I have a question on machine driven tapping:
When I was in school, our teacher cut a thread on some half-inch section, continuously turning the die all the way. He then showed us the resulting broken thread caused by chips fouling the die.
I have used the "half-turn, back-to-break-chip" thread cutting method ever since, but I wonder how tapping machines avoid this problem?
If you are tapping thru holes, so called gun taps are the way to go. The chips produced are "driven forward" by the tap's cutting geometry. So there is no jamming of chips between the workpiece and the tap.
If you are tapping blind holes, there is some advantage to using gun taps, but you still have to remove the tap, remove the produced chips and have another go at it to ensure you are tapping to the full depth your tap can produce [assuming you don't have bottoming taps].
Hope this helps.
Jimmy K. Ramirez / Kingsville, Texas
use an "express tap",there is no chips at all
Gun taps or "spiral point" taps push the chips forward and are used for through holes. "Spiral flute" taps pull the chips back out of blind holes. I don't know if there are external threading dies with similar features. (I found none in the MSC catalog.)