Rennie Tools - Box of 10 x 7.5mm HSS Gold Cobalt Jobber Drill Bit Set For Stainless Steel, Hard Metals, Aluminium, Cast Iron, Copper. Twist Drill Bit Sets Supplied In A Box. 7.5mm Drill Bit Set

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.

I've been using these drill bits for quite a while now and they are simply the best drill bits I've ever used. I'm a curtains and blinds fitter and often find myself drilling into steel lintels or, even worse, RSJ's. In the past I had always used the dewalt equivalent of these bits, they're OK, but hard work, expensive and you don't get many holes in a RSJ with a single bit before it blunts or breaks. These, however, are a different class. Much easier, much faster, much cheaper and last MUCH longer. If you have to drill hard steel you probably won't find a better value tool than this. They're excellent.

I purchased these and then before even recieving them doubted they would be good enough for a particularly hard drilling task I had where all my other metal drill bits had failed and snapped or blunted under the pressure without hardly making an impression in the work surface.To cut a long story short, the much more expensive drill bits I purchased to do the job that arrived the same time as these also failed to work and upon falling back on these with near zero expectation that they would be any better, to my astonishment they worked and cut through the steel like butter! Amazing, I will definitely buy more from this brand.

I have a set of drills that look to be identical to these and they are complete rubbish. They shatter, go blunt quickly, are really not worth giving shelf-space.I bought these because of positive reviews from people who had obviously used them hard and been surprised at the quality for the price. They're right. These are very durable and perfectly equal to drilling through steel - including chromium and vanadium steels. Buy a box: I don't think you will be disappointed.

These drill bits are extremely sharp, not because I have been using blunt bits, I get new bits often just I purchased these specially for drilling hardened steel and they work great ( taking my time and allowing the bits to cool and using a lubricant)Other than that the only reason I have given them a 4 for durability is because, like all extremely hard bits they snap so easy with side leverage put on them, unfortunately that is because of where their strengths lay,Would I buy these again? Definitely yesCons: only the one I mentioned, but!, that is the same for all hardened drill bitsPlease NB: if you intend to use these for drilling out a broken stud, use a Battery drill for lower RPM and use a bit lubrication paste or WD or 3 in 1 to help cool and lubricate the bits and take your time, if these type of bits over heat they loose their cutting edge and unlike black HSS bits that can be sharpened until they are a nub, these bits,! although can be sharpened will loose their edge and never be a good as they where with the hardened edge on them.

Well worth the risk , I've bought so many drill bits in my time, big box sets, singular, and this lot of 10 which when buying you think why supply 10 are they no good! Well I was wrong, I bought these to drill just one hole, that being on an expensive watch case made of stainless steel. I repair watches and where I think there should be an improvement I will do just that . The hole had to be accurate, I did it by hand, to my surprise it cut the steel like a knife through butter. I was impressed because the bit had not lost any of its sharp leading edge. The hole was for a screw down crown mod, which went to plan. I'd recommend these drill bits to anyone, to cut through stainless steel they have to be good. Ten out of ten for me.