Rennie Tools - Box of 10 x 4mm HSS Gold Cobalt Jobber Drill Bit Set For Stainless Steel, Hard Metals, Aluminium, Cast Iron, Copper. Twist Drill Bit Sets Supplied In A Box. 4mm Drill Bit Set

I am drilling into metal miniatures, and these bits are perfect for it. Would highly recommend.

Fair quality for this price

They worked

Bought a pack of 10 4mm jobber drills, thinking I would need several of them to drill 32 holes in a 1.5mm stainless steel sheet, having burned out a standard HSS drill attempting just two holes, and failing completely. Armed with the right advice (see below) I did all 32 holes in one sitting with the same drill, and it seemed to be as sharp at the end as it was at the start. Having read some of the small number of poor reviews I was very pleased with the result.The right advice to drilling stainless steel, all of this is based on the metallurgical properties of stainless steel which doesn't conduct heat as well as mild steel, so the metal at the sides and bottom of the hole you're drilling gets very hot very quickly and the stainless steel becomes "work hardened" by the heat and becomes much more difficult to drill!:1. Use a lubricant to reduce friction between drill and work piece and keep the steel cool : cutting oil or drilling paste would be perfect, but for small amateur jobs engine oil would be fine - a small drop on the steel surface will work, so it's easier if the surface you are drilling into is horizontal.2. Use the slowest drill speed you can, adjust a portable drill to the slowest speed and even then go as light as you can on the trigger. You want the drill to bite into the metal and carve off steel shavings rather than spinning at high speed just getting hot... and hardening the steel.3. Use moderate to high pressure on the drill; tricky if it's a very small drill, but I found I could exert plenty of pressure on a 4mm drill without breaking it - but good eye protection advised.4. For deep or large diameter holes take frequent breaks and add more lubricant; if the lubricant starts to boil into vapour it's time to stop for a minute.5. Be aware that if you're drilling right through a work piece that the bottom of a hole metal is likely to catch the drill hard and may spin the drill bit in the chuck. You may need more speed and less pressure to cut this last part of the hole.

good quality

Bought these as I regularly use a 3mm bit to start holes when drilling hard steel, and consequently I break 3mm bits more than any others.These bits are extremely tough and they cut through hard steel effortlessly! My first one in use has cut dozens of holes so far and hasn’t lost its sharpness at all. Also cuts faster than the Heller Cobalt bits I was using (and breaking) in the past too!Highly recommend these, I will stock up so that I don’t run out!

Good quality product

Good quality