Q&A / 

Drilling and Chipping Solid Rock

Quick Column Summary:

  • How to create trail features in granite
  • Cordless tools will do this job
  • Corded or gas power tools work well too
  • All accessories should be from same tool manufacturer

DEAR TIM: I lead a group of volunteers who build new and maintain existing walking trails on a small mountain range in central New Hampshire. We have to drill into solid granite and chip away at it to create steps and other trail features. What are my options to do this in the field where there's no commercial electricity? Please don't tell me we have to do it the way the laborers did it for blasting the old railroad tunnels. Hal G., Sanborton, NH

DEAR HAL: I read a book a few years back about the creation of the trans-continental railroad here in the USA. There was some discussion in the book about the enormous amount of work required to blast tunnels through the Sierra Nevada mountain range and to create a flat roadbed for the iron monster's tracks.

All of the blasting holes were drilled by hand with laborers who used sledge hammers and large star bits. To me, it's unimaginable as to how mind-numbing that work was. You'll not have to subject yourself nor your volunteers to using the star bits and hammers unless your modern tools break.

I clearly remember back when I first entered the construction industry. If you wanted to use a power drill or saw, you had to have 120 volts of electricity. Period. You could plug into a commercial power source or you could start up a heavy and bulky portable generator.

The 18-volt cordless drill shown here drilled a deep 5/8-inch diameter hole into solid granite in less that a minute!. Photo Credit: Tim Carter

The 18-volt cordless drill shown here drilled a deep 5/8-inch diameter hole into solid granite in less that a minute!. Photo Credit: Tim Carter

Technology has made major advancements both in the power tool and generator areas. You can now carry in a backpack an 18-volt cordless hammer drill that will easily bore holes up to 7/8-inch diameter into solid granite. I've done this myself and know the tools will work.

This same cordless hammer drill, with the flip of a switch, can be transformed into a chipping hammer that will allow you to shape rock on the trail. These hand-held hammer drills are much smaller than the large pneumatic hammers you see workman use to break up concrete slabs, but they'll get the job done eventually. It's all a matter of power.

The new cordless electric tools have seen major improvements in the motors. Many brands offer brushless motors that are more reliable. The Milwaukee cordless hammer drill that I've used offers longer life, 40 percent more runtime and a hammer mechanism within the tool that is 35 percent harder hitting. Those features will help you drill more holes faster.

I've been very impressed over the past few years with the giant strides in the battery power packs the cordless tools employ. Lithium-ion is now the industry standard and tool engineers are constantly improving the batteries by installing miniature computers in the tool to maximize the energy in the battery. These small computers also protect the motors and battery from damage if the operator tries to overwork the tool. It's fascinating technology.

There are other manufacturers that offer similar tools with these great batteries and onboard micro-computers. You're hardest task, in my opinion, will be selecting what tool you want to purchase. Keep in mind that price is almost always the most accurate barometer of quality. The best tools often cost more because they contain the best parts and best engineering.

The biggest problem you'll have with the cordless tools is the depletion of the energy in the batteries. You can purchase extra batteries so you have lots of power, but this might not even be enough to provide you with power for the entire day if you're drilling and chipping for hours on end.

If you need to drill and chip rock for hours and hours, you may want to invest in a traditional corded power tool that operates on 120 volts of alternating current. You can then purchase a very small and quiet electric generator that can be carried on a strong volunteer's back to the job site on the mountainside. Some of these generators weigh less than 50 pounds. Two volunteers can trade off carrying the power pack up the trail to where it's needed to make the task easier.

This small, quiet gasoline-powered generator can run all day on just one gallon of gasoline. It will produce 2000 watts of clean electricity. This is plenty of power for one of the larger corded hammer drills or rock-chipping hammers.

Realize not all hammer drill bits and chipping tools are the same. I highly recommend purchasing the bits and tools from the same manufacturer that makes the drill you buy. The manufacturers go to great lengths to produce bits and chipping tools that are made to help make the power tool work to it's maximum capability. Cheap bits and chipping tools will wear out faster and slow your progress in the field.

My guess is you want happy volunteers that get work done quickly, efficiently and with as little effort as possible. Purchase the best tools, and you'll achieve those goals! Thanks for all you do to provide great walking trails for us!

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