Generally, carbide tipped drills use a grade of carbide and tip geometry
for cast iron, formulated for cutting abrasive materials. They aren't
intended for steel but might work for a few holes.
For drilling harder steels, there are solid carbide twist drills ($$$)
but carbide is very brittle and very easy to break in a hand drill. A
straight flute die drill will drill very hard materials because of its
carbide and geometry. The swarf is more like shavings than chips or
spirals. It has a much larger cross section area so is harder to break.
Another problem in drilling alloy steels and stainless is most work
harden. It's like the local heating hardens the steel. Continuous
heavy thrust and good coolant is needed to keep the drill edge cutting
below the hard layer left from the prior flute's cutting. Back off on
the thrust and then even more is needed to break thru it. Very hard on
drills. Junk steel like fence posts usually have carbide and other hard
inclusions embedded waiting for a drill tip.
McMaster, Travers Tool, MSC supply, KBC Tool carry almost all drill
varieties.
Save your Chinese made drills for woodworking.
Grant KZ1W
On 7/28/2020 22:32, K9MA wrote:
After recently ruining several drill bits trying to drill through a cast
iron fence post, I discovered there are carbide tipped bits for drilling
metal. I haven't tried them on anything, let alone cro-moly, but they
might work.
73,
Scott K9MA
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