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|Basic Knowledge Series for lockstitch machines
Basic knowledge of the presser foot, feed dog and throat plate
There are a variety of feeds according to the "feeding method" and "feed-dog configuration." In this issue, basic feeding methods and feed dogs are introduced.
1. Role of the feed
The feed has the following roles:
(1) To move the sewing material along on a stitch-by-stitch basis
(2) The amount by which the material is moved can be changed to form a seam which matches the sewing material.
(3) Stretching/shirring is possible, depending on the "feeding method", to prevent puckering or to promote gathering.
2. Type of feed
(1) Bottom feed
The bottom feed is the standard feeding method which feeds the sewing material only by means of the bottom feed dog (the feed dog located under the throat plate). (Fig. 1)
Example) The DDL-9000, -5570N, -5580N and -8700-7 type models
* Only the bottom feed dog feeds the sewing material. With this feeding method, sharp curves in the sewing material can be sewn. The bottom feed is best suited for general sewing.
* The bottom feed promises improved operability when handling the material fabric being sewn and is suited for fine work such as the sewing of corners of the material.
* The needle entry point is easily viewable.
* The bottom feed is applicable to a wide range of sewing such as runstitching, topstitching, and the sewing of small articles.
* Uneven material feed is likely to occur.
(2) Needle feed
The needle feed is a feeding method in which the needle bar moves in synch with the bottom feed dog. (Fig. 2)
Example) The DLN-9010 and -5410N-7 type models
* The needle feed feeds the material fabric with a greater increased accuracy than the bottom feed.
* Slippage between the upper and lower materials is reduced, but undesired stitch gathering is likely to occur due to highly-tensed stitches.
* The needle feed is suited for joining slippery materials or joining three plies of materials, promising a neat finish without any slippage between them.
* The needle feed is suited for the feeding of hard-to-feed materials.
* The needle feed slightly lacks in sharp-curve feeding capabilities.
(3) Differential feed
The bottom feed dog is divided into front and back parts centering at the needle. The amount of feed of the front and back parts of the feed dog can be respectively changed. (Fig. 3)
Example) The DLD-5430N-7 type models
* The differential feed is applicable to elastic sewing materials. It supports stretching and shirring.
* Using the differential feed in conjunction with the gathering attachment, the machine is able to perform gathering.
* Uneven feed is likely to occur. The differential feed is slightly inferior to the bottom feed in terms of sharp-curve feeding capabilities.
(4) Bottom and variable top feed
This type of feed utilizes with both the bottom feed dog and top feed dog (feed dog located on the throat plate). The amounts of feed of the bottom and top feed dogs are respectively adjustable. (Fig. 4)
Example) The DLU-5490N-7 and -5494N-7 type models
* The bottom and variable top feed effectively prevents slippage between upper and lower materials which are of a different in kind.
* With the bottom and variable top feed, the machine is able to perform gathering of the upper material fabric. The operator can perform sewing while visually checking the state of gathering.
* With the bottom and variable top feed, the machine is able to perform partial shirring.
* The bottom and variable top feed is inferior to the bottom feed in terms of sharp-curve feeding capabilities.
3. Type of feed dog teeth
(1) Angular feed dog teeth
Angular feed dog teeth are generally used. This configuration offers increased feed efficiency in the forward feed direction. (Fig. 5)
(2) Zigzag feed dog teeth
This type of feed dog teeth excels in securing the material fabric in the crosswise direction.
It is used for the top feed dog of zigzag stitching machines and bottom and variable top feed machines. (Fig. 6)
(3) Diagonal feed dog teeth
This type of feed dog teeth does not leave many marks on the material fabric.
It is used for bottom and variable top feed machines (cloth puller). (Fig. 7)
(4) Urethane rubber feed dog teeth
This type of feed dog teeth is effective for sewing materials which are easily damaged by the other types of feed dogs. The urethane rubber feed dog teeth come in several different configurations, such as angular and flat.
* This type of feed dog is effective for sewing delicate materials such as georgette and glossy fabric.
