Martin Bevel & Miter Gears

Bevel Gears are used as right angle drives where high efficiency is required. They are carried in stock as 1:1 to 6:1 ratios. Bevel Gears are cut with the long and short addendum system and 20 degree pressure angle to compensate for tooth undercut in gears and pinions having low numbers of teeth. Most all of              Martin Bevel Gears are cut with the Coniflex tooth form to allow for a slight misalignment at assembly and during operation. Gears should be mounted at the correct distance from the core of apex center with thrust bearings being used in back of hubs to absorb the backward thrust created in this type of gearing.
Miter Gears are ordinarily used as right angle drives, transmitting horsepower between intersecting shafts at a 1:1 ratio. They are used where high efficiency is required. Only miters of the same number of teeth, pitch, and pressure angle can be operated together. More than two miters may be used in sets, as in a differential.

The thrust of Miter Gears causes the gears to separate; therefore, ball bearings or roller bearings should be used rather than sleeve bearings. Provisions should be made using thrust bearings to absorb backward thrust.

All standard stock Miter Gears must be mounted at right angles (90 degrees) for proper tooth bearing.

All Martin Miter and Bevel Gears are generated with the Coniflex tooth form. A slight misalignment of gears is permissible because of the localized tooth bearing running lengthwise along the gear tooth.

The mounting distance must be held in order to maintain proper backlash between gears. This will also insure that the ends of the gear teeth will be flush with each other. The use of a straight mineral oil as a lubricant is recommended for most Miter Gear applications.

Martin Stock Miter Gears are manufactured from .40 carbon steel.

The “M” Series is furnished unhardened with plain bore.
The “HM” Series is furnished hardened teeth with plain bore.
The “HMK” Series is furnished hardened teeth with keyway and setscrew for installation on the shaft.

Hardened Miter Gears have approximately 50% more horsepower capacity and provide greater gear wear than untreated gears.

All Martin Miter Gears are cut with the 20° pressure angle system. They will not operate with any other pressure angle system.

Martin Worm & Worm Gears

Originally, worm gearing was used to secure, by compact means, a large reduction of speed between driving and driven shafts with a proportionate increase (except for frictional loss) in the torque of the driven shaft. Worm gearing is still used for this purpose, and frequently the wheel is driven by a single-thread worm of such low helix angle that the drive cannot be reversed; that is the wheel cannot drive the worm as the gearing automatically locks itself against backward rotation. (*See note below.)

Although a multiple-threaded worm when applied under like conditions is much more efficient than a single-threaded worm, it does not follow that the multiple-threaded worm should always be used.

A single-threaded worm might be preferable when the most important requirement is to obtain a high ratio and especially if the worm must be self-locking.

When power is the primary factor, the multiple-threaded worms should be used.

LUBRICATION is an important factor when using worm gearing. An increase in heat generated means a decrease in  efficiency. The amount of power which can be transmitted at a given temperature increases as the efficiency of the gearing increases.

Materials for worm and worm gears are generally confined to steel for worms and bronze or cast iron for gears. When steel worms are run with bronze gears at high speeds, the worm is usually hardened with ground threads.

NOTE: SELF-LOCKING ABILITY
There is often some confusion as to the self-locking ability of a worm and gear set. Martin worm gear sets, under no condition should be considered to hold a load when at rest. The statement is made to cover the broad spectrum of variables affecting self-locking characteristics of a particular gear set in a specific application. Theoretically, a worm gear will not back drive if the friction angle is greater than the worm lead angle. However, the actual surface finish and lubrication may reduce this significantly. More important, vibration may cause motion at the point of mesh with further reduction in the friction angle.
Generally speaking, if the worm lead angle is less than 5°, there is reasonable expectation of self-locking. Again, no guarantee should be made and customer should be advised. If safety is involved, a positive brake should be used.