VGS3721-8 - Sewing machine Yamato - Free user manual and instructions

Product Type	Sewing machine
Brand	Yamato
Model	VGS3721-8
Dimensions (approx)	40 x 18 x 30 cm
Weight	7 kg
Power Supply	220-240 V, 50/60 Hz
Power Consumption	85 W
Stitch Types	Basic, zigzag, buttonhole, blind hem, stretch
Stitch Length	Adjustable, up to 4 mm
Stitch Width	Adjustable, up to 5 mm
Sewing Speed	Up to 800 stitches per minute
Needle System	130/705H (standard)
Bobbin Type	Drop-in top loading
Thread Tension	Adjustable dial
Presser Foot	Multiple feet included (all-purpose, zipper, buttonhole, etc.)
Lighting	LED light
Free Arm	Yes
Reverse Sewing	Yes, with lever
Safety Feature	Safety switch (machine stops when cover is opened)
Maintenance	Clean bobbin area and oil moving parts periodically
Accessories Included	Seam ripper, needles, bobbins, screwdriver, oil, dust cover
Repairability	Spare parts available through authorized service centers

Frequently Asked Questions - VGS3721-8 Yamato

How do I thread the Yamato VGS3721-8 sewing machine?

Follow the numbered threading path on the machine. Start by placing the spool on the spool pin, then guide the thread through the top tension disc, take-up lever, and needle eye. Use the thread guide diagram on the machine for reference.

What type of needle should I use?

Use standard household needles (system 130/705H). For different fabrics, choose appropriate needle sizes: 70/10 for lightweight, 80/12 for medium, 90/14 for heavy fabrics.

How do I wind the bobbin?

Place an empty bobbin on the bobbin winder spindle, push it to the right, then guide thread from the spool through the bobbin winding tension disc. Start the machine slowly and stop when full.

Why is my machine skipping stitches?

Possible causes: bent needle, incorrect needle size, improper threading, or tension issues. Replace the needle, rethread, and check tension settings. Ensure the needle is inserted correctly.

How do I adjust the stitch length?

Use the stitch length dial on the front of the machine. Turn it to the desired setting: higher numbers give longer stitches. For buttonhole or special stitches, consult the manual.

What maintenance does the machine require?

Regularly clean lint from the bobbin area and feed dogs. Oil the machine every 8 hours of use with sewing machine oil. Remove the needle plate for thorough cleaning.

How do I sew a buttonhole?

Attach the buttonhole foot, select the buttonhole stitch (usually step 1-4), and place the button in the holder. Lower the presser foot and slowly press the foot pedal. The machine will sew the buttonhole automatically.

Why is the thread bunching underneath?

This indicates incorrect upper tension or bobbin threading. Re-thread the upper thread and make sure the bobbin is inserted correctly. Adjust the upper tension dial to a lower number if too tight.

What accessories come with the machine?

The VGS3721-8 includes multiple presser feet (all-purpose, zipper, buttonhole, blind hem), bobbins, needles, a seam ripper, screwdriver, oil, and a dust cover.

How do I troubleshoot if the machine won't start?

Check power cord connection, ensure the foot pedal is plugged in, and verify that the machine is not in a locked position. Also check the safety switch on the side cover (must be closed).

USER MANUAL VGS3721-8 Yamato

WITH LEFT HAND TRIMMING AND TOP FEEDER

VGS3721-8

Thank you for having purchased the Model VGS3721-8.

Before using your VGS3721-8, please read the instruction manual and understand the contents well.

After reading the instruction manual, please keep it in a location where it is easily accessible to the operator.

Safety instructions

i - iv

1. Name of each part

1

2. Installation

2

2.1	Table cutting diagram	2
2.1.1	Table top type (Type A: standard)	2
2.1.2	Table top type (Type B)	3
2.2	Table top type	4
2.3	Motor and belt	5
2.4	Hanging belt	5
2.5	Belt cover	6
2.6	Eye guard and finger guard	6
2.7	Accessories	7

3. Sewing speed and rotating direction of pulley

8

4. Lubrication

9

4.1	Lubricating oil	9
4.2	Lubricating	9
4.3	Changing oil	10
4.4	Checking and replacing oil filter	10

5. Proper operation

11

5.1	Needle system	11
5.2	Installing needles	11
5.3	Threading	12
5.4	Adjusting thread tension	13
5.5	Pressure of presser foot	13
5.6	Adjusting position of presser foot	13
5.7	Adjusting movement of differential feed dog	14
5.8	Adjusting stitch length	15
5.9	Adjusting feeding amount of top feed dog to lower feed dog	16
5.10	Folder(left)	17
5.11	Trimming width of fabric	17
5.12	Folder(right)	18
5.13	Fabric guide(right)	18
5.14	SP device and HR device	19
5.15	Cleaning the machine	19

6. Adjustments 20

6.1	Needle thread tension	20
6.2	Top cover thread tension	21
6.3	Looper thread tension	21
6.4	Needle and spreader	22
6.4.1	Spreader	22
6.4.2	Top cover thread guide	23
6.4.3	Top cover thread eyelet	23
6.5	Distance between needle and looper	24
6.6	Using timing gauge	24
6.7	Height of needle	25
6.8	Front-and-rear position of needle and looper	25
6.9	Needle and needle guard(rear)	26
6.10	Needle and needle guard(front)	27
6.11	Height of feed dog	27
6.12	Changing range of differential ratio	28
6.13	Presser foot lift	29
6.14	Replacing fabric presser	30
6.15	Clearance between top and lower feed dogs	30
6.16	Pressure of top feed dog	30

7. Trimming mechanism 31

7.1	Adjusting trimming position of fabric	31
7.2	Adjusting suction pipe(front)	32
7.3	Adjusting suction pipe cover	32
7.4	Removing and resetting lower knife	33
7.5	Removing and resetting upper knife	34
7.6	Adjusting upper knife stroke	35
7.7	Sharpening knives	36
7.8	Stop the movement of left knife	37
7.9	Cancellation of left knife	38

8. Specifications 39

Attention

This instruction manual is designed mainly for technicians, but it is advisable that also operators read the instructions with mark to use the machine properly.

