JUKI MF-7923 User manual

3
INSTRUCTION MANUAL
MF-7900
No.03
70002027

i
CONTENTS
!. SPECIFICATIONS ..........................................................................................................1
@. CONFIGURATION OF THE MACHINE COMPONENTS ...............................................2
#. INSTALLATION ..............................................................................................................3
1. Installing the machine head onto the table ........................................................................... 3
2. Selecting the motor pulley and the belt................................................................................. 9
3. Installing the motor.................................................................................................................. 9
4. Setting the belt ........................................................................................................................ 9
5. Installing the belt cover......................................................................................................... 10
6. Installing the chain ................................................................................................................ 10
7. Installing the thread guide .................................................................................................... 10
8. Installing the needle bar thread take-up cover ................................................................... 11
$. LUBRICATION AND OILING .......................................................................................11
1. Lubricating oil ........................................................................................................................ 11
2. Oiling....................................................................................................................................... 11
3. Silicon oil lubricating unit..................................................................................................... 12
%. OPERATION.................................................................................................................12
1. Needle ..................................................................................................................................... 12
2. Attaching the needle.............................................................................................................. 12
3. Threading the machine head ................................................................................................ 13
(1) Standard threading .................................................................................................................. 13
4. Adjusting the stitch length.................................................................................................... 14
5. Adjusting the differential feed ratio ..................................................................................... 14
6. Adjusting the presser foot pressure......................................................................................... 15
7. Adjusting the thread tension ................................................................................................ 15
^.
ADJUSTING THE SEWING MACHINE.......................................................................................16
1. Adjusting the silicon container thread guide...................................................................... 16
2. Adjusting the needle bar thread take-up thread receiver .................................................. 16
3. Adjusting the rocking thread take-up .................................................................................. 17
4. Adjusting the spreader thread guide ................................................................................... 17
5. Adjusting the looper thread cam thread guide and the looper thread cam ..................... 17
6. Adjusting the looper.............................................................................................................. 18
7. Adjusting the height of the needle....................................................................................... 18
8. Adjusting the rear needle guard.................................................................................................................19
9. Relation between the rocking thread take-up timing and the needle thread loop ..............19
(1) Adjustment by the crank ......................................................................................................... 19
(2) Adjustment by the eccentric cam ........................................................................................... 20
10. Adjusting the height of the feed dog ................................................................................... 21
11. Installing position of the spreader ....................................................................................... 21
12. Adjusting the spreader thread guide and the needle clamp thread guide....................... 22
13. Adjusting the front needle guard ......................................................................................... 22
14. Adjusting the presser foot lift............................................................................................... 23
15. Adjusting the micro-lifter ...................................................................................................... 23
16. Adjusting the feed locus ....................................................................................................... 24
(1) Retarding the feed driving motion.......................................................................................... 24
(2) Retarding the feed rocking motion......................................................................................... 25
17. Adjustment value of balloon................................................................................................. 26
&. MAINTENANCE ...........................................................................................................28
1. Cleaning the sewing machine............................................................................................... 28
2. Replacing the lubricating oil ................................................................................................ 28
 3. Inspectingandreplacingtheoillter .................................................................................. 28

– 1 –
!. SPECIFICATIONS
Model name High-speed, cylinder-bed coverstitch machine
Model MF-7900 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
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)
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 #12S (standard #10S)
Needle bar stroke 31mm (33 mm, when the eccentric pin is changed)
Dimensions (Height) 450 x (Width) 468 x (Length) 264
Weight 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-xed 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.

– 2 –
@. CONFIGURATION OF THE MACHINE COMPONENTS
1Presser spring regulator !4 Needle tip silicon oil lubricating unit
2Needle bar thread take-up cover !5 Differential lock nut
3Oil circulation inspection windows !6 Micro-adjustment knob
4Oil hole cap !7 Finger guard
5Micro-lifter !8 Rocking thread take-up
6Needle thread silicon oil lubricating unit !9 Front cover
7Thread guide No. 1 @0
Needle bar thread take-up thread receiver
8Upper pulley @1 Silicon container thread guide
9Thread tension nut @2 Belt cover
!0 Oil gauge @3 Differential feed regulating lever
!1 Feed regulating knob
!2 Eye guard cover
!3 Throat plate
1
2
346
8
9
!1
!3
!5
!6
!7
!8
@2
!9
@0
@3
@1
5
!2
7
!4 !0

– 3 –
#. INSTALLATION
 Attach the pins and the rubber cushions as shown in
the illustration and properly install the sewing machine.
1
Rubber cushion (Black) x 3
2Washer
3Spring washer
4Nut
5Pin
6
Rubber cushion (Gray) x 1
Attach the supporting board and the rubber seats as
shown in the illustration and properly install the sewing
machine.
1Bolt
2Spacer
3Washer
4Spring washer
5Nut
6Supporting board
7Spring pin
8Rubber cushion (Black) x 3
9Rubber cushion (Gray) x 1
Semi-submerged type
1. Installing the machine head onto the table
WARNING :
Do not insert the power plug of the motor into the receptacle until all works have been completed. There
is a danger of injury by being caught in the machine.
WARNING :
The weight of the sewing machine is more than 42 kg. Be sure to perform the work with two persons or
more in case of unpacking, transportation or installation.
1
5
2
3
4
1
2
3
4
5
6
7
8
6
9
■Installing the rubber cushion
Install the gray dust-proof rubber to section A only.
Part No. Part name Q'ty
140072505 Dust-proof rubber (Gray) 1
213155403 Dust-proof rubber (Black) 3
A
1
2
2
[For the V-belt type]