If you are building a machine where precision and durability of the linear system are priorities, the hardened shaft is the component that makes the difference. Unlike ground and chrome-plated shafts (which we have covered in a dedicated article), hardened shafts undergo a heat treatment that transforms their surface properties.
The hardening treatment
Hardening is a heat treatment that heats the steel to a high temperature and cools it rapidly (in oil or water). The result is a surface with a hardness of 58-62 HRC (Rockwell scale C), which is vastly superior to the mild steel of ground shafts. This hardness is essential when the shaft works with linear ball bushings: the steel balls must slide on a surface that is at least as hard in order not to create indentations and premature wear.
Hardened versus chrome-plated hardened shaft
The hardened shaft offers optimal hardness and wear resistance for dry and clean environments. The hardened chrome-plated shaft adds a hard chrome coating that brings additional benefits: corrosion resistance for wet or coolant environments, even lower coefficient of friction with the bushing balls, smoother surface with better finish, and protection against surface scratches during handling.
Tolerances: h6 vs g6
Hardened shafts DHM are available with tolerance g6, which is narrower than the h6 typical of ground and chrome-plated shafts. In practice, an 8 mm shaft with g6 tolerance has an effective diameter of between 7.991 and 7.978 mm (as opposed to 8.000-7.991 mm for h6). This seemingly small difference translates into more controlled and consistent play with linear bushings, smoother movement without tight spots, and greater positional repeatability.
When to choose the hardened shaft
A hardened shaft is the right choice when using linear ball bushings (LM, LME, LMF): the balls require a hard surface to function properly. For CNCs that need to maintain precision over time under repeated work cycles. For professional or semi-professional 3D printers where movement quality directly affects print quality. For any machine with a long life expectancy and intensive use.
Available sizes at DHM-online
At DHM-online you will find hardened and tempered chrome-plated shafts in sizes from 3 to 40 mm diameter, in lengths from 100 to 3000 mm. A cut-to-length service with tolerance on the cut end is also available. In the Linear Motion section you will also find SK and SHF shaft supports, locking rings and compatible linear bushings to complete the system.