◇ The numbers in lower left corners of figures are figure numbers. We use them in texts as needed for your reference.

Attention

The description in this instruction manual is subject to change for improvements of the commodity without notice.

1. To ensure safe use

Always observe the following instructions to ensure the safe use of the industrial sewing machines and devices.

1-1 Application and purpose

The sewing machine is designed to improve productivity in the sewing industry and must not be used for other applications and purposes. Do not use this sewing machine until it can be confirmed that safety measures for the drive units have been taken.

1-2 Before use

Read all instruction manuals thoroughly before starting the use of this machine and follow them.

Also, read the instruction manual for the installed drive unit.

1-3 Working environment

DO NOT WORK IN THE FOLLOWING ENVIRONMENTS:

• Place where atmosphere temperature and humidity give a bad influence the performance of sewing machines.
• Outdoors and place where the sewing machines are exposed to sunlight directly.
• Atmosphere containing dust, corrosive gases or flammable gases.
• Place where voltage fluctuation exceeds ± 10 % of the rated voltage.
• Place where power capacity necessary for the used motor specifications cannot be secured.
• Place where strong electric or magnetic fields are generated such as near large-output high frequency transmitters or high frequency welding machines.

1-4 Unpacking and transportation

(1) Unpack from the top.
(2) Never hold the parts near the needle or threading parts when removing the sewing machine head from the buffer of box.
(3) When carrying the sewing machine head, have an assistant.
(4) Pay attention not to get excessive impact or shock when moving the sewing machine

head with a pushcart.

2. Installation and preparation

2-1 Instruction and training

Operators and workers, who supervise, repair or maintain the machine head and machine unit, are required to have the adequate knowledge and operation skills to do the job safely. In order to establish such necessary conditions, it needs for the employer to plan and enforce the safety education and training to those workers.

2-2 Sewing table and motor

(1) Prepare a machine table that has enough strength to withstand the weight of the sewing head and any reaction while operating.
(2) Maintain a comfortable working environment with considering the lighting and the arrangement of sewing machine so that the operators can work smoothly.
(3) When installing the control box and the related parts on the sewing machine, take care about the posture of the worker.
(4) Install the drive unit correctly according to the instruction manual.

2-3 Wiring

(1) Never connect the plug for power supply until assembly is finished.
(2) Fix the connectors securely to the sewing machine head, motor, and electric apparatus.
(3) Do not apply excessive force to the connection cords.
(4) Connect the cords away from the driving parts.
(5) Place the ground wire securely to the designated position on the machine head.

2-4 Before operation

(1) Take care not to attach lubricant, silicone oil, and grease on the eyes or skin.

Keep them away from children.

(2) Be sure to fill or drop lubrication oil before operating the sewing machine. Use the Yamato SF oil as specified.
(3) Never put your hand under the needle or near the moving parts of the machine when turning on power supply switch.
(4) When operating a new sewing machine, make sure the rotating direction of pulley agrees with the rotating-direction mark.

2-5 During operation

(1) Be sure to operate the sewing machine with the safeguards such as belt cover, finger guard, and eye guard.
(2) Never place the finger, hair or objects under the needle or close to the moving parts while operating the sewing machine.
(3) Be sure to turn off the power supply switch when threading or replacing the needles.
(4) Never place your hands close to the knives when operating the sewing machine with the trimming devices.
(5) Be sure to turn off the power supply switch when terminating the sewing work or leaving the sewing machine.
(6) If the sewing machine malfunctions, abnormal sound or smell something unusual while operating, be sure to turn off the power supply switch.

2-6 Removal

(1) Turn off the power supply switch if removed or replaced any parts or during adjustment of sewing machine.
(2) Do not pull the cord when removing the plug. Be sure to hold the plug itself.
(3) A high voltage is applied inside the control box. Turn off the power supply switch and wait more than 5 minutes before opening the cover.

3. Maintenance, inspection, and repair

(1) Follow the instruction manuals for maintenance, inspection, and repair.
(2) Entrust the maintenance, inspection, and repair to specially trained personnel.
(3) Be sure to turn off the power supply switch and make sure the sewing machine and motor completely stop before the maintenance, inspection, and repair. (If using a clutch motor, take care that the motor keeps turning for a while even after turning off the power supply switch.)
(4) Do not modify the sewing machine by the customer's judgment.
(5) Be sure to use original replacement parts for repairs or maintenance.

4. Caution signs and alert pictorial markings

This instruction manual contains the following caution signs and alert pictorial markings to prevent you from injuring yourself or the sewing machine from being damaged.

Please follow the instructions.

4-1 Meanings of caution signs

WARNING indicates potentially hazardous situations which, if not heeded, could result in death or serious injury to you and others.

Caution indicates hazardous situations which, if not heeded, may result in minor or moderate injury to you and others, or may result in machine damage.

NOTE is used to emphasize essential information.

4-2 Alert pictorial markings

This mark indicates the warning which, if not heeded, could result in death or Serious injury.

This mark indicates the caution for high temperature.

This mark indicates the warning which, if not heeded, could result in death or Serious injury.

High-voltage applies in the control box. This label indicates that electric shock may be caused.

This mark indicates the caution which, if not grounded, the machine or device could malfunction and could result in personal injury.

