There are hairs & whiskers on my cut ends! How do I get rid of them?

When cutting some plastics with a Servo-Torq® fly-knife rotary cutter a whisker, or hair, remains on the very edge of the cut piece.  Whilst they are noticed mostly on rigid plastics, they may be seen on some flexibles. 

They sometimes stick onto the cut piece; at other times most fall off to form a “dust”.  The hairs can be located only on the upstream side of the cut, or on the bottom of the cut.  Regardless of location, these hairs are undesirable.

There are two possible causes of these hairs:

  1. A film accumulates on the side of the knife as it passes through the plastic.  Material from this film build-up is then deposited, or scraped off, by the next cut onto the edge of the material being cut. 
  1. The cutting edge of the knife pushes some material ahead of it as it cuts through the plastic. This pushed material rolls over forming a lip or a hair on the edge of the piece being cut. 

To eliminate the first cause (re-deposited film), the less friction on the blade the better.  The blade edge should be kept as sharp as possible with intermittent touch-up honing as necessary.

Lubrication with water, Isopropyl Alcohol, or low viscosity Silicone fluid has shown some positive results.  Lubrication can also act as a blade wash which entraps the hairs and carries them away. 

Tip: all Gillard machines come with a standard blade lubrication system. Please refer to the FAQ here for more details:

The angle between the knife edge bevel and the blade body proper should also be smooth & rounded off.  The back of the blade can be cut away to decrease the hold-up area.  A single bevel edge on the downstream side of the blade might also reduce hairs appearing on the upstream side of the cut.

To eliminate the second cause (pushed material forming a lip), the less blade distortion as it cuts through the plastic, the better.  It is assumed that the blade being used is the thinnest possible; keeping in mind that too thin a blade can give a non-square cut. 

Warming the extrudate before the cut, heating the knife blade & heating the inlet bush can all help as such actions can change the reaction of the plastics being cut. This is particularly so for rigid plastics.

Tip: Gillard can offer standard heated blade, heated inlet bush & pre-heater solutions. Please refer to the following pages on this website:

You can try using an anti-static blower to eliminate hairs, or at least stop them clinging to the cut pieces due to a static charge.

There is no question that the solution to the hair problem is empirical; trial and error of one or a combination of the above ideas.  There are just too many variables to recommend one solution. 

For more assistance please contact our Tech Team by email:

Downloads (PDFs):

> Extrusion cutter blade design datasheet.