Drills and drilling. Today’s drills usually come in 5 flavours.
1 cheap and nasty - Carbon steel.
2 cheap - M02 (straight HSS)HSS with or with out coatings- coating only lasts as long as the moment you wear through it, then it’s just a M02 HSS drill.
3 M35 HSS ( 3-5% cobalt HSS) with or without coatings.
4 M42 HSS (5-8% cobalt HSS) with or without coatings.
5 Carbide Drill bits.
Most people will buy #1 or #2 drills.
Stainless is a soft material, except if you overheat it! Then it becomes super hard and will destroy the chiselpoint and lands on all #1 and #2 drills and some #3 drills.
Slow down your speed and it will cut it like butter. I mean really slow it down.
Tapping stainless is best done with sharp taps, check your taps if you can see a reflection from the edge they are blunt and throw them away. Use gun taps or spiral taps for stainless and you will have no problems. Make sure they are at least M35 grade HSS.
The general rule of predrilling is to make the predrill slightly larger then the chiselpoint. Chiselpoint thinning can remove the necessity to predrill upto about 25mm drills. When drilling brass, bronze, thin steels etc, just run a fine grind or hone along the lip of the cutting edge parallel to the drill to produce a neutral or slightly negative rake angle will help greatly.
Metric taps use the rule diameter minus pitch to give you the tapping drill size for an 82-85% thread profile. The #19 is perfectly fine for drilling a M5 tapping hole, the problem will be twofold in stainless if you are having issues:
1. You overheated the steel and hardened it.
2. Your tap is blunt(usually this one)shiny edge, bin it! (Yes they can be reground)
Also lubricant is always used for tapping Stainless(make sure it’s a high pressure one suited to Stainless), never for brass or bronzes or cast iron.
Kerosine or lard kerosine mix for Aluminium.
Just from my 50years in the trade this is what works.
Wes
