JUKI LBH-781 User Manual

BE078130B0A
MODEL LBH-781-782-783-784
Before operating your JUKI Lock
stitch Machine, please read this In
struction Book carefully in order to
operite it in the correct and efficient
HIGH SPEED SINGLE NEEDLE LOCKSTITCH STRIAGHX
BUTTON HOLING SEWING MACHINE
Instruction Book
CAUTION IN OPERATION
SPECIFICATIONS
1. The machine should rotate counterclockwise as observed
from the pulley. Take care not to rotate the machine in
the opposite direction.
2. Never start the machine before filling the machine base
with lubricating oil.
3. Remove the bobbin case and the needle thread from the
machine before performing the trial operation.
4. Clean up the sewing' hook and the bobbin thread
trimmer every day after sewing work. Also check the
level of the lubricating oil.
Application
Sewing speed
Buttonhole
length
Bar-tack width
Needle
Presser lift
Lubricating oil
1. MOTOR PULLEY AND V BELT
1. Motors of 300W, 4-pole are used for single-phase or three-phase
operation.
(If a 250W motor has to be used, operate the machine
at 3,100 s.p.m. or less.)
2.
M-type V belts are used.
3. Refer to the following table for the motor pulleys, V belt length,
and sewing speed.
Sewing speed Frequency Motor pulley Part No.
3,600 s.p.m.
B7262-781-000
B7263-781-000
3,400 s.p.m.
B725 6-781-000
B7257-781-000
B725 3-781-000
High speed
Vbelt
44 inch
43 inch
44 inch
42 inch
43 inch
Low speed
Vbelt
42 inch
42 inch
43 inch
42 inch
42 inch
LBH-781 LBH-782 LBH-783 LBH-784
Buttonholing for ordinary cloth, knit, etc.
Max. 3,600 s.p.m.
6.4~19.0mni 6.4~25.4mm 6.4~31.7mm 12.7~38.0m
(l/4"~3/4") (1/4"~1") ,i®/4"-l-l/4") (l/2"-I-l/2
mrATn''\ -S.Omin (3/32"~3/l 6")
DPx5 #11~#14
12mm {15/32")
JUKI New Defrix Oil No. 1
i
3,100 s.p.m.
B7254-781-000
42 inch
2,900 s.p.m.
B7258-781-000
B7259-781-000
42 inch
42 inch
42 inch
* How to install motor pulley
Place motor pulley 0 into the motor shaft so that
flat part © of the motor shaft aligns with first
setscrew o Then securely tighten setscrews 0 and
41 inch
(V belt Part No.: MTJ-VMOODDOO, V belt length)
*
How to install V belt
1. Mount high-speed V belt O oti accelerating pulley 0 and the largediameters of the motor pulley.
2. Mount low-speed V belt 0 on low-speed pulley 0 and the smalldiameters of the motor pulley.
3. By moving the motor from side to side, adjust the tension of V belts 0 and 0 so that they give an approx. 10 mm slack
when their middle portions are pushed lightly by hand.
4. Move the motor pulley back and forth to align V belts 0 and 0.
42 inch
i
Motor pulley
From the library of: Superior Sewing Machine & Supply LLC

JUKI LBH-781 Specifications

General

Brand	JUKI
Model	LBH-781
Category	Sewing Machine
Language	English

Summary

Motor Pulley and V Belt Installation

How to Install Motor Pulley

Mounting the motor pulley onto the motor shaft and securing it with setscrews.

How to Install V Belt

Mounting V belts, adjusting tension for optimal slack, and aligning them.

Setting Up the Thread Stand

Setting Up the Machine Head

Attaching the Flat Belt

Belt Cover Installation and Removal

Lubrication Procedures

Before Starting Machine Lubrication

Filling the oil reservoir, supplementing oil, and checking oil circulation.

Adjusting Lubrication for Sewing Hook

Adjusting oil volume to the sewing hook using oil adjusting screws for fine and rough adjustments.

Other Lubricating Points

Applying oil to specific points weekly or bi-weekly, and for new setups or machines out of use.

