Machinery's Handbook, 31st Edition
2184
Thread Cutting
25.4
. 175 254 145 . =
Equivalent thds/in pitch in mm to be cut =
use 14 thds/in
. (
)
=
gearbox setting in thds/in pitch in mm to be cut ×
5
. 127 5 14 175 × ×
×
=
127
. 24 127 24 5 14 175 × × × × ^ h h
. . 24 127 5 14 24 175175 × × × × ^ h
h
^
^
=
=
driven gears driving gears
24 127 70 42 × ×
=
Odd Inch Pitch Threads: The calculation of the modifying change gears used for cutting odd pitch threads that are specified by their pitch in inches involves the sizes of the stan dard gears, which can be found by counting their teeth. Standard gears are those used to enable the lathe to cut the thread for which the gearbox setting is made; they are the gears that are normally used. The threads on worms used with worm gears are among the odd pitch threads that can be cut by this method. As before, it is usually advisable to calculate the actual number of threads per inch of the odd pitch thread and to select a gearbox setting that is close to this value. The following formula is used to calculate the modifying-change gears to cut odd inch pitch threads: Standarddriven gear Standard driving gear pitch to be cut in inches gearbox setting in thds/in # # = Example: Select the quick-change gearbox setting and calculate the modifying change gears required to cut a thread having a pitch equal to 0.195 inch. The standard driving and driven gears both have 48 teeth. To find equivalent threads per inch: driven gears driving gears
in. Thds
pitch 1
0.195 1 5.13 (use 5 thds/in) =
=
=
Standard driven gear Standarddriving gear pitch to be cut in inches gearbox setting in thds/in 48 48 0.195 5 1000 1000 0.195 5 500 2 195 5 100 2 39 5 50 2 2 8 39 5 8 ^ h # # # # # # # # # # # # # # # = = = = ^ ^ h ^ h
=
h
driven gears driving gears
50 32 39 40 # #
=
=
It will be noted that in the second step above, 1000 ∕ 1000 has been substituted for 48 ∕ 48. This substitution does not change the ratio. The reason for this substitution is that 1000 × 0.195 = 195, a whole number. Actually, 200 ∕ 200 might have been substituted because 200 × 0.195 = 39, also a whole number. The procedure for calculating the modifying gears using the following formulas is the same as illustrated by the two previous examples. Odd Threads per Inch on Inch Lead-Screw Lathes: Standard driven gear thds/in to be cut Standard driving gear gearbox setting in thds/in driven gears driving gears # # =
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