A brand-new solid carbide drill that still cuts oversize or taper tempts teams to open the drawing and “add stock on diameter.” That move often locks in a setup error as a permanent tool change.
This page is a diagnosis order for oversized/tapered holes with a new carbide drill: separate the defect, measure assembled runout and stickout first, then review entry and point—without fake feed charts or blind diameter compensation.
Separate oversize, taper, and bellmouth
| Symptom | What it usually means | Do not assume |
|---|---|---|
| Uniform oversize | Scale/measurement, runout, or wrong nominal | “Need larger grind stock” |
| Taper (entry ≠ exit) | Deflection, uneven load, heat, entry walk | One diameter offset fixes all |
| Bellmouth at entry | Entry condition, point/walk, fixture | Coating alone |
Name the shape before you change geometry. Related exit defects: Exit breakout & burr control.
Measure assembled runout and stickout first
With the intended holder on the production spindle, measure runout at an agreed stickout. Long overhang and poor clamping create uneven edge load that looks like wrong diameter.
Primary setup guide: Stickout, runout & toolholders. If runout is unresolved, resizing the drill drawing will not stabilize Cost per Good Part.
Entry, point, and feed effects (no invented feeds)
After setup checks, review entry strategy, point geometry, and whether feed is rubbing at start. Use process-first setup thinking—Carbide drill speeds & feeds (process-first)—but do not paste a universal SFM/IPR table into this diagnosis.
Geometry vocabulary: Solid carbide drill geometry. Breakage that follows forced “push through” after oversize compensation: Why solid carbide drills break.
Gauge and temperature discipline
Oversize debates die when the gauge method and part temperature are uncontrolled. Agree dial bore / air gauge / CMM rules and a cool-down practice before declaring the new drill “large.” A hot part and a cold master make honest drills look guilty.
Worn vs new: do not compensate diameter blindly
If the old worn drill was undersize from wear and the new drill reads “large,” you may be seeing correct size against a process that had drifted offsets. Freeze gauges and temperature, compare both tools under the same holder, then decide.
Blind +0.01 mm on the grind is how plants create a second scrap mode.
Scrap and offsets → RFQ with measured runout
Log scrap, rework, and offset edits into cost per accepted hole. When setup is documented and still wrong, send drawing, measured runout/stickout, holder type, entry notes, and gauge method via Custom Cutting Tool RFQ · product Solid Carbide Drill.
Frequently Asked Questions
New drill oversize—change diameter first?
No—measure assembled runout/stickout and gauges first.
Taper always a point problem?
Often deflection or entry; confirm setup.
What to send?
Drawing, measured runout, stickout, holder, scrap shape (oversize/taper/bell), gauge method → RFQ.
How do gauges and temperature affect the call?
Agree dial/air/CMM rules and cool-down before declaring a new drill oversize; hot part vs cold master creates false “large.”