3 Jaw Chuck Mechanism

 3 Jaw Chuck Mechanism

In this blog you will learn how does 3 Jaw mechanism work
Let first see all the parts inside the three chuck mechanism. 
Hard Solid ID jaw: The purpose of this part is to hold the job or part tightly . it contains some groove so that it can easily place and align in the body
Body : It is solid casing which contains groove to give horizontal guidance to hard solidworks id jaw
Scroll plate: this is the main part that of the 3 jaw chuck mechanism . this parts contains teeth as well as spiral  we will talk about more details letter onwards
Pinion  gears: these gears are placed in  bearing above cover for proper alignment of bearing
Base thread : it is the part that contains spiral threading at the bottom normally hard solid id jaw and base thread jaw is made a  single part but in this video they have shown separately.
Cover : it is the base of the chuck which attach to the lathe machine. the cover is the part that attach to the main spindle of the lathe machine

Now lets talk about how this mechanism works. When the pinion gear rotates it rotate the scroll plate as you can see that at the below surface scroll plate has gear . even a single pinion rotation will give movement to all the jaw because of spiral mechanism as you can see in the video . 
In this video the ratio between the pinion gear and scroll plate is .1875  it means  when pinion complete a 360 degree turn then a scroll plate only turn 67.5 degree . 
The distance travelled by the jaw is depend upon spiral pitch in this case it is 6 mm which means when  a spiral plate move 360 degree it  can move jaw to 6 mm  
3 jaw  chuck is used normally use for cylindrical shape and hexagon shape

Advantage  a 3-jaw:

  1. self-centering (means even if you rotate any pinion it will all jaws equally that will make ensure that job lies in the center of the chuck)
  2. Only circular and hex shape can hold (some other shape can also hold but 3 jaw chuck not best for it low grip)
  3. quick and easy to use.

Disadvantages of a 3-jaw:

  1. can't hold square bar-stock
  2. run-out/off-center can't be easily fixed
  3. can't hold irregularly shaped work
  4. can't turn off-center

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