting directions since all con-
nectors have the inserting directions. (When using a type with lock, insert the connectors until they go to
the lock.) The sewing machine is not actuated unless the connectors are inserted properly. In addition, not
only the problem of error warning or the like occurs, but also the sewing machine and the control box are
damaged.
The connector for the operation panel is provided.
Paying attention to the orientation of the connector !5,
connect it to connector (CN38) !6 located on the circuit
board. After the insertion, securely lock the connectors
to prevent them from coming off easily.
!5
!6
7
4
5
8
3
6
9
!2!0
!1
!3
!4
1
A
2
B

– 5 –
4
321
4
321
4
321 Type of machine head Model name
F79
MF-7900/UT55
MF-7900/UT56
MF-7900/UT57
F79d
MF-7900D/UT55
MF-7900D/UT56
MF-7900D/UT57
(4) Setting procedure of the machine head
For the operation panel other than CP-18, refer to the Instruction Manual for the operation panel to be used
for the setting procedure of the machine head.
1) Call function setting No. 95.
2) The type of machine head can be
selected by pressing switch
3
(
switch
4
).
* Refer to the "MACHINE HEAD
LIST" on the separate sheet or the
Instruction Manual for the machine
head of your sewing machine for the
type of the machine head.
3) After selecting the type of machine
head, by pressing switch 1(
switch 2), the step proceeds to
96 or 94, and the display automatically
changes to the contents of the
setting corresponding with the type of
machine head.

– 6 –
4
321
Fig. 1
(5) Setting the lower stop position of the needle bar
Call function setting No. 122. Check to
be sure that the lower stop position of
the needle bar is as shown in Fig. 1. If
not, adjust the lower stop position of the
needle bar properly using function setting
No. 122. (Adjustment can be made within
the range of ±15°).

– 7 –
$. AIR PIPING DRAWING
WARNING :
To protect against possible personal injury due to abrupt start of the machine, be sure to start the
following work after turning the power off and ascertaining that the motor is at rest. In addition, cut the air
supply from air compressor.
1. Piping of the thread trimmer device (UT57)
!1
3
4
9
1
2
!0
9
!0
!1
@3
9
!1

– 8 –
2. Piping of the thread trimmer device (UT55)
3
4
@3
9
!1

– 9 –
1
2
3A
@3
3. Piping drawing for air blow (UT56)
Air hose
1) Insert the air hose to air regulator 1.
2) Use the air pressure at 0.4 to 0.5 MPa (4 to 5 kgf/
cm2).
3) Draw up regulator knob 2, turn knob 2and adjust
the pointer to 0.4 to 0.5 MPa to adjust the air
pressure.
4) After the adjustment, press downward regulator
knob 2.
5) When drainage is collected at section Aof
regulator 1during using, press drain cock 3to
discharge the drainage.
4. Adjusting the air regulator
3
4
6
1
@3
3
5
3
5
2

– 10 –
* For the adjustment procedure other than the above, refer to the Instruction Manual for MF-7900.
12
1
2
Thread the machine head according to the following threading illustrations.
WARNING :
To protect against possible personal injury due to abrupt start of the machine, be sure to start the
following work after turning the power off and ascertaining that the motor is at rest. If threading is wrong,
stitch skipping, thread breakage, needle breakage or irregular stitches will be caused. So, be careful.
%. THREADING THE MACHINE HEAD
When the small thread tension in the face plate is used for the machine with the thread trimmer device,
the length of remaining needle thread after thread trimming becomes short and slip-off of thread at the
start of sewing may occur.

– 11 –
1) Stroke of air cylinder 3is 18 mm.
When adjusting the stroke, loosen setscrew 2of
collar 1and move collar 1to the right or left to
adjust.
^. ADJUSTING THE LOOPER THREAD TRIMMER MECHANISM
WARNING :
To protect against possible personal injury due to abrupt start of the machine, be sure to start the
following work after turning the power off and ascertaining that the motor is at rest. In addition, cut the air
supply from air compressor.
1. Adjusting the thread trimmer
air cylinder
1
3
18 mm
2

– 12 –
1) The looper thread is held by clamp pressure
adjusting spring !2 after thread trimming.
2) Holding pressure of the looper thread can be
adjusted by turning screw 8.
3) When screw 8is turned clockwise, the holding
pressure is increased and turned counterclockwise,
the pressure is decreased.
4) Make the holding pressure as low as possible
within the range of holding the looper thread.
1) Loosen screws 7and 8, and adjust the position
of upper knife !0 so that the engagement of the
upper knife !0 with the lower knife is 0.5 mm when
lower knife 4moves to the extreme right.
2) At the same time, adjust so that a clearance of
0.5 to 1 mm is provided between knife pressure
adjusting spring !1 and clamp pressure adjusting
spring !2.
3) After the adjustment, tighten screws 7.
1) Set lower knife 4and lower knife holder 5with
setscrews 6at the position of the illustration.
2. Adjusting the Lower knife
3. Adjusting the position of clampAdjusting the position of clamp
pressure adjusting spring
1) Loosen screws 9.
2) Adjust so that a clearance of 2.5 ± 0.5 mm is
provided between the top end of clamp pressure
adjusting spring !2 and the top end of lower
knife 4when the lower knife 4is brought to the
rightmost position.
3) After the adjustment, tighten screws 9.
4. Adjusting the knifeAdjusting the knife
engagement and the knife
pressure adjusting spring
5. Adjusting the pressure of
clamp spring
4
5
6
65.5 mm
0.5 mm
4
8
!0
79
!1
!2
2.5 ± 0.5 mm
Clearance of 0.5 to 1 mm
!2
!1
4

