The nature of the steel stud may matter. Do you know what it is? Stainless steel work hardens but can be drilled with ordinary HSS provided the right technique is used. (Basically pressing hard enough to cut, but not overdoing it. Needs practice.)

Assuming your stud is hardened within ordinary limits, I'd try a TCT drill as offered for drilling stainless steel. If that fails, solid carbide, but they're expensive and brittle. Attempting the job with a hand drill is disadvantageous because they move about and magnify operator mistakes. Getting the cut to start can be tricky because the point tends to skate about. Good idea to centre-pop the stud (if you can) to steady the cutting point and to use split-point drills. Easier to drill the stud if the drill's held firmly in a stand, even a home made one.

I made three using the process above, the other 2 had a 6 and 7.5 mm hole. The two nuts were then separated and the bolt removed. The joining nut then screwed onto the snapped stud that was on the engine. The drilled bolt with the 4mm hole then screwed into the joining nut. I had a guide.

In the end I think the problem was the 4mm bit not being very good. I apologise if I have wasted your time but when I posted I was desperate and you guys I thought would know.

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I found a clip on Youtube on how to drill a stud that had snapped below the surface. Mine is above the surface but it gave me an idea on how to make a guide.

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Solid carbide would be the answer if you could use a drill press, but with a hand held drill you would just break the bit. However, there are Bosch Multiconstruction drills in sets which have carbide tips and steel shanks like masonry drills. It is certainly possible to sharpen the tip of a regular masonry drill, hard going with a standard grinding wheel, but easy with a green wheel, or diamond wheel.

If this is to drill out an exhaust manifold stud or thermostat housing it is probably rusted in and the welding method is best

From excellent resistance to heat and wear in the Cobalt and TiN coated series to HSS ground split point, these HSS drills are the perfect choice for drilling in a wide range of applications. Find your nearest stockist online or download our catalogue for more information.

A far better way is to build up a pillar of weld on the exposed end of the stud using a mig welder, then when the pillar is high enough to then weld a suitable nut on top of the whole lot. The heat of the weld is almost always enough to free off the stud and is a simple twist-out job. Use an aluminium bush to prevent the weld and spatter sticking to the surrounding metal.

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Welding, drilling (even dissolving in alum might be appropriate on the odd occasion in the right circumstances – I just removed a broken tap from a brass item that way – although this is presumably into steel as even really tough bolts are not usually needed into aluminium).

Other hardened metals are too hard for HSS, or at least blunt it rapidly. Various choices for these, in rough order of rising hardness and cost. HSS coated with yellow TiN, Cobalt (5 or 8%), Coated Cobalt, Carbide Tipped (TCT), solid Carbide, and exotics like Diamond or Boron Nitride. DIY store drills are best avoided, buy from someone selling to metalworkers.

Whilst getting replies I changed the 4mm guide for the 6mm guide, not sure why. Anyway the 6mm drill bit worked. My cordless drill went flat so had to recharge it. Then progressed to the 7.5mm guide. I was not gentle enough, the bit bit got stuck and sheered the rest of the stud as the walls were now thin.

Personally I wouldn't attempt to drill a hardened steel stud unless it was with a drill press or mill and with the component clamped in place.

I don't have a good track record drilling out hardened studs – broken drills, blunted drills, and scars around the work. No help at all, but the professionals use spark-erosion or weld a temporary new head on the stud to get it out. I expect someone else will offer better advice!

I am confused as to what type of drill bit I need to drill a hardened steel stud that has snapped due to someone's ham fistedness.

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Some sort of drill bush to keep the drill on line would help if it is possible, and maybe using a Dremel to create a start point for the drilling especially if the fractured end is not flat.

The DART range of HSS drill bits features precision-engineered, high-speed steel drill bits, ideal for drilling into metal surfaces. The tip is designed to cut the material, while the spirals work to remove debris from the hole. Our HSS drill bits include Cobalt, TiN Coated, Ground, and Rolled, plus a range of Stub, Long Series and Reduced Shank Blacksmith drill bits.

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You say a hardened stud, how hard. I would think the stud would be tough not hard, as in En8 or 16. Hardening would make the thread brittle and likely to break. Usually studs can be drilled out and removed with normal HSS drills. I have never come across a hard stud since forces are in tension with no abrasive action requiring hardness.

Home › Forums › Manual machine tools › Help and advice on a drill bit for hardened steel This topic has 10 replies, 8 voices, and was last updated 14 October 2019 at 22:03 by old mart. Viewing 11 posts - 1 through 11 (of 11 total) Author Posts 14 October 2019 at 11:59 #433243 Ian m 1Participant @ianm1 I am confused as to what type of drill bit I need to drill a hardened steel stud that has snapped due to someone's ham fistedness. I think I need cobolt, is this correct 5% or 8%? what tip angel and helix angle do I need? Seeing references to these on the internet has blown my mind. I'd appreciate what good brands to look at. I want to get 4mm, 6mm and 7.5mm drill bits. These will be used in an electric hand drill not a pillar drill or lathe.

I used a 10mm joining nut on a 10mm bolt, I added a single 10mm nut and locked the joining nut and ordinary nut together. I cut the bolt to the length of the two nuts. placed the lot into the chuck of the lathe holding by the joining nut and pushed back in the chuck so the single nut was clear of the jaws. I then centre drilled and followed this with a 4mm hole all the way along the length of the bolt.