All posts by Charles D. Schultz

Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Where Do Allowable Stresses Come From?

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

One of the most important aspects of a gear rating standard is the allowable stress charts. For spur and helical gears we want to calculate durability and strength ratings for a wide variety of materials and heat treatments, so the charts have gotten large and require many footnotes.

AGMA and other standards agencies work very diligently to keep commercialism out of technical matters. All proposed changes are scrutinized by a broadly based committee of engineers from AGMA members before being adopted as part of the standard. Completed standards are then submitted for membership comments and approval. The objective is to deliver a reliable methodology for making gears that will meet industry expectations for performance.

Unfortunately, the allowable stress values cannot be directly derived from the material properties you would test in a metallurgical laboratory. There is no formula for taking tensile, impact, or other physical test results and calculating an allowable contact or bending stress allowable.

The values shown in the charts were negotiated over the years based upon committee member input and their field experiences. The process has been compared to making sausage; you don’t always want to know what goes into the sausage but as long as it tastes good and no one gets sick we come back for more sausage.

This situation frustrates companies that would like to use new materials, but protects the general public from untested products. All AGMA standards include language that permits the use of alternate methods and procedures — provided the design is properly tested. The “standard” methods represent the consensus of the best engineers in the trade and hundreds of years of collected experience.

On the Helical Gear Rating Committee we jokingly refer to the area beyond what the standards endorse as a “Land of Dragons.” Brave engineers can go there if needed. We enjoy hearing the tales of the survivors of those journeys and use them to redefine the borderline to Dragonland when the standards are revised. If you are one of those survivors your input is welcome at the AGMA committee near you.

 

Great Moments in Gear Rating

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

By now readers of this Blog are aware of my interest in gear trade history. The more I learn about how we got to this point in our understanding of gears, the more I want to know. Part of what I miss about going into the office every day is the opportunity to talk about gears with others; hence the motivation for writing this Blog.

A long-term project is to assemble a timeline on gear rating methods. As it turns out, I was “in the room” when the most recent “big change” was made in the general helical and spur gear standard. Had I been more aware of what was going on, I should have taken better notes and gotten more explanation from the experts on the committee. Sadly, many of those leaders are no longer available for interviews.

So I’m reaching out to our readers for help in developing this timeline. If you have old rating standards, domestic or foreign, that you can share, I’d love to have a copy. If you have correspondence or stories about gear rating, those would also be helpful.

Eventually I hope to publish the timeline along with the calculated rating of some reference gear sets or gearboxes at different points along the way. Any help will be greatly appreciated and publicly acknowledged.

Action Items for the Gear Trade

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

Recently I learned that it took over 20 years for the gear industry to agree on its first “standard” tooth form — and that was after spending 25 years experimenting with alternative forms. We have been using a reprinted magazine article for the rating of splines for almost sixty years. Despite the high interest in epicyclic drives for wind turbines, we still don’t have an AGMA rating method for the bending strength of internal helical gear teeth.
One was first proposed in 1953!

We are making progress on the internal helical gear bending strength; look for it to be included in the next version of the basic gear rating standard, perhaps as early as 2015. A committee was formed to develop a spline rating standard several years ago, but progress has been slow. With the amount of splines used in machinery and vehicles, this topic should be getting more attention. Perhaps the method reprinted in Machinery’s Handbook is all our designers need.

Standards development is a collaborative effort and reaching consensus takes time. Gone are the days when a single gear company could take on a major “science project” and share the test results with the rest of the industry. We need to identify topics that deserve study and find ways to get the testing done.

We sincerely appreciate the increased activity in the comments section and hope to make this blog more of a two-way street. Let’s use this forum to develop a things-to-do-list for the next generation.

PS: Anyone have drawings of the finger gears used in the famous Hulet self-unloaders? I want to reference them in my upcoming Fall Technical Meeting paper and would prefer to show an actual drawing rather than a sketch based upon my memory of making spare parts back in 1981.

PPS: A completed word search is attached; hope you enjoyed hunting for those (50) gear terms.

