Many “bad drills” are long stickout and runout problems—the same geometry that is stable short becomes chipped or oversized when overhang grows.
When a new solid carbide drill cuts oversized, wanders at entry, chips one corner, or dies early, the first instinct is often to change point angle, coating, or grade. Those changes matter—but only after the assembled system can hold the tool on center with a realistic projection. Stickout and runout set the bending and unequal-load environment that geometry must survive.
This setup-first guide covers stickout vs rigidity, qualitative runout budgets (stricter at small diameters), holder-class trade-offs for production drilling, and what holder/stickout data to include in an RFQ. It links to breakage diagnosis without rewriting failure-mode catalogs, and it points small-diameter work to XRZ’s small-diameter holemaking resource.
Stickout vs Rigidity: Why Overhang Changes Everything
Stickout (tool projection beyond the holder face) increases the lever arm for radial and bending loads. A drill that is quiet and size-stable when clamped short can deflect, chatter, or chip when the same flute is extended for reach. Carbide is stiff compared with many tool materials, but it is still sensitive to bending and impact once overhang grows.
Practical planning rules:
- Use only as much projection as the hole depth and clearance require—extra stickout is not a safety margin.
- Treat deep holes and long-reach features as a system: flute length, neck, holder, and cycle together—not “longer drill equals deeper capability.”
- If quality collapses only after a holder or projection change, restore the previous stickout as a controlled test before redesigning geometry.
Deep-hole strategy (peck, through-coolant, process family) belongs in its own discussion; here the point is simpler: do not diagnose geometry while the tool is unnecessarily long.
Runout Budgets: Qualitative, Stricter at Small Diameters
Runout (TIR) means the cutting edges do not share the load equally. One lip cuts more, heat and wear concentrate, holes go oversized, walls score, and corners chip. Absolute runout that is tolerable on a larger drill can be unacceptable on a small diameter because the same radial error is a larger fraction of the tool size and chip thickness.
There is no single published TIR number that fits every carbide drill. Acceptable error depends on diameter, length/projection, tolerance, holder system, spindle condition, and material. Use qualitative discipline instead of a fake universal limit:
| Situation | Runout sensitivity | Setup priority |
|---|---|---|
| Larger Ø, short stickout, open tolerance | Lower relative sensitivity | Still clean interfaces; do not ignore obvious TIR |
| General production drilling | Moderate | Measure assembled TIR at production projection |
| Small Ø / micro work | High | Stricter holder hygiene, shorter stickout, careful clamping — see small-diameter holemaking |
| Long stickout + tight hole size | High | Reduce overhang and stabilize holder before changing point geometry |
Measure the assembled spindle–holder–tool stack at the intended production projection, not only the loose drill on a bench. Dirt, wrong collet range, worn nuts, and taper fretting show up only after clamping.
Holder Classes for Production Drilling (No Brand Pitch)
Holder choice affects how consistently you can reclaim low runout after tool changes. Classes differ in clamping mechanism, balance behavior, and sensitivity to operator technique:
- ER collet systems — flexible and common; quality depends on collet condition, correct size range, cleanliness, and nut practice. Convenient, but easy to introduce runout if maintenance slips.
- Hydraulic holders — often used when shops want more repeatable clamping force and lower sensitivity to small technique variations, within the holder’s diameter and balance limits.
- Shrink-fit holders — provide a rigid, concentric clamp for suitable shank diameters when the shop has controlled heating/cooling process discipline.
No holder class forgives contaminated tapers, damaged shanks, or extreme stickout. Pick the class that your process can keep clean and measure. For production drilling, the winning criterion is repeatable assembled TIR and stable projection—not catalog marketing labels.
Link to Breakage Diagnosis—Without Rewriting It
Uneven corner wear, oversized holes on a new drill, entry wander, and margin scoring are classic runout/stickout signatures. When the tool has already fractured, use XRZ’s diagnosis guide—why solid carbide drills break—to read break location and wear pattern. This stickout/runout page stays on prevention and setup control; it does not repeat the full failure-mode list.
RFQ: Tell Us Holder and Stickout
Geometry recommendations without holder data are incomplete. In the custom cutting tool RFQ, include:
- Holder type/class (ER, hydraulic, shrink, milling chuck, etc.) and spindle interface
- Planned stickout / gauge length and usable flute length
- Measured assembled TIR and where it was measured (if available)
- Hole diameter, depth, tolerance, material, and coolant method
- Current defect: oversize, wander, chipping, short life, or hole location error
XRZ reviews custom solid carbide drills as part of the complete setup, not as isolated catalog points.
Frequently Asked Questions
Why is a new carbide drill cutting oversized holes?
Assembled runout and excessive stickout are common causes: one edge removes more material and the hole opens up. Measure TIR at production projection and shorten overhang before changing geometry or coating.
How much stickout is acceptable?
Only as much as reach requires. Acceptable projection depends on diameter, tolerance, holder, and material. If quality falls off after lengthening the tool, treat stickout as the first experimental variable.
Is ER always worse than hydraulic or shrink for drilling?
Not always. A clean, correctly sized, well-maintained ER setup can drill well. Hydraulic and shrink classes often improve repeatability when processes demand it. Judge by measured assembled runout and changeover consistency, not by class name alone.
Should I change drill geometry to fix runout?
No. Geometry cannot reliably compensate for unstable clamping or high TIR. Correct the holder stack and projection first; then revisit point and flute design if defects remain. See also breakage diagnosis when tools are already damaged.
Send Holder and Stickout Data With Your Drawing
Share projection, holder class, measured TIR, material and hole requirements. XRZ will help specify a solid carbide drill that matches a realistic setup—not an idealized bench measurement.