Hi everyone,
I’d like to share a detailed history of an ongoing issue we’ve been facing with our Formlabs Form 4L. We’ve been trying to isolate the cause for months, but we’re still getting consistent warping/bow on any part that has:
• a flat surface,
• thin or wide planar sections, or
• features that need to be precisely square or dimensionally true.
Below is a full timeline and technical breakdown of everything we’ve done so far.
Printer History & Usage Pattern
• The machine was first put into service in May and performed light, occasional prints.
• From August onwards, it started being used much more heavily — especially for production jigs, fixtures, and alignment tools where dimensional accuracy and flatness are essential.
• Since this increased usage, we’ve never been able to obtain a truly flat or square part from the 4L, even when following all recommended procedures.
• The issue is present across multiple resins and multiple geometries. We mostly print on ESD resin
The Problem: Bowing / Warping on All Flat Areas
Consistently, prints come out with:
• Bowing across the centre (convex or concave depending on orientation)
• Edges not meeting flat surfaces
• Parts that should sit flush instead rocking on the table
• Thin or long flat geometries distorting even with heavy support
• Even when the oart is cured with supports, the part still warps
This happens regardless of orientation, support patterns, or material.
Full List of Troubleshooting Actions Taken
We’ve followed every piece of guidance — both from Formlabs documentation and direct support.
Orientation & Support Strategy
• Printed parts at:
• 0°, 10°, 15°, 20°, 30°
• Tilted in both X and Y axes
• Vertical + diagonal approaches
• Used:
• High-density supports
• Manual additional supports
• Reinforcement supports under mid-span
• Automatic supports + modified versions
• No orientation eliminates the bowing.
Washing
• Washed in IPA for 20 minutes as per instructions
• Confirmed no overwashing
• Completely air dried
• Tested reduced wash times
• Tested extended drying
Curing
• Cured with supports ON
• Cured with supports OFF
• Cured at recommended temperature
• Also tested lower temperature, longer duration
• Trialled flipping the part mid-cure
• No meaningful impact on the final bow.
Resin Tanks
• Tried multiple tanks, including different materials
• Same bowing behavior
• Tank film inspected and in good condition
Material Testing
• Tested multiple resins (including ESD)
• Warping effect appears across all materials
Diagnostics
• Printer passes all LPU and mechanical diagnostics . Got the LPU to be replaced as well two months ago and still the same issue
• No errors, no calibration warnings
• Accuracy test prints show no catastrophic distortion, but flatness issues remain
Recreation of the Issue by Formlabs Support
• Formlabs Support printed our own .form file using their print farm
• Their print ALSO warped, although slightly less than ours
• Their conclusion was “orientation/support” related
• But we have already tested dozens of orientations and support configurations, and the issue remains consistent
Support Interaction
• Support recommendations exhausted
• No definitive cause identified
• No viable solution yet provided
• At this point, we suspect mechanical behaviour in the peel, LPU uniformity, or tank deformation that diagnostics do not detect
Why We Believe This May Be a Mechanical or System-Level Issue
Despite best practice and correct post-processing:
• Warping is repeatable, independent of orientation, and independent of material
• Bowing occurs during printing, not post-cure
• Definitely not caused by overwash or overcure
• Tank swapping didn’t fix it
• Formlabs’ own print farm replicated part of the issue
Based on our assessment, this suggests:
• Possible subtle LPU optical variance not flagged by diagnostics
• Uneven peel forces across the wide 4L build area
• Tank flexion under peel load
• Mechanical tolerance variation in Z-axis or platform flatness
• Stress accumulated mid-print on large planar layers
None of this is visible to software diagnostics, but it would explain the consistent bowing across all geometries.
What We Are Asking the Community
Has anyone experienced persistent bowing on the 4L, specifically:
• Large flat sections
• Brackets, jigs, trays, alignment plates
• Thin planar parts
• Square surfaces that print slightly curved
If so:
• Did you identify a root cause?
• Was hardware inspection needed?
• Did any mechanical adjustments resolve it?
We are ready to provide photos, STL, Form files, and data if helpful.
Why This Is Critical for Us
We print production tooling — jigs, fixtures, and alignment aids — where flatness, squareness, and dimensional stability are essential.
These prints must be flush, true, and shape-stable.
At the moment, our 4L cannot reliably produce critical parts.
Closing
Any insights from other Form 4L users (or Formlabs engineers) would be greatly appreciated.
We’ve put a huge amount of effort into isolating the cause, and at this point we believe a hardware inspection or calibration may be required to rule out deeper mechanical factors.
Thanks in advance