Rigid, Accurate, and Dependable Workholding

Greater accuracies, faster cycle times, and better surface finishes are all byproducts of choosing the right workholding solution for gear production.

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As I sit down to write this article, I realize that in one week I will have spent 35 years of my life manufacturing and designing chucks. I began working here at Speedgrip Chuck, Inc. in March 1979, shortly after leaving the military. My first position here was as a machinist, working nights while attending college classes during the day.

Several years later I was asked to come into the engineering department as a detailer—later my responsibilities changed to being a designer, and now to my present position of chief designer for Speedgrip, Cameron, and Madison Face Driver.

I have seen great changes in my various positions here: from running numerous machines throughout the manufacturing process; to drawing on the board for several years; to the transition of 2D CAD use. Today we have very powerful 3D CAD, FEA, and simulation software used to design our chucks.

Every day we receive new applications for which to review and design workholding solutions. The typical request for a quote will include a part print or a part CAD model, information on the machine spindle, drawbar connection, any envelope or weight restrictions, and a description of the machining operation: forces, accuracy requirements, special loading or chip clearance needs, part sensing, etc.

One of the first things I will do as a designer is to check our past designs. Speedgrip has been in business for more than 60 years, and all our engineering drawings are in electronic format. Not long after coming into the engineering department, I realized the need for a naming system for our chucks, a categorized nomenclature system to provide better access for this library.

I drew upon my experience in the U.S. Army. The military has a unique part number for virtually everything they use. From bullets to Band-Aids, there is a unique number that describes pretty much everything you can think of.

Speedgrip’s chuck nomenclature system has 24 actuation types, 34 chuck mechanisms, 10 size ranges, 37 special chuck features, and 25 operations each option representing a chuck configuration. If there were an entry for every possible unique nomenclature entry, there would be 279,276,000 unique chucks (we include space in our system for two different special features in the nomenclature).

As a designer, one of the first things I do is to check with the customer for reference design and then decide on an acceptable “ballpark” price. If one is reached, then I will enter in the nomenclature of the chuck required in this new application. If I find a good match, I will send the customer a picture of a chuck we have made in the past for a similar application, and I will give our sales department the reference chuck number for them to price.

Rather than starting from a blank piece of paper design, this takes a fraction of the time, and, especially for budgetary inquiries, it is sufficient. In any respect, even if the customer wants an actual design for their specific part, this is a good starting point, as they can look at the reference design, tell me what they like or don’t like about the design for their application, and even if I’m doing a full-blown design for a customer, the nomenclature search will very often give me a past chuck for a starting point in the new application, thereby saving me hours of work.

It comes as little surprise, therefore, that in the past 35 years, there has been an unending demand from our customers for higher RPMs, greater accuracies, faster cycle times, better surface finishes, easier loading, freer chip evacuation, and sealing. Through our use of 3D CAD, FEA analysis, and simulation software, we are able to design for requirements that we would have declined in the days of drafting boards, trig tables, and manual calculation.

This is really an exciting time to be a designer. I spend significant time each week running FEA studies on chucks, chuck components, and models of customer parts. I tweak the design, track the changes, and tweak it again until I can be very confident that the chuck will perform and to the customer’s requirements.

Our customers are doing amazing things, holding tolerances and finishes in turning, gear cutting, milling, and welding unheard of years ago.

The science of workholding has greatly matured in the last 35 years. Through software, and statistical methods, we better understand and are able to quantify the forces and stresses in our workholding mechanisms.

When people come to us for design ideas, they usually have preconceived notions of what we have to offer. The Speedgrip, Cameron, and Madison Face Driver companies are largely known for collet chucks, hydraulic arbors, and face drivers, but as I mentioned, we have 34 different families of workholding mechanisms in our arsenal. That’s 34 different distinct types of chucks. We’re not talking about just big collet chucks, little collet chucks, short collet chucks, long collet chucks, heavy collet chucks, or light collet chucks. We have 34 different mechanisms that we have manufactured in the past with which to address a new application that comes in the door.

