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Worksheets3-Jaw Chuck Worksheet- Answers
Total questions: 20
Worksheet time: 10mins
What is the primary function of a 3-jaw chuck on a lathe?
To securely hold and rotate a workpiece while keeping it centered
To sharpen cutting tools during machining
To measure runout and concentricity of the spindle
To automatically change cutting speeds
A 3-jaw chuck is considered self-centring because all three jaws move simultaneously and equally when the chuck key is turned. What does this synchronized movement ensure?
The workpiece is automatically centered along the lathe’s axis
The chuck pinions disengage from the scroll plate
The jaws lock independently for irregular shapes
The spindle speed matches the cutting feed
Which workpiece shapes are best suited for a 3-jaw chuck? Select the pair that matches the recommended types.
Round and hexagonal
Square and rectangular
Triangular and octagonal
Flat plate and angle iron
Why are the jaws of a 3-jaw chuck numbered?
To ensure installation in the correct sequence in the chuck slots
To indicate the maximum clamping force of each jaw
To match jaw numbers with toolholder IDs
To label soft jaws versus hard jaws
What may occur if 3-jaw chuck jaws are installed incorrectly?
Poor grip, misalignment, and potential damage
Improved concentricity and smoother rotation
Automatic speed reduction only
No noticeable effect during machining
In the chuck mechanism, what is the purpose of the pinions?
They engage with the scroll plate; turning a pinion rotates the scroll to move all jaws simultaneously
They provide coolant flow through the jaws for lubrication
They lock each jaw individually to prevent slippage
They act as balance weights to reduce vibration
Which description best explains how turning the chuck key affects the jaws?
Turning the key rotates a pinion that drives the scroll plate, moving all jaws inward or outward together
Turning the key directly pushes a single jaw while others remain stationary
Turning the key increases spindle RPM before jaw movement occurs
Turning the key tightens a belt that clamps the workpiece
Why is it important to clean the chuck regularly?
To prevent buildup of chips, dirt, and coolant residue that can make the chuck stiff and inaccurate
To remove protective grease that improves clamping force
To polish jaws for cosmetic appearance only
To ensure the spindle bearings remain oiled
If a chuck is not maintained, which problem is most likely according to the guidance?
Loss of accuracy and failure to grip properly, leading to unsafe conditions and poor machining quality
Immediate motor burnout due to electrical overload
Permanent deformation of the lathe bed within hours
Automatic tool wear reduction
Match each chuck component or feature to its role.
Pinion
Small gear turned by key
Scroll plate
Rotated by pinion to drive jaws
Numbered jaws
Ensures correct installation order
Self-centring movement
Moves all jaws equally and simultaneously
Which is a sign that chuck jaws are worn and need replacement?
Difficulty gripping workpieces securely
Reduced spindle noise only
Lower coolant temperature
Increase in toolpost rigidity
Which observation indicates poor concentricity due to worn jaws?
Increased runout during machining
Lower surface roughness on finished parts
Higher cutting fluid pressure
Longer tool life without changes
Which of the following best describes slippage caused by worn chuck jaws?
Workpiece slips under normal cutting forces
Workpiece only moves during tool changes
Workpiece slides when spindle is powered off
Workpiece rotates faster than the spindle
Select the most complete list of wear indicators for 3-jaw chuck jaws described in the material.
Difficulty gripping securely; visible wear on jaw surfaces; increased runout; slippage under normal cutting forces
Slight discoloration; reduced coolant flow; quieter operation
Higher spindle speed; improved surface finish; decreased vibration
Lower clamping force due to soft jaws; reduced machine power; automatic shutdown
Refer to the exploded diagram of the 3‑jaw chuck. Which component translates pinion rotation into synchronized radial movement of the jaws?
Cover
Scroll plate
Bearing
Body
In the diagram of the 3‑jaw chuck, which item directly engages with the scroll plate to drive it?
Pinion
Bearing
Hard solid ID jaw
Body
Match each labeled component in the exploded 3‑jaw chuck with its primary role.
Scroll plate
Provides spiral teeth that move jaws in unison
Pinion
Small gear that turns to rotate the scroll
Bearing
Reduces friction between rotating parts
Cover
Protective plate closing the front/rear of the chuck
Which jaw type shown is intended to grip an internal diameter (ID) in the 3‑jaw chuck diagram?
Base thread jaw
Hard solid ID jaw
Body jaw
Bearing jaw
A technician reports the chuck does not open evenly. Based on the exploded diagram, which component is most likely worn if all three jaws move inconsistently despite the pinion turning smoothly?
Scroll plate with damaged spiral teeth
Cover plate fasteners loosening
Body with cosmetic dents
Bearings missing grease
Arrange the following components in a logical assembly order from outer housing inward for the 3‑jaw chuck, based on the exploded diagram context.
Body → jaws → scroll plate → bearing → cover
Cover → bearing → scroll plate → body → jaws
Body → scroll plate → pinion → cover → bearing
Pinion → cover → body → jaws → bearing
