Greg
That said, I'm also interestested in hearing from anyone who can explain why those tiny carbide bits don't snap off everytime.
I have used a few of the sets mentioned here.
One set is the one that comes in an oval, dome shaped bit holder.
Another is the set that comes in in the flat dispenser type holder (blue plastic).
Be careful when buying the second one as some are carbon steel and some are High speed steel.
Both of the sets I have are high speed steel and are sizes #61 (.039") to #80 (.0135").
I have purchased replacements for bits that I have broken from MicroMark that are high speed steel and come in packs of 6. These seem to be a pretty good quality.
The Carbide set was 10 pieces and has only 5 sizes from .8mm (.0315") to 1.0mm (.0395"). I suppose there are other carbide sets out there with different sizes.
In use, the High speed steel sets are "jobbers length" and range from .780" in length, to 1.575" long. Because of the very small diameters, they tend to be kinda flexible, but brittle enough to snap if bent too much. I try to chuck the bit in a pin vice so that just the tip of the bit shows through the material I'm drilling, keeping the exposed part of the bit as short as possible and still allow me to see what I'm doing.
The carbide bits are specialty bits, I think, designed for drilling printed circuit boards and such, so the need for length is not great. The "twist" part on mine is only about .275" long. The rest of the bit, the shank portion, is .125" in diameter and about 1.050" long, allowing for a good grip in the chuck. There is a plastic ring pressed onto the shank, apparently used when installing the bit in CNC drilling equipment to control the depth and keep them uniform.
The result is, that to me, the carbide bits, even though more brittle than the high speed bits, seem to be a little more resistant to breaking because of the shorter length of the twist, the tendency to run in the larger diameters and the hardness of the carbide. Regardless of the bit you choose, a light touch and a tecnique that keeps the bit from bending is the key for these tiny things. If you have a model makers drill press, that helps a lot if you are drilling a lot of holes at a 90 degree angle to the work. I have noticed that the ground finish on the carbide tips and flutes are significantly smoother than most of the high speed bits in the micro-number range I've seen, although I've drilled wood, plastic, copper, brass (photo etch and mini bar) and even stainless steel photo etch with both carbide and high speed bits. I've broken a few, heck I've even broken 1/2" diameter cobalt bits doing construction work and steel fabricating.
I did buy a set that came in a steel, mini drill bit holder that looks like full size holders, but I found I had a bit of difficulty getting the bit I wanted out of the thing. I found I like the plastic dome one the best, kept on the bench and the flat plastic dispenser holder second, kept in my carry tool box and one on the bench. The carbides usually come in a type specific holder or individually in little plastic tubes with a cap on them. In the end, many of mine wind up loose on the bench or in my carry tool box, requiring a digital caliper to find out what size it is as none of these little bitty things have the size on them.
Hope all this helps. None of these sets are really expensive, so, in my case, I've tried them all. Find out what works best for your hands and go with it.
EJ
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