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## Main Question or Discussion Point

In a two stage reduction gearbox is it possible to have more teeth on the gear pair (helical-parallel axis) of the 2nd stage? I ran through a specification for gear sizes and Im wondering if this is ok.

- Thread starter cabellos6
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- #1

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In a two stage reduction gearbox is it possible to have more teeth on the gear pair (helical-parallel axis) of the 2nd stage? I ran through a specification for gear sizes and Im wondering if this is ok.

- #2

Danger

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- #3

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Even if the output shaft isn't in line with input shaft, the same thing should hold.

- #4

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It is certainly permissible to have a different ratio in one pair versus the other pair; this is the norm. It is important to assure that neither pair involves a pinion with less than the minimum number of teeth to avoid undercutting.

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true. but then the whole designs based on constraints which can vary very much from application to application. since the op didnt specify any constraints, i only assumed a set of constraints.The assumption that the input and output shafts are aligned (a reverted train) is an unnecessary design hindrance that can drive the cost up and is not justified except in very special cases where the layout requires this. It is rarely done as a matter of routine.

probably a not so useful assumption, it only messed up in the end.

true again, but the size should be minimized anyways(weight, inertia, space etc). surely undercutting is the deciding factor for minimum number of teeth.It is certainly permissible to have a different ratio in one pair versus the other pair; this is the norm. It is important to assure that neither pair involves a pinion with less than the minimum number of teeth to avoid undercutting.

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how should we go about finding the true minimum Dr.D?(i am not being sarcastic)

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- #9

FredGarvin

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In "the real world" you are given a basic set of criteria (variations are a certainty):how should we go about finding the true minimum Dr.D?(i am not being sarcastic)

- weight

- $/part

- performance

You and your team/management decide what goes into the requirements of a successful design. If you can meet all of your requirements, you are done. You may go back and revist a design in the future for any more refinements that can be made (usually weight savings).

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Fred's answer is exactly why I said that I do not recommend this minimization at all.

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duh Dr.D., I misread your post, i thought you were suggesting the true minimum based upon optimization of all the constraints.

need to read carefully

- #12

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the relation is d=[tex]\frac{N}{p}[/tex] where

d is the diameter of the gear

N is the number of teeth

P is the diametral pitch ( number of teeth per unit length )

the P for all your gears should be the same ( other wise it wont work) and you should have no problem finding the number of teeth

of course you should have already decided the gears properties i.e ( material, width, tooth type & number of teeth in your smaller gear )

all of thees things can be determined by revising the catalogs of the gear manufacturer, based on load, speed of rotation and temperatures

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