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I was trying to drill 1,5mm 304 steel but the bits were burning out fast. I burnt out 6 standard HSS bits and decided to give these a go. I have to say I am very impressed. They do heat up and you still have to keep them lubricated while cutting but I managed to cut all the holes I needed with one bit which looks like it could keep going! Happy with the purchase!
Verified purchase: Yes | Condition: New
I bought these drills as I had previously failed to make much impression on a piece of stainless steel with HSS drills. These Heller drills were described as being suitable for use on stainless steel and in fairness they were marginally better than the HSS ones. I started off with the 2mm drill intending to progressively increase the drill size and end up with 8mm holes. However, each drill bit managed about two holes before becoming completely useless except for the 6mm which didn't manage even one hole. Bearing in mind that the steel plate I was drilling was only 2mm thick I regard this purchase as a complete waste of money. I don't know the exact grade of the stainless steel I am using but I have some cheap Chinese made files that cope with it easily, which is good because I ended up having to enlarge the holes with a round file once the drills had given up the ghost. So to sum up, after failing to drill four holes in a piece of 2mm thick stainless steel, these drills are now scrap.Read full review
Verified purchase: Yes | Condition: New
I have used Heller bits before and I knew the quality was good. This set has suitable sizes in a useful case. I can recommend it.
Verified purchase: Yes | Condition: New
I'd never heard of Cobolt drills before this product and had struggled with hss drills. These drills make drilling hardened steel possible and relatively easy.
Verified purchase: Yes | Condition: New
I was trying to drill through some toughened steel, approx 2.5mm thick. These drills had a real hard time going through it after approx one hour and constantly spraying with cold water to cool them down, I managed to make the 8mm hole.
Verified purchase: Yes | Condition: New
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