A-A-52298B
2.3 Tripod head. The bearing surface of the tripod head (see firure 1) shall be machined
finished with center hole 2.25 to 2.50 inches in diameter to accommodate the instrument fastener and the plumb line holding device. The instrument fastener and the plumb line holding device shall permit the fastening or removal of an instrument by an operator wearing arctic gloves. The tripod head shall be protected with a removable headcap, secured to the tripod head. The head shall be provided with three coplanar surfaces for attachment of the tripod legs.
2.3.1 Instrument fastener. An instrument fastener (see figure 1) shall hold the surveying instrument in place on top of the tripod head. For interface with current equipment the fastener shall be attached to the tripod head by a sliding bar arrangement. The sliding bar arrangement shall be fastened at one end to the bottom of the tripod head to pivot and allow the instrument to be positioned anywhere within head center hole. Threads on the instrument fastener shall be
0.625-11 UNC-2A conforming to ASME B1.1. When the instrument fastener is pushed upward to its extremity, it shall protrude above the tripod head not less than 0.38 inches and not greater than 0.50 inches. When not in use, the instrument fastener shall drop below the surface of the head.
2.3.2 Plumb line holding device. The plumb line holder shall be an industry standard, quick disconnect type allowing the plumb bob to be removed without tools (see figure 1). The plumb line holding device shall suspend a plumb bob from the bottom, center of the instrument fastener. With an instrument fastened to the tripod, the plumb line holding device shall ensure that the pivot point of the plumb bob line will be within 0.50 ±0.06 inches of the top of the tripod head. The total unobstructed plumb line swing shall be not less than ± 5 degrees from the vertical.
2.4 Tripod legs. The tripod legs shall be of the extension-leg type, hinged to the tripod head
and extending to an end shoe. The extended length, measured from the center of the hinge to the tip of the end shoe, shall be 70.00 ±2.00 inches and the collapsed length shall be 44.00 ±2.00 inches. The legs shall be adjusted to the desired length with no binding or distortion. A locking device shall secure each leg at any extended position and when fully retracted. An integrated device shall be provided to secure the legs together for transporting the tripod. A device shall be provided for attaching the removed headcap in such a way as not to interfere with the tripod head or equipment operation. A device shall be provided for attaching a standard survey instrument portable battery box.
2.4.1 Hinged attachment. The hinged attachment shall provide a firm connection between the legs and the tripod head. The hinged attachment shall allow the legs to move freely through a minimum 90° arc from vertical to horizontal, and lock in any position within the arc.
2.4.2 End shoes. Each end shoe shall be 4.00 to 7.00 inches long and tapered to a hardened, replaceable point. Use of magnetic material shall be acceptable. Each end shoe shall have a permanently attached foot spur to assist in firmly placing the shoe into ground. The foot spur shall be on the outside of the shoe and extend from the shoe 1.50 ±.06 inches. The end shoe points shall be replaceable without the use special tools.
2.5 Plumb bob assembly. The plumb bob shall have hardened, replaceable points. The points shall be replaceable without the use of special tools. The plumb bob shall be furnished with a minimum of 7.50 feet of non-binding cord, a cord length adjuster, and a plumb line holding device.
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