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[5] [3] As a rule of thumb, the depth should be 1 ⁄ 24 of the span. [5] The width of the ribs is typically 130 mm (5 in) to 150 mm (6 in), and ribs usually have steel rod reinforcements. [5] The distance between ribs is typically 915 mm (3 ft). [3] The height of the ribs and beams should be 1 ⁄ 25 of the span between columns. [3]
Laser machine shops care a lot about the M 2 parameter of their lasers because the beams will focus to an area that is M 4 times larger than that of a Gaussian beam with the same wavelength and D4σ waist width; in other words, the fluence scales as 1/M 4. The rule of thumb is that M 2 increases as the laser power
The rule of thumb is that M 2 increases as the laser power increases. It is difficult to obtain excellent beam quality and high average power (100 W to kWs) due to thermal lensing in the laser gain medium. The M 2 parameter is determined experimentally as follows: [2]
The beam quality factor M squared (M 2) is found by measuring the size of the beam at its waist, and its divergence far from the waist, and taking the product of the two, known as the beam parameter product. The ratio of this measured beam parameter product to that of the ideal is defined as M 2, so that M 2 =1 describes an
The designation for each is given as the approximate height of the beam, the type (beam or column) and then the unit metre rate (e.g., a 460UB67.1 is an approximately 460 mm (18.1 in) deep universal beam that weighs 67.1 kg/m (135 lb/yd)).
[citation needed] If we assume that a certain 1" x 1" beam will sustain a load of 100 pounds, then a beam 1" thick and 2" wide will sustain 200 pounds. An old rule of thumb suggests that rails of 3" or more in width should be 1 1/8" thick, while rails less than 3" wide should exceed 11/8" in thickness. [citation needed]
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The 1/e 2 width is equal to the distance between the two points on the marginal distribution that are 1/e 2 = 0.135 times the maximum value. In many cases, it makes more sense to take the distance between points where the intensity falls to 1/e 2 = 0.135 times the maximum value.