There are lots of air shafts and manufacturers to choose from. Here are some guide lines to consider when choosing an air shaft:
Types:
Leaf type air shafts offer excellent concentricity for high speed applications and they will not distort or damage your cores (great if you recycle cores). However, their beam strength is not well suited for heavy roll weights.
Lug and button type shafts offer very high beam strength for very heavy, demanding applications. But they can harm most cores inside diameters, so reusing cores may not be an option when using these air shafts.
Materials:
Aluminum is great for lightweight air shafts. However, aluminum's stiffness is roughly 1/3 that of steel so for extremely heavy roll weights aluminum is not a choice.
Steel has very high beam strength to handle heavy roll weights but is 3 times heavier than aluminum so handling can be a problem.
Carbon fiber has roughly the weight of aluminum and the strength of steel. However, its cost is extremely high. It does not take shock loads well so its lifetime can be limited. Carbon fiber is difficult to machine and journal designs can be difficult to accommodate.
Manufacturers:
Finally, air shaft suppliers come and go frequently. Often times it seems many try to build a "better mouse trap". Try to choose a manufacturer that has been building air shafts for a long period of time. Make sure their design is field tested. Ease of repair is a huge consideration when choosing a specific design.
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