5. Warning labels on sewing machines

This label indicates that removal of the safeguards and works except for sewing performance while the power supply switch is on are prohibited. (For details, see the next page.)

High-voltage applies in the control box. This label indicates that electric shock may be caused.

This label is affixed on the safeguards. Considering the operation, it is not affixed on the finger guard and eye guard. Be sure to

Stepping motor and solenoid may overheat if used continuously. To prevent a burn, take care not to touch.

If not connected earth line, static electricity may be generated and inflict injury on person. In addition, the malfunction of

Simple black curved arrow and upward arrow inside a rectangular border (no text or symbols)

Check the rotating direction of machine pulley agrees with 'ROTATING-DIRECTION SYMBOL'.

1. Name of each part

Fig. 1

2.1 Table cutting diagram

2.1.1 Table top type(Tyep A: standard)

Refer to the instruction of the motor
Ttable dimensions 1200 × 595 × 50
for dimensions A, B, C, and D.

Fig. 2

2.1.2 Table top type (Type B)

Fig. 3

2.2 Table top type

Install a machine correctly referring to Figs. 4 and 5.

Fig. 4

Fig. 5

2.3 Motor and belt

See the instruction manual for the motor used and install the motor properly.

To install the clutch motor, align the center of the machine pulley with that of the motor pulley when the motor pulley shifts to the left with toeing down the pedal.

Note: Table 1 shows the outside diameter of the motor pulley, rpm of the machine, and size of the belt when using the clutch motor of 3-phase, 2-pole, 400W(1/2HP).

The outside diameter on the table shows the nearest size to the calculated values based on the commercial available pulleys at intervals of 5 mm.

CAUTION

Use only those motor pulleys applicable to the machine. If not, the sewing machine will be over maximum and it can cause the damage to the machine.

2.4 Hanging belt

WARNING

Before hanging belt, ALWAYS turn the power switch OFF and check that the machine has already stopped.

Use the M-type of V-belt.

(1) Hang the belt① on the machine pulley②, and then on the motor pulley③ while rotating the machine pulley.
(2) Adjust the belt tension so that the belt has a slack of 10 - 20 mm when its center is pushed with 10N(1.02kgf).
(3) Lock the motor with the nut④.

Fig. 6

Outside diameter of pulley (mm)	rpm of machine (rpm)
	50Hz	60Hz
90		4500
100		5000
105	4500
110		5500
120	5000
125
130	5500

Table 1

Fig. 7

2.5 Belt cover

WARNING

Be sure to install belt cover to prevent you from injuring and a material from being caught by the belt.

(1) Install the belt cover①. (Fig. 8)
(2) Push the belt cover support ② to the belt cover ① to install it.
(3) Fix the belt cover(lower)③ on the machine table. (Fig. 10)

Fig. 8

Fig. 9

Fig. 10

2.6 Eye guard and finger guard

To ensure safe use, always install the eye guard④ and the finger guard⑤ on the prescribed position when operating.

Fig. 11

2.7 Accessories

Install the accessories as the suction pipe(rear), the suction pipe support, the flexible hose and the speed controller on the machine as follows:

(1) Install the speed controller⑧ in the screw hole on the bottom of the lower knife holder.
(2) Insert the suction pipe(rear)① into the hole of the bottom of the lower knife holder bracket ② and fix them with the screw ③.
(3) Remove the screws④ at the rear of the machine frame.
(4) Install the suction pipe support ⑤ with the screws ④ at the place the screws ④ were located.
(5) Install the suction pipe(rear)① on the suction pipe support⑤.
(6) Insert the flexible hose⑦ fitted with the hose band⑥ into the suction pipe(rear)①. Then, fix them with the hose band⑥.

i Supplement

If the suction pipe(rear)① is clogged with chips because of large trimming width, remove it, insert the suction pipe (lower)⑨ into the hole of the bottom of the lower knife holder bracket ②, and connect to the flexible hose ⑦.

Note: For table top type B, drill a hole of 50 mm in diameter into the machine table to pass the flexible hose ⑦.

Fig. 12

3. Sewing speed and rotating direction of pulley

The maximum sewing speed is 5500 rpm (during intermittent operation).

Run a new machine at 4500 rpm during the first 200 hours (for about one month) so that the machine can offer a long service life in good condition.

The rotating directions of the machine pulley① and the handwheel② are clockwise as shown in the figure.

CAUTION

If rotating in reverse direction, oil cannot be supplied properly. It can cause the damage to the machine.

Fig. 13

4. Lubrication

WARNING

Before lubricating, ALWAYS turn the power switch OFF and check that the machine has already stopped.

4.1 Lubricating oil

Use YAMATO SF OIL No. 28.

CAUTION

Never add additives to the oil.

If added, it can cause the deterioration of the oil and the damage to the machine.

4.2 Lubricating

When using a new machine, or a machine which has not been run for a while, supply a few drops of oil to the needle bar ① and the looper bar ②.

Remove the seal plug③ indicated "OIL" and supply oil to the upper line of the oil sight gauge④.

Check that oil splashes from the nozzle inside the oil sight window⑤ while running a machine.

If oil does not splash from the nozzle, see "4.4 Checking and replacing oil filter" on page 10.

CAUTION

1. Too much oil or insufficient oil can cause oil leakage and machine trouble. Be sure to keep the oil level between the lines. Also too much lubrication can cause the oil scatter and material stain.
2. Supply with a few amount of oil into the hole ⑥ periodically.

Fig. 17

Fig. 14

Fig. 15

Fig. 16

Technical line drawing of a mechanical assembly with no visible text or symbols

Fig. 18

WARNING

Before lubricating, ALWAYS turn the power switch OFF and check that the machine has already stopped.

