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Posted by: bobthedog

04/19/2007, 10:34:09

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Based on the lewis formula using stainless steel at 30 000 psi

S = allowable unit stress for material at given velocity
L = Maximum safe tangential load at pitch diameter in lbs
Ss = allowable static unit stress for material psi
V = velocity FPM at pitch diameter
F face width of gear in inches
Y = Outline factor
P = diameteral pitch

S = Ss x 600
600 + V PSI


Now both this equations make sense but what is PSI thought that was the pressure in a car tyre isnt it? Is it a pressure measurement

Static torque capacity Ts = LXP.D
where P.D is pitch diameter in oz


What do they mean by pitch? Pitch of what??

It has face width 3/16 of an inch how is that worked out

how is 1/16 of an inch worked out??

The amount of this load distribution is dependent upon the contact ratio of the particular gears in mesh typical values are from 1.2 and 1.8 . 1.2 and 1.8 are the contact ratios but what does this mean exactly????


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Re: GEAR STRENGTH CALCULATIONS -- bobthedog Post Reply Top of thread Forum
Posted by: jboggs

04/20/2007, 17:46:10

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What does "---" mean? Is that the same as the divide sign (/)?

"PSI" is the units of S. Yes, its lbs per sq. inch. Same units as car tire pressure but in this case is an indication of the load applied to an area of material. You see typically something like 30,000 PSI as the YIELD STRENGTH of some steels for example.

I'm suspicious of their formula for Ts. Should be based on radius, not diameter.

And the "in oz" above is the units of torque, Ts. Stands for "inch-ounces".

What they mean by "pitch" is actually DP, Diametral Pitch. It is a unitless number that indicates the spacing of gear teeth around the circumference of the pitch diameter. The larger the number, the "smaller" the tooth form.

I don't understand your questions about face width. It is what it is. What do you mean "worked out"?

Contact ratio? The ratio of the arc of action to the circular pitch.

If you had problems with the basics of gear design, which it appears from your questions that you did, then I would recommend you stay away from any detailed gear form calculations until you understand the basics better. Get a copy of "Machinery's Handbook" or "Mark's Standard Handbook for Mechanical Engineers" and digest the sections on gear design thoroughly.

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