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ADVANCED MECHANICAL DRAFTING

ADVANCED MECHANICAL DRAFTING. LECTURE #6. MMC & LMC. MMC = M aximum M aterial C ondition Largest shaft diameter Smallest hole diameter. Worst case in most assembly situations. LMC = L east M aterial C ondition Smallest shaft diameter Largest hole diameter.

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ADVANCED MECHANICAL DRAFTING

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  1. ADVANCED MECHANICAL DRAFTING LECTURE #6

  2. MMC&LMC • MMC = Maximum Material Condition • Largest shaft diameter • Smallest hole diameter Worst case in most assembly situations • LMC = Least Material Condition • Smallest shaft diameter • Largest hole diameter Certain uncommon situations only

  3. 1.494 1.490 1.505 1.500 Ø Ø FITS HOLE SHAFT CLEARANCE FIT CLEARANCE AT MMC = 1.500 – 1.494 = .006 CLEARANCE AT LMC = 1.505 – 1.490 = .015

  4. 2.756 2.752 2.747 2.741 Ø Ø FITS HOLE SHAFT INFERFERENCE FIT INTERFERENCE AT MMC = 2.756 – 2.741 = .015 INTERFERENCE AT LMC = 2.752 – 2.747 = .005

  5. 3.321 3.315 3.328 3.319 Ø Ø FITS HOLE SHAFT TRANSITION FIT INTERFERENCE AT MMC = 3.321 – 3.319 = .002 CLEARANCE AT LMC = 3.328 – 3.315 = .013

  6. GENERAL FIT CONCEPT MMC= MAXIMUM INTERFERENCE or MINIMUM CLEARANCE LMC= MAXIMUM CLEARANCE or MINIMUM INTERFERENCE

  7. FITS IN THE MHB • Five Major Fit Classes • RC – running or sliding clearance fits • LC – locational clearance fits • LT – locational transition fits • LN – locational interference fits • FN – force or shrink interference fits • Each fit class contains several subclasses • All values in fit tables must be multiplied by 1000 before using them in calculations

  8. EXAMPLE Calculate Shaft and Hole diameters and clearances or interferences for a Ø1.50” basic mating shaft and hole in the following fit conditions: RC-7 FN-4 LT-3

  9. HOLE SHAFT CLEARANCE .003O @ MMC .0071 @ LMC 1.50 + .0025 = 1.5025 1.50 + 0 = 1.5000 1.50 - .0030 = 1.4970 1.50 - .0046 = 1.4954

  10. HOLE SHAFT INTERFERENCE .0031 @MMC .0015 @ LMC 1.50 + .001 = 1.501 1.50 + 0 = 1.500 1.50 + .0031 = 1.5031 1.50 + .0025 = 1.5025

  11. HOLE SHAFT CLR or INT .0007 INT @MMC .0009 CLR @ LMC 1.50 + .001 = 1.501 1.50 + 0 = 1.500 1.50 + .0007 = 1.5007 1.50 + .0001 = 1.5001

  12. GSH END DESIGN

  13. CHANGING DIMENSION PROPERTIES • Left click on dimension to show grips • Right click to display change menu • Select PROPERTIES • Change or add prefix, suffix, precision, tolerances etc.

  14. ADD PREFIX OR SUFFIX • Prefixes: • 2X, Ø (%%C), R, SØ, SR • Suffixes: • TYP, MAX, MIN, etc.

  15. .877 .872 Ø TYP CHANGE TO LIMIT EXAMPLE: Dimension .875 Lower limit .003 Upper limit .002 Precision 0.000

  16. 1.505 1.497 MOVE DIMENSION OUTSIDE OF EXTENSION LINES

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