4.3 Changing oil

Period of changing:

When using a new machine, change the lubricating oil after running a machine for 250 hours (for about one month). After that, change the oil once or twice a year.

Procedure for changing:

(1) Remove the belt cover. (See page 6.)
(2) Remove V-belt from the motor pulley. (See page 5.)
(3) Remove the machine from the machine table.
(4) Set a container received the oil under the screw①.
(5) After removing screw①, oil is drained.

NOTE

Be careful not to soil the V-belt and the machine pulley with the oil.

(6) Reset the screw①.
(7) Change the oil. (See “4.2 lubricating” on page 9.)
(8) Reset the machine on the machine table.
(9) Hang V-belt on the motor pulley and reset the belt cover. (See pages 5 and 6.)

4.4 Checking and replacing oil filter

◆ If the oil filter② is clogged with dust, lubrication cannot be done properly.
◆ Remove the oil filter cap③ and the oil filter ② to check them every six months. If clogged or cracked, clean or replace the oil filter.
If oil is splashed from the nozzle insufficiently or includes many bubbles though the oil is sufficiently kept, check or replace the oil filter.

NOTE

Carefully check and replace them without spilling oil stagnant in the oil filter ② when loosening screw ④.

Fig. 19

Fig. 20

5. Proper operation

5.1 Needle system

Use UY × 128GAS (UY128GAS).

Select a proper needle in size depending on the thickness and type of fabric.

5.2 Installing needles

WARNING

Before installing, ALWAYS turn the power switch OFF and check that the machine has already stopped.

(1) Loosen the screws① with a screwdriver. (Fig. 21)
(2) Remove an old needle with a pair of tweezers.
(3) Insert a new needle into the needle clamp② as far as it will go with facing its scarf to the right back. (Figs. 22 and 23)
(4) Tighten the screws① with a screwdriver.

NOTE

Tighten the screws ① with a tightening torque of 0.6N·m (6kgf·cm).

Japanese standard	9	10	11	12	13	14
Metric standard	65	70	75	80	85	90

Table 2

Fig. 21

Fig. 22

Fig. 23

5.3 Threading

When not threaded, thread correctly as shown in Fig. 24.

When threaded, rethread after knotting preset threads.

☆ Needle thread

Pull out the thread until it is in front of the needle. Then, cut off the knot before needle eye to rethread.

Thread correctly for the left needle in the inmost position as shown in the figure.

☆ Looper thread

Pull the thread until the knot is out.

Then, cut off the knot.

Note: Threading for sewing with "UT" or "UT-A" device

* For standard type of thread, thread through the looper thread eyelet(left)④ via the looper thread release③. (Thread A)

* For stretchless thread, thread directly to the looper⑤ through the looper thread release③. (Thread B)

Note: For easy threading, pull the lever ② of the thread take-up eyelet holder ①.

After threading, push the lever② to reset the thread take-up eyelet holder① to the original position.

5.4 Adjusting thread tension

Adjust the thread tension with the thread tension spring caps ① depending on fabric type, thread type, seam width, stitch length, and other sewing conditions.

● To tighten the thread tension, turn the caps clockwise.
● To loosen the thread tension, turn the caps counterclockwise.

5.5 Pressure of presser foot

Loosen the lock nut ② and turn the adjusting screw ③ to adjust the pressure.

● To increase the pressure, turn it clockwise.
● To decrease the pressure, turn it counterclockwise.

Keep the pressure to a minimum for stable sewing performance.

Fig. 25

Fig. 26

5.6 Adjusting position of presser foot

WARNING

Before adjusting, ALWAYS turn the power switch OFF and check that the machine has already stopped.

Adjust left-and-right position of the needle holes of the presser foot.

Loosen the screw④. Move the front of the presser foot right or left so that the needle drops in the center of the needle drop.

Then, tighten the screw④ securely.

Fig. 27

WARNING

Before operating, ALWAYS turn the power switch OFF and check that the machine has already stopped.

5.7 Adjusting movement of differential feed dog

The differential ratio has been set from 1:0.7 to 1:1.4 at shipment.

When aligned the differential feed lever(right)① with the line ② of the differential feed graduations, the movement of the differential feed dog is the same as that of the main feed dog (differential ratio 1:1), resulting in uniform sewing.

(1) Loosen the lock nut③.
(2) Turn the adjusting screw④ to adjust the movement of the differential feed dog.

● To increase the movement for gathering, turn it clockwise.
● To decrease the movement for stretching, turn it counterclockwise.

(3) Tighten the lock nut③ securely.

Fig. 28

Fig. 29

WARNING

Before operating, ALWAYS turn the power switch OFF and check that the machine has already stopped.

5.8 Adjusting stitch length

Stitch length is adjustable from 1.4 to 3.6 mm. Table 3 shows the number of stitches per inch (25.4 mm) and 30 mm converted to the stitch length.

The main feed lever stopper⑤ has been adjusted so as to stop at 3.6 mm at the maximum with the screw ⑥ at shipment.

Adjusting procedure:

(1) Loosen the lock nut①.
(2) Align the end of the main feed lever④ with the required position on the main feed graduations ③. Turn the main feed bar adjusting screw② to adjust it.

● To make the stitch length smaller, turn it clockwise.

● To make the stitch length larger, turn it counterclockwise.

Stitch length (mm)	Number of stitch (per 1 inch)	Number of stitch (per 30 mm)
1.4	18	21
2.0	13	15
3.0	8.5	10
3.6	7	8

Table 3

Fig. 30

Fig. 31

WARNING

Before operating, ALWAYS turn the power switch OFF and check that the machine has already stopped.

5.9 Adjusting feeding amount of top feed dog to lower feed dog

The top and the lower feed dogs drive independently. Adjust the top feeding amount after changing the lower feeding amount.

