Microgeometry

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)


Much of my design work involves “math modeling” gearsets to determine the lowest-cost components which will meet the requirements. Over the years, a designer develops his or her own set of guidelines for what geometry is acceptable and what is objectionable. A group of gear experts may agree on eighty percent of a design and argue for hours over the remaining twenty percent. This is particularly so in the area of “microgeometry” — lead and involute modifications that help improve performance at the extremes of loading.

Software packages include sub-routines to suggest values for these modifications. Unfortunately, microgeometry requires a very strong understanding of what loading conditions are. Many times we do not have adequate data to support the assumptions we have to make. Pushing buttons on software input is easy; modern grinders make it possible to produce whatever shape the program asks for.

Sadly, this mechanization can compound the problem. We once got FOUR different revisions to a lead chart during an eight-hour period. The machine’s operator could be forgiven for being slow to implement the second and third changes. The lesson we took away was to spend more time reviewing assumptions, and agreeing on them, before pushing the buttons for modification simulation.

Sometimes the charts just “don’t look right” to the experienced eye. If this happens on your project, don’t get angry. Instead take the time to review with the commentator why the assumed load conditions would result in the shape shown on the chart. If you can’t convince them, you might want to take another look at those assumptions.

The beauty of computer simulation is that you can consider many possible configurations in a short period of time without endangering the precious physical parts. The ugly side of computer simulation is that it is so easy to input faulty assumptions. The old adage — “garbage in, garbage out” — still applies. Spend the time needed to understand and verify load conditions before pushing those buttons.

Feedback and Comments

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)


We are starting our second year of this blog and are pleased that it was named one of the Top 50 Design and Development Blogs on the Internet. Only #48 on that list but it is a big Internet and we are the only gear-oriented blog mentioned. Most of the credit belongs to the magazine’s searchable archives, in my opinion. The blog is just the gateway in.

Our initial hope was for the blog to feature an active comment stream. Unfortunately this plan has been ruined by spammers posting inane remarks with links to their scams. We have had a few legitimate comments that I will respond to here.

Matt Poulter asked about Stress Coat. When he Googled it, all that came up was an additive for tropical fish tanks. Now sold under the name StressKote (one word), Stress Coat was/is a brittle spray-on coating for use in testing castings and fabrications. Back in the Dark Ages, before Finite Element Analysis (FEA), we had to apply Stress Coat, load the part up statically, and “read” the cracks in coating to properly orient the strain gages. If you are doing development work scientifically, you still need to do these things in parallel to your FEA work. Without real-world modeling to back it up, FEA might be just pretty pictures.

Robert B. Price noted that he uses reverse engineering to replace damaged or missing parts on 1901-vintage motors. Many restorers and modelers face this challenge — the older the machine, the bigger the challenge becomes. As noted in earlier postings, gear geometry didn’t even standardize on the involute tooth form until 1921. Mr. Price’s motor could have had cycloidal teeth in any number of “systems.” To the casual observer, once the restored machine is up and running, the use of “modern” gears would hardly be noticeable. To an expert like Mr. Price, however, it would be an irritant worse than squeaky chalk in the lecture hall. Oh, wait a minute; some of you may not have ever suffered through an actual chalk-on-blackboard lecture. Perhaps a better analogy would be wearing an Alabama Crimson Tide sweatshirt with an Auburn University hat. It just doesn’t work for high-end restorations.

Both commenters raised topics that might merit further coverage in the blog or the magazine. If you have comments, please don’t let the spammers scare you off. We read all the comments and will respond in the blog. Editorial suggestions and contributions are best handled via e-mail. We enjoy hearing from you.

Trust, but Verify

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)


Lest you come away from my last posting thinking I am completely trapped in the past, I’ve invested a fair amount in new software during the past few years, and have been trying hard to learn to use it. My “inner curmudgeon” has good reasons for being skeptical of change, so I have to do some things by both the old method and the new before completely letting go.

