Irregular surface drilling

Drilling irregular surfaces can lead to excessive, uneven forces on drill cutting edges, which leads to premature wear. It is important to follow the guidelines and reduce feed when necessary.

Learn more about the challenges and strategies for each drill type.

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Indexable insert drills

Exchangeable-tip drills

Solid carbide drills

Indexable insert drills

Irregular surface drilling

Irregular

Convex

Concave

• Use shortest drill possible to minimize vibration tendencies and decrease the effects of deflection
• Recommended start values for cutting speed and lowest recommended feed
• Not recommended for 6–7×DC when concave radius is same or smaller than drill radius

Pre-drilled holes

• To keep the cutting force balanced between the central and peripheral insert on an acceptable level, the pre-drilled hole should not be larger than DC/4

Cross hole drilling

Challenges:

• Chip evacuation is affected, might become more problematic
• Deburring in the crossing is hard.  Burr formation must be as small as possible
• Causes more tool wear than conventional drilling

Guidelines:

• For holes with different diameter: drill the larger hole first to reduce burr formation
• Start with lowest recommended feed during the crossing of holes
• Not recommended in long-chipping materials due to chip evacuation while crossing holes

Drilling inclined entrances/exits

Generates uneven and excessive forces acting on the cutting edges

• Intermittent cutting as the drill enters/exits the workpiece
• Increases chance of vibration
• Can distort the drilling profile
• Causes more tool wear than conventional drilling

General recommendations:

• Stability is crucial. A small length to diameter ratio will help to keep the tolerances
• Milling a small flat surface is recommended when entering workpieces with a large inclination

Angled or inclined surfaces, entry

• Use shortest drill possible to minimize vibration tendencies and decrease the effects of deflection
• Start with lowest recommended cutting speed and 1/3 of lowest recommended feed (or lower) until fully engaged and then return to normal feed
• 4–5×DC the inclined entry can be angled up to 15º
• 6–7×DC the inclined entry can be angled up to 10º

Angled or inclined surfaces, exit

• Use shortest drill possible to minimize vibration tendencies and decrease the effects of deflection
  • Recommended start values for cutting speed and lowest recommended feed (or lower)  
• 4–5×DC the inclined exit can be angled up to 15º
• 6–7×DC the inclined exit can be angled up to 5º 

Drilling asymmetrically curved surfaces

• Use shortest drill possible to minimize the drill bending outwards from the center, similar to an inclined surface
• Reduce feed to 1/3 of the initial penetration rate for a concave surfaces
• Radius of curved surface should be bigger than drill radius
• Not recommended for 6–7×DC drills

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Exhangeable-tip drills

Irregular surfaces

• Reduce feed rate to ¼ of normal rate to avoid chipping
• If unstable conditions, make a pilot hole (preferably with short CoroDrill® 870) or spot-mill to create a flat surface

Convex/Concave surfaces

Convex

Concave

• The hole must be perpendicular to the surface
• Min. recommended radius of surface
  • Convex: 4×DC
  • Concave: 1×DC
• Ensure stable conditions and use shortest possible drill
• Reduce feed during entrance
  • Convex: ½ of normal rate
  • Concave: ¼ of normal rate
• Hole quality and tool life could be affected compared with favourable conditions
• Make a pilot hole or spot-mill to create a flat surface if radius is smaller than recommended

Pre-drilled holes

• Not recommended due to risk of chipping on cutting edge

Cross hole drilling

Challenges:

• Chip evacuation is affected, might become more problematic
• Deburring in the crossing is hard.  Burr formation must be as small as possible
• Causes more tool wear than conventional drilling

Guidelines:

• Always drill the larger hole first in order to minimize internal burr formation
• Min. recommended diameter on the hole to be crossed is 2×DC (to ensure that the centre of the tip enters the workpiece first)
• Ensure stable conditions and use shortest possible drill
• Reduce feed to ¼ of during entrance and exit of holes
• Reduce retract feed
• Hole quality and tool life could be affected compared to favourable conditions

Drilling inclined entrances/exits

Generates uneven and excessive forces acting on the cutting edges

• Intermittent cutting as the drill enters/exits the workpiece
• Increases chance of vibration
• Can distort the drilling profile
• Causes more tool wear than conventional drilling

Angled or inclined surfaces, entry

• Maximum recommended angle from centre to corner is 6 degrees to ensure the tip enters the workpiece first
• Ensure stable conditions and use shortest possible drill
• Reduce feed to 1/3 of normal rate during entrance
• Make a pilot hole (preferably with short CoroDrill® 870) or spot-mill to create a flat surface if larger angle or longer lengths

Angled or inclined surfaces, exit

• Maximum recommended angle is 30 degrees
• Ensure stable conditions and use shortest possible drill
• Reduce feed to 1/3 of normal rate during hole exit
• Reduce retract feed
• Hole quality and tool life could be affected compared with favourable conditions

Drilling asymmetrically curved surfaces

Causes the drill to bend away from the centre line of the hole

• Initially only the periphery of the cutting edge is in contact
• Similar but not identical to inclined surfaces

• Maximum recommended angle from centre to corner is 6 degrees
• Stable conditions
• Use shortest possible drill
• Reduce feed to of normal rate during entrance
• Hole quality and tool life could be diminished compared to drilling in favourable conditions
• Make a pilot hole or spot-mill to create a flat surface if there is a larger angle or longer length

