Indexable drilling: diagnosing and fixing tool damage

The wear is not an even band but patchy, and looks different on the inner and outer insert. Tool life is unpredictable.

• Cutting speed too high — flank wear and thermal breakdown of the coating.
• Cutting speed too low — adhesion and a built-up edge tearing away.
• The coolant is not reaching the zone: too little pressure, blocked channels, the wrong concentration.
• The machine or the workpiece is not rigid enough.
• The hole diameter is too small for this drill — conditions on the inner insert become too severe.
• The wrong grade for the material.

1. Establish which way the error goes from the look of the edge: even wear and melting mean reduce Vc; adhesion means raise it.
2. Check the coolant supply through the tool: pressure and cleanliness of the channels.
3. Check the rigidity of the workpiece clamping and the overhangs.
4. Move to a harder grade for abrasive wear, or a stronger one for chipping.

The insert nearer the drill axis is failing. The outer one may be in good condition at the same time.

• The web is too small or absent: the distance between the inner edge and the centre of rotation is less than it should be.
• The machine or the workpiece is not rigid enough.
• The hole is started incorrectly — entering an uneven or inclined surface.
• A high-hardness part.
• Packed chips that are not leaving the hole.
• The insert is fitted incorrectly or not tightened down.

1. Check the distance from the inner edge to the centre of rotation (the web diameter) and increase it.
2. Reduce the feed at the start of the hole; enter at a reduced feed rather than at working feed.
3. Prepare the entry surface: face it or centre it.
4. On hard materials reduce Vc and f.
5. Against packed chips — raise the coolant pressure and reduce the feed.
6. Refit the insert, check the pocket and the screw.
7. Clamp the workpiece more securely, shorten the overhang.

The peripheral insert — the one that forms the hole diameter — is failing. Often together with scoring on the drill body.

• The machine or the workpiece is not rigid enough.
• The hole is started incorrectly.
• A high-hardness part.
• Poor chip evacuation: the chips are being recut at the periphery.
• The insert is fitted incorrectly.

1. Clamp the workpiece more securely, shorten the overhang, check the rigidity of the assembly.
2. Reduce the feed on entry.
3. On hard materials reduce Vc and f.
4. Raise the coolant pressure — in drilling this is the main remedy for chip problems.
5. Refit the insert, check the pocket.

Scratches and rub marks on the body, most often along the chip flutes and on the guiding portion.

• Chips pack into the flute and rub against the body.
• The machine, the workpiece or the holder itself is not rigid enough.
• The web diameter is too large: the flute is narrower and the chips are cramped.

1. Raise the coolant pressure, reduce the feed.
2. Reduce the web diameter.
3. Check the rigidity of the setup; when working on a lathe, the rigidity of the drill holder.

The hole is larger or smaller than nominal, sometimes tapered or out of round.

• The machine, the workpiece or the holder is not rigid enough.
• The tool is set inaccurately: runout, misalignment, an unchecked overhang.
• Packed chips.
• The web diameter is too large.
• The hole is started incorrectly.
• The wrong coolant flow.

1. Check the runout of the drill and the alignment; on a lathe, use an adjustable bush to set it on centre.
2. Reduce the feed on entry and raise the coolant pressure.
3. Reduce the web diameter.
4. Clamp the workpiece more securely, shorten the overhang.

A hum on plunging and through the hole, vibration marks on the hole wall, fine breakouts on both inserts.

A combination of cutting data and setup: feed too low, too much overhang, non-rigid workpiece clamping.

1. Increase the feed — a thicker chip stabilises the cut.
2. Reduce Vc.
3. Shorten the overhang, clamp the workpiece more securely.
4. Check the tool setting and the runout.

The chip comes out as a continuous ribbon, wraps around, clogs the flutes and stops the cycle.

The feed is too low for this geometry, or the chipbreaker was not designed for this material.

1. Increase the feed.
2. Move to inserts with a different chipbreaker — one suited to this material and feed range.
3. Raise the coolant pressure through the tool.

Spindle speed dropping, the load protection tripping, the cycle stopping at large diameters.

The machine does not have the power for this diameter and cutting data. Indexable drilling draws more power than any other operation at the same diameter.

1. Reduce Vc and the feed.
2. Check the condition of the inserts: worn ones raise the load sharply.
3. Split the operation: pilot drill at a smaller diameter, then open the hole out.
4. Move the operation to a more powerful and more rigid machine.