A core bit that stalls the moment it reaches reinforcement is usually not a bit problem. It is a mismatch between feed pressure, rpm and the segment's ability to cut steel, and it gets worse the deeper the hole.

Read the symptom

Symptom	Likely cause	Action
Sudden stall, motor overload	Too much feed at rebar contact	Reduce feed 50%, raise rpm slightly
Ring of sparks, slow progress	Segment glazed on steel	Dress the segment, light feed
Bit wobbles at depth	Core broken free and jamming	Retract, clear the core, restart
Water stops flowing	Sludge packing around the bit	Retract, flush, resume

Feed discipline

Diamond does not cut steel well; it cuts it by attrition. At rebar, halve the feed and keep the bit moving. A rigid rig with a mechanical feed holds a constant load, which is why rig-mounted coring gets through rebar more reliably than hand-held work.

Speed and water

• Keep the surface speed in the manufacturer's band; too slow glazes, too fast overheats.
• Water flow is the cooling system. If the return water is hot or the slurry is thick, increase flow before increasing feed.
• On deep holes, retract every 40-50 mm to let the slurry out and the segment cool.

Segment choice

For walls known to contain heavy reinforcement, use a bit with a segment designed for mixed material rather than a pure concrete segment. The difference shows up as less glazing and fewer stalls, at a small cost in pure concrete speed.

When to stop coring

• The bit has stalled repeatedly at the same depth: you are cutting a headed anchor or a coupler, not a bar.
• Water has stopped and the bit is hot: continuing destroys the weld.
• The core is jammed: retract, break it out with a chisel or a smaller core, do not force the bit.

Diagnose the bind by where it happens

A binding bit is a message, and where it binds tells you which part of the setup is wrong. Chasing it with more force or more water is how a five-minute job becomes a burned crown and a replacement rig coupling.

Where it binds	Most likely cause	First fix
At entry, within the first 20 mm	Bit wandering, no pilot, tilted rig	Re-pilot with a guide plate, level the rig
Mid-hole, suddenly	Rebar strike or a hard aggregate lens	Reduce feed, raise water, let the segment cut through
Throughout, from the start	Bit too large for the rig torque, or wrong bond	Smaller diameter or a reinforced-concrete specific crown
On exit, at breakthrough	Segment grabs as the load drops	Support the rig, reduce feed at the last 20 mm
After a pause, on restart	Slurry or dust packed around the crown	Pull, clean, restart with water running before contact

Each of those has a different fix, and applying the wrong one makes it worse. Raising water on an entry-wander bind does nothing; pushing harder through a rebar strike glazes the segment and can stall the motor into a breaker trip.

Feed, speed and water by diameter

Core diameter	RPM guide	Feed feel	Water
25-50 mm	High, 700-1200	Light and steady	Low flow, continuous
50-100 mm	Medium, 400-700	Firm but never forced	Moderate, visible return
100-200 mm	Low, 200-400	Slow, let the segments cut	High, keep the crown cool
200 mm+	Lowest, rig-specific	Very slow, watch amps	Maximum, with slurry extraction

Two signals tell you the feed is right without a gauge: the sound stays even, and the slurry coming out carries fines rather than chunks. A bit that rings or squeals is glazing; a bit that grinds and slows is overloaded. Both mean stop and reset before the crown takes damage it cannot recover from.

When a rebar strike is worth stopping for

• If the bit stops advancing at constant feed and water, stop. Continuing heats the segment and work-hardens the rebar, which is worse for the second attempt.
• Pull the core, inspect the crown. A blue or glazed segment needs dressing on a block before it will cut again.
• Mark the strike depth and record it. The same depth will be hit on every adjacent hole, and the crew should expect it.
• Where reinforcement is dense and continuous, switch to a crown designed for reinforced concrete rather than fighting it with a standard segment.
• Never reverse the rig to free a stuck core while the motor is under load; unload first, then reverse briefly, then pull.

On post-tensioned or heavily reinforced slabs, a strike is also a stop-work signal for the scan. Cutting through a tendon is a structural event, not a drilling problem, and no amount of feed discipline makes that hole safe to continue.

Binding costs more in bit life and schedule than the extra five minutes of careful feed ever does. Slow down at the rebar and speed up everywhere else.