Answers to Word Search

Limited Opportunities for One-Trick Ponies

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

When you work as an engineer for smaller companies you get to wear a lot of hats. Whether it was an emergency structural repair — snow causing a roof collapse right over a parked crane — or the owner’s latest idea for an invention — don’t ask — the company “engineer” is expected to have an answer. Once you get over the fear of total and complete failure, these unexpected challenges can be educational and fulfilling.

Our profession has not always been as specialized as it is today, so it was accepted that management expected this versatility. A steamship foundering mid-ocean couldn’t wait for an expert to helicopter in to fix a ballast pump or patch a hull leak.

In the same January 1912 issue of Industrial Engineering that published Percy C. Day’s article on herringbone gears, we find a paper by Sterling H. Bunnell on “Expense Burden: Its Incidence and Distribution.” Yes, in 1912 engineers were expected to be informed and involved in financial decisions as well as technical ones. To quote Mr. Bunnell:

“The engineer must now master the problems of financial operation, the principles of estimating correctly and providing for fixed charges, as well as operating expense, and all the other details of accounting required for the continued successful operation of the enterprise.”

Not exactly the cruise most of us signed up for! But keep in mind that the professional engineering exams place equal value on the “engineering economy” questions as they do on the stress analysis ones. More companies fail due to unsustainable overhead rates than due to product failures. Today’s complex world economy makes controlling production and development costs as important as being on the cutting edge of design.

Another point Mr. Bunnell makes is that not everything that can be done should be done. Management and your co-workers need your honest appraisal of whether a policy, practice, or investment is in the best interest of the company. Would Commander Montgomery Scott ever tell Captain James T. Kirk that something “wasn’t his job?” Certainly not, if the fate of his beloved Enterprise was at stake.

After all, while he wasn’t a miracle worker, he was an engineer. And that was usually enough.

           

 

Lost Technology

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

floppy disks

Writing this Fall Technical Meeting paper has me digging through old files for references I am certain are in there some where. Of course I am finding many things I had forgotten about and this is not helping me get things done in a timely manner.

Amongst the treasures unearthed was a box of 3.5 inch floppy disks and a few of the earlier 5.25 inch versions as well. Some of my younger readers may not have ever seen or used floppy disks but there was a time when they were the cutting edge of computer technology. For engineers of a certain age, our first “network” was the “sneaker network,” as in lace up your shoes and run this disk over to NC programming or accounting.

Anyway, I have several boxes of 3.5 inch floppy disks I can’t bring myself to discard. The programs that used them are around somewhere and, who knows, if the zombie apocalypse really happens I may be the only guy left who can still boot up a 2-D CAD program. My secret weapon? A portable floppy disk drive!

And just to prove it still works I provide today’s special diversion: a Gear Technology word search. These came in very handy back in the day while waiting for the sneaker network to respond. We’ll publish the solution in a later posting.

Gear Word Search

The Beginning of Wisdom

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

agmalogo

An old proverb posits that “The beginning of wisdom is calling things by their proper name.” In my previous posting I brought up the need to identify the meaning of the acronyms when you cite them. Our trade has many names for the same “thing,” and where you first learned something may affect what you call it.

AGMA has a nomenclature committee which develops definitions, symbols, and terms for use in the standards. They also coordinate with ISO to insure that our standards can be understood around the world. It is a testimony to the fine work these people do that we have a thriving international discussion of gear technology without more disagreement over what certain symbols “mean.”

It hasn’t always been this way. I have a 1972 copy of H.E. Merritt’s Gear Engineering that is tricky to use because of the different Greek letters used for key angles. I have to constantly convert formulas and keep a “cheat sheet” in the book to remind me.

I mention this topic in conjunction with earlier exhortations on teaching and mentoring. Make sure your pupils learn the common understanding of gear terms and can recognize non-standard usage when they see it. No matter what your “local dialect” is, they need to be able to converse with people outside your firm without having a translator present.

When AGMA first introduced software to rate gears according to ISO 6336, they held training sessions around the country. I was able to attend the class in Chicago and was embarrassed for some of my classmates. They knew “gears” in their local dialect but were unable to accurately fill in the input forms because of nomenclature differences.

This isn’t a new situation and it isn’t easy to resolve. AGMA and ISO are doing their part to make the standards consistent. No one is going to go back and revise all those cherished reference books. You can do your part by making sure our “newbies” learn to call things by their proper name.

