19-12-2019, 12:59 PM
there are many thousands of pages on the mini forum whose crank uses the good ol' 5/8 16tpi. Someone did a CAD comparison as the UNS and W F seem to be interchangeably used by various sectors of mini race engine builders! Here is the comparison. (Interestingly, for mere clean up, there is a chinese UNS tap and die pair on ebay for under 9 quid...
Whitworth_UNS_Profiles.jpg (Size: 189.13 KB / Downloads: 147)
dklawson's notes from Mini Forum:
"The JPG shows what you see if you superimpose the two thread forms. Note that there is minimal interference between the two due to the way their geometries overlap. A 5/8-16 UNS tap would barely cut the major diameter of the female threaded hole... hence, almost no swarf would be removed if the UNS tap is run in a Whitworth form threaded female hole. Owing to manufacturing tolerances, I'd say that the UNS tap will only cut material when the MINOR diameter of the female threads have been damaged.
EDIT: Note in the JPG that the UNS thread is shown in blue in all instances and the Whitworth form in grey. The UNS thread form has the flat crests. The root radius/bottom of the UNS thread is not defined by any standards I've seen. While I show potential interference there, it's not likely to exist as it's probably removed by the tap drill for the Whitworth form tap.
EDIT2: I went back and took some information from KC's earlier emails. He mentions that the tap drill is called out on the drawings as 0.557"diameter. Superimposing the tap drill on the section view details in the picture below... there's virtually no contact between either tap's minor diameter and the tap drill hole. The only interference will be the minor amount occurring at the crest of the threads."
Whitworth_UNS_Profiles.jpg (Size: 189.13 KB / Downloads: 147)
dklawson's notes from Mini Forum:
"The JPG shows what you see if you superimpose the two thread forms. Note that there is minimal interference between the two due to the way their geometries overlap. A 5/8-16 UNS tap would barely cut the major diameter of the female threaded hole... hence, almost no swarf would be removed if the UNS tap is run in a Whitworth form threaded female hole. Owing to manufacturing tolerances, I'd say that the UNS tap will only cut material when the MINOR diameter of the female threads have been damaged.
EDIT: Note in the JPG that the UNS thread is shown in blue in all instances and the Whitworth form in grey. The UNS thread form has the flat crests. The root radius/bottom of the UNS thread is not defined by any standards I've seen. While I show potential interference there, it's not likely to exist as it's probably removed by the tap drill for the Whitworth form tap.
EDIT2: I went back and took some information from KC's earlier emails. He mentions that the tap drill is called out on the drawings as 0.557"diameter. Superimposing the tap drill on the section view details in the picture below... there's virtually no contact between either tap's minor diameter and the tap drill hole. The only interference will be the minor amount occurring at the crest of the threads."