Drafting and Draft Constant Calculation of Roving Frame

Last Updated on 25/02/2021

Experiment name:
Study on drafting and draft constant calculation of Roving Frame.

It is an important factor to make fibers long and thick by drawing while making yarn from fibers. It is known as drafting. This work is done by pairs of rollers. In roving frame or simplex machine using any of the following drafting system drafts applied.

1. Conventional/roller drafting system.

  1. 3 over 3 roller drafting system
  2. 4 over 4 roller drafting system

2. Modern drafting system

  1. With apron
  2. Without apron

In this roving frame machine conventional 4 over 4 roller drafting is used.

There are 4 pairs of rollers which are situated up and down in pairs. Usually the bottom rollers are made of steel and snarled type, which are kept on u type bearing. Usually the front roller can not be moved but the others can be moved according to fiber length. There is a steel trap at the back of the last roller which is spreaded along the full length. This strip has a hole through which the sliver is entered. These holes are called guide hole. These guide holes help the sliver to pass through the specific place of the rollers and the stip moves to and fro by a cam so that the rollers are not harmed in same place. The top rollers are coated with leather, flannel etc and loaded on the bottom rollers. The total draft given to the sliver is divided in to two. In back zone that is between the 3rd and back roller, the draft given is called break draft. This draft prepares the sliver for the final draft of the front zone and break the twist if remains in sliver. Its amount depends on twist, amount of feed, characteristics of fiber etc. It is usually form 1.1 to up to 2. The rest draft of the total draft is given between 1st, 2nd and 3rd rollers. The total draft in simplex is usually 10-15.


  1. To find out the total draft of m/c.
  2. To find out the draft of every zone.
  3. To find out the draft constant of m/c.


  • Diameter of front  roller = 9/8″
  • Diameter of 2nd roller = 9/8″
  • Diameter of 3rd roller = 7/8″
  • Diameter of back roller = 1″
  • Teeth of back gear = 21
  • Teeth of 3rd gear = 21
  • Teeth of 2nd gear = 19
  • Teeth of front gear = 20
  • Teeth of DCCP = 70
  • Teeth of DCP = 70
  • Teeth of gear, a = 28
  • Teeth of gear, b = 76
  • Teeth of gear, c = 80
  • Teeth of gear, d = 21
  • Teeth of gear, e = 50
  • Teeth of gear, f = 81

Gearing diagram 4 over 4 roller drafting system of roving frame:

Gearing diagram 4 over 4 roller Drafting System
Fig: Gearing diagram 4 over 4 roller drafting system

Drafting and draft constant calculation of roving frame:

drafting and draft constant calculation of roving frame


  1. Draft of front zone = 3
  2. Draft of middle zone = 0.85
  3. Draft of back zone = 2.63
  4. Total draft = 6.76
  5. Draft constant = 473.68

In roving frame the weight of the processed sliver is reduced per unit length by drafting as the resultant roving can be easily transformed in to yarn applying draft within draft range of ring frame. This draft should be proper and sufficient. Otherwise cut roving, slub roving, irregular bobbin may produce in result. So we should properly maintain the roller setting, roller weight etc.

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