The Strike: How to Know It Was Rebar
A rebar strike announces itself three ways at once: a sharp metallic ring instead of the dull hammer drone, penetration that stops dead within a few millimetres, and bright steel glitter in the grey dust. With a brazed bit, stop within the first second and you usually save it; lean harder and you usually lose the carbide.
Hard aggregate feels different. A flint or granite pebble bounces the bit and slows progress, but the note stays dull, there is no metal in the dust, and the bit normally works past it within ten to fifteen seconds. If the hole stops at the same depth whatever you do and the dust sparkles, you are on steel. For the other reasons a bit stops advancing, see our drill bit failure analysis.
What a Strike Does to a Brazed Carbide Tip
Most concrete bits carry brazed carbide: a 2-cutter plate or a 4-cutter cross soldered into a slot in the steel body. The carbide is hard, in the HV 1300–1500 class, and ground to crush a brittle material. Concrete fails by fracture. Reinforcing bar does the opposite: ductile steel of around 500 MPa yield that does not crack under the blow and grabs the cutting edge instead.
Three failure modes follow, in rising order of severity:
- Corner chipping. The blow lands a brittle carbide corner on steel that will not give way, and the corner flakes off. The bit still drills, but it wanders and cuts oversize.
- Braze-line shear. On a 2-cutter the long chisel edge lands half on bar, half on concrete, and levers the plate sideways. The braze joint takes the full shear load; a hairline crack here is the start of tip loss.
- Heat damage. Keep pushing and the strike point becomes a friction brake. Braze alloys weaken from roughly 600–700 °C; a blued band just behind the head means the joint has been cooked.
A full-carbide head does not have this weak point. The whole head is one sintered carbide piece joined to the body behind the cutting zone, so there is no insert to chip loose and no braze line in the cut. That is why it is the head built to keep drilling through a bar (see the last section).
The 60-Second Bit Inspection
After a suspected strike on a brazed bit, back it out and run this check before drilling another hole:
| Check | How | Pass | Retire the bit |
|---|---|---|---|
| Carbide corners | Look at the tip head-on under a light | All corners present, edge line continuous | A corner is missing or the edge is visibly stepped |
| Braze line | Inspect the seam where carbide meets the steel body | Clean, unbroken seam | Any hairline crack: a detached tip jams in the hole |
| Heat colour | Check the body just behind the head | Original finish or a light straw tint | Blue or purple band: the braze has been overheated |
| Runout | Roll the bit on a flat surface or spin it slowly | Tip stays centred | Visible wobble: the bit is bent |
A bit with one chipped corner but a sound braze can finish non-critical holes; expect wander and a slightly oversize hole, which rules it out for anchor holes. A cracked braze line means the bit is done: fishing a loose tip out of the bore costs more time than a new bit.
What to Do Next Depends on the Head in the Chuck
Global brands now sell three different answers to steel in the hole, and so do we. Know which one is in the chuck before you decide.
| Head in the chuck | At the bar | Next step |
|---|---|---|
| Brazed 2-cutter or 4-cutter (IZ, ZHPLUS-5X, ZHMAX-5X; most standard concrete bits) | Stop: hammering on steel chips the carbide or shears the braze | Relocate the hole, or cut the bar with a rebar cutter and come back |
| Full-carbide head (ZHPLUS-8 Ø4–25 mm, ZHMAX-8 Ø4–25 mm; Bosch EXPERT 7X / max-8X, Hilti TE-YX, Diablo Rebar Demon) | Keep hammer mode on and hold a steady feed | Drill concrete and bar in one pass, no bit change |
| Rebar cutter (SDS-Plus Ø12–32 mm) | Rotation only, hammer off | Cut the bar, then switch back to the hammer bit |
Relocate the hole. With a brazed bit this is the default answer. Move at least 50 mm from the strike, and for an anchor check the approval’s minimum spacing and edge distance before you shift: moving a hole into a spacing violation swaps a tooling problem for a structural one. Our anchor drilling guide covers the spacing logic.
Cut the bar with a rebar cutter. When the hole position is fixed, drill the concrete to the bar, fit a rebar cutter of the same diameter, switch the hammer off, cut through the bar, then go back to the hammer bit for the rest of the concrete. A rebar cutter is a hollow crown with carbide teeth; hammer blows break those teeth. The full sequence is in how to drill through rebar in concrete.
Drill on with a full-carbide head. This is the one head built to go through: keep the hammer on, hold a steady, moderate feed and let it cut. Where bars are hit on most holes, this is the head to stock, because it removes the bit change altogether.
The step no bit changes: approval. Reinforcement carries tension. Cutting a structural bar, whatever the tool, is the structural engineer’s decision, and on post-tensioned slabs striking a tendon is a life-safety event. Scan first; if the bar is structural and the hole cannot move, stop and escalate.
Drilling Around Rebar in the First Place
- Know the cover. In most structures the first steel layer sits 20–50 mm below the surface, set by the exposure class. Shallow fixings that stay inside the cover, such as cable clips and conduit saddles, rarely meet steel.
- Expect a grid. Slab mesh typically runs on a 100–200 mm grid; beam stirrups follow regular centres. One strike tells you where the neighbours are: offset half the grid spacing diagonally and you land mid-bay.
- Scan when it matters. For anchor groups and core positions, a cover meter or radar scan takes minutes; a strike on hole three of a four-bolt pattern costs the layout.
- Start gently. Drill the first 20 mm with reduced feed so you can feel a shallow bar and stop before full hammer energy lands on it.
Why a Full-Carbide Head Keeps Drilling
Strike tolerance comes from how the carbide is held, not only from how many edges it has. A brazed 4-cutter cross shares the blow across four edges and survives incidental contact better than a 2-cutter, but its inserts still sit on braze joints. A full-carbide head takes the joint out of the cut:
- One piece of carbide. The cutting edges and the centre point are sintered as one part, so steel contact cannot lever an insert out of its slot.
- The joint sits behind the cut. Our ZHPLUS-8 and ZHMAX-8 heads are joined to the steel body by resistance friction welding (RFW), a separate construction from our controlled-atmosphere mesh-belt-brazed insert lines, with the joint checked on metallographic cross-sections.
- The edges share the blow. Four short edges around a centre point meet the bar instead of one long chisel edge, so no single corner takes the full energy of the steel contact.
That is the construction behind Bosch EXPERT SDS plus-7X and SDS max-8X, Hilti TE-YX and Diablo Rebar Demon (Diablo states up to 7× the life of a standard 2-cutter), and behind our ZHPLUS-8 full-carbide SDS-Plus line (Ø4–25 mm) and ZHMAX-8 for SDS-Max (Ø4–25 mm). Our current four-cutter full-carbide programme covers Ø4–25 mm in SDS-Plus and SDS-Max. For larger holes, we match a multi-insert ZHMAX-7, a rebar-cutter changeover or a diamond-core system to the approved drilling path and machine. For the full selection by job, see best drill bits for reinforced concrete; distributors sourcing a rebar program direct from the factory should start at the SDS OEM & wholesale page.
Source Rebar Cutters for Your Drilling Range
For distributors and tool brands, we supply SDS-Plus rebar cutters and separate full-carbide rebar bits. Choose rotation-only crowns for the steel-cutting changeover stage, or the specified full-carbide line for reinforced-concrete drilling.
Send hole diameters, rotary hammer model and quantities. We confirm working and overall lengths, the selected operating mode, bulk pack format, private-label packaging and delivery. MOQ is reviewed for the actual order. Rebar cutters are supplied through normal purchase orders without a separate sample service.
Wholesale rebar cutters, custom specifications & private-label OEM · Request a purchase quotation
