How to Drill Holes

Know-How Notes: How to Drill Holes

You may not believe it, but there is a lot more to drilling holes that just a drill and a bit. Sure, you can make a hole, but if you want your hole to be in the right spot and your drill bits to last, there are some techniques that you should learn. How you drill and what you use makes a big difference in the quality of the work and longevity of your tools. Here’s a primer on how to drill holes in almost anything.

Speed

Run your drill on the slowest setting when drilling through harder materials. You can get away with a faster speed on things like wood, but metal needs to be drilled slowly.

Run your drill on the slowest setting when drilling through harder materials. You can get away with a faster speed on things like wood, but metal needs to be drilled slowly.

The most critical issue that kills the most drill bits is speed. Yes, you want to get the job done as soon as possible, but good bits are expensive, don’t give it a premature death by spinning it too fast. Speed means heat, and heat takes the temper out of your drill bits. Even Cobalt bits can be killed with too much heat over time, but the typical high speed steel (HSS) bits are more susceptible to heat. If you see smoke coming from the part and you are not using lubricant, the edge on that bit is likely already gone. The rule of thumb for drilling speed is the harder the material, the slower the speed. You can blast through wood on high-speed, you can get away with high speed on a chunk of aluminum, but mild steel and cast iron must be drilled on slow, and stainless must be done very slow.

Material

The material you are drilling makes a difference in how you drill. As mentioned above, the speed varies by the material, but also how you drill. The thicker the material, the more important the technique. Soft materials like aluminum and brass generate long spirals of swarf instead of chips. This can bind up your bit. The way to avoid this is to do break every 10-15 seconds or so. A break is to stop drilling, reverse the bit to break the swarf, remove the bit to clear away any residual chips, and then continue drilling. Once you have the process down, it only adds a couple seconds to the process.

Stainless steel is very hard to drill. You need to use a lot of lubrication, very little pressure, and run as slow a speed you can.

Stainless steel is very hard to drill. You need to use a lot of lubrication, very little pressure, and run as slow a speed you can.

Stainless steel is trickier. Chances are, you won’t be drilling thick stainless, rather you will encounter sheet metal. Stainless steel is very difficult to drill because it is so hard. The trick with stainless steel is using very slow speed and low pressure. The problem with stainless steel is that it work hardens at fairly low temperatures, meaning that it the act of drilling stainless can actually make it even harder than it already was. Once it is work hardened, you are never going to get through. You can literally melt a high speed steel bit on work hardened stainless and never get a hole in the material.  

Lubrication

Any quality lubricant like this one from Sea Foam will aid in breaking the friction. Keeping the bit cool is the key.

Any quality lubricant like this one from Sea Foam will aid in breaking the friction. Keeping the bit cool is the key.

Adequate lubrication is the best way to ensure a long life for your drill bits and quick and easy drilling. The lubrication reduces friction and heat, which makes the process easier. When adding lubrication, spray the drill bit before drilling and add lube as needed. You may see smoke as your are cutting, that is okay, as long as you are working slow. If you are pushing too hard or spinning the bit too fast, then you are generating too much heat and killing your bit. It is a fine line that takes some practice to figure out.

Technique

Let the drill and drill bit do the work. You need pressure to keep the bit cutting, but too much pressure means excessive heat. Ease up on the drill and let the bit cut.

Pushing too hard or a dull bit leads to this problem, which is drilling off-center. You can see some galling on the upper left side, whereas the lower right is much wider.

Pushing too hard or a dull bit leads to this problem, which is drilling off-center. You can see some galling on the upper left side, whereas the lower right is much wider.

Before drilling, mark your location with a marker or pencil. Using a center punch and a hammer, make a center punch mark in the center of your dril location. A properly placed and struck center point will keep the bit from walking as you start the hole. Bad things happen when the drill bit catches or binds in the material being drilled. Usually this mean twisting your wrist or with small parts, whipping the part around. You can be seriously injured when this happens. To avoid it, make sure your part is clamped in a vise or on your workbench before you drill. This frees up your other hand to support the drill and will result in a much better job.

This part, an exhaust flange, was marked with a pencil for the three bolt locations. It is clamped firmly to the workbench.

This part, an exhaust flange, was marked with a pencil for the three bolt locations. It is clamped firmly to the workbench.

If you are making a hole larger than 1/4”, it is a good idea to use a drill a pilot hole with a smaller bit, such as 1/8”. This ensures that the new hole is in the right place and it helps aid in faster cutting with the larger diameter bit. It is a good idea to step the drilling process with several sizes up to the final size for thick materials. The less you cut each time, the less strain you put on the drill, the bit, the part, and yourself. This also cuts down on the heat.

These are the bits we are using to make these holes. You can skip the middle size, but sometimes it is easier to step a couple times.

These are the bits we are using to make these holes. You can skip the middle size, but sometimes it is easier to step a couple times.

 

Use a center punch to mark the center of the hole. This will keep the bit in the middle so it does not walk on you.

Use a center punch to mark the center of the hole. This will keep the bit in the middle so it does not walk on you.

Another tendency when drilling is to get the bit at an angle. This is tough to overcome once the hole is already drilled. Take extra care to ensure the bit stays running in the alignment that is necessary for the application. Small diameter holes mean thin drill bits. This always leads to a larger possibility of breaking a bit. The longer the bit, the more likely it is to break. This is one of the reasons that maintaining adequate pressure but not too much is critical. When a bit breaks, if you are pushing too hard, you can stab yourself with the drill or the be impaled on the broken piece. It is not something you want to happen, so wear gloves and be mindful of the pressure you are exerting on the bit.

We have drilled the part with the pilot bit. Note the wood board underneath, this is to backup the part so that the drill does not hit the bench, which would keep it from completing the hole and damage the bench top.

We have drilled the part with the pilot bit. Note the wood board underneath, this is to backup the part so that the drill does not hit the bench, which would keep it from completing the hole and damage the bench top.

Any time you are drilling on a surface (not suspended on the vehicle or in a vise), you need a soft backup surface to drill into. All drill bits have a cone shaped tip, in order to complete the hole, the bit has to go all the way through the part. A piece of wood is a good backup surface and readily replaceable.

The completed holes are clean, within the lines we marked for the holes, and nothing was damaged in the process. Success!

The completed holes are clean, within the lines we marked for the holes, and nothing was damaged in the process. Success!

 

Large holes require a hole saw like this one. This is a broaching saw, which is heavy duty and lasts for a long time. A standard bi-metal hole saw works too.

Large holes require a hole saw like this one. This is a broaching saw, which is heavy duty and lasts for a long time. A standard bi-metal hole saw works too.

 

If you need to open up a smaller hole, a uni-bit step-drill like this is the perfect solution. These are also great because they cut larger holes without needing a large bit.

If you need to open up a smaller hole, a uni-bit step-drill like this is the perfect solution. These are also great because they cut larger holes without needing a large bit.

Drilling a necessary task for many repairs and modifications, getting the job done right and safely is important. Take your time, be patient, and always protect your eyes and skin from potential damage. Always use sharp bits, if your bits are dull, they need to be sharpened or replaced. A dull bit is an accident waiting to happen.

Check out all the tools & equipment available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to drill holes, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

about author

Jefferson Bryant

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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