RE: [mfg-smartcam] off topic preplate threads

Wed, 16 Jul 2003 08:03:30 -0700

Title: off topic preplate threads

Lee, If you're zinc plating any external thread that meets class 1 or 2 standards, what you end up with is parts that meet no standards.  With electroless nickel, you have a small chance of being within tolerance if your thread is on the low side.  The "profile" of plating build up is totally different with different types of plating.  If it is critical, you should use a comparator to examine some test pieces before & after plating.

We solved plating thread problems by requiring all plated threads to be cut .002 undersize.  Since we (did) cut so many different threads and had so many people doing it, we use wires for gaging.

To resolve these and other problems, about 15 years ago, we published a shop practice handbook, which included these guidelines:

  • EXTERNAL THREADS

    • Stainless parts should be threaded to standards for class 2 threads.
    • All CRS parts should be threaded to .002" smaller than standard for class one threads to allow for plating.
    • Chamfer the ends on all external threads, unless drawing notes say no chamfer.

    KLIKLOK THREAD STANDARD MEASURES

    Measure Over Wires
    Thread Standard Wire Plated (before plating) Unplated Suggested
    Size Min Max Min Max Tap Drill
    6-32 UNC 0.024 0.1570 0.1598 0.1590 0.1618 #32 0.106
    8-32 UNC 0.024 0.1828 0.1857 0.1848 0.1877 #29 0.136
    10-32 UNF 0.024 0.2075 0.2117 0.2107 0.2137 #21 0.159
    10-24 UNC 0.029 0.2075 0.2108 0.2095 0.2128 #26 0.147
    1/4 - 28 UNF 0.024 0.2599 0.2649 0.2636 0.2669 #3 0.213
    1/4 - 20 UNC 0.029 0.2525 0.2581 0.2564 0.2601 #7 0.201
    5/16 - 24 UNF 0.029 0.3277 0.3332 0.3315 0.3352 I 0.272
    5/16 - 18 UNC 0.032 0.3150 0.3211 0.3201 0.3231 F 0.257
    3/8 - 24 UNF 0.029 0.3900 0.3957 0.3939 0.3977 Q 0.332
    3/8 - 16 UNC 0.040 0.3905 0.3970 0.3946 0.3990 5/16 0.312
    7/16 -20 UNF 0.029 0.4392 0.4454 0.4432 0.4474 25/64 0.391
    7/16 - 14 UNC 0.040 0.4387 0.4458 0.4431 0.4478 U 0.368
    1/2 - 20 UNF 0.029 0.5012 0.5079 0.5056 0.5099 29/64 0.453
    1/2 - 13 UNC 0.045 0.5075 0.5149 0.5119 0.5169 27/64 0.422
    9/16 - 18 UNF 0.032 0.5641 0.5709 0.5684 0.5729 33/64 0.516
    9/16 - 12 UNC 0.055 0.5898 0.5976 0.5944 0.5996 31/64 0.484
    5/8 - 18 UNF 0.032 0.6264 0.6334 0.6307 0.6354 37/64 0.578
    5/8 - 11 UNC 0.055 0.6404 0.6487 0.6452 0.6507 17/32 0.531
    3/4 - 16 UNF 0.040 0.7643 0.7715 0.7688 0.7735 11/16 0.688
    3/4 - 10 UNC 0.055 0.7508 0.7596 0.7557 0.7616 21/32 0.656
    7/8 - 14 UNF 0.040 0.8750 0.8831 0.8797 0.8851 13/16 0.812
    7/8 - 9 UNC 0.063 0.8822 0.8917 0.8874 0.8937 49/64 0.766
    1 - 8 UNC 0.072 1.0124 1.0226 1.0176 1.0246 7/8 0.875

    • Plated standards are .002" less than standard for class one threads to allow for plating.
    • Unplated standards are for class two threads.

-----Original Message-----
From: Lee Greer [mailto:[EMAIL PROTECTED]
Sent: Tuesday, July 15, 2003 11:21 AM
To: Mfg-Smartcam (E-mail)
Subject: [mfg-smartcam] off topic preplate threads

Group,
 I am looking for a chart or formula to calculate the effects of plating buildup on internal and external thread and how this effects the thread class?

Lee Greer
CAD\CAM department
Midwest Precision Tool & Die

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