My cut quality is not acceptable. Why?

There could be a number of reasons why your cut quality is poor:

The bush <> blade gap is too large:

It is critical that the knife blade actually touches both cutter guide bush faces during the cut.  Reset the cutter bushes if necessary.

The guide bushes should be as tight as possible to the knife blade. The ideal is a gap between the bushes just sufficient to allow the blade to pass when turned by hand. You want to be able to hear a “whoosh” sound as you turn the blade.

TAKE CARE! Disconnect the power before attempting to set the cutter guide bush gap or rotate the knife blade by hand!

If the gap between the guide bushes is too wide, then material can be pushed down into the gap by the blade. This will seriously affect the cut quality & will probably also cause a blockage of material in the guide bushes.

The knife blade I'm using is not the correct shape or thickness:

The knife blade shape & thickness are critical factors in obtaining the optimum cut end finish.

Please refer to our FAQs on blades by clicking on these links:

The cutter guide bush edge is not sharp:

The guides bush faces in contact with the knife blade should be straight and clean.

The 90° angle between the bush face and the product bore should be as sharp. Under no circumstances should there be a bevel or radius on this edge.  It is recommended that you check for wear on this edge from time-to-time.

The knife blade is not sharp:

This might sound obvious, but check the cutting edge on the knife blade from time-to-time. Check the double bevel is even.  Replace the blade if appropriate.

The blade speed is too slow:

Generally speaking you want to use the fastest blade speed possible. This reduces product hold-up & improves the squareness of the cut end.

The blade is located the wrong way in the blade holder:

With our older cutting machines it is possible to fit the blade incorrectly into the blade holder. The blade can be 1800 out of position. It could even be back-to-front, so you are cutting with the unsharpend rear edge of the blade rather than the sharp front edge!

There is a reference notch on the blade holder to assist blade location. The blade must be set in the correct position relative to this notch. Please refer to the downloads section below for a drawing showing this position.

Also check that the sharpened edge of the blade is actually facing in the correct direction, i.e. towards the extruded product.

Material is sticking to knife blade:

The knife blade must be kept clean at all times.

For most applications this isn’t a problem. However, for “sticky” materials (typically rubbers, some plastics, such as PU, food & non-polymer materials (adhesives, putties & similar)), there can be a build-up on the blade over time. This will seriously degrade the cut finish.

To avoid this build-up, we recommend you use the standard blade lubrication feature fitted to all our Servo-Torq® rotary cutters.

For many products lubricating the blade also greatly assists the cutting action and eases the rotation of the blade through the extrusion. This will reduce blade wear & lessen the cutting power needed to cut the product.

Simply fill the integral blade lubrication system with a suitable lubricant. We recommend plain tap water with a tiny dash of washing-up liquid for most products.

For medical applications, where a sterile lubricant is required, we suggest Isopropyl Alcohol or similar. For food or other non-polymer products you can try Vegetable Glycerine or Propylene Glycol liquid (diluted as required).

Please refer to our specific FAQ on blade lubrication here:


For more techncial advice please email our Tech Team on:

Downloads (PDF):

> Technical datasheet # 52 - Getting the best results.

> Technical datasheet # 51 - Blade design.

> Cutting Hints.

> Knife blade location drawing - straight blade.

> Knife blade location drawing - curved blade.