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4A-36
NADCA Product Specification Standards for Die Castings / 2012
Engineering & Design: Coordinate Dimensioning
Cored Holes for Formed Threads: Precision Tolerances
The Precision Tolerance recommendations for cored holes for formed threads, on the opposite page, are based on allowing 75% of full thread depth at the bottom D 2 (small end) of the cored hole and 50% at the top D 1 (large end) of the cored hole. When required, cored holes in alumi-num, zinc and magnesium may be tapped without removing draft.
Cold form taps displace material in an extrusion or swaging process. As a result, threads are stronger because the material is work hardened as a part of the process for forming threads. Because material is displaced, a countersink is recommended at the ends of through holes and at the entry of blind holes.
Tests indicate that thread height can be reduced to 60% without loss of strength, based on the fact cold formed threads in die castings are stronger than conventional threads. However, the use of 65% value is strongly recommended.
Since cored holes in castings must have draft (taper), the 65% thread height Y should be at a depth that is an additional one-half of the required engagement length of the thread in the hole. Blind holes should be cored deep enough to allow a four (4) thread lead at the bottom of the hole. This will result in less burr around the hole and longer tool life. Hole sizes of #6 or less, or metric M3 or less, are recommended for through holes only.
Cold form tapping is not recommended for holes with a wall thickness less than two-thirds the nominal diameter of the thread.
The Precision Tolerance recommendation should be considered as a starting point with respect to depth recommendations. There are many applications that do not require the percent of thread listed here. If a lesser percent of thread can be permitted, this would, in turn, allow more draft and a deeper hole. Amount and direction of required strength can be determined by testing.
NADCA PRECISION TOLERANCES
Cored holes for formed threads are specified in die castings as Precision Toler-ances, because they require special control in production. The specific diameter, depth and draft required will deter-mine the added cost.Note:
Tolerances for cored holes for thread forming fasteners (self tapping screws) should be provided by the manu-facturer of the specific type of thread forming fastener to be used.
4A-37
NADCA Product Specification Standards for Die Castings / 2012
Engineering & Design: Coordinate Dimensioning
4A
Cored Holes for Formed Threads: Precision Tolerances
The tolerances below apply to AI, Mg, Zn and ZA die casting alloys, as footnoted. Note that, when required, cored holes in aluminum, zinc, and magnesium may be tapped without removing draft.
Guidelines are provided on the opposite page
regarding thread height, depth, and limitations on wall thickness.
The Precision Tolerance values shown represent greater casting accuracy involving extra precision in construction and/or special control in production. They should be specified only when and where necessary, since additional cost may be involved.
