The threading tool clips the first threads while the G71 cycle rapids back to its start point. Graphics show a clear return, but the physical X axis moves inward before the tool has cleared the work. Follow the motion command from programmed endpoints through the trajectory planner, servo response, and actual tool position. The first corrective branch is more radial clearance; the parameter branch is Rapid Droop Control.
Where does the motion stop matching the graphics?
The OSP-U10L graphics display validates programmed geometry, not every transient position produced by rapid-axis acceleration, deceleration, following error, and machine mechanics. A return can look safe on-screen while the actual tool follows a different path between the same endpoints.
| Command-path stage | Reading to take | Outcome | Next check |
|---|---|---|---|
Program and G71 interpretation |
Displayed start, end, and clearance coordinates | Endpoint enters the thread envelope | Correct the programmed clearance |
| Rapid trajectory | Actual X and Z positions during reversal |
X starts returning before Z is safely clear |
Increase clearance, then examine rapid behavior |
| Servo response | Axis following-error or droop diagnostic available on the control | Error grows at reversal or rapid acceleration | Inspect Rapid Droop Control settings |
| Physical machine | Tool, holder, stock, and thread crest clearance | Displayed clearance exists but the hardware still interferes | Correct setup geometry before another cycle |
Layer one first: confirm the insert and holder clear the largest physical diameter, not merely the nominal thread diameter. Run above the work in single block with the lowest practical rapid override and watch the machine-position display through the return. Stop before allowing the insert to reach the existing thread.
Is the programmed X clearance physically large enough?
The reported program used X3.1. A proposed diagnostic change was X3.5, adding 0.4 programmed coordinate units. Whether that represents 0.4 radial units or half that radial distance depends on the machine's radius-or-diameter programming convention. Confirm the active convention and unit system on the control before calculating tool-to-work clearance.
| Setting or value | Meaning | Decision |
|---|---|---|
X3.1 |
Reported return/start coordinate | Insufficient if the real return path clips the thread |
X3.5 |
Proposed test coordinate | Use for an air-cut test if increasing X moves the tool away from the spindle centerline |
15 mm clearance |
A conservative shop practice offered when space permits | Not an ES-L8 requirement; use only when travel, tooling, and nearby hardware permit |
Measure clearance at the instant X begins moving toward the next-pass start, not only at the programmed turnaround endpoint. If the larger X coordinate removes the near-contact during an air pass, retain a clearance that covers trajectory variation without approaching an axis limit, chuck, tailstock, or adjacent shoulder.
Does the rapid return follow the path shown on-screen?
Rapid moves are governed by axis acceleration limits and the control's trajectory strategy. Two axes commanded in one block can reach their endpoints on a path that differs from a feed-interpolated cutting line. One axis may decelerate while the other reverses or accelerates. The resulting corner rounding or diagonal motion matters when the programmed clearance is only slightly larger than the thread crest.
Separate the return into observable phases during a safe air run. Record the displayed X position when Z leaves the thread, the minimum physical gap during the rapid, and the point where X starts moving inward. If the programmed endpoints are safe but the intermediate path is not, the fault is trajectory clearance rather than thread depth.
Do not use graphics as collision verification. Graphics can confirm that the cycle parses and that nominal endpoints appear correct; it cannot prove the real servo path clears the stock. A resolving test must reproduce the same rapid direction and travel distance above the part.
Is Rapid Droop Control changing the corner behavior?
Rapid Droop Control was identified as a machine setting that can produce this symptom. Droop represents the positional lag between a commanded axis trajectory and actual servo position. A control strategy that permits more lag can shorten cycle time or smooth rapid response, but the actual path near a multi-axis reversal may encroach on a tight clearance envelope.
| Test result | Interpretation | Action |
|---|---|---|
More X clearance removes the contact |
The original path had inadequate margin | Keep the larger clearance; parameter changes may be unnecessary |
| Following error rises during the return | Servo lag contributes to the path deviation | Review the Rapid Droop Control setting and tolerance |
| Droop control disabled or tolerance tightened and the path clears | The setting affected the rapid trajectory | Validate the change across the complete cycle |
| Path still enters the thread envelope | Program geometry, axis sequencing, or setup remains wrong | Return to the endpoint and physical-clearance checks |
No parameter identifier or factory value is given for the OSP-U10L. Read the current setting from the control and use the machine documentation for its valid range and change procedure. Record the original value before changing it. Tightening the droop tolerance or turning the function off can alter rapid response elsewhere, so test the entire toolpath rather than only the visible collision point.
Is the insert synchronized with the existing thread?
Clearing the return path solves the collision but does not by itself make an existing thread safe to chase. The insert must enter the original groove with matching pitch, hand, spindle phase, tool geometry, and axial registration. A cycle that cuts a correct new thread can still cross-thread a previously machined part if its synchronization reference differs.
Before cutting, align the insert visually in a clean groove and run a non-cutting synchronized pass with radial clearance. Marking compound or another witness method can reveal whether the insert tracks the groove without removing material. Check alignment at more than one axial position: alignment at one point with drift farther along the part identifies a lead mismatch rather than a simple start-position offset.
The parts were previously accepted by measurement over wires because the thread gage was unavailable; the gage now fails to enter. Use the wire measurement to distinguish pitch-diameter error from lead, form, damage, or phase problems. A corrective pass cannot reliably repair a thread whose lead differs from the programmed cycle.
How should the resolving branch be applied and verified?
- Inspect the insert, holder, thread crests, chuck, and nearby shoulders. Establish the actual collision envelope.
- Confirm that increasing the programmed
Xcoordinate moves the tool outward. Account for radius-or-diameter programming and the active units. - Change the reported clearance from
X3.1to a safe test value such as the proposedX3.5, subject to the machine's available space. - Run the complete
G71motion above the stock in single block. Observe actualXandZpositions during every rapid return. - If the intermediate path still approaches the thread, read the servo droop or following-error diagnostic. Record the current Rapid Droop Control configuration before tightening its tolerance or disabling it according to the machine documentation.
- Repeat the full air cycle after each single change. Confirm clearance at the reversal, during the diagonal return, and at the next-pass approach.
- Verify spindle-phase and groove alignment with a non-cutting synchronized pass before allowing the insert to touch the existing thread.
- Make the corrective cut only after both return clearance and groove tracking pass. Recheck measurement over wires and test the finished thread with the intended gage.
FAQ
Why does an Okuma G71 return clip the thread?
The programmed X clearance can be too small for the actual multi-axis rapid trajectory. Axis acceleration, reversal, and permitted servo droop can move X inward before Z has cleared the thread.
Why does the OSP-U10L graphic show a safe path?
Graphics show interpreted cycle geometry and endpoints, not necessarily the physical transient path under rapid-axis dynamics. Verify the return with an air run and the actual-position display.
Why should I try X3.5 instead of X3.1?
X3.5 adds 0.4 programmed coordinate units of outward margin when larger X is away from centerline. Convert that to physical radial clearance using the active radius-or-diameter convention.
Why can Rapid Droop Control affect thread clearance?
It governs permitted lag between commanded and actual rapid-axis motion. Read the current droop diagnostic and setting, record the original value, and test whether a documented tighter tolerance or disabled state changes the return path.
Why can a correctly programmed cycle damage an existing thread?
The new cycle can have correct pitch yet enter at the wrong spindle phase or axial registration. The final verification is a non-cutting synchronized pass that tracks the groove, followed after correction by measurement over wires and acceptance with the intended thread gage.