In some cases, the exported interface from CAD has a larger diameter than the true connection. When you run Replace, MillBox may over-cut the external mesh so the replacement implant appears higher than the STL.
Fix: Create a Cutting Rule to limit where MillBox is allowed to cut before you execute the replacement.
Why This Happens
Some CAD exports include an oversized interface sleeve/offset relative to the actual connection. Replace treats that sleeve as valid geometry and trims surrounding the mesh, producing a “proud” (too high) fit.
Before You Start: Quick Checks
Confirm the library interface (system/connection/height) is correct.
Ensure you’re importing the final watertight STL (no construction splines/sleeves).
Use the latest stable MillBox build.
Step-by-Step Resolution
1) Review the symptom (optional)
Figure 1. Exported interface larger than design → external mesh over-cut; implant appears higher than STL.
2) Open Tools
Figure 2.Tools menu entry point.
3) Open Connections
Figure 3.Connections workspace.
4) Click Replace
Figure 4.Replace command.
5) Select the interface to replace
Figure 5. Selecting the interface to replace.
6) Open the Cutting Rule panel
While you are in Replace – Step 1 (select the current interface), click the Cutting Rule icon at the lower-left of the screen.
Figure 6.Replace – Step 1 with Cutting Rule icon at the lower-left.
7) Name the rule
In the Cutting Rule window, enter a clear name (e.g., Bridge_36–38_CutRule).
Figure 7.Cutting Rule dialog—name the rule.
8) Align Coupling position (recommended)
Click Coupling position and move the black dot to center on the interface. When alignment is accepted, the icon shows a check mark.
Figure 8.Coupling position—move the black dot to center.
Figure 9. Coupling position indicator showing check mark after alignment.
9) Define the cut volume
Click the “+” button to start defining the region MillBox can cut.
Figure 10. Start defining the cut region with the “+” button.
10) Size the cylinder (Height & Diameter)
Use the + / – controls to adjust Height and Diameter. The preview cylinder updates in real time—match the intended boundary precisely.
Figure 11. Adjust Height and Diameter; cylinder updates live in the viewport.
11) Confirm and proceed
Click the check mark to save the Cutting Rule. It will be highlighted/active automatically. Continue the Replace workflow as normal, then recalculate.
Figure 12. Cutting Rule active—continue Replace and recalc.
Do / Don’t
Do
Center the Coupling position before sizing the cylinder.
Keep the cylinder tight to the seating area—minimum height/diameter that still covers the interface.
Simulate after Replace to confirm there’s no residual over-cut.
Don’t
Oversize the cylinder “just in case” (you’ll still clip external mesh).
Skip the coupling re-center step; off-center cuts cause tilt or wall loss.
Run Replace with heavy background apps (large bridges may stall).
Verification Checklist
Cylinder centered and just larger than the true interface
Replace completes with no external wall loss
Simulation shows clean seating; no red collisions at the platform
Screw-access and margins remain unchanged
CAM outputs regenerate without errors
Troubleshooting
Still looks high after Replace
Reduce cylinder diameter by 0.2–0.5 mm and retry.
Re-check Coupling position is dead-center.
Ensure only one Cutting Rule is active (remove duplicates).
Interface under-cuts (too small)
Increase height slightly first, then diameter if needed.
Confirm the library interface matches the CAD connection platform/hex.
Multiple units
Build and test one rule on a single unit, then reuse/clone the sizing.
Edit or Remove a Cutting Rule
Open Cutting Rule → select the rule → Edit (adjust height/diameter) or Delete (trash icon). Re-run Replace and Simulation.
When to Use an Alternative
Prefer Copy/Rip Interface + Replace Library instead of a Cutting Rule when:
The original CAD interface is wrong (wrong platform/connection),
You need to standardize across many cases, or
You want validated geometry saved for future jobs.
Support Hand-Off
Send to [email protected]:
Case ID and MillBox build number
STL(s) + library interface used
Screenshot of Cutting Rule (Height/Diameter)
Short clip or image of the simulation result
Need a quick review of your rule sizing? Attach the STL and we’ll verify your setup.
Need Further Help?
Still have questions? Reach out via our Support Portal or email us at [email protected].
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