Boring bars

Because of its high modulus of elasticity, molybdenum is used in machine-tool accessories such as boring bars and grinding quills. Molybdenum metal also has good thermal-shock resistance because of its low coefficient of thermal expansion combined with high thermal conductivity. This combination accounts for its use in casting dies and in some electrical and electronic appHcations. 

StUl another ore preparation is the nodulizing process where the ore is heated in a rotary kiln to incipient fusion. The tumbling action in the kiln causes the phosphate ore to cohere and form spheroidal agglomerates. Combustion of carbon monoxide from the furnaces is used along with supplemental fuel to supply heat to 1300—1500°C. A boring bar is used near the kiln discharge to aid in breaking up the fused ore. The material is then cooled, cmshed, and screened to the appropriate size for furnace feed. 

The high elastic modulus, compressive strength, and wear resistance of cemented carbides make them ideal candidates for use in boring bars, long shafts, and plungers, where reduction in deflection, chatter, and vibration are concerns. Metal, ceramic, and carbide powder-compacting dies and punches are generahy made of 6 wt % and 11 wt % Co ahoys, respectively. Another apphcation area for carbides is the synthetic diamond industry where carbides are used for dies and pistons (see Carbon). 

Anti-vibration tool holders (HM). Heavy metal is an excellent material for damping torsional vibrations. Tools with longer shafts are typical applications. Examples are turning shanks, boring bars, endmills, grinding quills, pinion type cutter supports, etc. (Fig. 7.20). 

FIGURE 7.20. Heavy metal boring bars with simple and multiple cutter heads. By courtesy of Plansee AG, Austria. 

Boring Adjustable boring bar thin wall of round hole... 

All these principles are however scarcely suited to compensation for the deflection of thin boring bars. In this area, mechatronic initiatives with additional actuators have great potential. In the solutions already known (Bushuev 1991 Katsuki et al. 1992 Koren et al. 1999 Brecher et al. 2005), the tool cutting edges can be adjusted to compensate for deflections of the boring bar. The active boring tool shown in Fig. 6 consists of... 

Actuator, Fig. 6 Active boring bar to compensate for the deflection of the cutting edges boring processes (Brecher et al. 2005)... 

Mount a boring bar in the tool post and bore to 1/2" diameter 5/16" deep. Remove and recenter the mold blank in the 4-jaw to work from the opposite end. Counter bore 9/16", 3/8" deep, then tap through 3/8-16. 

A detailed drawing of the top mold section for the plastic container is shown in figure 89. Make It from a 1" length of 2-1/2" X 2-1/2" bar stock. Face off both ends of the mold blank. With the mold half centered in the lathe use the tail stock chuck to center drill, then drill 1/4" through. Mount a boring bar in the compound rest and increase the bore of the 1/4" hole to 1-... 

The bottom mold half is shown in figure 92. Begin by cutting a 1-3/8 length of 2-1/2 x 2-1/2 aluminum or C.R.S. bar stock. Face off both ends. Center the mold in the 4-Jaw chuck. Using the tail stock chuck drill a 1/2" hole 1 deep. Mount a boring.bar in the tool post and increase the diameter of the 1/2" hole to 1-1/4", I deep. Adjust compound rest to 79 degrees and bore the mold cavity 1 deep. Dimension at bottom of cavity to be 1-1/4". Dimension at the top of the cavity to be 1-5/8 diameter. Then bore to 1-5/8 diameter, 1/16" back from the end. 

Large quantities of finely ground barite is stirred into water to a highly concentrated, heavy suspension, which is pumped down into the bore holes during drilling for oil. The suspension cools and lubricates the bore bars, tightens the walls of the boreholes and prevents blowouts. This use accounts for more than 80% of all the barite used. 

For a boring bar a kind of adhesive that has high damping characteristics for vibration is required. Figure 5.19 shows a typical structure adhesive of epoxy-polyamide. The following results were... 

Fig. 5.18. Application parts of adhesive in hydraulic chuck for boring bar.

In contrast, self-excited vibration called chatter vibration often occurs on the boring bar of a cutting tool being used to expand the bores in metal parts. It is especially disturbing in iron boring operations. When chatter vibration is excited, it not only affects the finishing... 

Utilizing the vibration damping ability of VEM (visco-elastic material, a pressure-sensitive adhesive of acrylic resin), as shown in Fig. 5.19, boring bars with an extremely high stability against chatter vibration have been developed. 

Such boring bars have internal structures in order to keep the core constructed with four carbon steel parts bonded by VEM in the tube part of the bar as shown in Fig. 5.20. A sheet of VEM is adhered on the periphery of the core and the core is inserted into the bar tube and then bonded by an epoxy-polyamide adhesive. In addition, the boring bar is completed with a tool-point part bonded on it. The reason why the core is divided into 4 parts is to prevent the occurrence of aeolotropy of the damping ability of the bar. 

Fig. 5.20. Construction of adhesive-bonded high damping boring bar with...

Fig. 5.21. Stability for chatter vibration of boring bar with adhesive bonded...

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