The standard ratio of top feeding to lower feeding is 1:1.

Note: The mark with stitch length of the top feed graduation① is as below.

S: 1.6 mm

L: 7.0 mm

Turn the adjusting screw② to adjust it.

● To increase the feeding amount, turn it clockwise.
● To decrease the feeding amount, turn it counterclockwise.

CAUTION

Run a machine at 5000 rpm or less when feeding amount of top feed dog is 6.0 - 7.0 mm.

Fig. 32

5.10 Folder (left)

(1) Loosen the screw② of the folder(left)①.
(2) Align the right on the guiding part of the holder (left)① with that of the upper knife③.
(3) Tighten the screw② securely.

i Supplement

See "7.1 Adjusting trimming position of fabric" to adjust the left-and-right position of lower fabric.

Fig. 33

5.11 Trimming width of fabric

Install or remove the folder spacer⑤ on the guiding part of the folder(left)① to change the trimming width of a fabric.

When sewing with the folder spacer⑤, the trimming width is 3.0 mm.

When sewing without it, the trimming width is 5.0 mm.

Remove the screw④ to remove the folder spacer⑤.

Fig. 34

5.12 Folder (right)

(1) Loosen the screw② of the folder(right)①.
(2) Align the right of the folder(right)① with that of folded fabric set for hem width.
(3) Tighten the screw② securely.

Fig. 35

5.13 Fabric guide (right)

(1) Loosen the screws④ of the fabric guide(right) ③.
(2) Align the left end of the fabric guide(right) ③ with the guiding part of the folder(right) ①.
(3) Tighten the screws④ securely.

Fig. 36

WARNING

Before operating, ALWAYS turn the power switch OFF and check that the machine has already stopped.

5.14 SP device and HR device

Use SP device (needle thread oiling) equipped as standard to prevent thread breakage and skip stitch when running a machine at high speed or using synthetic thread and/or synthetic fabric.

Also use HR device (needle point cooling) as an extra.

Use dimethyl silicon oil.

Open the lid① of SP container and the lid② of HR container to check the oil level.

CAUTION

1. When not using SP device and HR device, remove the felts. If not removed, it may occur irregular condition during sewing.
2. If silicone oil is attached to the parts other than SP and HR devices, it can cause the machine trouble. Be sure to wipe it away.

Technical line drawing of a mechanical clamp or bracket assembly (no text or symbols)

Fig. 37

Technical line drawing of a mechanical device with labeled parts (no text or symbols present)

Fig. 38

5.15 Cleaning the machine

Clean waste thread and dust inside the machine at the end of work a day.

Remove the seal plug③ at the back of the machine and clean the grooves in the stitch plate, feed dog area, and oil filter screen area once a week.

NOTE

If the oil filter screen is clogged with dust, oil in the cylinder does not return to the oil reservoir. It can cause oil leakage.

Fig. 39

WARNING

Before adjusting, ALWAYS turn the power switch OFF and check that the machine has already stopped.

6.1 Needle thread tension

Needle thread eyelet:

As standard, align the center of the screw with the line of the needle thread eyelet bracket④ as below.

Right needle thread eyelet①: top line Middle needle thread eyelet②: middle line Left needle thread eyelet③: bottom line

● To loosen the needle thread tension, lower the needle thread eyelet.
● To tighten the needle thread tension, raise the needle thread eyelet.

Fig. 40

Needle thread guide:

Make the distance between the center of the eye in the needle thread take-up ⑥ and the top of the needle thread guide ⑤ to 4.0 mm when the needle thread take-up ⑥ is at the lowest point as standard.

Loosen the screw⑦ to adjust it.

● To make the needle thread loop larger or when using stretchable thread, raise the needle thread guide⑤.
● To make the loop smaller, lower the needle thread guide⑤.

Fig. 41

6.2 Top cover thread tension

Align the center of the slot of the top cover thread eyelet (upper) ① with the center of the screw ② as standard.

Loosen the screws② and ③ to adjust it.

● To increase the feeding amount, raise the top cover thread eyelet (upper)①.
● To decrease the feeding amount, lower the top cover thread eyelet (upper)①.

NOTE

When using stretchable thread like woolly, adjust the top cover thread eyelet(upper)① higher than standard.

Fig.42

6.3 Looper thread tension

Align center of the eyes of the thread take-up eyelets(left)⑤ and (right)⑥ 3.0 mm under the lines④ on the thread take-up eyelet holder as standard.

Loosen the screws of both thread take-up eyelets to adjust them.

● To tighten the looper thread tension, raise both eyelets.
● To loosen the looper thread tension, lower both eyelets.

NOTE

When using stretchable thread, move the thread take-up eyelets ⑤ and ⑥ at the lowest points. Do not thread through the top cover tension disc ⑦.

Fig. 43

6.4 Needle and spreader

6.4.1 Spreader

(1) Loosen the screws ③ and ④ of the spreader holder. (Fig. 46)
(2) Make the clearance between the left needle and the hook② of the spreader① to 0.5 - 0.8 mm. (Fig. 44)
(3) Make the clearance between the center of the left needle and the hook② to 4.5 - 5.5 mm when the spreader① is at the extreme left. Then tighten the screw④ securely. (Figs. 44 and 46)
(4) Make the height from the top of the stitch plate to the bottom of the spreader① to 8.5 - 9.5 mm. Then tighten the screw③ securely. (Figs. 45 and 46)

NOTE

Adjust the height of the spreader so that the top cover thread passes behind the right needle and is caught by the left needle within adjustable range based on the needle distance.

