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Underground Focus Magazine Article
Small Boring System Handles
Big Jobs Accurately & Quickly
The simplest solution is usually the best one, and that adage is exemplified
by a lawn-mower size device that bores holes as big as 15 inches in diameter
under roads and highways. The device, called the Porta-Mole , has recieved
industry awards based on the benefits it brings to the process of underground
The machine, manufactured by Carlton Int. Mfg. Co. of Hurst, TX, uses a 5-9 hp
motor to drive a drill stem at 600 rpm. A small stream of water goes through the
stem to cool the bit and flush out the cuttings. Different bits allow drilling through
virtually any rock or soil. The Porta-Mole can be purchased for less than $5,000.
According to Tina Bradley, vise president of sales for Carlton, the machine's
most highly prized feature is it's accuracy. She explains that a special drill stem
guide controls the depth and angle of the bore. Direction is controlled by a sight
that can be aimed at a target stake up to 200 feet away.
When the boring is underway, forward speed is controlled by a hand winch
mounted on the machine. "The operator can feel impulses from the drill bit
that are transmitted up the drill stem," Bradley said. "From this feel, the operator
knows when to slow down or change the bit. But, if the propulsion were mech-
anized, the drill would be automatically forced forward and be deflected off of
rocks and other obstructions.
The 600 rpm speed of the drill rotation is also a factor in accuracy, according to
Bradley. "Any physics teacher will tell you that the faster you spin an object, the
more it wants to stay in it's original path... it's a principle called 'conservation of
angular momentum'. Bradley added. "the Porta-Mole is so accurate that some
of our customers use it for sewer placement. You can maintain the exact grade
needed for drainage flow."
Because of the low cost of the Porta-Mole, it is proving extremely popular with
public works departments in smaller communities with very limited budgets.
Officials of the city of Roanoak, TX. reported they were able to save nearly
$50,000 on a water project. In nearby Farmers Branch, the public works people
reportedly drilled through 44 feet of "solid whiterock" in less than 90 minutes.
An Oklahoma contractor reported he has been using a Porta-Mole to install
telephone cables and gas pipelines. "Overall, it's been a good machine," he
said. "It works better in some terrains than others, but it does go through rock
Art Harbolt, Tool manager for Henderson Electric Company of Louiville, KY,
said his first experience with Porta-Mole was during a highway project. His
company was already behind schedule and was paying penalties when they
experienced problems getting pipe under the highway. As the crew waited,
one manufacturer demonstrated his boring system and promptley lost $28,000
worth of boring equipment bebeth the roadbed. "The state wouldn't let him dig
into the road to retrieve it either," Harbolt said.
Next, Harbolt tried the Porta-Mole. "We went through hard rock, pulled the pipe
under that highway, cleaned up and were back at the shop in less four hours,"
he said. "I just love the thing (the Porta-Mole). As a tool manager, when I find
something that works this well, I get really excited about it."