Precision Indexing

Roller chains can be made to position parts close enough for many automated operations. However, a machine must sometimes put items in a specific place, within extremely close tolerances. In this case it may be better to have the chain position the item close to the desired position and use another means, such as pilot pins, to move the item into the exact position. The machine designer should work closely with an ACA manufacturer to obtain a precise and reliable machine. 

Standard length tolerances normally apply regardless of how closely the chains are matched. In other words, all of the chains in one set can be matched for length (be the same length) as close as 0.002 in/ft, but the next set may differ in length by as much as 0.032 in/ft. 

For this class of match, the mamrfacturer normally uses special procedures to select or make the parts and assemble the chain. This ensures that the difference in length between the strands in a set is no more than 0.006 in./ft to 0.008 in./ft. There usually is a nominal extra charge for this class 

In this case, the user negotiates with a manufacturer to make multiple sets of chain to a specific length within a closer-than-standard length tolerance. There are no uniform standard tolramrces for this class of matching. Each manufacture sets their own tolerances and no two manufactures arc likely to have the same tolerances. Thee is usually a very large extra charge for this. 

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Equivalent Weight and Volume an d Their Precision Indexes for Comparison of Explosives in Air. Data for mean peak pressures and positive impulses determine figures of merit which express performances of expls fired in air. Equivalent Weight (EW) Equivalent Volume (EV) are easily interpretable by ordnance designers. The EW of a new expl is the ratio of wt of a known expl to the wt of a new expl which gives. equiv power as measured by peak pressure or positive impulse. The EV is similarly defined... 

Equivalent weight and volume and their precision indexes for comparison of expls in air 5 El 11-El 12... 

Thus for numerical solution, the equations are the (at) equations n. C. 9., the (x-at) equations n. C. 10., n. C. 11. andH. C. 12. for the p + 2 variables T, P, and pX1. With all quantities known at some starting point z = 0, a computing machine can be programmed to calculate the derivatives in equations n. C. 10-12. Various machine integration routines are then available to solve simultaneous, first order differential equations. Such routines should have a variable step-wise feature for automatically doubling or halving the internal to satisfy a chosen precision index. 

The catalytic coefficients for all acids do not fall on the same Bronsted plot and Bronsted exponents from 0.56—0.71 are obtained depending upon the catalyst type. Observations like these may mean that the Bronsted exponent is not a precise index of transition state structure [183],... 

The quantity Apx is the reciprocal of the so-called precision index of the Gaussian error curve and is larger than the probable error by the factor 2.10 see R. T. Uirge, Phys. Rev. 40, 207 (1932). 

Measurement of the surface area and pore diameter of a silica by conventional techniques can be used to classify its surface structure, approximately as in Table 7-1. The ratio of reactive to total hydroxyls SJSt) is a more precise index of silica surface structure, and this quantity—along with silica surface area—can be determined easily by a simple procedure described in Appendix II. Most chromatographic silicas in use today, and especially those silicas used for thin-layer chromatography, have surface areas of 300-600 m /g and pore diameters of 100-250 A. For the most part they can be classed as large pore silicas. However, small pore silicas are also commercially available. For a further discussion of the surface structure of various commercial silicas and the variation of chromatographic properties with the quantity see Refs. (14,19). 

Elastie stretch can be a large amount in long conveyors. One shonld calcnlate the amount of stretch when the conveyor is more than 20 ft long and anything on the conveyor must be located within 0.5 in. One should always calculate the elastic stretch when the chain is nsed for precision indexing. 

Sometimes a long single-strand chain is used for precision indexing. A long single chain is made in short sections for easier handling. In this case, each section of chain should be matched for length to the other sections. This ensures that the chain will index uniformly no matter which section is active. 

A basic, but sometimes overlooked need in precision indexing is that the spacing between each of the attachments in the chain must be nearly the same. The manufacturer may have to use spedal procedures to ensure that the spacing is as uniform as is needed, and this may increase the cost of the chaiiL... 

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