The Driller
  • Sign In
  • Create Account
  • Sign Out
  • My Account
  • NEWS
  • CLASSIFIEDS
  • EQUIPMENT
  • SAFETY
  • VIDEOS
  • EDUCATION
  • SOURCEBOOK
  • EVENTS
  • SUBMIT
  • ABOUT
  • SIGN UP
cart
facebook twitter linkedin youtube
  • NEWS
  • Water
  • Geothermal
  • Construction
  • Environmental
  • Mining
  • All Industry News
  • EQUIPMENT
  • Rigs & Heavy Equipment
  • Consumables
  • Pumps
  • Featured Products
  • VIDEOS
  • Newscast
  • Drill Talks
  • Ask Brock
  • Emerging Drillers
  • EDUCATION
  • Drilling Business Insights
  • Reference Desk
  • Sponsored Insights
  • EVENTS
  • Conferences & Demo Days
  • Newscast LIVE
  • SUBMIT
  • Drillers @Work
  • ABOUT
  • Contact
  • Advertise
The Driller
search
cart
facebook twitter linkedin youtube
  • Sign In
  • Create Account
  • Sign Out
  • My Account
The Driller
  • NEWS
    • Water
    • Geothermal
    • Construction
    • Environmental
    • Mining
    • All Industry News
  • CLASSIFIEDS
  • EQUIPMENT
    • Rigs & Heavy Equipment
    • Consumables
    • Pumps
    • Featured Products
  • SAFETY
  • VIDEOS
    • Newscast
    • Drill Talks
    • Ask Brock
    • Emerging Drillers
  • EDUCATION
    • Drilling Business Insights
    • Reference Desk
    • Sponsored Insights
  • SOURCEBOOK
  • EVENTS
    • Conferences & Demo Days
    • Newscast LIVE
  • SUBMIT
    • Drillers @Work
  • ABOUT
    • Contact
    • Advertise
  • SIGN UP

How a Bit Drills

By Wayne Nash
June 1, 2005
Wayne Nash discusses bit selection.

It could be a helpful exercise to examine your company's used bits: A consistent failure pattern could suggest areas for improvement. A worn drill bit. Photo courtesy of the USGS.
Proper bit selection is part science and part art. An understanding of the formations to be drilled is part of it and is based on experience in the field. The other part is understanding how the bit actually drills.

The basic idea of a bit is to remove formation ahead of the drill string in order to advance the hole. The cuttings must be small enough to circulate out freely with- out balling or bridging the hole, but not so small as to force the bit to regrind them. Regrinding slows the progress of the bit and accelerates wear. The economy of bit also is a factor. A bit that lasts forever but doesn't make much hole is just as expensive as a bit that drills like a house-afire, but has to be changed before you reach total depth.

The first consideration in bit selection is the formation's compressive strength. In general, a formation's compressive strength is classified as low, medium and high. Low compressive strength formations include unconsolidated sands and the softer clays. Medium compressive strength formations include such formations as shales and sandstone. High compressive strength formations include granite, basalt, dolomite and volcanic tuff. Knowledge of the area in which you are going to drill is very helpful in bit selection.

A bit removes formation and advances the hole one or more of three ways - gouging, scraping or impact.

Gouging is an action where the cutting surface of the bit actually penetrates the formation and plows it up ahead of the bit. It works the same as when you stick the knife in a jar of peanut butter to make a sandwich. You plow up the formation (in this case, peanut butter) ahead if the bit. Formation removal is ahead of the bit teeth.

Scraping is an action where the teeth of the bit scrape and compress the formation to failure. It works like scraping your knife across the top of a frozen stick of butter. Some of the formation is removed ahead of the tooth and some is removed by the rebound effect behind the tooth.

Impact is an action where the tooth of the bit does not actually penetrate the formation, but transmits shock, which causes the formation to fail and advance the hole. It is like when you whack a piece of peanut brittle against the counter to fracture it: The counter doesn't penetrate the formation - the impact causes it to structurally fail. In impact-mode, formation removal is behind the tooth of the bit.

Roller cone rock bits come with a bewildering array of options, all of which are designed to enhance one feature or another. Tooth length, tooth spacing and tooth overlap all are bit design considerations.

Long teeth are important in soft formations to allow the tooth to gouge deeply into the formation. Tooth spacing is important because the number of teeth acting on the bore face dictates the amount of force, or energy, used.

