39500 Material Trimming Knives

Most overedge machines (also called sergers) use knives to trim the edge of the material just before it is sewn. The knives generally operate as a pair, one in the lower position and one in the upper position. They come in a variety of shapes, widths, edge configurations and materials. Here are some guidelines to follow when choosing knives for your machine.

Knife width: most lower and upper knives for the 39500 are available in a narrow or wide width.  The narrow width is used for general seaming of light to medium weight fabrics. The wide width is used for general seaming of medium to heavy weight fabrics as well as serging with a long stitch length. 

The width of each series of knife is:

• Narrow lower 11/32" (8.7mm)

• Wide lower 13/32" (10.3mm)

• Narrow upper 1/4" (6.4mm)

• Wide upper 11/32" (8.7mm)

• Straight upper 5/16" (7.9mm)

Knife edges: the knife edges can be of a plain or corrugated edge.  The plain edge is used for general seaming and serging of standard knit and woven fabrics. The corrugated edge is used for hard-to-cut knit and woven fabrics, and helps to keep the fabric from being pushed towards the operator during the trimming function.

Material types: the knives are generally made of a high-carbon steel and are hardened to keep the edges sharp longer. Carbide tipped knives are also available to reduce the wear and increase the life of the knife. When using carbide knives, it is recommended to use one (1) carbide and one (1) steel knife, rather than two carbide knives. Using two carbide knives increases the chance of chipping each of the knives and reducing the life expectancy of both.

Upper Knife type: The upper knife can be an angled type, which crosses the lower knife at a 45° angle, or a straight type, which crosses parallel to the lower knife. The angled type is the most common, and is used for most types of material trimming. The straight type is used when heavy or bulky material needs to be trimmed, where a corrugated-edge knife cannot be used because it would damage the fabric. (Note: the straight upper knife requires a different knife holder than an angled knife.)

Knife sharpening: steel knives can be sharpened using a standard knife grinding wheel, whereas carbide knives require the use of a diamond-impregnated wheel to sharpen them.

Listed below are the standard knives for the 39500 Series machines. Other knives are also available for special applications.