Gears load 4

[Nashanas]

Hello everyone,

I have a very basic question about gear train design.

In this design, it can be seen that there is a set of 3 gears with same ratio, which are being used to move the bigger gear. I want to usa only one gear instead of three to move the bigger gear. But I have been told that 3 gears are used to reduce tooth stress. But according to Shigley, the delivered load from one gear tooth to another depends on the pitch, face width and material. If all these variables are same, I dont see any reason for using 3 gears instead of one, as the load delviered will remain the same.

 

[mfgenggear]

quote : CWB1 (Mechanical)24 Nov 21 01:38
Quote:
t is well know 3 points not four or more are best to stabilize objects.

Disagree, three points of contact is generally a terrible method of supporting anything. Stability is a function of the Cg's relationship to the supports. More supports/points of contact provide a larger/wider "footprint" and thus more stability, hence tables commonly having four legs, office chairs 4-5, etc.
as Hydtools stated this was taught in my apprentice days basic 101 mechanical inspection and tool making. and tool design, unless they are leveling feet

 

[RolMec]

3 pts of support: statically determined, you know where you are with the loading from basic mechanical calc.
4+ pts: statically indetermined, its more difficult to calc. or you build larger than strictly necessary. However: it is more stable, as the footprint is larger, there's a longer way for the CG to reach the next boundary (looking from above).

Roland Heilmann

 

[CWB1]

CWB1, don't tell toolmakers and fixturemakers that.

Nahh....most every decent toolmaker will swear the world is a limp noodle. I know many having grown up in the family job shop. One of the first lessons they learn is the relationship between rigidity, accuracy, and repeatability, and how materials flex and move from small amounts of heat and stress. I'm not one to support the old notion that engineers should spend years in the trades, but I'll be the first to say that trades often understand rigidity and deflection better than many engineers. In practice, three point mounting is pretty rare vs more.

 

[rb1957]

the difference between theory and practice ?

in theory three points are best 'cause they define one single plane, and if your points of contact can support "tension" loads then all is well.
But if your structure is "just" sitting on the ground, then four points would probably be best, particularly if they (or one at least) are adjustable.
Having more adjustment allows you to achieve a specific surface (independent of the ground plane).

another day in paradise, or is paradise one day closer ?

 

[Scuka]

There are times to use minimum constraint design (i.e. the '3 points of contact' philosophy), and are times when not to use it.

It's your job as an engineer to figure out which one to use in a given situation.

 

[David-T]

I think there are two reasons why people always think of 3 small gears.
1: In the same time, the small gears turn more times than the larger gears, each tooth work more and wearing more.
2: The small gear is more likely to failure due to its low tooth contact strength and high sliding rate compared to the bigger gears.

David
Mechanical project manager
JLFY technology company

Https://www.customized-tech.com