When it comes to post hole digging, get Hank’s advice on power augers, hand held augers and more.
We’ve all seen them: old — and not so old — fence lines with posts akimbo, or pole structures with a serious wrack in the direction of prevailing winds. And while it’s true that sometimes the elements or environment make it difficult to set your posts perfectly vertical and tight, even under the best of conditions straight posts will have a tendency to wander. You can minimize unwanted post movement by following a few guiding principles and choosing and using the right tool to the best advantage. In general, if you focus on getting the posts set with as tight contact against undisturbed soil as possible, you will minimize problems later. If your posts will be subject to physical strain, you will need to install bracing (read The Kiwi Brace: Good Braces Make Good Fences).
Generally the tightest posts are those that can be driven straight into the soil, or into small-diameter pilot holes drilled into the soil. When posts are driven, the undisturbed soil is further compacted up against the post, and, in many cases, you will not be able to move the post back and forth at all after setting.
You can readily drive steel T-posts and relatively small diameter steel pipe posts using a sledge hammer, but it is much easier and safer with a hand-held or pneumatic post driver. The simplest of these tools are essentially 3- to 4-inch diameter pipes with a heavy solid steel plug welded to one end and handles welded to the sides. Slide the device over the post and slide it up and down to hammer the post home. The air-powered versions automate the hammering to some extent but still require a good workout to operate. The advantage to these tools is that they are inexpensive and effective — they can also be used in some instances to drive sharpened hardwood stakes, stout fiberglass rods, ground rods and heavy wall PVC pipe, depending on how hard the soil is.
If you have a long stretch of T-posts to install, you can start them with the hand-held post driver and finish by carefully pressing them into the ground using your loader bucket equipped with a clamp-on attachment that slips over the top of the post and prevents it from slipping out of contact with the loader.
While most folks are aware that T-posts are generally easy to drive into the soil, it might surprise you to know that it is also possible to drive wooden posts up to 10 inches in diameter, or more, in many soil types. In some cases the posts are sharpened at one end and in others a 2- to 3-inch diameter pilot hole is drilled in the ground ahead of driving a larger diameter post. In other cases, both sharpening and pilot holes are used.
Most large post drivers are tractor or truck attachments — front mount or three-point hitch mount on the tractor and flatbed or trailer mount for truck versions. These machines use a combination of hydraulics and heavy weights to slam (hammer) a substantial piece of steel into the protected top of the post repeatedly. In relatively soft soils, an 8-foot-long 5-inch-diameter post can be driven three feet into the ground in minutes. In central Ohio and elsewhere, driven posts are often installed right through thin limestone layers lying a foot or two below the surface. In places like Kansas, where raw limbs from Osage orange trees make up a good portion of the wooden posts in play, hydraulic post drivers are not generally impeded by bark, irregularities in trunk shape or mild crookedness.
Large power post drivers run in the thousands of dollars to purchase, so you might consider renting if you wish to employ this method on a single small project. These devices can also be used to drive large-diameter steel pipes into the ground.
When faced with the task of setting larger posts and driving them is not an option, you might simply take your best pointed shovel and dig a hole — keep the diameter as small as you can relative to the post diameter, and the sides of the hole as vertical as possible. You could also conceivably deepen such a hole beyond what is possible with the shovel using a smaller handheld trowel while lying on the ground with your arm down the hole. Alternatively, if you have access to a backhoe, you can certainly dig a deep enough hole relatively easily for a post of virtually any size. But even with the smallest bucket on the hoe, the hole will be much larger in diameter than ideal.
When setting posts in holes created by digging with more or less generic digging tools, it is very important that you backfill the hole around the post in very shallow layers that you pack the daylights out of, using a tamper or stick with a business end that is no more than a few square inches in cross section. Backfilling will probably take longer than digging the hole. An alternative is to dump a couple bags of pre-mix concrete into the hole (fill to at least 2/3 the depth) and then backfill the remainder in layers with tamping.
If you have only one or two posts to set, and the tools at hand, these options might make sense. However, you can make a much higher quality hole using digging devices designed specifically for making vertical-sided round holes in the ground.
Innovative blacksmiths have been forging and fabricating specialized post hole digging devices for more than a century. Their legacy arrived in the 21st century taking the form of two principal designs — the clamshell and auger.
The clamshell type consists of two pointed shovels attached to the same handle system and hinged at their bases. The shovels are driven into the ground and levered toward one another in clamshell fashion, trapping loosened soil between the two halves. Lift the clamshell digger out of the hole, open to dump, and repeat the process. These tools take a little while to get the hang of and require moderate strength to operate but can be quick and effective in relatively soft soils. In tougher soils, you may need to loosen the soil with a spud bar and use the clamshell to remove it from the hole. One advantage of the clamshell is that you can make holes as small in diameter as the shovels are wide to virtually as wide as you want. The downside is that you are limited by the levered handle system to about 3-feet total depth in most cases.
