Straightness
The maximum bow of a bar expressed in millimetres per metre of length, measured as deviation from a straight line over any one metre.
Why a bar feeder cares
A bar that bows runs eccentric in a magazine feeder, which vibrates the spindle, spoils surface finish and can throw the bar out of the guide channel at speed. Standard bright bar is supplied at 0.5 mm/m; heavy cold drawn above 80 mm is normally 1 mm/m; precision ground shafting can be held to 0.25 mm/m on request.
Where it goes wrong
Straightness is not permanent. Asymmetric machining releases residual stress and bows the bar afterwards, and so does careless storage — bar stacked on widely spaced supports will take a set. Store on continuous racking.
Related terms
Where this applies
Carbon Steel Bright Bars, Free Cutting Bright Bars
Need help applying this?
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