Die Casting Design
Cored Holes for Threads
Guidance on die cast tap hole sizes for tapped threads is found below.
Cut Threads: Standard Tolerances
Tapped holes require special diameters, depth and draft to optimize economic production. Draft may be retained, based on allowing 85% full thread depth at the small end and 55% at the large end. A countersink or radius is recommended to provide relief for any displaced material and also strengthen the core in the diecast tool.
Cut Threads: Critical Tolerances
Greater dimensional accuracy can be achieved on tapped holes, but at higher cost. Draft may be retained, based on allowing 95% full thread depth at the small end and the maximum minor diameter at the large end.
Formed Threads: Critical Tolerances
All formed threads require the greater die casting accuracy specified in these critical tolerances. Cored holes may be tapped without removing draft.
Pipe Threads: Standard Tolerances
The cored holes specified below are suitable for both NPT and ANPT. NPT should be specified where possible, due to the additional costs and steps required. The 1°47' taper per side is more important for ANPT than NPT.
No standards exist for metric pipe threads.