TL;DR
Die cut registration errors produce off-center cuts and wasted material. Check sheet feed timing, die lock-up, and impression pressure before adjusting register settings.
What you might see
- cut position varying from sheet to sheet
- cut image off-center relative to print
- cutting rule penetrating unevenly across the die
- nick and crease quality varying across the sheet width
Likely causes
Sheet feed timing drift causing sheets to arrive at the die at incorrect position
Die not fully locked in the chase, allowing micro-movement during cutting
Impression pressure uneven across the platen, causing variable cut depth
Worn front lays or side guides allowing sheet position variation before the die
Required tools
- Carbon impression paper
- Calipers for cut position measurement
- Torque wrench for die lock bolts
- Replacement front lays (if worn)
Safety first
- The die cutting platen closes with high force. Never put hands in the cutting area while the machine is energized.
- Cutting rules and ejection rubber are sharp. Use cut-resistant gloves when handling die chases.
Procedure
- 1
Sample 20 consecutive sheets and measure cut position deviation from nominal in both MD and CD. Determine if the error is systematic or random.[1]
- 2
Check the front lay stops for wear or damage. Replace worn front lays. Lays directly control sheet front edge positioning.
- 3
Verify die lock-up. Confirm all die lock bolts are tightened to specification. A loose die shifts position under the impact load of each cut.[1]
- 4
Run a carbon impression test across the full cutting area to check impression pressure uniformity. Adjust makeready patching to equalize cut depth.
Warning: Keep hands clear of the cutting area when advancing makeready sheets. The platen closes with significant force. - 5
Check the side guide setting against the sheet width. Over-travel side guides allow sheet yaw before the die.
- 6
After all mechanical checks, run the register fine-adjustment from the press control panel.
- 7
Sample and measure 20 sheets from the corrected run before releasing to production.
Sources
Bobst Bobst Mastercut / Expertfold / Vision Fold Die Cutter / Folder-Gluer general technical documentation, Bobst
Die cutter register adjustment and impression control, general die cutting practice (general)
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Stop fixing the same fault twice.
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