4. Feed dog teeth configurations
(1) Pitch (distance between teeth)
The feed dog teeth pitch varies from fine to coarse. (Fig. 8)
Fine pitch (for light-weight material) : 1.15 mm
Standard pitch (medium-weight materials) : 1.50 mm
Coarse pitch (for heavy-weight materials) : 1.80 mm
* Fine pitch: The feed dog with fine-pitch teeth is suited for soft light-weight materials. If used with a heavy-weight material, the feed dog does not securely catch the material and does not provide adequate efficiency of feed.
* Coarse pitch: The feed dog with coarse-pitch teeth is suited for heavy-weight and slightly rigid sewing materials. If used with a light-weight material, puckering may result.
* Puckering is likely to occur since stitches are formed in the state where the material is caught in the gap between the feed dog teeth.
(2) Number of teeth (number of rows)
* A smaller number of teeth (number of rows) provides better sharp-curve feeding capabilities.
* A larger number of teeth (number of rows) provides better straight feeding capabilities, increased efficiency of feed and increased stability of the material fabric.
[Features of the feed dog with three rows of teeth]
This type of feed dog is able to smoothly feed the material at sharp curves. However, the feed dog does not securely catch the material since it has no teeth on the near side of the needle entry. (Fig. 9)
It does not provide adequate efficiency of feed on multi-layered parts of the material, resulting in undesired stitch gathering.
* When putting in a heavy-weight material, such as a multi-layered part, from the right side of the feed dog, efficiency of feed is inadequate when starting sewing. In this case, undesired stitch gathering can result.
[Features of the feed dog with four rows of teeth]
This type of feed dog provides increased efficiency of feed since it has teeth on the near side of the needle entry. Therefore, the feed dog smoothly feeds a multi-layered part of material and securely catches the material at the start of sewing. (Fig. 10)
This type of feed dog does not smoothly feed the material at sharp curves.
* In particular, the feed dog is suited for sewing long materials which require smooth feeding of multi-layered parts at the start of sewing and a straight-feeding capability.
In general, the troubles described below are likely to occur according to the "teeth" configuration of the feed dog.
* When the feed dog teeth are as sharp as a blade: The teeth can be a cause of damaged materials, broken sewing-thread and broken chain-off thread.
* When the teeth surfaces are not level, the material may not be fed straight. (The material may skew to the right or left.)
In this case, slightly abrade the tooth surfaces with an oilstone or the like for correction. If the teeth have been significantly deformed and cannot be corrected, replacement of the feed dog is recommended.
5. Height and inclination of the feed dog
(1) Height of the feed dog
The feed dog height can be adjusted in the range of 0.5 mm to 1.2 mm according to the sewing material. Standard heights of the feed dog are as follows:
For light-weight materials -> 0.5 mm to 0.6 mm
For medium-weight materials -> 0.7 mm to 0.8 mm
For heavy-weight materials -> 0.9 mm to 1.2 mm
When the height of the feed dog is too high: Efficiency of feed is adequate, but puckering is likely to occur.
When the height of the feed dog is too low: Efficiency of feed is inadequate, but puckering is not likely to occur.
(2) Inclination of the feed dog
The feed dog should be positioned level, as standard, to the throat plate. The inclination of the feed dog, however, should be changed according to the efficiency of feed or sewing fabric properties. (Fig. 11)
* The feed dog is positioned with its side opposite the operator in a lowered position: This position of the feed dog is suited for knits which are likely to cause uneven material feed or material slippage.
* The feed dog is positioned with its side opposite the operator in a raised position: This position of the feed dog is suited for sewing materials which are likely to suffer puckering. (Cloth pulling effect)
* Refer to the instruction manual for lockstitch machines for how to adjust the position of the feed dog. (Written by: Masahiko Kimura, Apparel Manufacturing Research Laboratory)
|Fig. 1 Bottom feed||Fig. 2 Needle feed||Fig. 3 Differential feed||Fig. 4 Bottom and variable top feed||Fig. 5 Angular feed dog teeth|
|Fig. 6 Zigzag feed dog teeth||Fig. 7 Diagonal feed dog teeth||Fig. 8 Feed-dog teeth feed pitch|
|Fig. 9 Feed dog with three rows of teeth||Fig. 10 Feed dog with four rows of teeth||Fig. 11 Slope of feed dog|
|(1) Standard (level)||(2) Position of the feed dog with its side opposite the operator in a lowered position.||(3) Position of the feed dog with its side opposite the operator in a raised position.|