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How to Secure Your Tribrach

Leica-Tribrach_close-up

A tribrach is a simple connecting device between an instrument and its support. However, it must be secured correctly to ensure smooth operation. 

a detailed view (from below) of the upper tribrach plate, showing the instrument secured

The above diagram shows a detailed view (from below) of the upper tribrach plate when the instrument is ecured. (A) instrument studs, (B) upper tribrach plate, (C) lock assembly – spring holder, (D) holding screws for lock assembly, (E) lock assembly – clamping flange, (F) orientation spring, (G) tribrach clamping arm, (H) lock assembly – spring.

Before the clamping mechanism can work, your instrument must be placed in the tribrach. The initial position of the instrument studs is arbitrary. If the clamp is released, the orientation spring is loose.

a view of the upper tribrach plate showing the holes for the instrument studs and indicating the clamping direction

The above figure is a view of the upper tribrach plate showing the holes for the instrument studs and indicating the clamping direction. When tightening the clamp, the stud in Hole 1 is pressed to its edge through the orientation spring and the lock assembly ring is turned slightly eccentric because of the non-concentric position of the clamping arm.

The figure below shows a detailed view (from below) of the upper tribrach plate with the instrument released, as well as a detailed view of a clamping flange.

a detailed view (from below) of the upper tribrach plate showing the instrument released

Based on the special design of the clamping flanges (E) together with the tilted cut of the instrument studs, a buildup of pressure occurs when closing the clamp. Subsequently, the lock assembly (fixing star) presses the instrument studs against the upper tribrach plate.

Once the instrument is secure, you're ready to begin your survey work.

Shop the APE Online Marketplace for a wide selection of tribrachs and other surveying and construction accessories. For assistance in choosing or securing a tribrach, please contact us.