Frequently Asked Questions (and Other TLA or FLA)

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

The advent of texting naturally leads to a desire for reduced typing. I like websites that have a “Frequently Asked Questions (FAQ) tab as it shows an interest in making newcomers welcome. The gear industry, like many others, has built up its own “lingo” that can baffle neophytes. I understand the Federal government has a manual devoted to the development of three letter acronyms (TLA) and four letter acronyms (FLA) to speed communication.

Even the TLA for four letter acronym points out the problem of confusing some people while trying to help others. I am sure the Florida tourism folks thought they had “dibs” on that particular three letter sequence. My wife and I like to think we are savvy travelers, but find ourselves baffled by some of the TLA and FLA on those oval-shaped decals on various rear windows. (And don’t get me started on the stick figure families, either.)

The Federal manual no doubt tries to avoid permitting scandalous language, a task made all the more difficult by our rapidly changing texting scene. Case in point: the Wisconsin Tourism Federation woke up one day after 25 years with a pressing need to rename their organization.

The situation in the gear industry is complicated by the different languages of our participating companies and the different descriptions we use for the same gear features. Somewhere in my files I have the valiant attempt of one group to assemble a “cheat sheet” of gear terms and abbreviations in six languages. It is “incomplete” at six pages.

I know that I am not alone when my eyes glaze over (MEGO) at a jargon- and TLA/FLA-filled paper or specification. As I approach final editing of my own FTM (Fall Technical Meeting) paper on HCR (High Contact Ratio) gears, I will do my best to keep the reader in mind and explain the terms upon first use. The TDEC (Technical Division Executive Committee) will be recruiting peer reviewers for each of the papers, and if you are in a position to help, please do so.

We are open to your comments on any of these blog posts and encourage your questions on all things gear-related. Or as the young whippersnappers say AMA!

Hunting for an Argument

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

One of the first things I learned about gears was the importance of having a “hunting tooth” combination. This was not open to discussion. It was carved in stone in our gear technology handbook. I had no idea this was not a universally held belief until I found myself charged with designing new product lines and there was no gear technology handbook to lean on.

The available reference books had mixed advice on the importance of the hunting tooth; some saw no point in it, others agreed with my early mentors that it was as necessary as the blue sky. I decided to become a free thinker on this bit of doctrine and haven’t though much about it since.

As mentioned earlier, I bought a reprint of 1910’s American Machinist Gear Book, written and edited by Charles Hays Logue, formerly of R.D. Nuttall Company. Mr. Logue had strong opinions on hunting teeth, as expressed on page 31:

“It has been customary to make a pair of cast tooth gears with a hunting tooth, in order that each tooth would engage all of the teeth in the mating gear, the idea being that they would eventually be worn into some indefinite but true shape. Some designers have even gone so far as to specify a pair of ̒hunting tooth miter gears’ That is, one ̒miter’ gear would have, say, 24 teeth and its mate 25 teeth.

“There never was any call for the introduction of the hunting tooth even in cast gears, but in properly cut gears any excuse for its use has certainly ceased to exist.”

Strong words back in 1910. I think I would have enjoyed meeting Mr. Logue and talking about gears. His book covers a lot of topics and I am sure he rubbed some people the wrong way. Other prominent engineers contributed to the book, so he had friends, too.

The “hunting tooth” is but one of the design guidelines companies make. I’ve found some engineers were taught, for example, to never use helix angles over 15 degrees or 20 degrees. Others were shocked when they saw pinions with less than 21 teeth or gear ratios over 5:1. Now there may have been some logical reasons for that in certain circumstances, but over the years the underlying reasons were lost. Yet the guideline remained.

It reminds me of a story of Thanksgiving dinner being prepared by a multi-generational group of women. The chief cook, somewhere in the middle of the generations, was just telling the youngster present to “always cut off the last half-inch off the ham” before putting it in the pan. A junior member of the crew insisted upon getting confirmation from the oldest present. Great grandma scoffed at the idea. “The one time your grandmother helped cook the ham we had an extra big ham and it wouldn’t fit in the roaster.”

