Using a Power AugerUpdated: Jul. 29, 2019
Use a power auger to dig postholes and learn how to operate a gas auger
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Gas Auger Overview
You’ll need to dig up a very willing friend to help you run most power augers, and you’ll both need strong backs, legs and arms to wrestle the machine around. So what is an Auger? Augers are very powerful machines with a lot of torque that can throw you like a sack of potatoes if the auger bit encounters a rock or a root.
If your soil is loamy or sandy, you too can drill 30 holes in a day’s worth of rental. But rocky ground or heavy clay can stymie even the most powerful auger. Judging from my experience, about 25 percent of the holes attempted with augers end up being dug by hand.
If you only have a few postholes to dig, don’t bother reading this story. Just rent, borrow or buy the three hand tools shown below and get to work. By the time you run to the rental store and round up a buddy to run the other end of the machine, you’ll have a few holes dug already and save the one-day $60-plus auger rental fee. But if you have more than five deep, 12-in.-wide deck footings or a whole fence’s worth of postholes to punch, augers can make short work of an otherwise miserable job.
Call before you dig with a power auger!
Operating a power auger calls for eye and hearing protection, as well as gloves and sturdy boots. But the biggest hazard when using a post hole auger by far is posed by underground power and gas lines. To prevent that danger as well as the nuisance of severed television cable and telephone lines, simply call the utility companies to have underground lines marked before you dig. They’ll come out, usually within 24 hours, to mark underground utility lines (Photo 1) so you can safely miss them.
Before you begin, also call a building inspector to determine necessary posthole depths for your project and to find out if you need a building permit. They’re generally required for fences and decks.
Have your layout all set—time is money
Scrupulously lay out your postholes before renting an auger so you can be using the tool the whole time you’re paying for it. Pay close attention to locations and mark the exact centers of the holes with stakes. It’s nearly impossible to move or reposition a hole once you’ve started boring, so it’s important to begin in the right spot. If you need wider holes than the auger will drill or if you need to slightly reposition a hole, you can easily carve away the sides with hand tools.
Renting the gas auger
Photo 3: Start out slow
Advance the throttle slowly until the auger begins to spin and let the machine begin boring into the ground. Throttle up as needed.
Photo 4: Clean off the dirt
After the auger has penetrated 6 in. or so, release the throttle and pull the auger with its load of earth free of the ground, set it next to the hole and jiggle the dirt off the blade. Tip: If you’re trying to keep nearby sod free of soil, place extracted soil on a tarp. Your grass will be pristine after the job’s done.
Photo 5: Using an extension rod
Extend holes past the normal 36-in. limit by using an extension rod. First dig all the holes without the extension, then leave the auger in the last hole, extract the shear pin and lift off the power head. Then mount the extension bar and remount the powerhead with a second shear pin.
You may not have many auger choices at smaller rental stores, but if you go to a larger outlet or a home center that rents power tools, you’ll have to choose between a two- or one-person (power auger head, as well as select the correctly sized auger itself. Auger drills are interchangeable and come in 4-, 6-, 8- or 12-in. diameters. The one to choose depends on the type of posts you’re installing. Remember, the larger the diameter, the tougher it is to handle the machine.
If you’re pouring 12-in. footings for a deck, you’ll obviously need the 12-in. auger (Photo 3), but for 4×4 posts, pick up an 8-in. auger. You’ll be able to get away with a 6-in. auger for steel fence posts. Keep in mind that you’ll need a larger hole (and a larger auger) if you’ll be filling around the post with concrete. The 4-in. auger will work for any small post that doesn’t need concrete poured around it. I use the 12-in. auger for all but the smallest posts because the extra space allows me to move the post around for exact placement.
How Deep Can Power Augers Dig?
Most augers dig about 3 ft. deep, but for deeper holes, ask for an extension rod (Photo 5), usually for no extra fee. Deeper holes are typically required for footings for decks or other structures attached to houses located in very cold climates where frost depths exceed 3 ft. An extension rod will get you down as far as 4 ft.