– 13 –
When the needle is positioned at its upper dead point,
the clearance of 0 to 0.1 mm has to be provided be-
tween the under surface of lower knife 4and the top
surface of looper !3.
8. Adjusting the height of the
lower knife
When lower knifeknife 4is located at its leftmost position,
the top end of the lower knifeknife 4has to be spaced 22 ±
0.5 mm from the center of needle bar.
6. Initial position of the looper
thread trimmer mechanism
Check the leftmost point with the pneumatic device
turned on. Adjustment should be carried out with the air
pressure set at 0.5 MPa.
Adjust the position of stopper !4 so that a clearance of
0.3 to 1 mm is provided between looper !3 and clampclamp
pressure adjusting spring !2 when the counter knife is
located at its leftmost position (forward end).
7. Adjusting the stopper
Perform the work with the needle bar at the
highest position when actuating the thread
trimmer mechanism by hand.
When the lower knife moves from right to left, the lower
knife guide holder should lightly comes in contact with
the guide.
9. Adjusting the lower knife
holder guide
4
!3
0 to 0.1 mm
0.3 to 1 mm
!3
!2
Light contact
Center of needle
bar
22 ± 0.5 mm
4
!4

– 14 –
1) Bring the needle bar to its highest position.
2) Adjust so that the blade point of lower knife 4is in
the center of the thickness of looper !3 when the
clearance between the right-hand edge of looper
!3 and the blade point of lower knife 4is 9 mm.
3) Loosen nut !5, move lower knife holder 5to and
fro, and adjust the position of the blade point of
lower knife 4.
4) After the adjustment, tighten nut !5.
10. Adjusting the longitudinal
position of the blade point of
lower knife
The safety switch is installed so that the sewing ma-
chine does not start unless the looper thread trimmer
device returns to its home position.
1) Loosen setscrews !6.
2) Adjust switch plate !7 so that LED of thread
trimmer sensor !8 lights up in the state that the
thread trimmer device is fully returned to its home
position.
3) Tighten setscrews !6.
Speed of the looper thread trimmer device can be
changed with speed controllers @2 and @3 of air cylinder
3.
1) When you desire to change the protruding speed of
lower knife, loosen the nut of speed controller @2,
and turn the adjustment screw.
When you desire to change the returning speed of
lower knife, loosen the nut of speed controller @3,
and turn the adjustment screw.
2) After the adjustment, tighten the nuts of speed
controllers @2 and @3.
11. Adjusting the thread trimmer
sensor
12. Adjusting the speed of
looper thread trimmer
4
9 mm
Blade point of lower knife is in the
center of thickness of looper.
!3
!7
!8
!6
5
!5
@2 @3
3
Perform the work with the needle bar at the
highest position when actuating the thread
trimmer mechanism by hand.
Perform the work with the needle bar at the
highest position when actuating the thread
trimmer mechanism by hand.
• When the protruding speed of lower knife is
slow, thread trimming failure will be caused.
• When the returning speed of lower knife is
fast, lower thread clamp failure or uneven
needle thread remaining length will be
caused.

– 15 –
WARNING :
To protect against possible personal injury due to abrupt start of the machine, be sure to start the
following work after turning the power off and ascertaining that the motor is at rest. In addition, cut the air
supply from air compressor.
&. ADJUSTING THE THREAD RELEASE MECHANISM
1) Loosen setscrew 2in adjustment cam 1, turn
adjustment cam 1and disk-rise plate 3moves up
or down.
2) Adjust the clearance between the click section of
disk-rise plate 3and thread tension disk 4to 0.2
to 0.5 mm, and tighten setscrew 2.
3) If the click section of disk-rise plate 3comes in
contact with thread tension disk 4, sewing trouble
will be caused. So, be careful.
When the thread remaining length at the start
of sewing is short, stitch skipping or slip-off
of thread from needle eyelet at the start of
sewing is apt to occur.
1. Adjusting the disk-rise
2. Adjusting the thread release
hook
1) Loosen setscrew 5. Adjust so that the top end of
tension release rod 6is spaced 45 ± 1 mm from
the top end of take-up thread guide 7. Then,
tighten setscrew 5.
2) Loosen setscrew 9, move the position of thread
release hook 8up or down, and the thread
remaining length at the start of sewing can be
adjusted.
• When the position of thread release hook 8is
raised, the thread remaining length at the start
of sewing is decreased and when it is lowered,
the thread remaining length at the start of
sewing is increased.
• If stitch skipping occurs at the beginning of
sewing when using non-elastic thread, properly
adjust the remaining length of top-covering
thread at the start of sewing using setscrew !0
and minimize the remaining length of looper
thread at the start of sewing using screw !1.
*A
Clearance between click and disk is 0.2 to 0.5 mm.
(5 places)
1
2
3
4
5
6
7
8
9
*A
!0
!1
45 ± 1mm

