Trouble shooting

Paper cutters must be viewed as complete cutting systems with many factors contributing to the quality of the cut. Many cutter operators too quickly blame the knife or the knife grinder for poor cutter performance when the fault is elsewhere.

We have listed some common problems encountered and their probable cause to assist you in trouble shooting.

I. Wavy Cut

Vertical shadingVertical shading across edge of lift can be seen or felt as wavy areas.

Cause Correction
Heavy print in certain areas causes large thickness differences across the sheets. This produces uneven clamp pressure in areas of dense print. Knife finds these areas harder to cut since they are packed tighter and deflects slightly. Evenly distribute clamp pressure by applying felt or foam pad to face of clamp.
Knife burned in grinding which caused soft spots that dull too easily. Regrind knife correctly taking off at least 1/16" width to remove damaged steel.
Knife angle too sharp causing deflection in high density areas. Increase bevel angle by 2°, i.e., 22° to 24°.
Inconsistent paper quality thickness. Change paper.

Diagonal shadingDiagonal shaded areas in direction of knife travel can be seen or felt.

Cause Correction
Knife bevel too sharp and deflects easily. Increase bevel angle by 2°, i.e. from 22° to 24°.
Knife burned in grinding which caused soft spots that dull easily. Regrind knife correctly taking off at least 1/16" width to remove damaged steel.


II.  Overcut

OvercutOvercut is when the lower sheets in the lift are longer than the top sheets after trimming.

Cause Correction
Dull Knife. Change Knife.
Wrong Bevel. For soft paper, decrease bevel angle by 2°, i.e., from 22° to 20°. For hard paper, increase bevel angle by 2°, i.e., from 22° to 24°.
Too much clamp pressure - as knife gets further into lift of paper the density increases causing deflection of knife. Reduce clamp pressure.
Back gauge not set square to vertical. Correct back gauge setting.

 

III.  Undercut

UndercutUndercut is when the lower sheets in the lift shorter than the upper sheets after trimming.

Cause Correction
Clamp pressure too low causing sheets to pull out at bottom. Increase clamp pressure.
Wrong bevel on knife. Decrease bevel.
Rough or uneven material being cut, such as gummed labels or embossed stock. Adjust clamp pressure.
Back gauge not set square to vertical. Correct back gauge setting.

 

IV.  Hollow Cut

Sheets of paper are longer at ends and shorter in the center (not cut square).

Cause Correction
Lift is clamped only at center and not at ends of sheets. Check clamp edge and apply felt of foam pad to distribute clamp pressure.

 

V.  Arc Cut

Sheets of paper are shorter at ends and longer in the center.

Cause Correction
Lift is clamped only at center and not at ends of sheets. Check clamp edge and apply felt of foam pad to distribute clamp pressure.

 

VI.  Knife Rubbing

Knife face rubs clamp causing scratches on knife face and clamp.

Cause Correction
Knife dull. Resharpen knife more often.
Knife too thick. Decrease knife thickness.
Wrong bevel. Decrease bevel.
Gibs worn on cutter. Repair machine.
Combinations of above plus lifts too high. Reduce size of lifts being cut and look for improvement.

 

VII.  Knife Nicks Badly

Cause Correction
Knife at wrong bevel. Increase bevel angle by 2°, i.e., from 22° to 24°.
Knife burned in grinding producing small heat cracks which chip out. Regrind knife correctly taking off at least 1/16" width to remove damaged steel.
Knife set too deeply into cutting stick or stick groove has trash in it. Rotate to fresh stick surface and set depth of cut correctly (max. 0,1 mm / .004").
Poor cutting sticks. Choose better quality stick. Use FASSCO „YELLOW" stick.
Contaminated chip board. Try increasing bevel, do not use Carbide knives.

 






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