An unstable hole on a CNC rarely comes from the diameter on its own. Chipping, packed chips, and an oversized hole show up when the construction, the material, the depth, the coolant, and the holding do not match the job. Entry slip and holder runout put that same mismatch on the edge.
Choose a carbide drill for CNC from the hole itself. Match the construction to the diameter and the tolerance. Then check the material, the depth, the coolant, and whether the drill is the last tool in the hole. When one of those does not fit a catalog drill, the next page is a different tool or a drawing review.
If the next drill may still be HSS, HSS-Co, or a modular system, compare drill families for CNC metalworking before this carbide matrix.
What This Page Decides
This page decides which drill branch comes next on a CNC. Use the matrix for an ordinary hole, an angled or flat-bottom feature, coolant at the edge, a small diameter, a hole that depth dominates, a broken drill, an oversized hole, and a tolerance the drill cannot hold.
Material is part of the same decision. The word metal is not a grade. On steel, long chips pack a flute that cannot clear them. On stainless, the surface work-hardens and the chip is hard to break, so the edge chips. On aluminum, chips weld in the flute and pack the hole. On cast iron, the edge wears from abrasion. For hardened steel, report the grade and the hardness on the drawing. Geometry and coating are set when the print is read.
Choose the Drill Construction
Three tools share the name carbide drill bit, and they do not share a job. A solid carbide drill carries carbide through the working body. It fits a CNC when the holder keeps runout down and the machine is rigid enough for that body. A carbide-tipped drill puts carbide at the cutting area and another material in the body. The name does not set the accuracy or the rigidity. An indexable drill uses replaceable edges. When the hole is large and changing an edge suits the job, review that construction on its own. This page does not rank the three. The hole, the holder, and the machine decide.
solid carbide drills for CNC production
Selection Matrix
Match the hole to one row. The failure column is what you should expect when that branch does not fit.
| Branch | Check first | How it fails when it does not fit | Next page |
|---|---|---|---|
| Ordinary CNC hole, diameter and depth both in a normal range | Whether a solid carbide drill matches the hole and the machine | The wrong construction leaves rigidity and chip flow off this tool | Solid carbide drills for CNC production, linked above |
| Angled entry, a cross hole, or a blind hole that needs a flat bottom | Whether the entry is a flat face, and whether the bottom would stay a drill-point cone | The point slips on entry, or the bottom keeps a cone | flat bottom drills for angled and blind-hole features |
| Chips that will not leave, or heat that stays on the edge in a blind hole | Whether the machine can deliver coolant to the cutting edge | Packed chips, or a burned flank | through-coolant carbide drills |
| Diameter in the small-diameter range | Whether flute length, shank diameter, and overall length must be chosen together | A slim drill is used as an ordinary drill and lacks rigidity | micro carbide drills for small-diameter holes |
| Depth and chip flow dominate the diameter | Reach and chip evacuation. A longer copy of the drill on this page does not fix that | Packed chips, or the body walks | deep-hole carbide drills |
| The drill has broken | Whether it failed on entry, in the cut, at breakthrough, or on the way out | A new tool leaves the cause in place | Broken-drill diagnosis, covered below |
| A new drill opens the hole oversize | Whether the whole hole is large, the mouth is belled, or the hole is out of round | A parameter change hides holding error or wear | Oversized-hole diagnosis, covered below |
| The drilled hole cannot hold the tolerance or the wall | Whether the drill is the last tool | A reamer follows the hole it is given | Hole-finishing route, covered below |
Where a Catalog Drill Stops Fitting
A catalog drill stops fitting when the print asks for a size, a wall, or a bottom the drill cannot hold. Another drill of the same construction repeats that limit. If the drill is not the last tool, a reamer follows the hole it is given, including a belled mouth, a wander, or a rough wall. Leave this page and choose the hole-finishing route at that point. A step, a chamfer on the same tool, or a bottom a point cannot leave is the same kind of stop. Read the print before a catalog line is forced onto the job. The matrix already moves a small diameter, and a hole that depth dominates, off this page. Staying and stretching the same drill leaves chips packed and lets the body walk.
Setup Checks Before the First Hole
Check the holder, the entry, and the coolant path before the first hole. Holder runout lets one margin rub while the opposite edge chips. An angled or interrupted entry lets the point slip before the body is supported. Coolant that never reaches the edge leaves chips in the flute, and the flank heats. If the process already packs chips, write that on the drawing with the material and the depth. Speeds and feeds start from the supplier data for that drill and are verified on the machine.
When the Symptom Belongs on Another Page
A broken drill means you still have to name the stage. A replacement tool leaves the cause in place. Note whether it failed on entry, in the cut, at breakthrough, or on the way out, then diagnose carbide drill breakage.
A new drill that opens the hole oversize is a different job. Separate a hole that is large along its length, a belled mouth, and a hole that is out of round, then diagnose oversized drilled holes. A parameter change can hide holding error or wear. This page stops at that handoff and does not repeat those diagnoses.
What to Send with the Drawing
Send the drawing with the material grade and condition, the hole and its tolerance, the depth, the entry, the bottom form, and whether the drill is the last tool. Add how the machine delivers coolant, which holder is in use, and what the current drill does: chipping, packing chips, wandering, or opening the hole large. When the part is hardened, put the grade and the hardness on that same drawing. Geometry and coating are set when the print is read.
Carbide Drill Selection Questions
Are all carbide drill bits solid carbide?
No. Solid, tipped, and indexable drills are different tools.
When is a solid carbide drill the wrong next tool on a CNC?
When entry, bottom form, or a large replaceable-edge hole calls for another tool.
How should depth and coolant be chosen when there is no fixed depth rule?
Judge depth by reach and chip flow, and coolant by whether it reaches the edge.
When does the tolerance move the job off the drill?
When the drill cannot hold the size or the wall the print asks for.
What should be sent if the current drill is chipping or packing chips?
Send the drawing, grade, condition, depth, coolant path, and where the edge fails.
Does a small diameter or a deep hole stay on this page?
No. A small diameter leaves this page for the small-diameter drill. A hole where depth and chip flow dominate leaves for the deep-hole drill.
Send the Machining Data
The matrix is the decision this page can make. Send the machining data with the drawing, the material, the hole, the depth, the coolant the machine can actually deliver, and the failure on the current tool. The review uses that package to confirm the construction, or to agree that the job belongs on the page the matrix already named. Include the failure you see today. If a sample is the right next step, follow the sample validation process.