I ordered some replacement drill bits this week. I’ve still not really mastered regrinding bits and given my shed time is a bit limited it seemed better to just buy replacements and use the old bits for some project requiring HSS rods.
Given that I did not want to order a full set or a pack of 10, I ended up ordering a 7mm in HSS but 8.5mm with a TiN coating, I also got some HSS taps. This combination gave me the cheapest order and allowed me to get all the bits I wanted from one supplier.
This is the first TiN coated bit I’ve owned so it will be interesting to see if it performs better than the others. Given that it was over twice the price of the regular bit, I thought I’d investigate what the difference was.
TiN is Titanium Nitride, a compound of Titanium and Nitrogen which forms a very hard crystal. It has some great properties for a coating in that it bonds very well to the steel drill bit, is very hard and has low friction. It’s applied as a very thin coating to the steel and has a gold colour.
Apart from the price, I can’t see any disadvanages of the TiN coating. The coating means that if you regrind or reshape the bit then the coating will be removed from the cutting tip. However you should not need to regrind these as often as a HSS bit. Although the material has a higher high melting point than steel it does oxidise at 500ºC, but I can’t seen how you’ve generate that by drilling!
I’m not sure the size is a particular bit that I’ll use very often (it’s tapping size for M10 bolts) but I’ll let you know how much it got used before it goes blunt. I’ll also be considering getting some more of these if I have to work with any hard materials.