The most prevalent manual auger type generally consists of a handle attached to a cylindrical “bucket” with a pair of cutting edges on the bottom (www.Sey mourMfg.com/augers). As the device is turned clockwise into the ground, the cutting edges shave soil and it is forced into the bucket. When the bucket is full, the operator need only lift the entire device out of the hole and tip the bucket on its side to expel the soil. Since the handle on this type of digger is often made of threaded steel pipe, it is possible to add an extension or two to increase the digging depth to more than 6 feet — which can be an advantage in areas where the frost line is 4 to 5 feet deep and the posts are to support a structure of some kind. The downside with this auger is that in most cases it creates holes of a fixed diameter although at least one manufacturer makes one with an adjustable head. This tool also relies on relatively soft soil, few rocks and relatively light down-pressure to get the digging done. The upside is that it requires only twisting and lifting and is less physically jarring to operate than the clamshell.
Backfilling the hole once the post has been set requires carefully adding small amounts of soil followed with vigorous and complete tamping. Concrete or a combination of concrete and tamped soil will also work if time and money are not an issue.
Because the hand-auger relies on rotation to make it dig, it doesn’t take much of a leap to imagine powering it. In the powered form, the auger bit takes on a different design, however. In this case the business end of the auger consists of a small lead screw or centering pin and a pair of cutting edges. The screw helps pull the auger into the ground and helps keep the auger heading in the direction you wish it to go. Directly behind the cutting edges is spiral flighting that conveys the loosened soil up and away from the cutting edges. In practice, power augers still need to be lifted from the hole from time to time to expel the loose soil.
Power augers consist of a power head and a bit — bits of various diameters are available for most power heads. In most cases, the power head may be a tractor or frame mounted hydraulic motor or a gearbox receiving power directly from a small engine or a tractor’s PTO shaft.
Handheld power augers make use of lightweight gasoline engines mounted to the gearbox. The operator or operators control the device with handlebars and a hand-throttle. This machine takes on the turning effort associated with the hand-powered version, but the lifting and moving requires significant effort. Watch a video on how it works.
Mounted hydraulic augers are typically suspended by a proprietary mobile frame or a loader. The frame-mounted units require a separate, self contained hydraulic power system, consisting of engine or motor, hydraulic pump, reservoir, valves and lines. Loader mounted versions get their hydraulic power from auxiliary ports on the machine itself. Loader mounted augers are easy to move and relatively easy to operate effectively — especially if there is a built-in leveling system. The loader arms are used to raise and lower the auger, even applying significant down force in tough soils. The frame mounted units are tougher to move around and may rely on springs, levers, winches and hydraulic rams to raise and lower. Both types can be tough to use where the terrain is moderately rough or in tight quarters. Hydraulic augers tend to be expensive and robust.
The most prevalent power auger suited to post hole digging is the version that mounts to a tractor’s three-point hitch and is powered through the tractor’s rear PTO. With this device, the PTO control and the hitch’s lift arms on the tractor are used to position and operate the auger. It takes some practice to drill consistently plumb holes with a three-point hitch mounted auger and it is not ideal for tight quarters either, but its availability and price range make it relatively accessible.
As with hand-powered augers, backfilling the post must be done with care if you expect the posts to stand tall and tight for years to come.
When investing in tools of any kind, additional value can be gained if you can think of other ways to use them beyond their specifically designed function. Post hole diggers are designed to help you create round, straight-sided holes. You can use them to dig holes for planting trees and shrubs and to create small French drains. You can even use them to sink perforated and screened PVC pipe near a spring, pond or seep to help you collect water for irrigating the garden or livestock. Need to install some concrete pier type footings? Use a 10- or 12-inch auger to bore a hole past the frost line and fill it up with concrete. The possibilities are limited only by your imaginations.
Depending on the size of the job and the frequency with which you will be using your post hole digging tool, it may be worth it to go bigger. If you know of a friend or neighbor also in need of a post hole digger, split the cost and share the tool.
Read more: All You Need to Know About Backhoes with the help of Hank.
Hank Will raises hair sheep, heritage cattle and many varieties of open-pollinated corn with his wife, Karen, on their rural Osage County, Kansas farm. His home life is a perfect complement to his professional life as editor in chief at GRIT and Capper's Farmer magazines. Connect with him on Google+.