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Need education in gears

Need education in gears

Need education in gears

We are an aerospace mfg/eng group, not experienced with gears too much.  We have a design (not aerospace) that will require some gears.  Wondering if there are some references, charts, etc that would help us decide on a particular tooth cut for a given radius?  Basically we have some 1" shafts that will run about 3" apart on center so we would need (2) 3" gears to get both shafts running in unison.  I am a little lost from there..  We can do the load calculations but I know there are standards out there.   

RE: Need education in gears

Start by reading a Browning or Martin or Boston Gear or other stock gear catalog.

Mike Halloran
Pembroke Pines, FL, USA

RE: Need education in gears


Optimizing gears is ultimately an exercise in compromise.  And readily determining the best compromise for a particular application is something that usually takes many years of experience.

The AGMA standards (such as AGMA A901-A92) have some excellent step-by-step guidelines and basic calculations on how to design a gearset and optimize it for different applications and operating conditions.  The AGMA design guidelines will help you establish basics such as face width, tooth size, materials and heat treatments, pressure angle, etc.

As a first step, I would recommend doing a basic layout of your gears, shafts, housings and bearings.  This will give you an idea of the space available for bearings and supporting structure.  With highly loaded, small diameter  gears it is often difficult to find enough space for adequately sized bearings.

Good luck.

RE: Need education in gears

Gear design is part science and part art.  Factors like speed, torque and noise can not be ignored.  Some "good" designs can not be built in volume due to cost issues.

Don't forget, if you are using helical gears and applying a "significant" amount of torque, the gears will want to force themselves apart, possibly distorting the shafts or the even the case sides that the shafts are mounted in.  (I have seen it.)

RE: Need education in gears

Unless there are compelling weight or space constraints, or more significantly, a  substantial production volume, your concerns should concentrate on providing plenty of margin to keep all stresses generously low.  If you can tolerate the noise, spur gears are almost always the simper choice.

This sounds like a timing gear situation.  Is it possible that your needs could be better served by a timing belt drive rather than gears?  That choice eliminates gear lubrication as a potential source of problems.

My modest experience working for a gear drive manufacturer left me with a deeply held appreciation of how very much gear drive design depends upon judgement based on extensive practical experience.  How to interpret what really matters in the needed balance of design parameters for a particular application is not readily revealed by the ever-necessary computations and some generalized guidelines.

I trust that you are planning to purchase manufactured gears, and you are just seeking help for the selection process.  If you are contemplating manufacturing your own gears with the modest experience that your posting suggests, you really should reconsider that choice.

Valuable advice from a professor many years ago:  First, design for graceful failure.  Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs.  Only then can practicality and economics be properly considered.

RE: Need education in gears

Let me share this, but I apologize if it is too late.
I ever made a thorough calculation about sizing and selection for Chains and Sprockets based on ANSI standard using "Machinery Handbook 27th edition" and catalog of chain&sprocket as a reference.
I use example problem in the end of Transmission Chain part of Chapter "Machine Elements", and it is suitable for my calculation need
(using power to be transmitted, shaft diameter and rpm, countershaft diameter and rpm, and center distance as input data).
I think there is also calculation on gearing according to American standard in Chapter "GEARS, SPLINES, AND CAMS" of handbook I mentioned.


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