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Parallel and 90?Non-Intersecting Shaf Applications
Improved Tooth Strength
Greater Load Carrying Capacity
Increased Contact Ratio
Smoother Operating Characteristics
Selections From Stock

 Helicals, 45?Helix Angle
 Transverse Diametral Pitch (TDP)System
 Hardened Steel (24 TDP (R)C 6 TDP)
 Bronze (8 TDP (R)C6 TDP)
 Pitch Diameter .333" to 6.000"
 14-1/2?Pressure Angle Boston helical gears are stocked both right and left hand, made with a 45? helix angle. They are designed to transmit motion and power between nonintersecting shafts which are positioned either parallel (opposing hand) or at 90?to each other (same hand). Because these gears are top-hobbed, there is extremely close concentricity between the pitch diameter and the outside diameter.
Helical gears offer additional benefits relative to Spur Gears, those being:
-CImproved tooth strength due to the elongated helical wrap-around
-CIncreased contact ratio due to the axial tooth overlap
-CHelical Gears tend to have greater load carrying capacity than Spur Gear of similar size.
-CBecause of the above, smoother operating characteristics are apparent
All Boston Helicals are cut to the Transverse Diametral Pitch System, resulting in a higher Normal Diametral Pitch Number.
Boston standard stock helical gears are made with a 45?helix angle to transmi motion and/or power between non-intersecting shafts that are parallel or at 90?t each other. They are stocked both right and left-handed. For parallel shaft operation, helical gears having opposite hand helix angles are required, while for shafts at 90?the same hand helix must be used
For parallel shaft applications, helical gears provide overlapping tooth contact. This results in a smoother, quieter operation and higher horsepower capacity than afforded by spur gears of comparable size.
For 90?shaft applications, the tooth contact area is very small which considerabl limits the load capacity. Horsepower ratings are not tabulated in this catalog, for 90?applications
Boston helical gears are top hobbed, resulting in extremely close concentricity between the pitch diameter and the outside diameter.
Approximate horsepower and torque ratings for selected sizes (numbers of teeth) at various operating speeds (RPM) are given for hardened steel helical gears. The ratings are based on the beam strength of the gear tooth. These ratings are for parallel shaft applications under normal operating conditions, that is: properly mounted and lubricated, carrying a smooth load for not more than 10 hours per day or a moderate shock load not more than 15 minutes in two hours (Service Factor 1.0). Refer to Table 1, below, for other types of service. Ratings for gear sizes or speeds not listed may be interpolated from the values indicated. Pitchline velocities are limited as reflected by the lack of ratings for larger numbers of teeth at higher RPM/s in the selection chart. Application in this area is not recommended.
Ref. Parallel shafts are approximately 98% efficient 90?shafts are approximately 50% efficien
Horsepower ratings for bronze gears are approximately 33% of these ratings.
1.Determine service factor.
a. Using Application Classification Chart I, pages 152-153 determine service factor or
b.With knowledge of operating conditions and load classi- fication, select service factor from Table 1.
2.Determine Design Horsepower.
Design HP = Application Load Service Factor (Table 1)
3.Select pinion with horsepower capacity equal to (or greater than) design horsepower determined in Step 2. Reference Rating Pages 55, 56.
4. Select a driven gear with a catalog rating equal to (or greater than) the horsepower determined in Step 2.

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