Just a reminder to you teachers and mentors out there:

Teach your children well. Don’t just give them rules. Give them reasons.

What Did They Know and When Did They Know It?

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

No, I am not launching a criminal investigation. The title of this posting summarizes my ongoing study of the history of gear ratings. Most of you are aware that the American Gear Manufacturers Association (AGMA) was formed in 1914 by a group of gear makers who were concerned that the outrageous claims of some of their competitors were endangering the good reputation they were working to have with their customers.

The gear trade has attracted some of the greatest engineering minds in history, but prior to AGMA there were no recognized standards for the things we take for granted today. Other “standards” groups pre-date AGMA because of their involvement with public safety. I will not go over the rash of boiler explosions, bridge collapses, and structure failures that prompted the need for better understanding of those fields of engineering.

A gear failure was unlikely to be life threatening in the early 20th century, but AGMA’s founders foresaw a day when it could greatly interfere with the conduct of their business. They didn’t start the association in a vacuum either.

Thanks to the Internet and modern technology it is possible to gain insight into the pre-AGMA days of the gear business. I just received a beautiful reprint of the American Machinist Gear Book, edited by Charles Hays Logue in May of 1910. Mr. Logue, formerly of R. D. Nuttall Company, set out “to make a book for ’the man behind the machine,’ who, when he desires information on a subject, wants it accurate and wants it quick, without dropping his work to make a general study of the subject.” His preface continues “Controversies and doubtful theories are avoided.”

As author and editor, Mr. Logue relies upon noted experts for help in sorting out the topics. Wilfred Lewis, George B. Grant, and Percy C. Day are among those quoted. Engineering books dating back several hundred years are referenced in the very readable text. Many of the diagrams, drawings, and charts were very familiar from more modern reference books.

So the preliminary answers to the questions posed in the title are:

More than we give them credit for.
And,
Certainly by 1910.

I look forward to making a detailed comparison of the 1910 rating methods and our 21st century procedures.

Dr. Faydor L. Litvin: 100 Years a Genius

Charles D. Schultz

President at Beyta Gear Service
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

Latest posts by Charles D. Schultz (see all)

The Gear Technology gang wishes to congratulate Dr. Faydor L. Litvin of the University of Illinois at Chicago (UIC) on celebrating his 100th birthday in January. We had hoped to interview this distinguished engineer, inventor and author for a more in-depth review of his contributions to our industry, but have just learned he no longer entertains such requests.

Dr. Litvin began his UIC tenure in 1979 at the age most men retire, following a noteworthy life in his native Russia. Besides teaching and supervising over 75 graduate students, he continued to develop his gear theories and to publish books and papers that are widely used today. In Development of Gear Technology and Theory of Gearing (1997, NASA RP-1406), Dr. Litvin offered the following testimony to the hundreds of people who contributed to our trade without recognition. We at the Gear Technology blog share this excerpt from that preface in honor of Dr. Litvin’s centennial:

The history of developments in any area, including gear technology and theory, is the history of creativity, which has often gone unrecognized during one’s lifetime. The aspiration to create is a passion that enriches the life but requires unconditional devotion. Usually, creativity is associated with the arts (music, literature, painting), possibly because they have the greatest influence on our emotions. However, we do not realize the extent to which this passion conquers the daily activities of many in all levels of society. The desire of gifted persons to create is the driving force in their lives, bringing them joy and suffering and often no fame. For Fame, a capricious goddess, does not award in the proper time and may not award at all. My sympathy is for those who failed to achieve recognition for their accomplishments, and I share Dostoyevsky’s philosophy that suffering is necessary for spiritual achievement, but the price to be paid is sometimes too high. However, an individual who gives his heart to create should not look for fame. This was expressed with great emotion by Pasternak (1960) in his famous verse, “To Be That Famous Is Hardly Handsome”:

Creation’s aim—yourself to give,
Not loud success, appreciation.
To mean round nothing—shames to live,
On all men’s lips an empty sermon.

I sympathize with the heroes of Pasternak’s verse.

We at Gear Technology are thankful that Professor Litvin has been recognized for his achievements within his lifetime and encourage readers to become familiar with his writings.