1/4 inch holes - my own personal thorn

if cobalt squeals then use a solid fluted carbide. On occasion my thong tube hole on my 80crv2 is too hard for my cobalt bits and I switch over to carbide with no problem
 
Nathan the Machinist said:
It's the thickness of the core at the point. It's the part that doesn't really cut very well and just mushes its way through the steel. If you need a pilot hole, it's to provide clearance for the web on a large drill. But a 1/4" drill shouldn't need a pilot hole unless you're using a very small drill press.
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THIS ^^ could be my problem as well. i'm on a small table top drill press that only goes down to 600rpm or so and i wear out a lot of 1/4 bits as well... lube or no lube. don't have that problem with 1/8 at all but 1/4 seem to be a different matter for me as well
 
Nathan's advise is always gold!! The pilot choice about the web size i did by instinct but knowing for sure is an useful thing, thank you!!
Sharpening little drill bits could be a problem, and since they are quite cheap and go for a long time, when i'll wear mine i'll buy new, but for now i didn't have the need to replace many.
I don't even know the speed of my drill press, but it is on the medium/low side of the pulley capacity...just feed by feel, and i feel the bits are happy when they make nice curls.
 
I don't understand the problem. I routinely make size F -3/8" holes (and occasionally larger) in annealed steel of various types with a cheap B&D tabletop drill press and fairly standard HSS bits, with a bit of cutting fluid, in one pass. No "pilot holes".

I'm not a trained machinist, and I'm not particularly lucky... so... if I can do it... *shrug*

The only time I ever had problems was years ago when I was using cheap bits, pushing them too hard when they got dull, and work-hardened the stock I was trying to drill.
 
james terrio said:
I don't understand the problem. I routinely make size F -3/8" holes (and occasionally larger) in annealed steel of various types with a cheap B&D tabletop drill press and fairly standard HSS bits, with a bit of cutting fluid, in one pass. No "pilot holes".

I'm not a trained machinist, and I'm not particularly lucky... so... if I can do it... *shrug*

The only time I ever had problems was years ago when I was using cheap bits, pushing them too hard when they got dull, and work-hardened the stock I was trying to drill.
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I expect it may have a lot to do with the machine tool being used. I have an 8,000 pound mill that can't drill a 1/2" hole without a pilot hole because the 10 HP spindle motor doesn't have any gear reduction and it doesn't make the torque at 450 RPM. The little 2,000 pound Bridgeport can do it all day long without even going into back gear. There is no size limit where a pilot hole is needed from a tooling perspective, that boundary is about machine limitations. A 20 pound 1/4 HP drill press is prolly gonna need a pilot hole to drill a 1/4" hole.
 
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