Spring index lower limit: DASMA standard 102-2004 provides a lower limit of 6 for the spring index, which is symbol C in our formulas above (section 9.3). Other interesting items in this standard include an upper limit for how much the door sags when raised (no more than 1/120 of its width, section 9.2.1), that each of the two bottom brackets should sustain twice the door assembly's weight (section 9.2.2) for a total safety factor of about 4, and that the lift cables should provide a safety factor of 5.

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Garage Door Service

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