Sometimes my reluctance is informed by my own ‘horror stories” — as described in the previous blog. Other times it is based upon stories told to me by someone else. Our trade has a long memory, and it is important for those promoting “new things” to understand why certain “prejudices” are widely held.

Let’s start with some market sectors still skeptical of surface-hardened gears. It may come as a shock to those who have never built a device with “soft gears,” but few American suppliers offered carburized gears until the early 1990s. Europe fully embraced “hard gears” more than two decades earlier, and they saw the oil patch in particular as a market ready for change during the 1980 oil boom.

The classic “horse head” pump-jack gearbox had evolved into a commodity product with “soft” lower-quality herringbone gears and standardized interface dimensions. Converting to “hard” gears offered weight and cost savings; the resulting prototypes were way different from the existing drives. Where a herringbone box was the size of an office desk, the carburized box was the size of a suitcase — almost comic with big shaft extensions sticking out both sides. The rating calculations said it would work, and brave customers quickly put them into service — but not for long.

The horse head pump applies an impact load to the same teeth every cycle. The old herringbone units had the same durability rating as the carburized models, but the strength ratings were 50% higher. Teeth started popping off the “hard” gears within weeks of installation, and old oilfield hands have never again trusted “hard” gears.

Once the carburized gearboxes were redesigned to equal the herringbone strength ratings, they lost their cost advantage and much of the weight reduction. They are great pump-jack gearboxes, but still have to overcome those negative attitudes.

I would never want to go back to through-hardened gears; the advantages of modern, carburized designs are just too great when operating conditions are properly analyzed. As President Reagan was fond of saying: “Trust, but verify.”

Questioning New Techniques

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)

In my last blog I mentioned the great analysis tools available to today’s gear engineers. On a current project, we are eagerly awaiting the finite element analysis (FEA) of a critical part that was designed using far less-sophisticated methods, going back 40 years.

It would be a great surprise if the FEA reveals any hidden flaws. Without going “full-curmudgeon” on you, I have been disappointed in FEA many times, beginning with the first FEA course ever offered at my engineering school, back in 1974. Our instructor, a newly credentialed PhD, brought FEA technology with him. It had been the topic of his dissertation and he was an evangelist for this method of stress analysis.

Unfortunately, the computers of the day were far less user-friendly. They weren’t as powerful, either; and between that, the dial-up/phone cradle interface and monochrome 10-inch monitors, the class struggled to get simple homework assignments done. We wondered if the box of punch cards the professor had brought from his previous school had been scrambled at baggage claim. By semester’s end, we barely managed to get a tri-axial stress on a cube to run.

My plan to impress the supervisors who were paying my tuition by using FEA on some fabricated steel housings went up in error messages. It was up to Stress-coat and hydraulic jacks to back up the manual calculations derived from Omar Blodgett’s classic book, “Design of Weldments.”

Fast-forward 20 years and computers were finally up to the task of analyzing a full housing — in color and on a big monitor. We couldn’t afford our own installation, of course, but an important project had the budget to sub-contract the FEA to the local experts. It was almost engineering porn to watch the colors change as the housing model was checked for various loading conditions. The only drawback was that the FEA work took so long that the patterns had to be revised twice to incorporate the results.

But even this “improved” FEA experience turned out to be a disappointment, as the housings were later found to be cracking in areas that FEA said were “very low stress.” The usual finger-pointing took place on whether the FEA, design, or foundry practices were to blame.

But I came away skeptical of any design based upon colorful pictures.

Hopefully this latest incarnation of FEA will convince me to fully embrace the 21st century.

Studying the State of the Art

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)


A few years ago I presented a paper on reverse engineering at the AGMA Fall Technical Meeting. I heard through the grapevine that some folks were offended that “piracy” should be celebrated in such a prestigious forum. Reverse engineering is, and always has been, an important part of design engineering. In my opinion, to call it “piracy” is an insult to the great men and women who built the foundation of our trade.

