what material and what hardness please? Also some inputs regarding speed,type of drill chuck,coolant etc will be helpful in getting a meaningful reply.
An afterthought are these drill bits of China origin?
Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)
Inner coolant pressure? (must be more than 70 bars)
Is there any pilot hole?
Blind or through hole? If through, output face specs, angle with axis?
Material?
cutting parameters?
Run out on the tool at machine spindle?
Tool holder type?
Coolant Type and concentration?
It is not easy to say exact reason without these informations (even with these it is still not easy)
Then we can talk about the possibilities.
Any lateral motion will easily break carbide. Clamp the workpiece. It's easy to work harden some materials with small drills - make sure you are always feeding the drill. Make sure there are is no material stuck on the point of the drill or clogging the flutes.
Make sure you have a drill specific to your application both in material and drill design. Use fixture the bit as close to the work as you can using a drill press. Alternatively insert the bit deep in to the chuck so you have minimal exposure.
There are maybe 7,000 grades of carbide depending on how you count and how you feel about brand names. Wood drill bits won’t drill steel well.
To give you an idea of the range of applications, here are the traditional C grades from WW II.
C grades classification
C-1 to C-4 are general grades for cast iron, non-ferrous and non-metallic materials
C-1 Roughing
C-2 General Purpose
C-3 Finishing
C-4 Precision
Steel and steel alloys - these grades resist pitting and deformation
C-5 Roughing
C-6 General Purpose
C-7 Finishing
C-8 Precision
Wear Surface
C-9 No shock
C-10 Light shock
C-11 Heavy shock
Impact
C-12 Light
C-13 Medium
C-14 heavy
Miscellaneous
C-15 Light cut, hot flash weld removal
C-15A Heavy cut, hot flash weld removal
C-16 Rock bits
C-17 Cold header dies
C-18 Wear at elevated temperatures and/or resistance to chemical reactions
C-19 Radioactive shielding, counter balances and kinetic applications
The number 1 cause of breaking small drill bits, of any material, in any material, is running them too slowly, because they're small and expensive. Calculate the linear speed at the periphery of the drill in feet/min, and compare it with the recommended speeds you can get from the drill supplier or Machinery's Handbook.
Number 2 is inadequate fixturing that forces the drill to bend to find or follow the hole. Carbide drills don't bend; they fracture.
While you're running the numbers for number 1 above, also look at the feed rate per tooth, and calculate how long it should take you to reach the depth you want. Chances are you're running too little axial feed, babying the drill... and that just work hardens some metals and burns the drill.
Using the recommended feeds and speeds will produce cycle time numbers that will astonish you... and if the drill's geometry is right, when you try doing it that way, you'll also be astonished to see nice short chips flying out of the flutes instead of clingy birds nests getting tangled up and making a mess of things... and the drills will last longer.
