Tapping sizes

The first stage in tapping is to drill a hole of the correct size. This is known as the tapping size and is normally slightly larger than the root diameter of the thread. Table 2.2 shows the tapping sizes for ISO metric threads which have replaced most threads previously used in Great Britain. 

Why is it necessary to dril I the correct tapping size hole when producing an internal thread ... 

A combined tap and drill is available in a range from M3 to M12. This comprises a spiral fluted tap with the front portion ground as a drill to a diameter equal to the appropriate tapping size (Fig. 8.18). These are used for through holes where the drilling and tapping can be carried out in one operation. 

When the two parts are to be screwed together, the bottom part requires to be tapped while the top part requires a clearance hole. The sequence is the same as for spotting except that, having positioned, clamped, and spotted with the clearance drill, the drill is changed to the tapping size. The hole is then drilled and tapped. Fig. 8.22. 

If the hole drilled on the lathe requires threading, this can be carried out by hand, using hand taps. Having drilled a hole of the correct tapping size (see Chapter 2), it is essential that the tap is started parallel to the workpiece axis. The first step is to isolate the machine. This is a hand operation and power rotation of the machine is not required. Hold a taper or first tap in a tap wrench and offer it into the start of the hole. 

A fundamental requirement in powder processing is characterization of the as-received powders (10—12). Many powder suppHers provide information on tap and pour densities, particle size distributions, specific surface areas, and chemical analyses. Characterization data provided by suppHers should be checked and further augmented where possible with in-house characterization. Uniaxial characterization compaction behavior, in particular, is easily measured and provides data on the nature of the agglomerates in a powder (13,14). 

Wedg e Meters. The wedge flow meter consists of a flanged or wafer-style body having a triangular cross section dam across the top of the fluid conduit. Pressure taps are on either side of this restriction. Overall meter sizes range from 10 to 600 mm. Within each size several restrictions are available to provide the range of differential pressure desired for the appHcation. 

Tap Density. Tapping a mass of loose powder, or more specifically, the appHcation of vibration to the powder mass, separates the powder particles intermittently, and thus overcomes friction. This short-time lowering of friction results in an improved powder packing between particles and in a higher apparent density of the powder mass. Tap density is always higher than apparent density. The amount of increase from apparent to tap density depends mainly on particle size and shape (see Table 4). 

Specifications for Piezometer Taps The size of a static opening should be small compared with the diameter of the pipe and yet large compared with the scale of surface irregularities. For rehable results, it is essential that (1) the surface in which the hole is made be substantially smooth and parallel to the flow for some distance on either side of the opening, and (2) the opening be flush with the surface and possess no burr or other irregularity around its edge. 

The cross-sections of the conductor and the enclosure arc then checked for their adequacy to dissipate the heat generated. The cross-section is then adjusted suitably by permuialions and combinations to arrive at the most appropriate size, keeping in mind the available extruded sections, accounting for all such factors that may affect the rating or the fatilt level of the enclosure and the conductor, such as tap-offs, which are subjected to a cumulative faull level, openings in the conductor for heat dissipation or the enclosure for inspection windows that can infhience their ratings. A calculation in Example 31.1 will clarify the procedure to establish the size of the... 

The installed eost is primarily determined by the size of the unit. However, other faetors may have a signifieant impaet on this eost. The eonneetion to the gas system eould be expensive if speeial hot tap fittings are required. If sound attenuation is neeessary for the ehosen loeation, this ean also have an impaet on the overall eost. The eonneetion to the eleetrieal system ean add signifieant eost if distanees are far or high-voltage switehgear is neeessary. Equipment manufaeturers are able to provide eost estimates for major equipment. The installation eosts are site speeifie and require individual studies and estimates. 

The ratio of p JPmin be as high as 1.52 depending on the material. Consequently, when bulk densities are reported it is important to note whether the value was determined under loose or tapped conditions, along with the mean particle size. Most literature values report an average bulk density that is representative of the material most often handled. Loose solids may be broadly characterized according to their bulk densities ... 

On mating surfaces an allowance should be made for the thickness of the coating. For flat surfaces 1 mm is generally sufficient and on galvanised nuts and bolts the recommended practice is to galvanize the bolts full size and the nuts as blanks which are tapped out up to 0.4 mm oversize after galvanising. 

It is easy to see that an elementary size-n one-dimensional CA rule (f) is equivalent to a size-n feedback shift register with a G (0,1, taps at positions n — 2, n — 1 and n, and f 4>. The only difference is that it takes n shift-register time-steps to reproduce a single CA time step. 

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