While there are occasional instances where intellectual property rights have been violated, the majority of reverse engineering is done to keep old machines and process lines running. There is a huge amount of equipment for which parts and technical support simply does not exist in a timely manner. A sheet metal processing plant is not going to stop operating because an input shaft broke and the original equipment manufacturer wants 12 weeks to make a new one.

Another important aspect of reverse engineering is determining the “state of the art.” We are fortunate enough to live in a Golden Age of gear design. We have the machinery capable of routinely making parts which were once available only to front-line military equipment. Our computer capabilities are better than those that took us to the moon. Raw material quality and heat treat processing are better than ever. But if we don’t design our machines to fully utilize those capabilities we put our jobs, our companies, and our customers at risk.

When you consider the investments made to produce the material and equipment available, you have to be embarrassed when you make a crude or inelegant part. Every pound of material deserves to be made into a work of art; it is our job as designers and engineers to strive toward that goal. The first step, in my opinion, is to understand what is currently being done in your product area.

A side benefit to this situation is the pressure to make sure your own work will withstand study by your peers. There are no “gear cops” who will raid your plant for an aggressive interpretation of the rating formula, but your competitors will be happy to point it out to your customers. The American Gear Manufacturers Association was founded to rein in “outlaw” gear makers whose rating claims were putting the whole trade in a bad light. This “trust but verify” atmosphere has served our industry well because everyone benefits.

Do You Know Your Design DNA?

Design DNA

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 things I enjoyed about the gearbox repair business was the opportunity to study the design strategies of so many different companies, both foreign and domestic. Products made five, ten, even thirty years apart would have many similar design features. This proves the power of “design DNA” — of adopting a set of design rules to insure quality, performance, and manufacturability.

Features like bolt circle combinations, seal configurations, and minimum numbers of teeth may not seem important to the non-designer,but selecting them in a vacuum can really slow you down. Design is a lot like commuting in that every time one driver makes a decision it impacts every other person on that route. Quality decisions take time; this is why having some decisions “pre-programmed” is so important.

Sadly, some people adopt a set of design rules without even realizing it; as in building it into their computer programs and forgetting about it. Others stick with rules that are made obsolete by changing technology.

If you aren’t sure about your company’s “DNA,” ask around; read the project notes on product development, and, if needed, reverse engineer your own product.

What if you don’t have “company DNA”? That is where learning from others comes in. AGMA offers some outstanding seminars by well-known consulting engineers. Every issue of Gear Technology contains important articles on how other engineers make design decisions. If you have decisions to make, the Gear Technology data base is fully searchable and available 24/7 — all over the world. Make your own reference binder; you’ll be happy you did.

It is Nagging Time Again

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 posts of this blog encouraged participation in AGMA’s Fall Technical Meeting (FTM) “paper” program. Our magazine reprints many AGMA papers and, increasingly, from other international technical conferences. Without people stepping up to write and present papers, we will run short of content.

For 2015, the FTM abstracts will only be accepted electronically. Applications for this year close on January 15. I am taking a year or two off after presenting my fourth paper last year. Through this blog I offer coaching services to anyone who wants to submit an abstract this year or for 2016. We as an industry need new people up at that podium. It isn’t as difficult as you think and the long-term benefits to your career will be worth the effort.

Your topic doesn’t have to be groundbreaking; for example, new approaches to common problems are welcome. Proprietary information and “sales pitches” are not. If you’ve worked hard on understanding a particular area of gear technology or manufacturing, this is a great way to share the wealth. Has your company invested in new machinery, such as water jet cutting or wire EDM, and applied it to gearing in a unique way? Why not use FTM to alert potential customers? Have some advice on material selection or lab results you can share? This is the way to get the discussion started.

The AGMA website (www.agma.org) has instructions on submitting an abstract. For those not in a position to present a paper there is an ongoing need for people to help with peer reviews.

