A replacement DTH bit should not be approved from shank type and nominal diameter alone. The gauge-button ring, inner face-button pattern, carbide dimensions and shapes, face profile, and flushing layout form one working design. Two bits can connect to the same hammer and drill the same nominal hole diameter yet distribute impact, maintain gauge, and clear cuttings differently.
For purchasing teams, the practical rule is simple: treat the DTH bit button layout as a controlled specification. Compare a candidate bit with the approved drawing, a verified new reference bit, and actual rock and drilling conditions. Do not copy measurements from a heavily worn bit without correcting for wear, and do not assume that a higher button count automatically means a better or interchangeable design.
Quick answer: what must match before a DTH bit substitution?
| Specification layer | What to confirm | Why it matters |
|---|---|---|
| Hammer interface | Exact shank family, splines, shoulder and retaining geometry, and foot-valve or valveless arrangement | A bit that does not match the hammer interface is not compatible, regardless of its face layout |
| Nominal size | New-bit diameter, required finished-hole range, and any casing or clearance constraint | Diameter establishes the basic hole envelope but not the complete cutting behavior |
| Gauge zone | Number, diameter, shape, angle, and position of the outer buttons | The gauge row cuts and supports the borehole perimeter and helps maintain diameter |
| Face zone | Number, diameter, shape, and pattern of the inner buttons | The face buttons break the central rock area and share the impact load |
| Face and flushing | Flat, concave, convex, or other profile; flushing-hole count and location; groove geometry | Button placement and cuttings removal must work as an integrated system |
| Operating context | Rock strength, abrasiveness, fracture condition, water, pressure/flow, rotation, and observed wear | The same physical interface can support different application-specific configurations |
What does a DTH bit button layout include?
Button layout means more than the total number of carbide inserts. A useful drawing or inspection record separates the face into functional zones:
- Gauge buttons sit at or near the perimeter. Record their quantity, carbide diameter, exposed profile, gauge angle, and radial position.
- Face buttons occupy the central cutting area. Record their quantity, diameter, shape, and arrangement by ring or cluster.
- Auxiliary or protection buttons, when present, should be identified separately rather than mixed into the face-button total.
- Flushing holes and face grooves must be mapped relative to the buttons. A count without their positions is incomplete.
- Face profile establishes the three-dimensional surface on which the buttons are placed. A flat, concave, and convex face can use different patterns even at the same nominal diameter.
Carbide shape is a separate variable from count. For the application trade-offs between spherical and ballistic forms, use the published DTH button-shape guide. Button count, size, shape, and position should be evaluated together.
Why the same shank and diameter can still produce a different bit
The shank establishes the mechanical interface with the hammer. The outside diameter establishes the nominal hole size. Neither one uniquely defines the cutting face. Manufacturer catalogs commonly list multiple face profiles, carbide profiles, and button configurations inside one shank family and size range.
Boart Longyear’s DTH-bit tables, for example, list variants within the same QLX4T/TD40 family and nominal diameter using different face or carbide profiles. Epiroc describes its DTH face design, button population, carbide choice, and flushing as coordinated design features. These examples support an important procurement conclusion: compatibility and application suitability are two separate gates.
| Observed difference | Possible design purpose | Buyer’s decision |
|---|---|---|
| Fewer, larger buttons | May concentrate the available impact across a smaller number of contacts or provide more carbide volume per insert | Ask for the supplier’s intended rock and hammer conditions; do not infer performance from appearance alone |
| More, smaller buttons | May increase the number of rock contacts or change how energy and wear are distributed | Confirm the design is validated for the hammer’s energy, rotation, and flushing capacity |
| Different gauge-button angle or radial position | May change perimeter cutting, gauge retention, and wall contact | Compare new-bit drawings and required hole tolerance |
| Different inner pattern | May match a different face profile or cuttings path | Review face profile and flushing together, not as separate cosmetic features |
| Same count but different carbide shape | May change rock contact area, penetration behavior, and resistance to wear or breakage | Specify carbide profile in addition to quantity and diameter |
“More buttons” is not a universal upgrade rule. Epiroc states that more buttons are part of its own new DTH design and increase energy released when drilling, but that statement belongs to that coordinated product design. It should not be used to approve an unrelated substitution without checking the complete bit and operating system.
How to compare gauge and face buttons correctly
1. Establish the compatibility baseline first
Record the hammer manufacturer and exact model, the accepted shank code or controlled drawing, spline count and form, shoulder and retention details, and whether the system uses a foot valve. If any interface detail is uncertain, stop the comparison. The active PerfoMax DTH drill-bit selection page uses this interface-first process.
2. Use an approved new bit or controlled drawing
A used bit is evidence of service history, not a reliable master specification. Gauge buttons lose diameter and height; face buttons flatten or chip; the steel body can wash around flushing passages; and repeated grinding changes exposed carbide geometry. Use a new approved bit, supplier drawing, or inspection report as the dimensional baseline. Keep the worn bit to explain the failure or wear pattern.
3. Map the gauge row
Photograph the face square-on. Number the gauge buttons clockwise using a temporary external reference that does not mark the carbide. Record count, nominal carbide diameter, exposed shape, radial position, and any repeated angle. Check whether all gauge buttons belong to one ring or whether the design includes an additional protection or secondary gauge row.
4. Map the inner face pattern
Record the inner buttons separately by ring, cluster, or center position. A total such as “15 buttons” is ambiguous if it does not say how many are gauge buttons and how many are face buttons. For each zone, record the carbide size and shape. If a supplier uses different terminology, attach the annotated image and drawing so that the geometry controls the discussion.
