The Cutting Strip is the black or white strip on the Silhouette along the bottom of the cutting unit where the blade points down. It is designed to prevent damage to the blade or the actual unit when cutting materials that bypass the cutting mat (such as vinyl, for example).
If you cut too deeply with a material that bypasses the cutting mat, you can potentially cut too deeply past the material and into the cutting strip. You should always ensure that the cutting depth is such that it is cutting through the material as desired, but not so deeply that it continues to through the material and into the cutting strip. If such is experienced, you will need to back down the Thickness setting in the Silhouette Studio® program and/or adjust your blade setting (so that less of the blade's knife edge is exposed) to the lowest possible setting where the material is still be cut through properly.
Indentations on this strip are normal and will be experienced even if you do not cut all the way through into the strip. The cutting strip will be naturally indented with cutting passes performed. Fraying, however, should not be normal. Such would indicate that the Thickness level and/or blade level is too high and adjustments are necessary.
The cutting strip typically does not need to be replaced unless it is effecting your cutting results. For instructions on how to replace the Cutting Strip, please click here.