Fig. 44

Fig. 45

Fig. 46

6.4.2 Top cover thread guide

(1) Loosen the screws ② of the top cover thread guide ①. (Fig. 47)
(2) Make the clearance between the top of the spreader ③ and the bottom of the top cover thread guide ① to 0.5 mm. (Fig. 47)
(3) Set the hook④ in the center of the slot of the top cover thread guide ① when the spreader ③ is at the extreme right. Then, tighten the screws ② securely. (Figs. 47 and 48)

Fig. 47

6.4.3 Top cover thread eyelet

(1) Loosen the screw⑥ of the top cover thread eyelet⑤. (Fig. 48)
(2) Make the clearance between the top of the top cover thread guide① and the top cover thread eyelet ⑤ to 1.0 mm when the needle bar is at the lowest point. (Fig. 47)
(3) Set the eye of the top cover thread eyelet ⑤ along the extending line from the slot of the top cover thread guide ①. (Fig. 48)
(4) Tighten the screw⑥ securely. (Fig. 48)

Fig. 48

6.5 Distance between needle and looper

The distance between the looper tip and the center of the right needle depends on the needle distance when the needles are at the lowest points and the looper① is at the extreme right.

See Table 4 and loosen the screw② of the looper holder to adjust the distance.

NOTE

The distance between the center of the needle bar and the looper ① tip is 6.0 mm even if the needle distance changes.

needle distance (mark)	gauge mark	looper's distance
3.2 mm (32)	A	4.4 mm
4.0 " (40)	B	4.0 "
4.8 " (48)	C	3.6 "
5.6 " (56)	D	3.2 "
6.4 " (64)	E	2.8 "

Table 4

The timing gauge (No. 95220) makes it possible to adjust the distance easily.

The gauge is an extra part. Place an order with our agents or directly with us, if needed.

6.6 Using timing gauge

A timing gauge has the marks (A, B, C, D, E) for each needle distance.

Move the looper at the extreme right. Keep fitting the right needle into the groove "V" corresponding needle distance, and fit the looper tip to the gauge.

Then, tighten the screw② securely.

Fig. 49

Fig. 50

Fig. 51

6.7 Height of needle

(1) Install the needle to the left hole in the needle clamp.
(2) Check the looper is inserted into the looper holder fully.
(3) Turn the handwheel until the looper tip meets the center of the left needle.
(4) Loosen the screw① of the needle bar bracket and move the needle bar up and down. Adjust the looper tip to pass 0.8 - 1.3 mm above the top of the needle eye.
(5) Tighten the screw① securely. Check that the needle drops in the center of the needle hole of the stitch plate respectively.

Fig. 53

Fig. 52

Fig. 54

6.8 Front-and-rear position of needle and looper

(1) Turn the handwheel until the looper tip④ meets the center of the left needle⑤.
(2) Loosen the screw③ and move the looper holder back or forth. Make the clearance between the back of the left needle⑤ and the looper tip to 0.2 - 0.3 mm. Then, tighten the screw③ securely.

NOTE

When tightening the screw③, front-and-rear position of the looper may be shifted. Recheck the position after tightening it.

Fig. 55

6.9 Needle and needle guard (rear)

(1) Turn the handwheel clockwise to lower the needles at the lowest points.
(2) Loosen the screw①.
(3) Align the line③ on the needle guard(rear)② with the centers of the needle eyes.
(4) Tighten the screw① securely.
(5) Turn the handwheel until the looper tip meets the center of the right needle.
(6) Loosen the screws① and ④, and move the needle guard(rear)② back or forth. Make the clearance between the right needle and the looper tip to 0 - 0.05 mm.
(7) Check the clearance between the left needle and the needle guard(rear)② is 0 - 0.05 mm with keeping (6).
(8) Tighten the screws① and ④ securely.

Fig. 56

Fig. 57

Fig. 58

6.10 Needle and needle guard (front)

(1) Turn the handwheel clockwise until the looper tip meets the center of the left needle.
(2) Loosen the screw①. Adjust the height between the needle point and the angular part of the needle guard(front)② to 1.5 - 2.0 mm.
(3) Tighten the screw① securely.
(4) Loosen the screws① and ③. Adjust the clearance between the needle guard(front)② and the left, or right needles to 0 - 0.3 mm respectively.
(5) Tighten the screws① and ③ securely.

Fig. 60

Fig. 59

Fig. 61

6.11 Height of feed dog

Adjust the height between the top of the stitch plate and the tops of the differential feed dog④ and the main feed dog ⑤ to 1.0 - 1.2 mm when the feed dogs are at the highest points as standard. Also they are parallel to the top of the stitch plate.

Loosen the screws⑥ and ⑦ to adjust them.

Fig. 62

6.12 Changing range of differential ratio

Differential ratio 1:1.1 - 1:2:

(1) Remove the side cover① (three pcs. of screws).
(2) Remove the screw③ of the differential feed bar connection②.
(3) Fix the differential feed bar connection② in the hole④ with the screw③.

NOTE

Max. stitch length of the main feed dog is 2.3 mm in a differential ratio of 1:2, and 3.0 mm in 1:1.5 respectively.

Technical line drawing of a mechanical assembly with numbered components (no text or symbols)

Fig. 63

Fig. 64

Fig. 65

6.13 Presser foot lift

The presser foot lift for the needle distance 5.6 mm is as follows:

- with spreader: 6.0 mm - without spreader: 7.5 mm

(1) Loosen the lock nut ①.
(2) Push down the lifter lever② to make the lift between the top of the stitch plate and the bottom of the presser foot to 6.0 mm(7.5 mm).
(3) Apply the screw③ to the lifter lever② when the presser foot is raised by 6.0 mm(7.5 mm).
(4) Tighten the lock nut① securely.
(5) Loosen the screws⑤ of the collar④.
(6) Make the clearance between the presser bar bushing⑥ and the collar④ to 0.2 mm when the presser foot is raised by 6.0 mm (7.5 mm).
(7) Tighten the screws⑤ securely.