I researched our past designs and redrew the chuck below on CAD. This is an early example of a push-on collet chuck. This was drawn in 1971, when I was still in high school. The three names in the title block: designer, detailer, and checker were all great mentors to me. I learned so much from these men, for they freely shared with a young man their wealth of knowledge and experience.

For the purposes of this article I have added some involute splines to the push-on collet. These are simple, relatively inexpensive (compared to an actuated chuck), very highly accurate, and adaptable to a very large variety of applications. The part, in this case a female gear, is loaded by sliding over the push-on collet, thereby compressing the slotted splined area. This tension holds the female gear being worked on very accurately (Figure 1). Specifications of repeatability of the chuck within .0002” (5µ) are easily attainable.

It features a simple slotted steel sleeve, manufactured a bit over the high tolerance limit of the part being held. Years ago we left a good deal of stock in the ID and ground it out by trial and error until we came up with the tension in the fit we desired. Today, using FEA software, we can eliminate the guesswork in the stress and tension in the design, and as a consequence are able to greatly expand the tolerance ranges the unit can handle.

These have been used for inspection, welding, transfer, grinding, centralization in combination with clamps or other chuck types. This is an example of a mechanism that has been around for more than 40 years, but seems to really be coming into its own today. We sell far more of these today than we ever did 30-40 years ago.

This next mechanism, a finger collet, is relatively new to the workholding world. We have developed this product in the last ten years or so, and its use is growing greatly as we explore new possibilities with this design (Figure 2).

This is a hybrid cross between a collet and a diaphragm. With extensive use of FEA software in evaluating the customer’s part and in the design of the finger collet, combined with a unique mechanism for actuating each finger independently, this design offers excellent non-rounding properties. Before our use of FEA software there would have been too many engineering uncertainties to custom engineer this type of chuck on a regular basis, but today we offer finger collet design solutions very frequently.

One plant manager, who is replacing many of his second operation chucks with finger collets, told me that he isn’t woken up by production problem calls in the middle of the night with the finger collets, like he is with other types of chucks. The finger collet in Figure 2 is used for a thin walled splined transmission part, in a turning application.

Our Cameron division, among other products, manufactures hydraulic sleeve style chucks, of which Figure 3 is an example.

This style chuck is unique among all other chuck types. The hydraulic sleeve expands similarly to a balloon to fill the part bore. Collet chucks, diaphragm chucks, jaw chucks—really most every other style of workholding device expands or contracts to make only line contact with the part bore. Under hydraulic pressure, the slotted steel sleeve moves to most accurately locate the internal or external diameter’s centerline. This method of gripping the part, gives very high accuracy, great rigidity, and as a side benefit, very good vibration dampening characteristics.

Our Madison division specializes in face drivers. Figure 4 is an especially popular design for hobbing application.

The sky blue detail represents the piece being hobbed. The hobbing machine tailstock (not shown) applies force thereby compressing the royal blue die spring until the yellow colored center detail lowers allowing the chisel points of the driver ring to embed into the end of the part (Figure 5). This is a simple but very effective method of holding a part for hobbing.

Earlier in this article, I mentioned that in the Speedgrip companies we have more than 30 different chucking answers to workholding problems that we have manufactured in our 60+ years history. In this brief survey, we have looked at snapshots of four of those types. From holding 60” jet engine rings, to small dental tools, from holding a camera to inspect radioactive waste in a tank; or water jet cutting outdated artillery shells; to holding a gear being forged at red hot temperatures; or a part being formed at white hot temperatures; the unusual applications we see motivate us to continually expand our capabilities. We are able to draw on decades of history, and this continual industry wide cross pollinization of new applications, and new solutions.

Your workholding supplier can be a great partner in coming up with faster production methods. More rigid, more accurate, more dependable workholding. Don’t be afraid to push the envelope. Ask us hard questions. We thrive on challenges.