Drill Bits Buying Guide - Lowe's

Drill Bit Materials and Finishes

The materials from which bits are manufactured and the finishes applied to them play a significant role in the life and performance of the bit. Common materials and finishes include:

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• High-speed steel (HSS) drill bits can drill wood, fiberglass, polyvinyl chloride (PVC) and soft metals such as aluminum.
• Cobalt drill bits are extremely hard and dissipate heat quickly. They're mostly used for boring in aluminum and tough metals such as stainless steel.
• Black oxide-coated HSS drill bits have a finish designed to help resist corrosion and increase durability. They last longer than basic HSS bits and work well on a variety of materials including metal, hardwood, softwood, PVC and fiberglass.
• Titanium-coated HSS drill bits produce less friction. They're tougher than basic HSS bits and stay sharp longer. They work for drilling wood, metal, fiberglass and PVC.
• Carbide-tipped drill bits stay sharp much longer than steel, HSS or titanium bits. They're effective for drilling tile and masonry.

Drill Bit Construction

For most drill bit types, the angle of the point helps determine what type of material the bit can drill. Flatter points, such as those with 135-degree angles, are suited for drilling into harder material. They may require a pilot hole to keep the bit from wandering. Bits with steeper points, such as those with 118-degree angles, are suited for softer material. They stay on center better and produce cleaner entry and exit holes. Bits with split-point tips improve drilling accuracy by keeping the bit from wandering when you begin to drill.

Bit size reflects the diameter of the body. Some projects call for specific drill bit sizes, but a bit set that includes sizes from 1/16 inch to 1/4 inch will work for many jobs around the home and workshop. You can add larger bits — 5/16-inch, 3/8-inch, 7/16-inch and 1/2-inch bits — if you need them.

The chuck on a hand drill or drill press secures a drill bit to the tool along the bit's shank. A smaller drill for work around the house typically has a 3/8-inch chuck. More powerful drills for heavier applications have a larger, 1/2-inch chuck. Drill presses also have larger chucks, 1/2 inch or 5/8 inch, for example. The bit shank size must not exceed the chuck size of the drill. A larger bit may have a reduced shank — a shank with a smaller diameter than the body of the bit — allowing you to use it with smaller chucks.

• A round shank allows you to accurately center a bit in the chuck.
• A hex shank has flat surfaces, allowing the tool to grip the bit more securely for greater torque. Hex shanks such as the one in the image above work with quick-change chucks — common on cordless drills — allowing you to insert and remove them without tightening and loosening the chuck.
• A slotted drive system (SDS) shank is designed for use on a hammer drill. It fits a spring-loaded chuck that doesn't require tightening. The bit can move forward and backward with the hammering motion of the drill, while flattened areas and slots on the shank allow the chuck to hold the bit.

How to Choose the Right Drill Bit

When deciding which size and type of drill bit you need for the job, take into consideration the size of hole you want and the material you’re drilling into. In most cases, you should drill a hole slightly smaller than the diameter of the screw you’re using so the threads of the fastener have something to cut into. For example, you would need a drill bit with a 2 mm diameter for a 2.5 mm screw. For wall anchors, use a drill bit with the same diameter as the anchor.

When pondering metal vs. wood drill bits or any other types, you’ll need to choose a bit that’s designed specifically for the material. For example, drill bits for wood are not intended for drilling into steel.

Drill Bit Maintenance and Lubricants

Drill bits are tough power tool accessories, but they can wear and become damaged without proper maintenance and care. There are several things you can do to maintain your drill bits and keep them working effectively:

• Keep your drill bits clean. Remove loose debris with a soft brush or cloth.
• Use the right type of drill bit for your application. Using the wrong drill bit for a material is a safety hazard. It can also damage the bit, the workpiece and the drill.
• Store your bits in a dry location where they’re protected from accidental damage. Storing bits in a drill bit case or using divided storage trays and magnetic holders helps minimize the risk of damage.
• Use a cutting tool lubricant when necessary. Drilling into metal generates lots of heat and the heat can shorten the effective life of a bit. Using a cutting tool lubricant can help your bits last longer and let you drill into metal faster.
• If you do a lot of drilling, you might want to invest in a drill bit sharpener. This tool uses a grinding wheel to sharpen the cutting edges of many types of drill bits.
• Inspect a drill bit before using it. Replace the bit if you find any damage — don’t use a damaged drill bit.

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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.

thank you in advance

I don't know what your broken stud is screwed in to, aluminium,steel or cast iron.

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.

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.

I have never failed to extract a broken stud in this manner in forty years since I got a mig welder!

We had one welder who was so good he could build up a pillar on a 3mm stud and successfully get the offending stud out.

To get an idea of what's available, prices and 'good' brands have a look at RS Components.

Link to GSR

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.)

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.

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 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!

Dave

PS Must type faster, while I dithered Alastair got in first!

Edited By SillyOldDuffer on 14/10/ 12:58:54

gents thank you for the replies. An update.

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.

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.

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.

Things had gone well to this point but my 4mm drill bit would not touch the broken stud and so I turned to the forum.

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.

Anyway I progressed all by hand and no guide, 7.5, 8.5, 9, 9.5 and then finally 10mm.

OMG the guides were brilliant, if it were not for Youtube I would never have gotten the idea on how to create 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.

thank you for the advice. now to order a nut and bolt

all the best

If you are looking for more details, kindly visit drill bits for hard steel.