The new drill still cuts large, and the shop wants to add allowance on the drawing diameter. That change often freezes a setup error into the next tool's permanent size.
Name the shape before the grind changes. Uniform oversize, a bellmouth at entry, an out-of-round hole, a taper, and a reading taken while the part is still hot are different faults. Measure the assembled tool and agree the gauge before the drawing diameter moves.
Name the Shape Before the Grind
Name the shape before anyone changes the grind. A hole that is large all the way through, a mouth that is large only at the entry, two directions that do not agree, an entry that does not match the exit, and a reading taken on a hot part are different faults. The table is the order. The drawing diameter stays where it is until the shape has a name.
| Shape | Check first | Do not assume first |
|---|---|---|
| Uniform oversize | The whole hole is large. Check the gauge, the nominal diameter, and runout after the tool is assembled. | Do not start by enlarging the drawing diameter. |
| Bellmouth | Only the entry is large. Deeper in the hole the size is back near nominal. Check entry support and how the first cut enters. | Do not assume a coating change will close the mouth. |
| Out of round | The two directions do not agree. One lip is cutting more, or the workpiece is moving. | This is not the same fault as uniform oversize. |
| Taper | Entry and exit do not match. Check deflection, lost support at the exit, and load on one side. See exit breakout and burr control. | One diameter offset will not correct the whole hole. |
| Hot reading | The part is still hot, or the master is cold. Cool the part and measure again with the same gauge. | Do not treat the drill as made oversize. |
A Hot Part Is Not a Large Drill
A hot part is not a large drill. Use the same gauge and the same master, and judge the hole only after the part is cool. A hot part against a cold master can make a good drill look large. Cool the part. Measure again with that same gauge. If the size comes back, the drill was not the fault. If the size stays large after the part is cool, name the shape and move to the setup. Do not move the drawing diameter while the part is still hot. Write down whether the reading was taken hot or cold.
Measure the Assembled Tool First
Measure the assembled tool before the grind changes. Runout at the real stickout, in the holder that is on this machine, is the first setup check. A reading on a loose drill, or in a different holder, is a different setup. Follow the method to measure assembled runout and stickout. Holder types stay on that page. If the edge still does not match the hole after that check, read solid carbide drill geometry. One lip cutting more than the other shows up here. A workpiece that moves shows up here too.
When the Old Drill Had Already Drifted
The old drill may have been ground undersize. The new drill then reads large only because it is back at nominal. Compare the two drills in the same holder before you decide the new drill is oversize. If the old drill is small and the new drill matches the nominal, the hole did not grow because the new tool was made large. Keep both tools. Record which holder held them. Do not add allowance on the drawing until that comparison is written down.
What to Send with the Inspection
Send the drawing, the shape name, and the gauge. Say whether the part was hot or cold. Include runout at the real stickout and the holder that was on the machine. Say whether the old drill and the new drill were compared in that same holder. If the drill has already broken, read why solid carbide drills break. Only when drilling cannot hold the drawing size, choose the correct hole-finishing route. When the setup and the gauge are already recorded and the hole is still wrong, review solid carbide drills.
Oversized Hole Questions
Should the diameter be changed first when a new carbide drill cuts large?
No. Name the shape first, then measure the assembled tool and the gauge.
Is a bellmouth the same as a uniformly oversized hole?
No. A bellmouth is the entry. Uniform oversize is the whole hole.
Is an out-of-round hole the same fault as oversize?
No. Out of round means the two directions do not agree.
Can a hot part make a good drill look large?
Yes. Let it cool, measure again with the same gauge, and only then change the tool.
What should be sent before the drill diameter is changed?
The drawing, the shape, the gauge, whether the part was hot or cold, runout at the real stickout, the holder, and whether the old drill and the new drill were compared in the same holder.
Send Inspection Data
Send the inspection with the drawing and the shape name. Include the gauge, whether the part was hot or cold, runout at the real stickout, and the holder. Say whether the old drill and the new drill were compared in that holder. Leave the drawing diameter where it is until those notes are in the package. The grind waits on that record. Keep the gauge name in that package.
If a sample is the next step, use the sample validation process.