If you’d like some coaching on your paper, please contact me via e-mail (gearmanx52@gmail.com). There is no charge for this service, although I do expect you to “pay it forward” in the coming years. We all benefit from an engaged and well-informed gear community. Gear Technology has been dedicated to that goal for over 30 years.

It’s All About Context

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)


I was one of those kids that loved reading the dictionary to learn new words, and that interest has continued into my golden years. The gear trade has its own unique lexicon of terms, as does engineering in general. One of the cool things is the different meanings words take on due to their context.

This came to mind in church Sunday morning when we sang a hymn about being “free from sin’s alloy.” Like most of you, I am a big fan of alloys since we learned over the centuries that “pure” metals are weaker than those with the proper recipe of additives. While theologians and jewelers might think purity is a desirable goal, we mechanical engineers prefer the higher strength of a well-tested alloy.

Another word that needs context is “stress.” It can be just a point of emphasis or a deadly combination of events in your personal life. We engineers realize it is everywhere there is a “load” and work hard to quantify it, measure it, and make sure it is less than the “allowable.”

No wonder our “civilian” associates think we are a strange breed; we do speak a different language and have a much different view of the world. The smarter ones appreciate that without inquisitive tinkers, scientists, and engineers they’d still be beating their clothes against rocks in a stream.

At Marquette University, where I attended, there was a longstanding but good-natured joke war between the engineering and business administration schools. Several times a semester, mimeographed (boy, am I dating myself with that) “newspapers” would appear in the school’s lobbies with humorous shots at the other group. I have kept some of them for over 40 years and still find them funny.

Any of you have a favorite engineer/accountant/salesman or even lawyer joke you want to share? Send it to us and I’ll see that it gets into a blog posting.

Another Year Passes

2015 Happy New Year Strands Line Glow Dark Background

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)

As a child, I was usually disappointed with New Year’s. Even if I managed to stay awake until Midnight, it was still the same old life, the same lousy winter weather, and the same re-start of school at 12:01 AM as it was two minutes earlier. I am slightly less disillusioned these days as I realize the “magic” of New Year’s depends upon how much effort you put into it — much like New Year’s resolutions, I guess.

If you just go through the motions, don’t really commit yourself to the effort, no real change can or will take place. Last year, about this time, the idea of writing a Gear Technology blog was proposed to me. It seemed like a good way to get some name recognition, so I quickly agreed. We’ve been at it two or three times a week since then.

Not every posting has been memorable, but overall I am proud of the first year’s effort. It is difficult to come up with something topical twice a week; even tougher if you want it to be witty and of interest to the gear community. The second year won’t be any easier, but I look forward to the challenge.

What does any of this have to do with you? You probably aren’t writing a blog, but you, too, will go back to work after the New Year with challenges. Whatever your assigned duties are, I’d like you to stretch a bit. Work on your “name recognition” within your firm — and outside it too. Pick some task or activity where you think you can contribute just a bit more. Pick up a new skill. Volunteer for some training. Whether it is learning to estimate, mastering a new order entry system, or becoming a Scout leader, make a change in 2015. You’ll be glad 365 days from now.

Anticipation

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)

 

A lasting memory from childhood is how long it took for future events to occur. We started looking forward to Christmas when the Sears catalog arrived in late October, and it seemed like forever until the Big Day finally arrived. The same thing happened with summer vacation, except there was no catalog to moon over.

Time seems to speed up as we age; now the months fly by like some 1940s movie technique to alert the viewer to a change in time. Our family does not have any youngsters around at the moment, so the year-end holidays have been somewhat dull of late.

That doesn’t mean we aren’t enjoying the holiday decorations and celebrations, though. Instead of an early start on gift opening we’re sleeping in and watching favorite movies late into the night.

I prefer to think of it as recharging our batteries for a big 2015. Hopefully you have enjoyed 2014 and are already full of plans for a better new year. Holiday “down time” is a wonderful opportunity to anticipate the exciting days ahead. As Momma used to warn, “Anticipation is greater than realization.”

Or is it?