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Questions and Answers
What is the fundamental deviation for the tolerance of ‘f’ at a diameter of 25 mm?
For a GO and NO-GO gauge designed for assembly 20H7/f8, what is the wear allowance if the gauge tolerance is set to 10%?
What is the lead screw pitch of the lathe used for cutting left-hand threads of 5 TPI?
What is the maximum depth of cut for the mild steel bar during the turning operation?
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What is the cutting speed for a workpiece that requires a time calculation for a piece 350 mm long and 50 mm in diameter?
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Study Notes
Limit, Fits and Tolerances
- GO and NO-GO gauges are designed to check holes and shafts in assemblies, ensuring proper fitting.
- Gauge tolerances can be set at 10% with a wear allowance equal to one fifth of the gauge tolerance.
- Fundamental deviation for 'f' is calculated as -5.5 D^0.41.
- For assembly tolerances, the relevant Interchangeable Tolerance grades are IT7 and IT8, with IT7=16i and IT8=25i.
- Diameter steps for calculations are taken from ranges such as 18 mm to 30 mm.
- Specific assembly diameters of 25 mm, 20 mm, and 30 mm provide reference for gauge design.
Lathe Operations
- Change gears are essential for cutting various thread pitches, affecting thread types like left-hand (L.H.) and right-hand (R.H.) threads.
- It's crucial to determine gear arrangements for specific threads based on lead screw pitch (e.g. 6 mm and 8 mm).
- Cutting threads at different pitches (e.g., 5 TPI, 0.25″ pitch) requires careful computation of gear ratios.
- Sketching gear arrangements aids in visualizing and executing threading operations without feed reversing mechanisms.
Machining Time Calculations
- Calculating machining time involves material properties, piece dimensions, rotation speed, and feed rates.
- A mild steel bar turning operation from 50 mm to 45 mm diameter at 200 RPM with a feed of 0.1 mm/rev includes additional approach and over-travel distances.
- For a 350 mm long and 50 mm diameter workpiece, cutting speed and feed should be factored in to estimate time for complete cuts.
- The complexity of machining operations and the required precision can significantly influence total machining time.
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Description
This quiz explores the concepts of limits, fits, and tolerances in engineering design. Participants will design GO and NO-GO gauges for various assemblies, taking into account tolerances and deviations. A thorough understanding of dimensional inspection is essential for successful completion.
