Quote:
Originally Posted by TrevorW
Recently purchased a $5 HSS drill bit from Bunnings to drill through 2.5mm thick galv angle iron well lets just say ever melt the tip of the drill bit?, I did on the first use. Took it back to Bunnings and exchanged it, paid the extra $5 for a HSS Cobalt drill bit which cut through the relatively thin piece of metal like butter. What I did notice was that all the drill bits where either made in China, PRC or Vietnam. Lesson learnt don't buy cheap HSS drill bits they just don't cut it  |
When drilling steel you need to use the following:-
1) A sharp drill (which you had)
2) Cutting Oil (Lubricant) when the steel is thicker than about .8mm
3) Really slow speed with reasonable down pressure.
4) A drill press really helps in drilling steel / stainless steel, because you can set the speed and control the low speed rpm. You can get it much slower with 100% speed control, which you can't get with a cordless or corded hand drill. You can also get consistent down pressure (and more of it) which helps cut a consistent 1 piece swarf. The drill press helps to the extent that if I am drilling a piece of steel / stainless steel over about 2.5mm that I can easily unbolt and take the piece to the drill press, I will do that rather than use a portable drill in situ.
I have multiple sets of drill bits and countless single drill bits. You won't find much better than Australian made Sutton, or Patience and Nicholson (P&N). Buying a few boxes of these for a couple of dollars at a garage sale is better than a tray of new Chinese bits from Bunnings. You'll probably just need a friend with a bench grinder and the know how to re-sharpen them. I also have several of the newer cobalt bits. I also have a lot of cheap Chinese drill bits. The reason I have the cheaper bits is that I use them as "sacrificial" bits. If I have to get into a tight awkward space where there is any risk of breaking the drill bit, I would rather snap a $2 bit, than a $22 bit.
With drill bits, like most things in life you get what you pay for. The 2.5mm galvanised angle iron would have been galvanised mild steel. Had you followed the correct practices mentioned earlier for drilling mild steel, you would have found the $5 bits worked fine. They don't stay sharp as long, last as long and break easier. The cheap bits aren't as "forgiving" as the better quality bits and the cobalt bits.
Drilling stainless steel is even trickier. 304 stainless isn't too bad. 316 stainless can be quite tricky, if you don't know what you're doing. 316 work hardens as it gets hot, which means the faster you go the hotter the piece and the bit gets and the harder the piece becomes and the softer the bit gets. If you're not careful and use proper practices you end up with a melted munted mess. Some people will tell you that you need special bits for stainless like Cobalt and Titanium Nitride. If you were drilling it all day every day, I would agree, as the bits would last a lot longer and are slightly better for the purpose. For the occasional stainless hole HSS bits are fine. You need to go really slow, plenty of down pressure and plenty of lube. The other thing which can help drilling stainless is to sharpen the bit with a slightly shallower "lead", than you might otherwise have, but that isn't necessary for the occasional hole.
Cheers
John B
