Cutting and Sizing Cable Housing
This article will discuss the cutting and sizing of both brake and derailleur housing.
The Park Tool CN-10 Cable Cutter is designed to cut multi-strand wires such as gear and brake cable, brake housing, and compressionless gear housing. Compressionless shift housing uses many inner support wires running longitudinally with the inner plastic liner. Compressionless shift housing is intended for shifting systems only, not braking. Brake housing is commonly made of a wire wound around a plastic liner. Use ends caps or ferules at the ends of housing when ever possible. Woven or braided-type housing may also be used for both brake housing and shift housing. It is recommended to lubricate inside the housing when the cable is installed.
Cutting Shifter Housing
The jaws of the cable cutter surround and then shear the material. Using plain diagonal cutters can simply flatten and smash cables. As with all cutting tools, it is recommended to wear eye protection.
Grab and hold the cable or housing close to the jaws. Use care not to cut your fingers. Hold cable or housing perpendicular to jaws and squeeze levers quickly for a clean cut, as seen below.
After cutting the compressionless gear housing, inspect the end to see if it flattened a bit. Use the crimper section of the CN-10 to open up the housing and inner liner before installing an end cap and cable. You can also use the crimper section cutter to crimp on a cable end cap, as seen below.
Cutting Brake Housing
Brake housing is typically made of single strand flat wire wrapped around an inner plastic tube. This housing may be cut with the CN-10 or diagonal cutting pliers such as the SP-7.
Because of the design of the housing wire, it is not always possible to get a flat, clean cut. It is best to finish any burr with a file. Lightly grinding the end will also improve the housing and reduce friction. NOTE: Compressionless housing does not require finishing.
Brake and gear housing allow the cable wire to be routed around bends and connects the levers to the frame stops. The less drag on the cables, the better the shifting and braking performance. Housing that is too short will kink and bind, creating even more friction. As a rule of thumb, try to size the housing so it is as short as possible but it still enters the stops and barrel adjusters in a straight approach.
For rear derailleur housing, note especially how the housing enters the barrel adjuster.
In the left image above, the housing bends immediately upon leaving the barrel adjuster. This can actually bend the housing end cap. The image to the right shows how longer housing in this case allows the housing to enter straight.
The routing of housing may affect the length. Typically the front derailleur shift housing is run on the left side of the frame, while the rear derailleur shift housing is run on the right. This may at time cause unnecessary bending in the housing. In some cases, it is possible to “cross over” the housing, running the front shifter to the right side stop, and the rear shifter to the left side stop. It will then be necessary for the cables to cross back over underneath the downtube. Consider this option, but if the cable ends up rubbing the frame, it is not a good idea. There may be some light rubbing between cables, but this would result in less friction than poorly routed housing.