Methods of Inserting Carbide Buttons for Button Bits

Button bits live or die on insert retention. A tungsten carbide button can be perfectly manufactured, but if it’s installed with the wrong fit, poor hole geometry, or uncontrolled heat, you’ll see the usual field symptoms: buttons popping out, early chipping, cracked buttons, or premature bit retirement.

1) Quick comparison: cold press vs hot-fit vs brazing

Method	What holds the button	Where it’s commonly used	Main advantages	Main risks
Cold press (interference fit at room temp)	Mechanical interference between button OD and hole ID	Moderate duty; cost-sensitive production	Fast, no heating setup	High press forces can damage button or pocket if fit is wrong; retention variability if tolerances drift
Hot press / shrink fit	Hole expands during heating, then grips during cooling	Mainstream button bits (especially demanding duty)	Lower insertion force; strong, stable retention	Requires temperature control and clean pockets; overheating or rework cycles can reduce reliability
Copper/silver brazing	Brazed filler metal bonds button to steel body	Specialized designs or certain applications	More gap-tolerant; less dependent on precise interference	Thermal stresses and oxidation risks; joint quality depends heavily on heat/cleanliness/process control

2) The non-negotiables before you insert anything

No matter which insertion method you use, these controls determine whether you get stable retention or “random” field failures.

2.1 Button OD quality and surface integrity

Button OD tolerance and surface condition affect retention quality (press-fit stability or braze joint integrity). Poor surface integrity can become a crack-initiation site under impact cycles.

2.2 Hole (pocket) geometry quality

Retention is not just hole diameter. It includes:

Roundness and straightness

● Entry chamfer(reduces edge damage during insertion)

● Bottom condition(debris or burrs can create point loads)

● Surface finish(affects real contact and stress concentration)

2.3 Cleanliness

Oil, chips, oxide scale, or flux residue can reduce retention reliability—especially for brazing and hot press.

3) Method 1: Cold press (room-temperature interference fit)

Cold press uses an interference fit and presses the button into the pocket at room temperature—often with a hydraulic press.

When cold press makes sense

● Production where cost and speed are priority

● Duty is not extremely hard/abrasive

● You can hold consistent pocket machining and tight dimensional control

Typical process flow

1. Inspect and sortbuttons by OD group (reduces variation).

2. Gauge the pocket(ID, roundness, chamfer, depth).

3. Cleanpocket and button (dry, oil-free).

4. Alignbutton to pocket axis (avoid tilt).

5. Press to seating depthusing controlled stroke/force.

6. Final check: protrusion/height consistency, visual cracks, pocket deformation.

Fit control: what “interference” really means

Both cold press and hot press rely on interference between button OD and pocket ID. The correct interference depends on steel body material, heat treatment, button diameter, pocket design, and insertion equipment.

4) Method 2: Hot press (shrink fit using thermal expansion)

Hot press is widely used because it reduces insertion force: heat expands the pocket, you insert the button, then cooling contracts the steel around the carbide button bits for a strong grip.

When hot press is the better choice

● Hard and/or abrasive formations where retention must be very stable

● Higher-end bits where consistency matters

● When cold-press forces risk button damage or pocket damage

Typical hot-press process flow

1. Pre-inspection: OD groups, pocket gauges, chamfers, depths.

2. Heat the bit body/skirt uniformlyto target temperature.

3. Insert buttons quickly and squarely(minimal force, correct seating).

4. Controlled coolingto room temperature (avoid thermal shock and process drift).

5. Final inspection: button protrusion, seating depth, pocket integrity.

Why hot press is often “mainstream”: it can deliver strong retention while avoiding the high mechanical press loads that can damage carbide or pockets during installation.

5) Method 3: Copper / silver brazing

Brazing bonds the carbide button to the steel body using a filler alloy. Typical steps include preparing the pocket, placing alloy/flux, heating until the filler flows, and controlling cooling to complete the joint.

Where brazing is still used

Brazing can be used for specialized bit designs or specific applications where the joint design benefits from a brazed layer, or where dimensional conditions make interference-fit retention less practical.

Why brazing can be attractive

● More tolerant to dimensional gap variation than strict interference fit

● Can be useful for certain joint designs and repair scenarios

The real brazing risks (what process engineers watch)

● Thermal stressesfrom high temperature cycles and unequal cooling

● Oxidation / contaminationif cleanliness and heating atmosphere are not controlled

● Joint variabilitydriven by flux behavior, clearance control, and heat uniformity

6) Choosing the right insertion method

Your reality	Best starting method	Why
Hard/abrasive formation + high impact + long runs	Hot press (shrink fit)	Strong retention with reduced mechanical insertion stress
Cost-sensitive production + moderate duty	Cold press	Fast and simple—if you can hold tight tolerances and process consistency
Specialized bit design or certain niche applications	Brazing	More gap-tolerant, but requires careful thermal/process control

FAQ

Question	Answer
What is the most common modern method for installing carbide buttons in button bits?	Many modern button bits use precision-ground cylindrical button inserts pressed into the bit body as an interference fit, often implemented via controlled hot pressing/shrink fitting to reduce insertion stress and improve retention stability.
Why do carbide buttons pop out after drilling for a while?	Common contributors include inconsistent interference/fit, pocket damage, poor cleanliness, or process variation—leading to fatigue under cyclic impact and vibration.
Is brazing still used for button bits?	Yes. Brazing is still used in certain specialized applications, but press-fit designs dominate many mainstream button-bit systems because they can offer more stable retention when the pocket/fit process is well controlled.