5. Add face profile and flushing
A button map without the surrounding face geometry is incomplete. Confirm the profile and then record each flushing hole and open groove. The cuttings path must remain clear between impact contacts. See the DTH face-design comparison and the DTH flushing guide for those variables.
A practical DTH bit substitution workflow
- Identify the current approved configuration. Gather the supplier part number, controlled drawing revision, hammer model, shank details, new diameter, and original button and flushing specification.
- Document the application. Record hole diameter and depth, drilling direction, rock hardness and abrasiveness, fracture condition, water conditions, compressor and hammer setup, and the reason for changing the bit.
- Separate interface compatibility from face selection. Pass the shank and retention gate before comparing button layouts.
- Build a zone-by-zone comparison. List gauge, face, protection, and back-reaming buttons separately, including quantity, dimensions, shape, and position.
- Compare flushing and face geometry. Confirm that the candidate’s holes and grooves are part of the quoted drawing, not inferred from a catalog photo.
- Review the wear evidence. Note gauge loss, flat spots, chipping, pop-outs, steel wash, blocked passages, uneven wear, and the drilled interval under known conditions.
- Approve a controlled configuration. Put the final drawing, revision, inspection points, and accepted sample or pilot-lot criteria into the purchase record.
Inspection points before approving a replacement
| Check | Accept only when | Reject or clarify when |
|---|---|---|
| Identity | Part number, drawing revision, shank family, and nominal diameter agree | The quotation uses only “4-inch bit” or another broad class |
| Gauge layout | Count, size, shape, angle, and position are shown | Only total button count is listed |
| Face layout | Each inner group is dimensioned or unambiguously illustrated | A generic catalog image replaces the controlled configuration |
| Carbide | Profile and nominal sizes are specified by zone | “Tungsten carbide buttons” is the only description |
| Flushing | Hole count, positions, and grooves agree with the design | Flushing is missing from the drawing or conflicts with the photo |
| Sample comparison | Measurements are taken on a new sample using an agreed method | A worn field bit is used as the sole dimensional master |
| Application review | Supplier has the rock, hole, hammer, and air information | Suitability is claimed without operating conditions |
Common mistakes that cause an incorrect substitution
- Ordering by button total. The same total can be divided differently between gauge and face zones.
- Counting flushing holes as empty button positions. Map passages and carbide inserts as separate features.
- Measuring only button height on a worn bit. Wear changes diameter, profile, exposure, and the surrounding steel.
- Ignoring the gauge row. Inner buttons may look healthy while perimeter wear has already reduced the effective hole diameter.
- Treating a website photo as a drawing. Product images can represent a family, not the ordered configuration.
- Changing layout and operating parameters at the same time. If a trial also changes pressure, rotation, feed, or flushing, the cause of any result becomes difficult to isolate.
- Assuming more buttons are always better. Button population must match carbide size, face geometry, available impact, rotation, and cuttings removal.
What to include in the RFQ package
- hammer brand, exact model, serial or version where relevant, and the approved shank drawing;
- foot-valve or valveless requirement and all retention features;
- new-bit diameter and required hole or casing-clearance condition;
- face profile;
- gauge-button quantity, nominal diameter, shape, angle, and position;
- face-button quantity, nominal diameter, shape, and pattern;
- other protection or back-reaming buttons, if present;
- flushing-hole count, positions, and face-groove layout;
- rock hardness, abrasiveness, fractures, water, hole depth, and drilling direction;
- hammer operating pressure/flow basis and observed penetration or wear issue;
- square-on photographs of a new approved bit and the worn field sample with scale; and
- required drawing revision, inspection evidence, sample quantity, packaging, Incoterm, and destination.
For the wider commercial specification, use the published DTH drill-bit RFQ checklist.
Frequently asked questions
What is the difference between gauge buttons and face buttons?
Gauge buttons work around the outer cutting perimeter and help maintain the hole diameter. Face buttons break the central rock area. Their loads and wear environments differ, so buyers should specify each group separately.
Can two DTH bits with the same shank and diameter use different button layouts?
Yes. The same interface and nominal diameter can be offered with different face profiles, carbide profiles, button populations, and flushing arrangements. Physical connection does not prove application equivalence.
Does a higher button count always improve drilling?
No. Button count is only one design variable. Carbide size and shape, face profile, button position, hammer energy, rotation, flushing, and rock conditions determine whether the complete design is suitable.
Can I copy button dimensions from a worn bit?
Use a worn bit to document wear and failure evidence, not as the sole new-part master. Compare it with a new approved reference or controlled drawing because service and regrinding change the measurable geometry.
What is the minimum information needed to request a substitute?
At minimum, provide the exact hammer and shank interface, valve arrangement, new-bit diameter, face profile, gauge and face button details, flushing layout, rock and hole conditions, and clear photographs. A controlled drawing should govern final approval.
Technical references
- Epiroc: DTH drill-bit face design, flushing, button population, and carbide options
- Epiroc DTH drill bits: coordinated flushing, buttons, carbide, and bit-body design
- Boart Longyear DTH bits: manufacturer selection tables by shank, diameter, buttons, flushing holes, carbide, and face profile
These manufacturer examples explain industry design variables; they do not establish interchangeability with another brand or the final PerfoMax-supplied configuration. The approved quotation and controlled drawing must define the ordered bit.
Make the replacement decision drawing-specific
A reliable DTH bit substitution starts with the hammer interface and ends with an approved, application-specific face configuration. Compare gauge and face buttons separately, include flushing and face profile, and use worn tools as evidence rather than master samples. To prepare a controlled quotation, review the active PerfoMax DTH drill-bit selection page and send the hammer, hole, rock, layout, and drawing details with your inquiry.