Drilling through steel

[opps]

At work today I had to remove a some knobs from cabinet doors. The screw heads were a mess so I decided to drill them out. I carry a set of Heller cobalt drill bits in my ruck sack but the size I wanted I used the week before to drill out about 8 decking screws and noticed that on screw number 8 it had slowed massively.

Today I used a TCT bit.

I appreciate that the machine screws used for the knobs are less hard than the decking screws but is there a reason for not automatically resorting to a TCT drill bit whenever drilling through metal?

My experience of drilling through metals is very limited. I did work as a lift engineers mate over 30 years ago (for 6 months). We mainly drilled through mild steel using HSS jobbers which were treated as disposable.

 

[JohnD]

TCT drills can be used to open safes, but the sharpening angle on the common masonry bits is not correct for metal.


BTW, do you use left-handed drills? They will often wind out a recalcitrant screw by a combination of torque, vibration and heat.

 

[opps]

TCT drills can be used to open safes, but the sharpening angle on the common masonry bits is not correct for metal.


BTW, do you use left-handed drills? They will often wind out a recalcitrant screw by a combination of torque, vibration and heat.

Sorry John, when I said TCT drill bits, I was referring to the type that are often referred to as locksmiths' bits rather than the impact/hammer drill for bricks. They do look similar though.

With regards to the decking screws, I did try using screw extractors- I have the Trend, and Chinese ones. Perhaps I am not using them correctly but over the last 15 years, I have only been successful in removing mild steel grub screws.

 

[SFK]

Simple answer is cost. HSS are cheap.
But as TCT are typically faster to cut into steel then this can be negated if considering ROI.
Not sure if relevent to drill bit, as this is for planar blades, but with regards to finish then:
- HSS or High Speed Steel planer blades are sharper, which gives you the smoothest planing result.
- TCT (Tungsten Carbide Tipped) blades, also called HM (Hard Metal) blades, are less sharp. They give a slightly less smooth result than HSS blades, but the result is still very good.

This is a nice summary - but no conclusion:
https://www.jeiuk.com/blog/hss-or-tct-cutters