What's with thees drill bits?

I have a 1/4" or so solid carbide drill bit with coolant holes. Definitely not twisting one of those. I would say they are cast like that somehow.
 
Start with a flat section (I'm sure the pre-twist shape could be optimized), drill the coolant holes, twist it, stress relieve and heat treat, then finish grind.

Carbide? Hmmm, perhaps something analogous to lost-wax casting?
 
I would think twisting after drilling. I too have seen that video, and cannot find it. Could it be done on the tiny drills? I would bet they can. I cannot imagine cast would be as strong. Another idea, is something like EDM. I have no expierience with that so I do not know its capabilities.
 
Superburban said:
I would think twisting after drilling. I too have seen that video, and cannot find it. Could it be done on the tiny drills? I would bet they can. I cannot imagine cast would be as strong. Another idea, is something like EDM. I have no expierience with that so I do not know its capabilities.
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Not cast for the metal tools, I was thinking more like cemented carbide.

EDM can drill long straight tiny holes. Could one form a wire electrode into a spring and wind it into the hole as it cuts? Theoretically yes, but in practice I doubt you could control it well enough.
 
I believe they are made by sintered powder metal process. Like how carbide inserts are made. Coolant through drills are usually made of carbide.
 
Here's a bit of a blurb on how the coolant holes are made in carbide drills.


I would think there is a similar process used on HSS drills substituting the "fishing line" with nichrome wire.
 
I'm making a guess here, but I would bet the drills being formed by heat and twisting are carbon steel rather than HSS. Every current day manufacturer I am aware of hardens and tempers the blanks in a vacuum oven to eliminate hydrogen embrittlement or other problems that can be caused by exposing the heated metal to oxygen. Once the blanks are properly tempered the chamfers, flutes and cutting surfaces are ground into them.
 
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