Start Here: The Five Rules
I teach new operators five things before they run their first part. These five rules prevent most of the problems I see with new operators. Operators who follow them become good operators quickly. The ones who skip them learn the hard way, usually by scrapping a part or breaking a tool.
- Check coolant pressure before every cycle.
- Watch the chips.
- Inspect the guide bushing before every job.
- Stop the machine if something does not look or sound right.
- Ask for help when unsure.
Rule 1: Check Coolant Pressure
The coolant pressure reading at the pump is not the same as the pressure at the tool tip. Pressure drops across the filter, the rotating union, the drill tube, and the coolant holes in the drill. I have seen a pump showing 80 bar while the tool tip sees only 35 bar because of a clogged filter.
I train operators to trust the gauge at the tool tip, not the pump gauge. If the machine does not have a tool-tip pressure gauge, I install one. The gauge should be mounted at the drill holder or the guide bushing holder, as close to the cut as possible.
| Pressure at Tool Tip | Assessment | Action |
|---|---|---|
| Above 80 bar | Normal for small diameters | Continue |
| 40-80 bar | Normal for medium diameters | Continue |
| 20-40 bar | Low for gun drilling | Check filter and lines |
| Below 20 bar | Critical | Stop cycle immediately |
I check coolant pressure at the start of each cycle and monitor it during the cut. A pressure drop during the cut indicates a chip clog forming. If I see the pressure drop by more than 10% during a cycle, I stop and check the drill.
Rule 2: Watch the Chips
Chip shape tells you more about the process than any gauge. The chips coming out of the bore are a real-time signal of what is happening at the cutting edge.
Good chips are short crescents or commas, about 2-5 mm long for most materials. They flow freely out of the chip flute and fall into the chip pan without packing.
Problem chips fall into three categories:
| Chip Type | What It Means | Corrective Action |
|---|---|---|
| Long stringy chips | Feed too low | Increase feed by 10-20% |
| Fine powder or dust | Feed too high or tool dull | Reduce feed or check tool |
| Blue or discolored chips | Excessive heat at cutting edge | Increase coolant flow or reduce speed |
| Thick, heavy chips | Depth of cut too high | Reduce feed or check peck parameters |
I look at the chips every few minutes during a cycle. A sudden change in chip shape is the earliest warning of a problem. I have caught clogging events minutes before they would have broken a tool just by noticing a change from short chips to long stringy chips.
Rule 3: Inspect the Guide Bushing
The guide bushing supports the drill at the entry point and maintains alignment. A worn bushing causes multiple problems that no amount of parameter adjustment can fix: hole deviation, surface finish degradation, tool vibration, and eventual tool breakage.
I inspect the bushing before every job, not just when I see a problem. The inspection takes 30 seconds:
- Look at the wear surface for scoring or galling.
- Measure the ID with a telescoping gauge or bore gauge.
- Compare the ID to the drill diameter. Clearance should be less than 0.03 mm for gun drilling.
- Check for any chips or debris in the bushing bore.
A bushing that is worn beyond 0.05 mm clearance needs replacement. The bushing is the cheapest component in the drilling system and the most important for hole quality. I keep a stock of spare bushings at each machine.
Rule 4: Stop When Something Seems Wrong
It is always cheaper to stop and check than to clean up after a crash. A drill breakage costs 100-1000 USD for the tool, potentially thousands for the scrapped part, and hours of downtime for cleanup.
I teach operators to trust their senses. Changes in sound are the most reliable indicator. A gun drilling machine makes a consistent high-pitched cutting sound during normal operation. If the sound changes to a lower pitch, a rumble, or a squeal, something has changed.
Other sensory cues to stop for:
- Sight: Coolant flow from the drill decreases or stops
- Sound: Cutting sound changes pitch or becomes rough
- Smell: Burning odor from the cutting zone
- Feel: Machine vibration through the floor or the workpiece
When an operator stops the machine for an unusual observation, I never question the decision. I investigate and either confirm the problem or clear the machine for continued operation.
Rule 5: Ask for Help
No question is stupid when the alternative is a scrapped part. I encourage operators to ask questions before they start a new job or when they see something unfamiliar.
The questions I hear most from new operators:
- “This bushing looks worn to me. Can you check it?”
- “The chips look different from the last job. Is that normal for this material?”
- “I am not sure I loaded the drill correctly. Can you verify?”
I answer every question promptly and explain the reasoning behind the answer. This builds the operator’s knowledge for next time.
Daily Startup Checklist
Beyond the five rules, I use a daily startup checklist:
- Check coolant level in the tank.
- Verify coolant pressure at the tool tip.
- Run a test cycle without cutting to verify coolant flow.
- Inspect the guide bushing.
- Check the drill condition under magnification.
- Verify the workpiece is clean and properly located.
- Start the first part at reduced feed (50%) for the first 5 mm of cut.
The startup checklist takes 3-5 minutes and prevents most common startup problems.
Key Takeaways
- Check coolant pressure at the tool tip, not the pump gauge.
- Watch chip shape as a real-time indicator of cutting conditions.
- Inspect the guide bushing before every job and replace if clearance exceeds 0.05 mm.
- Stop the machine the instant something looks or sounds wrong.
- Follow the daily startup checklist to prevent common problems.