Fewer teeth and most of the energy is expended in a small area; more teeth and the energy used to drill is expended in a larger area. Tooth overlap also is important. When the teeth of each adjoining cone overlap, the bit is a lot more self-cleaning and resistant to balling in sticky clays.

Another design consideration is skew angle. This angle is a relationship between the axis of the cones and the centerline axis of the bit itself. A large skew angle causes the teeth to gouge and scrape more; a small, or no, skew angle depends on scraping and impact to drill.

After selecting a bit and drilling with it, close examination, when you pull it, can help a lot in the selection of your next bit. Wear patterns and failure analysis are crucial steps to proper bit selection. Ideally, a roller cone bit failure is when the cutting structure (teeth) wear out at the same time as the bearings. There are other factors but, simply put, if the teeth wear out first, it probably is because of too much weight and/or not enough RPMs on the bit. If the bit is flat-spotted, it has balled up and a less-than-attentive driller has allowed it to fail. Conversely, if the bearings fail before the teeth, it usually can be traced to not enough weight, RPMs that are too high, or poor solids control. I've seen bits with the center cut out completely because the driller essentially was pumping “liquid emery-cloth” through the system. Imagine what his pump, swivel and pipe must look like!

I hope this helps in your bit selection. As an exercise, why not go out behind the shop and take a look at that pile of used bits lying around? I'll bet you can find a consistent failure in most of them. Recognizing that and fixing the problem, and maybe selecting a slightly different type of bit, should help raise your penetration rates and lower your bit cost, both of which go directly to the bottom line.
ND

Share This Story

Looking for a reprint of this article?
From high-res PDFs to custom plaques, order your copy today!

Wayne nash 200px
Wayne Nash is a regular contributor to The Driller. He can be reached at rockbit8@hotmail.com.

Recommended Content

JOIN TODAY
to unlock your recommendations.

Already have an account? Sign In

  • geotechnical drilling rig

    6 Onsite Phrases Environmental Drillers Hate

    Here are six phrases that highlight common frustrations...
    The Underground Network
    By: Jeff Garby
  • Wayne Nash

    Pipe Stuck? Common Causes and Solutions for Drillers

    If you have drilled for any length of time, sooner or...
    Oil & Gas Drilling
    By: Wayne Nash
  • submersible pumps, water well pumps

    Selecting and Sizing Submersible Pump Cable

    This article helps pump installers and servicers decide...
    Markets
    By: Bob Pelikan
You must login or register in order to post a comment.

Report Abusive Comment

Subscribe For Free!
  • eNewsletters
  • Online Registration
  • Subscription Customer Service
  • Manage My Preferences

The Driller Newscast: New York Geo Talks 2025 Conference with Hands-on Driller Education

The Driller Newscast: New York Geo Talks 2025 Conference with Hands-on Driller Education

The Driller Newscast, Episode 147: Global Geothermal Collaboration at NY-GEO 2025

The Driller Newscast, Episode 147: Global Geothermal Collaboration at NY-GEO 2025

The Driller Newscast: Coiled Tubing Drilling and the Future of Geothermal

The Driller Newscast: Coiled Tubing Drilling and the Future of Geothermal

The Driller Newscast: 21st Century Drillers | Part 1 DEMAND

The Driller Newscast: 21st Century Drillers | Part 1 DEMAND

More Videos

Sponsored Content

Sponsored Content is a special paid section where industry companies provide high quality, objective, non-commercial content around topics of interest to the The Driller audience. All Sponsored Content is supplied by the advertising company and any opinions expressed in this article are those of the author and not necessarily reflect the views of The Driller or its parent company, BNP Media. Interested in participating in our Sponsored Content section? Contact your local rep!

close
  • demo of a DM450 drilling rig during a customer factory visit
    Sponsored byGeoprobe

    Built for You: Smarter Drill Rigs, Stronger Support, Bigger Opportunities

Popular Stories

MainPhotoTwoBrothers.jpg

Two Brothers' Journey Through the Drilling Industry

Tariffs

Tariffs Shake Up the Drilling Industry

AI and Drought Concerns

AI’s Growing Thirst for Water and Power

The Driller Classifieds

COMPRESSORS

EAST WEST MACHINERY & DRILLING IS BUYING AND SELLING AIR COMPRESSORS, AIR BOOSTERS, AIR ENDS & PARTS
Company: East West Machinery

DRILL RIGS

LOOKING FOR LATE MODEL TOPHEADS & DRILLTECH D25'S
Company: Spikes’s Rig Sales

DRILL RIG PARTS

MEETING DRILLERS NEEDS AROUND THE WORLD
Company: East West Machinery

ELEVATORS

SEMCO INC. PIPE ELEVATORS
Company: Semco Inc.