After you’ve made your choices, ask the clerk to check the gas and engine oil levels, and demonstrate starting and operating procedures. Also, make sure you have all of the shear pins (Photo 5) that lock extension rods and augers to the power head. By the way, you’re usually responsible for furnishing your own fuel unless the unit you’re renting is a two-stroke model that requires premixed fuel.
Tip: After the holes are dug, cover them with scraps of plywood to keep your kids or your toy poodle from falling in and to keep the holes from caving in if it rains.
The Must-Have Hand Tools
It’s generally not enough to only have a power auger on hand. Some hole locations will likely have to be adjusted, rocks will need to be dislodged and extracted, and roots will have to be chopped out. All of that calls for extra hand tools to augment the power auger.
- 6′ DIGGING BAR: Used for dislodging stones, chopping away roots and softening hard soil so the auger can penetrate.
- DRAIN TILE SHOVEL: The long skinny blade on this special shovel is designed for digging narrow trenches. That makes it ideal for elongating or reshaping holes after they’re dug and also for loosening soil at the bottom of the hole.
- CLAMSHELL POSTHOLE DIGGER: You’ll use this tool to extract stones and roots, to remove loose soil at the bottom of completed holes and to deepen holes that are at the depth limit of your auger.
Operating the power auger
Photo 6: Don’t over dig!
Start the engine and begin digging again, being careful not to over dig. The whole rig just got a lot heavier and you have to lift a lot higher.
When you turn the throttle of the auger, you’ll feel a substantial clockwise force through the handles. You do, after all, have to counteract the torque of the auger digging into the soil. Both operators should brace their left side near the left handles to get their body into the act. Be sure not to dig too deep without cleaning the dirt out of the hole. If you go deeper than 12 in. or so, the auger will be extremely heavy to lift out of the hole, or worse, you can corkscrew the auger in so deep that it’ll get stuck. Photo 7 shows you what to do if that happens.
There are two ways to clear the hole. We show stopping the auger and lifting it and the soil out of the hole and emptying the soil in one pile near the hole. That keeps the soil in one place for easy backfilling and prevents it from scattering over nearby grass. An alternative is to dig down a few inches, then throttle back to slow the turning and pull it free to spin off the collected dirt. Then drop it back down to pull up more soil. This method is faster (and more physically demanding), but dirt will fly everywhere and be harder to reclaim. It’s a good method if you’re backfilling with gravel or concrete and/or don’t care about the mess.
If you’re moving the auger more than a few feet to the next hole, shut off the engine and restart it again with the auger resting in the next pilot hole. When you’re not using the auger, just shut it off and leave it in one of the holes, or rest it on the ground with the spark plug facing up to prevent fouling, or sideways if fuel leaks from the gas cap.
For deeper holes requiring the extension rod (Photos 5 and 6), dig all the holes first with the unextended auger. Never start holes with the extension rod in place. It’s much harder to hoist a 4-ft. long auger filled with earth. After the holes are dug to 36 in., attach the extension rod and dig the remaining depths all at once. At times, I’ve found it easier to simply dig the remaining few inches by hand rather than use the extension rod, especially if fatigue is setting in.
Above all, clear the hole frequently. It can be a gut-busting experience to lift an auger overfilled with earth free of the hole, or worse, free a stuck auger.
One-Person Power Augers
One-person augers are less powerful, lighter machines designed to drill holes for small-diameter uses like anchoring 2-in. steel or 4×4 posts for fences. They come with interchangeable 4-, 6- or 8- in. augers. One-person augers are generally powered by two-stroke engines, so the rental store should provide a container of premixed fuel along with the machine. If you’re boring more than just a few 8-in. holes, you’re better off rounding up a partner and the more powerful two-person machine.
Required Tools for this post hole auger project
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
- Hearing protection
- Safety glasses
Required Materials for this post hole auger project
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.
- Marking stakes
- Scrap plywood