Fig. 66

Fig. 67

Fig. 68

6.14 Changing fabric presser

The fabric presser ② for hem width 19.1 mm (3/4 inches) has been set on the right of the presser foot ① at shipment. Also packed for 25.4 mm (one inch). Use the fabric presser depending on hem width. To remove the fabric presser ②, loosen the screw ③ of the presser foot ① and pull out the pin ④. To set it, insert it between the presser foot ① and the washer ⑤, fix with the pin ④, and tighten the screw ③ securely.

Fig. 69

6.15 Clearance between top and lower feed dogs

Adjusting the clearance between the top and the lower feed dogs can be obtained the stable feeding of a fabric depending on the application, type, and weight of fabric.

Adjust the clearance between the top and the lower feed dogs is as thick as one piece of a fabric at the lowest point of the top feed dog⑥ and the highest point of the lower feed dog⑦. Loosen the screw⑧ to adjust it.

Fig. 70

6.16 Pressure of top feed dog

Make the distance from the end of the lock nut ⑨ to the top of the adjusting screw ⑩ to 23.0 mm as standard.

Loosen the lock nut⑨ and turn the adjusting screw ⑩ to adjust it.

● To increase the pressure, turn it clockwise.
● To decrease the pressure, turn it counterclockwise.

Keep the pressure to a minimum for stable sewing performance.

Fig. 71

7. Trimming mechanism

WARNING

Before operating, ALWAYS turn the power switch OFF and check that the machine has already stopped.

7.1 Adjusting trimming position of fabric

Loosen the screw① of the lower knife braket to move the lower knife holder② right and left.

Adjust it as follows:

(1) Loosen the screw①.
(2) Turn the adjusting screw⑦ to move the lower knife holder② at required position.

● To move it② to the left, turn it⑦ clockwise.
● To move it② to the right, turn it⑦ counterclockwise.

(3) Tighten the screw ① with a tightening torque of 1.5 - 2 N·m (15 - 20 kgf·cm).

(4) Rotate the handwheel to check the sharpness of the blades by setting a thread between the upper knife③ and the lower knife④.

(5) Set the top of the lower knife④ 7.0 mm apart from the upper knife③ tip (at the base of the blade). Then, tighten the screw⑤ of the collar (left)⑥.

(6) Recheck the knives cut properly.

NOTE

Refer to "7.2 Adjusting suction pipe(front)" and "7.3 Adjusting suction pipe cover" after changing trimming position of a fabric.

Fig. 72

Fig. 73

7.2 Adjusting suction pipe (front)

Set left-and-right position of the suction pipe (front)② about 5 mm apart from the left side of the chip receiver④.

Loosen the screw③ to adjust the position or remove it.

☆ Suction by compressed air:

Adjust the suction power with the speed controller①.

Keep the pressure to a minimum for suctioning the chips.

☆ Suction by vacuum system:

Connect the flexible hose to the vacuum dust collector to adjust the suction power.

Keep the pressure to a minimum for suctioning the chips.

Fig. 74

7.3 Adjusting suction pipe cover

Adjust the position of the suction pipe cover ⑤ after changing the position of the suction pipe (front) ②.

(1) Loosen the screw⑥ on the suction pipe cover ⑤.
(2) Align the right side of the suction pipe cover ⑤ with the inlet of the suction pipe(front)②.
(3) Tighten the screw⑥ securely.

Fig. 75

7.4 Removing and resetting lower knife

Removing the lower knife:

(1) Loosen the screw② of the collar(left)①.
(2) Move the upper knife holder④ to the left and make the clearance between the upper knife③ and the lower knife⑤.
(3) Tighten the screw② temporarily.
(4) Loosen the screw⑥ of the lower knife⑤ and pull out the lower knife⑤ downward.

Resetting the lower knife:

(1) Make the lower knife⑤ blade even with the top of the stitch plate. Then, tighten the screw⑥.
(2) Loosen the screw②. The upper knife③ touches the lower knife⑤ with its spring.
(3) Rotate the handwheel manually to check the sharpness of the blades by setting a thread between the upper knife③ and the lower knife ⑤.
(4) Set the top of the lower knife⑤ 7.0 mm apart from the upper knife③ tip (at the base of the blade). Then, tighten the screw② securely.
(5) Recheck the knives cut properly.

Fig. 76

Fig. 77

Fig. 78

7.5 Removing and resetting upper knife

Removing the upper knife:

(1) Loosen the screw⑥ on the upper knife holder④.
(2) Remove the upper knife holder④.
(3) Remove the screw⑦ on the upper knife③.
(4) Remove the upper knife③.

Resetting the upper knife:

(1) Attach the upper knife ③ to the pin ⑧ in the upper knife holder ④ and tighten the screw ⑦ securely.
(2) Set the left end of the chip receiver⑨ fixed on the left of the upper knife holder④ 1.5 mm apart from the left end of the upper knife shaft⑩. (Fig. 81)
(3) Rotate the handwheel manually to lower the upper knife ③ at the lowest point. Move the upper knife holder ④ to place the upper knife tip 0.5 mm above the top of the lower knife. Then, tighten the screw ⑥ securely.
(4) Loosen the screw② on the collar(left)①. The upper knife③ touches the lower knife⑤ with its spring.
(5) Rotate the handwheel manually to check the sharpness of the blades by setting a thread between the upper knife③ and the lower knife ⑤.
(6) Set the top of the lower knife⑤ 7.0 mm apart from the upper knife③ tip (at the base of the blade). Then, tighten the screw② securely.
(7) Recheck the knives cut properly.