GROUTERS

GROUTING EQUIPMENT - GROUT PUMPS & GROUT HOSE REELS
Company: Geo-Loop Inc.

PUMP HOISTS

SEMCO INC. - BASIC PUMP HOISTS
Company: Semco Inc.

WELL PACKERS

LANSAS PRODUCTS - INFLATABLE WELL PACKERS
Company: Vanderlans Lansas Products

WELL SCREENS

WELL SCREENS & SLOTTED PIPE
Company: Alloy Screen Works

Products

Water Quality Engineering: Physical / Chemical Treatment Processes

Water Quality Engineering: Physical / Chemical Treatment Processes

By carefully explaining both the underlying theory and the underlying mathematics, this text enables readers to fully grasp the fundamentals of physical and chemical treatment processes for water and wastewater.

See More Products

Subscribe to The Driller Newscast

Related Articles

  • Wayne Nash

    How Do I Drill a Straight Hole for a Well?

    See More
  • A Bit for Every Application

    See More
  • Wayne Nash

    How to Keep a Mud Pump Running Well on a Drilling Job

    See More

Related Products

See More Products
  • M:\General Shared\__AEC Store Katie Z\AEC Store\Images\ND\new site\a-builders-guide-to-wells-a.gif

    A Builder's Guide to Wells and Septic Systems, Second Edition

  • M:\General Shared\__AEC Store Katie Z\AEC Store\Images\ND\new site\water-and-wastewater-treatm.gif

    Water and Wastewater Treatment: A Guide for the Nonengineering Professional, Second Edition

See More Products

Related Directories

  • Little Beaver Inc. | Lone Star Drills

    Little Beaver is a manufacturer of safe and productive drilling equipment and accessories, including augers, trenchers, extensions, points and blades. Lone Star Drills are an innovative addition to the Little Beaver product family, designed to be convenient, powerful solutions for soil sampling, geotechnical testing and auger drilling.
  • Bit Brokers International Ltd.

    Founded in 1988, BBI is a family-run business specializing in high-quality drilling tools and solutions. We offer a wide range of products, including tricone bits, PDC bits, reamers, Hammers, Hole Openers, and cutters. Our dedication to innovation and customer satisfaction makes us a trusted partner for drilling projects worldwide.
×

Dig deeper into the drilling and water supply industry!

Build your knowledge with The Driller, covering the people, equipment and technologies across drilling markets.

SIGN UP NOW
  • RESOURCES
    • Advertise
    • Contact Us
    • Directories
    • Store
    • Want More
    • Classifieds
  • SIGN UP TODAY
    • Create Account
    • eNewsletters
    • Customer Service
    • Manage Preferences
  • SERVICES
    • Marketing Services
    • Reprints
    • Market Research
    • List Rental
    • Survey/Respondent Access
  • STAY CONNECTED
    • LinkedIn
    • Facebook
    • YouTube
    • X (Twitter)
  • PRIVACY
    • PRIVACY POLICY
    • TERMS & CONDITIONS
    • DO NOT SELL MY PERSONAL INFORMATION
    • PRIVACY REQUEST
    • ACCESSIBILITY

Copyright ©2025. All Rights Reserved BNP Media.

Design, CMS, Hosting & Web Development :: ePublishing

The Driller
search
cart
facebook twitter linkedin youtube
  • Sign In
  • Create Account
  • Sign Out
  • My Account
The Driller
  • NEWS
    • Water
    • Geothermal
    • Construction
    • Environmental
    • Mining
    • All Industry News
  • CLASSIFIEDS
  • EQUIPMENT
    • Rigs & Heavy Equipment
    • Consumables
    • Pumps
    • Featured Products
  • SAFETY
  • VIDEOS
    • Newscast
    • Drill Talks
    • Ask Brock
    • Emerging Drillers
  • EDUCATION
    • Drilling Business Insights
    • Reference Desk
    • Sponsored Insights
  • SOURCEBOOK
  • EVENTS
    • Conferences & Demo Days
    • Newscast LIVE
  • SUBMIT
    • Drillers @Work
  • ABOUT
    • Contact
    • Advertise
  • SIGN UP