– 16 –
*. ADJUSTING THE TOP COVERING THREAD TRIMMER MECHANISM
WARNING :
To protect against possible personal injury due to abrupt start of the machine, be sure to start the
following work after turning the power off and ascertaining that the motor is at rest. In addition, cut the air
supply from air compressor.
Make sure that the moving knife does not
interfere with other components such as
presser, needle, spreader, etc. within the
working range of moving knife 2.
1. Adjusting the engagement of
knives
1) Adjust so that the engagement of xed knife 1
with moving knife 2is 0.5 mm.
2) When adjusting the engagement, loosen setscrews
4and move knife holder 5up or down to adjust.
2. Adjusting the pressure of
clamp spring
1) Top covering thread is held with clamp spring 3
after thread trimming.
2) Holding pressure can be adjusted by loosening nut
6and turning screw 7.
3) Holding pressure is increased when tightening
screw 7and it is decreased when loosening screw
7.
4) After the adjustment, tighten nut 6.
5) Make the holding pressure as low as possible
within the range of holding the top covering thread.
3. Adjusting the position of the
blade point of moving knife
1) Bring the needle bar to its highest position.
2) When hinge screw 8is lowered, moving knife 2
lowers together.
3) Adjust so that the hook of moving knife 2enters
the recess in the top face of spreader 9to be
brought to the position where the moving knife
catches the top covering thread when moving
knife 2is brought to the lowermost position. Then,
tighten screws !0, !1 and !2.
Adjust the moving knife vertically so that a
clearance of 0.5 mm is provided between the
recess section of spreader 9and the moving knife,
and laterally so that the moving knife 2is brought
to the center of the width of recess in spreader, as
illustrated in Figure A.
4) Screws !2 are for adjusting vertical position of the
knife, screws !0 for adjusting lateral position of
the knife, and screws !1 for adjusting angle of the
knife.
0.5 mm
1
23
4
5
6
7
8
0.5 mm
Fig. A
2
9
2
9
!1
!0 !2

– 17 –
・ When the protruding speed of moving
knife is slow, thread trimming failure will
be caused.
・When the returning speed of moving knife
is fast, needle thread clamp failure will be
caused.
4. Adjusting the speed of
moving knife
Stroke of air cylinder 1is 20 mm.
Speed of the moving knife can be changed with speed
controllers 2and 3.
1) When you desire to change the protruding speed
of moving knife, loosen the nut of speed controller
2and turn the adjustment screw.
When you desire to change the returning speed of
moving knife, loosen the nut of speed controller 3
and turn the adjustment screw.
2) After the adjustment, tighten the nuts of speed
controllers 2and 3.
1
2
3

– 18 –
(. ADJUSTING THE AIR-BLOW WIPER (UT56)
WARNING :
To protect against possible personal injury due to abrupt start of the machine, be sure to start the
following work after turning the power off and ascertaining that the motor is at rest. In addition, cut the air
supply from air compressor.
1. Installing the air-blow wiper
1) When using air-blow wiper 1, remove the top
covering thread trimmer device.
2) Tighten air-blow wiper 1with setscrews 2.
3) Perform piping referring to “$. AIR PIPING
DRAWING” p.7.
2. Adjusting the air-blow wiper
Adjust the air-blow position of air-blow wiper1.
1) Adjust so that the air outlet of air-blow wiper 1is
positioned in the rear of needle and slightly on the
lower side of needle eyelet of the left needle when
the needle bar is in the highest position.
2) After the adjustment, temporarily tighten setscrews
2.
3) Supply air from the air compressor and turn the
power ON.
4) When the back part of the pedal of sewing
machine is depressed, the presser goes up and
simultaneously air blows from air-blow wiper 1.
Re-adjust the position of air-blow wiper 1so that
air blows only to the needle thread in the rear of
the needle eyelet.
5) After the re-adjustment, tighten setscrews 2.
・When air blows in front of the needle,
needle thread slips from the needle eyelet.
So, be careful.
・Adjust the air-blow strength with speed
controller 3.
・ Handwheelmayrotateuptothexedposi-
tion when turning ON the power. So, be
careful.
1
2
3