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Solid carbide drills

Irregular surfaces

• Can damage drill when penetrating the surface and/or exiting the hole
• Pay special attention for small diameter drills, deflection may occur causing miss-alignment, hole wander and even tool breakage
• Reduce feed to 25% of recommended rate until full diameter is in cut to reduce risk of chipping

Convex surfaces

• Possible to drill if radius is > 4 times drill diameter and the hole is perpendicular to the radius
• Feed: 50–100% of recommended rate until full diameter is in cut
• Alternatively, mill a small flat on the surface before drilling

Concave surfaces

• Possible to drill if radius is >15 times drill diameter and the hole is perpendicular to the radius
• Reduce feed to 30% of recommended rate until full diameter is in cut
• Alternatively, mill a small flat on the surface before drilling

Pre-drilled holes

• Not recommended due to risk of chipping on cutting edge

Cross hole drilling

Challenges:

• Chip evacuation is affected, might become more problematic
• Deburring in the crossing is hard.  Burr formation must be as small as possible
• Causes more tool wear than conventional drilling

General guidelines:

• Feed reduction is generally necessary as the drill crosses the existing hole
• For holes with different diameters: drill the largest hole first to reduce burr formation

• For drilling depths below 12×D, reduce feed to 25% of recommended rate when crossing the existing hole
• For holes with different diameters: drill the larger hole first to reduce burr formation

Drilling inclined entrances/exits

Generates uneven and excessive forces acting on the cutting edges

• Intermittent cutting as the drill enters/exits the workpiece
• Increases chance of vibration
• Can distort the drilling profile
• Causes more tool wear than conventional drilling

General recommendations:

• Stability is crucial. A small length to diameter ratio will help to keep the tolerances
• Milling a small flat surface is recommended when entering workpieces with a large inclination

• Inclinations up to 10 degrees
  • Reduce feed to 30% of recommended rate until full diameter is in cut
• Inclinations of more than 10 degrees
  • Not recommended for drilling
• Alternative for large inclinations – mill a small flat surface, then drill the hole

Drilling asymmetrically curved surfaces

• Cannot be used - only parts of the cutting edge will cut and the tip may not contact the surface first
• High risk of chipping

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Internal Grooving

Internal grooving covers techniques to manage deflection and chip evacuation issues. chevron_right

If you want to learn more, please visit our website Surface Drillngtooling.

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Milling Troubleshooting

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Drilling Troubleshooting

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Surface drilling, also known as open-pit or open-cast drilling, is a method used in mining, quarrying, construction, and geotechnical engineering to extract minerals, rocks, or other materials from the earth's surface. The process involves drilling holes into the ground to access and extract valuable resources or to gather geological data for engineering purposes. Here's an overview of how surface drilling works:

1. Site Preparation: Before drilling begins, the site is prepared by clearing vegetation, removing topsoil, and leveling the ground to create a suitable working area for drilling equipment and personnel.

2. Selection of Drill Rig: Surface drilling operations utilize various types of drill rigs, depending on factors such as the depth of the hole, the hardness of the rock, and the required drilling method. Common types of drill rigs include rotary, percussion, and rotary-percussion rigs.

Mineral Exploration Drilling Rig 

3. Drilling Process:

Drill Setup: The drill rig is positioned at the designated drilling location, often on a stable platform or drilling pad. The rig's mast is raised to a vertical position, and stabilizing legs or anchors are deployed to secure the rig in place.

Hole Preparation: The drilling process begins with hole preparation, where the drill bit is lowered into the ground to create a pilot hole. The pilot hole serves as a guide for subsequent drilling operations and helps maintain drilling accuracy.

Drilling Operation: Once the pilot hole is established, the drill rig continues drilling to the desired depth using rotary, percussion, or rotary-percussion drilling methods. During drilling, the drill bit rotates and applies downward force to penetrate the rock or soil formation.

Cuttings Removal: As the drill bit advances, it generates rock cuttings or soil fragments that need to be removed from the borehole to facilitate drilling progress. Cuttings are typically flushed to the surface using drilling fluid (mud) circulated through the drill string or by air or water jets.

Engineering Drilling Rig

Sampling and Logging: At regular intervals, drilling may be paused to retrieve core samples or conduct geophysical logging to gather information about the subsurface geology, mineral composition, and structural characteristics.

Monitoring and Control: Throughout the drilling process, various parameters such as drilling depth, penetration rate, torque, and fluid circulation are monitored and controlled to optimize drilling performance and ensure safety.

4. Completion and Wellbore Stabilization: Once the desired depth is reached, the drill string is removed from the borehole, and casing may be installed to stabilize the wellbore and prevent collapse. Cement may be pumped into the annular space between the casing and the borehole wall to provide additional support and seal off groundwater zones.

5. Post-Drilling Activities: After drilling is completed, the site may undergo reclamation and rehabilitation efforts to restore natural habitats and minimize environmental impacts. Depending on the project requirements, additional activities such as blasting, blasting, or mineral extraction may follow surface drilling operations.

Overall, surface drilling plays a vital role in resource extraction, geological exploration, and infrastructure development, providing access to valuable resources and essential data for various industries. Efficient and safe drilling practices are essential to maximize productivity while minimizing environmental and safety risks.

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