Fig. 81

Fig. 79

Fig. 80

Fig. 82

7.6 Adjusting upper knife stroke

Adjust the stroke of the upper knife to 3.0 - 6.5 mm. It has been adjusted 4.0 mm at shipment. Adjust the stroke as follows:

(1) Loosen the screws① to remove the bracket cover② and the bracket cover gasket③.
(2) Loosen the nut⑤ on the upper knife adjusting lever pin④ to adjust it.

● To make stroke smaller, move it in the direction Y.

● To make stroke larger, move it in the direction X.

(3) Tighten the nut⑤ securely.
(4) Loosen the screw⑦ on the upper knife holder⑥ to tighten it temporarily.
(5) Rotate the handwheel manually to lower the upper knife⑩ at the lowest point. Move the upper knife holder⑥ to place the upper knife tip 0.5 mm above the top of the lower knife. Then, tighten the screw⑦ securely. (See Fig. 82)
(6) Loosen the screw⑨ on the collar(left)⑧. The upper knife⑩ touches to the lower knife⑪ with its spring.
(7) Rotate the handwheel manually to check the sharpness of the blades by setting a thread between the upper knife ⑩ and the lower knife ⑪.
(8) Set the top of the lower knife⑪ 7.0 mm apart from the upper knife⑩ tip (at the base of the blade). Then, tighten the screw⑨ securely.
(9) Recheck the knives cut properly.
(10) Reset the bracket cover② and the bracket cover gasket③ with the screws①.

Fig. 83

Fig. 84

7.7 Sharpening knives

If the knives cut badly, re-sharpen the lower knife ②.

Prepare the cold water and re-sharpen the lower knife with keeping it cool.

Re-sharpen the correct angle as in the figure.

NOTE

Normal grinder is not useful to sharpen the upper knife made of super hard alloy. Contact us directly or the dealer for re-sharpening it.

Fig. 85

Fig. 86

7.8 Stop the movement of left knife

(1) Loosen the two screws② 2 mm or more from the knife drop collar① to adjust following procedure. The knife drop collar① moves to the right with the spring.
(2) With an Allen wrench inserted in the lower one of the screws②, turn the collar① until an Allen wrench touches on the top of the bracket cover③.
(3) With keeping it, push down the upper knife holder ④ tip slightly to the chip guard ⑤. Then, tighten the two screws ② securely.
(4) Reset the side cover⑥ and the front cover⑦.
(5) Loosen the screws⑨ on the suction pipe cover ⑧.
(6) Move the suction pipe cover⑧ to the right to fill the clearance.
(7) Tighten the screws⑨ securely.

Fig. 87

Mechanical assembly diagram showing a shaft, spring, and housing components (no text or labels)

Fig. 88

Fig. 89

Fig. 90

7.9 Cancellation of left knife

(1) Loosen the screws② on the suction pipe cover ①.
(2) Move the suction pipe cover ① at the extreme left.
(3) Tighten the screws② temporarily.
(4) Open the front cover③ and side cover④.
(5) Loosen two screws⑥ on the knife drop collar⑤.
(6) With an Allen wrench inserted in lower one of screws⑥, set the convex part of the knife drop collar⑤ on the concave part of the upper knife adjusting lever⑦ without clearance between them.
(7) Tighten two screws⑥ securely.
(8) Rotate the handwheel manually to lower the upper knife⑧ at the lowest point. Check the upper knife⑧ tip is 0.5 mm above the top of the lower knife⑨. (See Fig. 82)
(9) Rotate the handwheel manually to check the sharpness of the blades by setting a thread between the upper knife⑧ and the lower knife ⑨.
(10) Reset the front cover③ and the side cover④.
(11) Loosen the screws ②.
(12) Align the right side of the suction pipe cover ① with the inlet of the suction pipe(front)⑩ in on line. (See Fig. 75)
(13) Tighten the screws② securely.

Fig. 93

Fig. 91

Fig. 92

Fig. 94

8. Specifications

Model	VGS3721-8
Description	High speed cylinder bed 3-needle chainstitch machine with left hand trimming and top feeder
Dimensions	470 mm (L) ×237 mm (W) ×415 mm (H)
Circumference of Cylinder	340 mm
Weight	48.5 kg
Stitch Type	ISO 406, 407, 602, 605
Application	Henming operation of knitted fabric for lightweight material
Sewing Speed	Up to 5500 rpm (during intermittent operation)
Stitch Length	1.4 - 3.6 mmNumber of stitches per inch(25.4 mm) 7 - 18 stitchesper 30 mm 8 - 21 stitches
Needle System	UY×128GAS #10 - #14 (standard: #10)
Needle Distance	3-needle: 4.8 mm, 5.6 mm, 6.4 mm(2-neelde: 3.2 mm, 4.0 mm)
Needle Stroke	31 mm
Upper knife stroke	3.0 - 6.5 mm
Suctioning chips	Ventury or vacuum system
Presser Foot Lift	For 5.6 mm of needle distancewith spreader: 6.0 mm, without spreader: 7.5 mm
Feed Regulation	By adjusting screw (available for micro adjustment)
Differential Ratio	Standard: 1 : 0.7 - 1 : 1.41 : 1.1 - 1 : 2(stitch length is 2.3 mm or less in max. normal differentialadjustable by changing position of feed bar connection)
Differential Feed Regulation	Micro adjustment by adjusterAdjustable by moving external lever even during operation
Lubrication	Lubrication automatically by trochoid-shaped pump
Lubricating Oil	YAMATO SF OIL No.28
Capacity of Oil Reservoir	800 cc
Installation	Table top type

1jamato

ヤマトミシン製造株式会社

YAMATO SEWING MACHINE MFG. CO., LTD.

4-4-12, NISHITENMA, KITA-KU, OSAKA, JAPAN

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