Installing the Needle

Bobbin Case Installation and Removal

Winding the Bobbin

Attaching the Bobbin

Threading the Needle-Thread

Sewing Speed Reduction and Emergency Stop

Reduction of Sewing Speed

Slowing down the machine by turning the hand stop crank downwards.

Emergency Stop Procedure

Stopping the machine immediately by turning the hand stop crank downwards and upwards.

Manual Feed Handle Operation

Holding the Descending Knife

Types of Stitches

Thread Tension Adjustment

Adjusting Thread Tension for Purl Stitch

Adjusting bobbin thread tension and needle thread tension for proper purl stitches.

Adjusting Thread Tension for Whip Stitch

Adjusting bobbin thread tension and needle thread tension for proper whip stitches.

Adjusting Thread Take-Up Spring (Purl Stitch)

Adjusting the stroke and tension of the thread take-up spring for purl stitch.

Adjusting Overedging Length (Buttonhole Length)

Replacing the Knife

Adjusting Overedging Width and Reference Position

Changing the Number of Stitches

Spur Gears Information

Information on selecting and using spur gears to control stitch count.

Attaching Spur Gears to Shafts

Instructions for securely mounting spur gears onto their respective shafts.

Adjusting Presser Bar Pressure

Needle-to-Hook Relation Setup

Setting Needle to Hook Relation

Detailed procedure for setting needle bar height and hook timing using a timing gauge.

Setting the Needle Bar

Specific steps for adjusting the needle bar height relative to the throat plate.

Setting the Hook

Steps for setting the hook's timing and clearance with the needle.

Adjusting the Bobbin Thread Winder

Adjusting the Speed Transmitter

Adjusting Belt Shifter Position

Adjusting the belt shifter to align with the correct pulley for low-speed operation.

Adjusting Stopper Screw

Adjusting the stopper screw to prevent the belt from coming off the pulley.

Needle Thread Trimmer Adjustment

Attaching the Trimmer

Mounting the trimmer and adjusting its height for minimal thread residue.

Closing Timing of Needle Thread Trimmer

Adjusting the trimmer's closing timing by moving the driving plate for complete closure.

Opening Timing of Needle Thread Trimmer

Adjusting the trimmer's opening timing by moving the driving plate for gradual opening.

Needle Thread Trimmer Holder and Limiting Plate Adjustment

Timing for Dropping the Knife

Trouble, Cause, and Remedy (1)

1. Needle Thread is Broken

Identifies causes like tight tension, hook damage, or incorrect threading and their remedies.

2. Thread Slips Out of Needle

Addresses issues like early trimmer opening, incorrect work clamp check, or wrong threading.

3. Wobbling Stitches in Overedging Seams

Covers loose tension discs, incorrect take-up spring tension, and high bobbin thread tension.

4. Wobbling Stitches at Start of Sewing

Points to loose tension discs, high needle thread trimmer, or excessive take-up spring stroke.

5. Needle Thread Lumps on Cloth Bottom

Indicates loose tension disc No. 1 or too high bobbin thread tension.

6. Stitches Float Over Cloth

Relates to insufficient bobbin thread tension or improper bobbin case threading.

7. Stitches are Skipped

Covers work clamp check size and material properties affecting stitch skipping.

Stitching Troubles Caused by Other Reasons (2)

1. Starting Pedal Does Not Work

Addresses clogged needle plate, trimmer, or interference with the work clamp check.

2. Machine Does Not Reach High Speed

Points to incorrect hand stop crank position or speed transmitter belt shifter.

3. Loud Noise or Speed Issues

Relates to low speed cam setting, loose flat belt, or loose low speed V belt.

4. Stop-Motion Not Smooth

Points to lubrication needs for the stop-motion lever or speed transmitter belt shifter.

5. Machine Does Not Lubricate

Covers low oil level in the reservoir or lack of oil circulation.

6. Knife Dropped During High Speed Rotation

Relates to incorrect knife tripping segment position or low speed cam setting.

7. Knife Dropped Even if Needle Thread Broken

Points to incorrect threading or incorrect needle/hook/trimmer positions.

8. Needle is Broken

Addresses bent needles, needle-hook touching, or trimmer hitting the needle.