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Home > Knife Sharpening > Knife Troubleshooting

Knife Troubleshooting


Knife Troubleshooting
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Features:

Recommended bevels for Paper Cutting Knives
 
For the European market all knives are supplied with a standard bevel of 22°. Listed below are various materials and suggested bevels to assist you in obtaining maximum benefit from your knives.

  MATERIALS
 
1 = 17° rubber tubes crude rubber soft rubber

1 = 19°

aluminum foils
lead foil
copy paper
felt
carbon paper

cork
blotting paper
NCR paper
absorbent
silk paper
plywood(max. 3mm)

textile fabric
velour paper
wood pulp
zinc foils
tin foils

1 = 22°

bible paper
jointing paper
normal printing paper
felt paper
felt board
glass paper
greyboard

hand board
hard rubber
wood board, soft
index cardboard
caseboard
lino

postcard board
PVC soft
emery cloth
writing paper
strawboard
security paper
celluloid

1 = 23°

leather

 

 

1 = 24°

Astralon clear vision
foil
cellulose foils
duplex board

duplex cardboard
photo paper
Manila board
pergamyne

pressboard
transformer pressboard
transparent paper

1 = 25°

acetate foils
cellulose acetate foils

hardboard
polyethylene foils

 

1 = 26°

synthetic fiber paper

transparent sheet

 

2 = 22°,1 = 19° (secondary bevel)

laminate aluminum foil
asbestos

veneers

PVC floor slab

2 = 24°,1 = 22° (secondary bevel)

cellophane
double wax paper
duplex paper
label paper

rubber paper
art paper
leather board
metal paper

parchment paper
PVC hard
triplex board
Troubleshooting
 
Paper cutters must be viewed as complete cuttings 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 causes to assist you in troubleshooting.


WAVY CUT (A): Vertical shading across edge of lift can be seen or felt as wavy areas.
CAUSE: CORRECTION:
Heavy print in certain areas causes thickness differences across the sheets. This produces uneven clamp pressure in areas of dense print. The knife finds these areas harder to cut since they are packed tighter and deflect slightly. Evenly distribute clamp pressure by applying felt or foam pad to face of clamp.
Knife burned in grinding causing soft spots that dull quickly. 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.


WAVY CUT (B): Diagonal 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., 22° to 24°.
Knife burned in grinding causing soft spots that dull quickly. Regrind knife correctly taking off at least 1/16" width to remove damaged steel.




OVERCUT: Overcut is when the lower sheets in the lift are longer than the upper 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.




UNDERCUT: Undercut is when the lower sheets in the lift are 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. 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°.
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.



HOLLOWCUT: Sheets of paper are longer at ends and shorter in the center (not cut square).
CAUSE: CORRECTION:
Lift is clamped only at ends of paper and not in the middle. Check clamp edge and apply felt or foam pad to distribute clamp pressure.



ARC CUT: Sheets of paper are shorter at ends and longer in the center.
 
CAUSE: CORRECTION:
Lift is clamped only at center of paper and not at ends of sheets. Check clamp edge and apply felt or foam pad to distribute clamp pressure.



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.



KNIFE NICKS BADLY:
 
CAUSE: CORRECTION:
Knife at wrong bevel. Increase bevel angle by 2°, i.e., 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. 0.1mm/.004").
Poor cutting sticks. Choose better quality stick. Use IKCO cutting sticks.
Contaminated chip board. Try increasing bevel, do not use carbide knives.


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