NADCA PRECISION
TOLERANCES
Table P-4A-10 Cor e d Holes for Formed Thr eads (Pr e cision)— Unified Series and Metric Series
Unified Hole Diameter
Thread Depth Hole Depth Series D
1, Max.D 2, Min.Y ,Max.X , Max.Class
inches inches inches inches 0-80, UNF/2B, 3B (0.0558)(0.0536)(0.090)(0.120)1-64, UNC/2B, 3B (0.0677)(0.0650)(0.110)(0.146)1-72, UNF/2B, 3B (0.0683)(0.0659)(0.110)(0.146)2-56, UNC/2B, 3B (0.0799)(0.0769)(0.129)(0.172)2-64, UNF/2B, 3B (0.0807)(0.0780)(0.129)(0.172)3-48, UNC/2B, 3B (0.0919)
(0.0884)(0.149)(0.198)3-56, UNF/2B, 3B (0.0929)(0.0899)(0.149)(0.198)4A-40, UNC/2B, 3B (0.1035)(0.0993)(0.168)(0.224)4A-48, UNF/2B, 3B (0.1049)(0.1014)(0.168)(0.224)5-40, UNC/2B, 3B (0.1165)(0.1123)(0.188)(0.250)5-44, UNF/2B, 3B (0.1173)(0.1134)(0.188)(0.250)6-32, UNC/2B, 3B (0.1274)(0.1221)(0.207)(0.276)6-40, UNF/2B (0.1295)(0.1253)(0.207)(0.276)8-32, UNC/2B 0.1530.1480.3280.4928-36, UNF/2B 0.1550.1500.3280.49210-24, UNC/2B 0.1760.1690.3800.57010-32, UNF/2B 0.1790.1740.3800.57012-24, UNC/2B 0.2020.1950.4320.64812-28, UNF/2B
0.2040.1980.4320.6481/4A-20, UNC/1B, 2B 0.2330.2250.5000.7501/4A-28, UNF/1B, 2B 0.2380.2320.5000.7505/16-18, UNC/1B, 2B 0.2940.2840.7030.9385/16-24, UNF/1B, 2B 0.2980.2910.7030.9383/8-16, UNC/1B, 2B 0.3540.3430.844 1.1253/8-24, UNF/1B, 2B 0.3610.3540.844 1.1257/16-14, UNC/1B, 2B 0.4130.4010.984 1.3137/16-20, UNF/1B, 2B 0.4210.4120.984 1.3131/2-13, UNC/1B, 2B 0.4740.461 1.125 1.5001/2-20, UNF/1B, 2B 0.4830.475 1.125 1.5009/16-12, UNC/1B, 2B 0.5340.520 1.266 1.6889/16-18, UNF/1B, 2B 0.5440.534 1.266 1.6885/8-11, UNC/1B, 2B 0.5940.579 1.406 1.8755/8-18, UNF/1B, 2B 0.6060.597 1.406 1.8753/4A-10, UNC/1B, 2B 0.7160.699 1.500 2.2503/4A-16, UNF/1B, 2B 0.7290.718 1.500 2.2507/8- 9, UNC/1B, 2B 0.8370.818 1.750 2.6257/8-14, UNF/1B, 2B 0.8510.839 1.750 2.6251- 8, UNC/1B, 2B 0.9580.936 2.000 3.0001-12, UNF/1B, 2B
0.972
0.958
2.000
3.000
Metric Hole Diameter Thread Depth Hole Depth Series D 1, Max.D 2, Min Y ,Max.X , Max.M1.6 X 0.35(1.481)(1.422)(2.4)(3.2)M2 X 0.4(1.864)(1.796)(3.0)(4.0)M2.5 X 0.45(2.347)(2.271)(3.8)(5.0)M3 X 0.5(2.830)(2.745)(4.5)(6.0)M3.5 X 0.6 3.296 3.1947.010.5M4 X 0.7 3.762 3.6438.012.0M5 X 0.8 4.728 4.59210.015.0M6 X 1 5.660 5.49012.018.0M8 X 1.257.5757.36316.024.0f M8 X 17.6607.49016.024.0M10 X 1.59.4909.23520.030.0f M10 X 0.759.7459.61812.530.0fM10 X 1.259.5759.36320.030.0M12 X 1.7511.4111.1124.036.0f M12 X 111.6611.4918.036.0f M12 X 1.2511.5811.3618.036.0M14 X 213.3212.9828.042.0f M14 X 1.513.4913.2421.042.0f M15 X 114.6614.4918.845.0M16 X 215.3214.9832.048.0f M16 x 1.515.4915.2424.048.0f M17 X 116.6616.4917.051.0f M18 X 1.517.4917.2427.054.0M20 X 2.519.1518.7340.060.0f M20 X 119.6619.4920.060.0f M20 X 1.519.4919.2430.060.0f M22 X 1.521.4921.2427.566.0M24 X 322.9822.4748.072.0f M24 X 223.3222.9836.072.0f M25 X 1.524.4924.2431.375.0f M27 X 226.3225.9840.581.0M30 X 3.5
28.81
28.22
60.0
90.0
Tip or Spherical Radius Optional
Table P-4A-10: Cored Holes for Formed Threads (Precision Tolerances) – Unified Series and Metric Series Values in italics and parentheses are achievable but should be discussed with the die caster prior to finalization of a casting design.
f = Fine Pitch Series。