Aligning Moulding Knives in Cutter Head

by Russ Rego

Here is some information on how to accurately cut & align high speed steel molding knife blanks for axial constant positioning in a cutter head with gib screw tightening recommendations. The image below will help give you a better understanding of how the acrylic template, knives and molder come into play with these set procedures.

Axial constant concept for moulding cutters
  1. Cut knife steel to even measurements with an industrial chop saw. Let them cool down at room temperature, dipping them in cold water to cool down the steel quicker is not recommended, it could cause fractures in the steel that you won’t even notice and lead to knife breakage while milling.
  2. On bench the grinder, grind off burn marks left over from chop saw and break edges so the steel blanks seats properly in the cutter head. Now weigh the knives to exact weight of each other on a 2000 gram or higher balance scale. Clean cutter head and corrugations in preparation for knife insertion, an old toothbrush works well for this procedure.
  3. Now place the cutter head lying horizontally on the workbench, corrugations parallel with your chest and gib screws pointing away from you. Keep in mind that rights and top cutter heads reference to the very end of the cutter head right side, and lefts and bottom cutter heads reference to the very end of the cutter head left side (see image below.) Reference points on a molding cutter head
  4. It is not necessary that the ends of the knife be perfectly square. When aligning the knives in a cutter head, always align the bottom ¼” corner of the knife flush with the edge of the cutter heads reference side. You will never grind this reference point away because you would be out of the safety zone; therefore, this practice keeps the knife reference point a constant. Remember the knives should never be more than ¼” above the bottom of the knife pocket, this keeps the knives fully locked in by the entire gib for safety purposes.

    Cross section of cutter head Out of square knife blank
  5. Tighten all gib screws equally; tightened with standard gib screw wrench supplied by the manufacturer, start from center and tighten in both directions. Although torque wrench is not necessary, it will give you the exact torque needed. All screws should be tightened equally to the following recommended by the manufacturer. I use Weinig moulder cutter heads so I will use their recommendations.
    • M10 gib screws - 25 Nm or 18 Ft. lbs.
    • M12 gib screws - 30 Nm or 22 Ft. lbs.

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