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:

• FIRST: INVOLUTE INTERFERENCE. TO AVOID THIS, ALL OF THE WORKING PROFILE OF THE INTERNAL TOOTH MUST BE OF INVOLUTE FORM.

• 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.

• 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...