From Manual of Gear Design: Helical and Spiral Gears, Volume III
Including Tables Giving Proportions of Internal Gears and their Pinions
IN PRINCIPAL, THE DESIGN OF INTERNAL HELICAL GEAR TEETH IS THE SAME AS THAT FOR EXTERNAL HELICAL GEARS ANY OF THE BASIC RACK FORMS USED FOR EXTERNAL HELICAL GEARS MAY BE APPLIED TO INTERNAL HELICAL GEARS. THE INTERNAL GEAR DRIVE, HOWEVER, HAS SEVERAL LIMITATIONS; NOT ONLY ALL THOSE WHICH APPLY TO EXTERNAL GEARS BUT ALSO SEVERAL OTHERS WHICH ARE PECULIAR TO INTERNAL GEARS. AS WITH EXTERNAL GEARS IN ORDER TO SECURE EFFECTIVE TOOTH ACTION, INTERFERENCES MUST BE AVOIDED. THE POSSIBLE INTERFERENCES ON AN INTERNAL GEAR DRIVE ARE AS FOLLOWS:
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FIRST: INVOLUTE INTERFERENCE. TO AVOID THIS, ALL OF THE WORKING PROFILE OF THE INTERNAL TOOTH MUST BE OF INVOLUTE FORM.
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SECOND: TIP INTERFERENCE. THIS EXISTS WHEN THE TIPS OF THE PINION TEETH INTERFERE WITH THE TIPS OF THE INTERNAL GEAR TEETH AS THE TEETH COME INTO AND GO OUT OF MESH. TO AVOID THIS, THE SIZE OF THE PINION MUST BE A SUFFICIENT AMOUNT SMALLER THAN THE SIZE OF THE INTERNAL GEAR.
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THIRD: FILLET INTERFERENCE. THIS EXISTS WHEN THE TIPS OF THE TEETH OF ONE MEMBER INTERFERE WITH THE FILLETS AT THE ROOTS OF THE TEETH OF THE MATING MEMBER PROPER TOOTH PROPORTIONS MUST BE SELECTED TO AVOID THIS INTERFERENCE.
ANOTHER LIMITATION AS REGARDS THE ASSEMBLY OF THE DRIVE MUST SOMETIMES BE CONSIDERED. WHEN THE DIFFERENCE IN THE NUMBERS OF TEETH BETWEEN THE PINION AND INTERNAL GEAR IS SMALL, THE TOOTH ACTION MAY BE CORRECT, BUT IT MAY NOT BE POSSIBLE...
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Gears are rotating mechanical devices employing 'teeth' in order to transmit torque between separate axes. Two or more cooperating gears are called a transmission and can produce a mechanical advantage by changing speed, torque or rotation direction.
Helical gears are cylindrilical gears whose teeth are not parallel to the axis of rotation. The teeth are angled and appear as a segment of a helix. Helical gears can transmit power between parallel or right angle axes.
Bevel gears are gears designed to transmit motion between intersecting axes. Perpendicular arrangements are most common, but bevel gears can be manufactured for nearly any angle. The teeth bearing surface of the gear, or surface pitch, is conically shaped or tapered. Miter gears are bevel gears manufactured in a 1:1 ratio, with the same number of teeth on mating gears and with perpendicular axes.
Spur gears are the simplest type of gear. Transmitting power between parallel axes, the teeth project radially on the disc.
Topics of Interest
Simple Planetary Drives PLANETARY GEARING IS COMPOSED OF A TRAIN OF GEARS WHERE SOME OF THEM REVOLVE ON FIXED CENTERS WHILE OTHERS REVOLVE ON MOVING CENTERS. SUCH TRAINS MAYBE ARRANGED IN A GREAT...
Overview In principle, the design of internal gear teeth is the same as that for spur gears. Any of the basic rack forms used for spur gears may be applied to internal gears. The internal gear...
11.1 INTRODUCTION A gear drive composed of external and internal gears is considered. Application of such a train enables us to reduce the loss of power caused by sliding of tooth profiles. This...
Examples and Solutions of General Gear Problems For involute functions (INV ?) from 0 to 60 degrees, see Section 1, MANUAL of GEAR DESIGN. Equations of Involute Curve Tooth Thickness at any...
GEARS AND GEARING External spur gears are cylindrical gears with straight teeth cut parallel to the axes. Gears transmit drive between parallel shafts. Tooth loads produce no axial thrust.
