Question

the depth of root in worm thread is​

Answer 1

A perfectly sharp 60° V-thread will have a depth of thread ("height" from root to crest) equal to 0.866 of the pitch.

Answer 2

worm is a gear with one or more cylindrical, screw-like threads and a face width that is usually greater than its diameter. A worm has a center hole (bore) for mounting the worm on a shaft.

Worm gears, like worms, also are cylindrical and bored for mounting on a shaft. However, unlike a worm, a worm gear’s diameter is usually much larger than the width of its face. Worm gears differ from spur gears in that their teeth are somewhat different in shape and are always formed on an angle to the hole (axis) in order to mate with worms.

In worms and worm gear sets, both the worm and worm gear are of the same hand. Right-hand sets are considered standard. As a result, right-hand sets will always be furnished unless otherwise specified.

Features:-
The efficiency of worm gear depends on the lead angle, sliding speed, and lubricant, surface quality and installation conditions. They offer smoothest, quietest form of gearing. They provide high-ratio speed reduction in minimal spaces.

Worm gears are used when large gear reductions are required. Worm gear has a unique property of easily turning the gear. The gear cannot turn the worm because the angle on the worm is shallow and when the gear tries to spin the worm, the friction between the two holds the worm in place. Worm gears work under difficult conditions, presenting unique lubrication demands. The types of oils most commonly used to lubricate worm gears are compounded mineral oils, EP mineral gear oils and synthetics.

Worm gear is always used as the input gear. For the operation of worm gear, torque is applied to the input end of the worm shaft by a driven sprocket or electric motor. The worm and the worm shaft are supported by anti-friction roller bearings. Because of high friction worm gears are very inefficient. There is lot of friction between a worm gear and the gear being driven by the worm gear. When used in high torque applications, the friction causes the wear on the gear teeth and erosion of restraining surface.

Worm Gear-Basic Dimensions
Gear dimensions are important because they provide valuable information when determining how best to meet a customer’s needs. Here are definitions we need to know in order to determine the basic dimensions of worm gears.
1. Pitch Diameter –The diameter of the pitch circle is the “imaginary” circle on which the worm and worm gear mesh.
2. Working Depth – The maximum distance the worm thread extends into the tooth space of the gear.
3. Throat Diameter –The diameter of the throat circle at the center line of the worm gear face (the lowest point on the tooth face).
4. Outside Diameter – The largest diameter of the worm gear teeth. It is equal to the diameter of the outside circle.
5. Root Diameter – The smallest diameter of the worm gear. It is equal to the diameter of the root circle.

Worm Gear-Tooth Dimensions
Worm Gear-Tooth Dimensions
Gear

1. Addendum – The distance from the pitch circle to the throat circle.
2. Dedendum – The distance from the pitch circle to the base of the tooth. It is equal to the addendum plus the working clearance.
3. Whole Depth – The distance between the throat and the base of the tooth. It is equal to the addendum plus the dedendum.
4. Working Clearance – The space between the top of the worm thread and the bottom of the worm gear tooth when properly
meshed.