What are these drills called?

[Bodgit Fixit and RunParticipant @bodgitfixitandrun]

Thank you Andrew. I Learned something new today.

[Trevor Drabble 1Participant @trevordrabble1]

Chris,

This drill is actually a slow helix drill and is designed for non-ferrous materials such brass , phosphor bronze ,gunmetal and the like . The reason for the slow flutes is to change the rake angle at the cutting lip to one more suitable for such duty , as opposed to a standard drill whose flutes produce a rake angle more suited to ferrous materials. In other words , each is simply a way of producing the same angles as found on any other cutting tools such as lathe tools or milling cutters . You will also find that the lands are narrower and the flutes wider than on a standard drill mainly to help reduce binding and also to aid rapid removal of the swarf. We always used to produce these drills with a standard 118 degree point because greater angles effected the cutting lips . Also , generally speaking, as would seem to be the case here , stub drills are produced with a standard helix , but with the flutes only half the length of a standard jobber drill . As usual, there are always exceptions . For example, originally we used to supply standard small jobber drills to Raleigh in Nottingham for the drilling of the spoke holes in bicycle wheels , but the breakages were so great, the asked us to supply double – ended versions , which we did. This work certainly kept the Hertline flute grinders busy. Hope this helps answer your queery.

[Chris DentonParticipant @chrisdenton53037]

Thanks for that.

I actually use them on aluminium, they drill an accurately located hole with a good finish. Otherwise I'd have to centre drill, pilot drill then final drill.

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