Dog Star
Western Thunderer
I had been drilling 0.45mm holes in circa 0.25mm nickel silver (half-etch holes in 0.45mm sheet), happily going along the sheet and had done about ten holes when the drill refused to cut any more metal. I looked at the drill bit using a magnifying glass and good illumination expecting to find either a blunt or a chipped tip to the drill. In silhouette the drill looked complete... and then I noticed that the flutes were mis-shapen, as in:-
Aplogies for clarity of image.
No kidding, the flutes about 1mm behind the tip of the drill had "unwound".... as if the tip had snagged in the hole and the remainder of the drill continued turning. However, under a magnifying glass the tip was still as formed with the cutting edges no longer able to contact the metal surface. Not just once, not just twice... this behaviour happened with four more drills. I bought what was described as HSS bits from an UK based supplier of repute.. a supplier used by, I suggest, modellers without a second thought.
The next time that I need to buy sub-1mm drills I shall be asking about supplier, material spec. (ie. HSS) and country of manufacture.
regards, Graham
Aplogies for clarity of image.
No kidding, the flutes about 1mm behind the tip of the drill had "unwound".... as if the tip had snagged in the hole and the remainder of the drill continued turning. However, under a magnifying glass the tip was still as formed with the cutting edges no longer able to contact the metal surface. Not just once, not just twice... this behaviour happened with four more drills. I bought what was described as HSS bits from an UK based supplier of repute.. a supplier used by, I suggest, modellers without a second thought.
The next time that I need to buy sub-1mm drills I shall be asking about supplier, material spec. (ie. HSS) and country of manufacture.
regards, Graham