Taking Hold with Hydraulics

April 01, 2007

Hydra-Lock has a long history of manufacturing custom-designed hydraulic workholding and toolholding devices that are constantly evolving to meet its customer's needs.


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For over 60 years Hydra-Lock Corporation has been the leader in hydraulic work and tool holding. We are the originators of hydraulic holding and have continuously developed new and innovative hydraulic holding concepts.

It all started with our Class “A” style of arbors and chucks. This solid steel construction is the most rigid of our three classes, allowing for maximum accuracy. Fulfilling the industry’s request for a hydraulic device demanding greater expansions, Hydra-Lock developed its Class “B” style of arbors and chucks. This precision holder uses a split steel over nylon construction, enabling the unit to achieve greater expansions than the Class “A” style.

Through continuous research and development, Hydra-Lock then developed its Class “C” holder. This style uses a special patented plastic material offering good memory, a high coefficient of friction, and excellent wear characteristics. This product is primarily used for thin-walled parts which are out of round. It has the ability to hold the part, averaging a center throughout the expansion or contraction range, without rounding it up. In other words, it conforms to the shape of the part, thus giving it its name, Conform-A-Arbor and Conform-A-Chuck.

For illustrative purposes, suppose a part bore had an out of round condition of .010. Hydra-Lock would design and build a Conform-A-Chuck that would contract on the outside diameter of the part. The Hydra-Lock Chuck will conform to the out of round condition on the outside diameter while averaging the center. Hydra-Lock guarantees that after the part bore has been machined and removed from the chuck, the bore will be out of round by only .003. What has happened in this instance is the Hydra-Lock chuck has taken out approximately 70 percent of the out of round condition on the inside diameter.

The next stage in obtaining a “round” part would happen by placing the machined part’s bore with an out of round condition of .003 onto a Conform-A-Arbor. After machining the outside diameter of the part, it is guaranteed that the Hydra-Lock arbor will have taken the out of round condition on the outside diameter to within .001. A simple way to determine what your out of round condition will be after using our product is to multiply your out of round condition by 30 percent. This simple formula applies to the out of round condition on the diameter that Hydra-Lock’s Conform-A-Product is locating on. In a normal chucking application, the chuck would squeeze the part “round.” Therefore, after machining, the part will “spring” back into its original out of round condition because of its thin-walled condition, thus rendering the part out of round, of which, certain applications call for.

Other applications that require conformability also create a demand for this uniquely manufactured material. For example, when a customer is in need of locating on a pitch diameter of a spline, we can still conform to the part shape by placing our patented sleeve under a split fulcrum sleeve, mimicking a customer’s involute spline data. By using our Conform-A-Product with this type of design, we are making the outer splined sleeve conform to the shape of the part. The idea behind this method involves using two sleeves to accommodate the customer’s request. We first design and build a basic Conform-A-Arbor that has our patented sleeve, which does the conforming process. We then design and build a splined sleeve matching the customer’s involute spline data, which allows for clearance between the customers’ part and our splined sleeve. By combining these two sleeves over our case-hardened body an expanding, conforming, pitch diameter locating arbor is created. While the need for conforming has been resolved in using our conforming sleeve design, we can still achieve a customer’s request by placing a differently configured sleeve on top of the conforming sleeve to give the arbor its dual purpose; to conform and to locate on the specified bore. What is ideal about this design is that the conforming sleeve is protected by an outer sleeve, keeping it free from wear and tear. The outer sleeve is of steel construction, allowing for longer life of the arbor before it needs to be resurfaced or replaced. Another benefit of this design is that the expanding arbor has many replaceable details. The detail most vulnerable to wearing out is the outer wear sleeve, which can be replaced or repaired. The typical repair of this split, splined sleeve usually involves adding material to the sleeve and then regrinding the sleeve back to print specification. In certain situations the sleeve is worn so badly that it is scrapped and a new sleeve is manufactured for the arbor or chuck. Again, what needs to be stressed here is the fact that the rest of the arbor is left alone, keeping repair costs to a minimum. These conforming arbors, used in production throughout the country and the world, have been a proven success for Hydra-Lock Corporation.

Another feature that we typically use with our Conform-A-Product is a retractable stop feature. This design aspect allows for the part to be loaded onto the arbor stopping on a solid, qualified stop. This stop feature provides a common indexing point for machining, using the same linear relationship for each part. After the arbor is expanded and is locating the part, the retractable stop moves out of the way by use of a secondary hydraulic system, typically supplied by the machine’s hydraulics or an added, air over oil hydraulic pump, which pulls the stop feature out of the way of the part. This enables the customer to turn each face of the part and grind the outside diameter. Essentially, the part is completely done with regards to the machining process, with the exception of the inside diameter. This method has given many of our customers the ability to do three different surfaces on their part while never letting go, hydraulically speaking, of the part. This helps to improve their T.I.R. of the part by using our hydraulics, which is putting the part on its own natural center. By doing the machining of multiple surfaces while staying expanded on the part, the part is guaranteed to be finished at what we hold our conforming device to be held at. Our typical guarantee is .0005 T.I.R. of an inch for Conform-A-Products. This means that the locating surface, the stop surface, and the mounting face and diameter are guaranteed to have a total run-out to each other within .0005. In addition, we can offer .0002 T.I.R. of an inch for splined expansion and contraction devices.

One recently patented development that has taken Hydra-Lock Corporation to a new level was made recently by a customer’s request to conform to the part shape and expand even greater than our traditional Conform-A material. This product use is ideal for rough castings—i.e. cylinder liners—for machining ID and OD bores. It has the ability for movements of .250” or greater, putting it in a class of its own. This style will average center with minimum distortion, allowing for machined surfaces to be parallel in the free state. The same idea of conforming is still here, but with an internal design that allows these sleeves to move in a linear direction without leaking past our internal sealing system. This gives our sleeve system the ability to grow and expand with ranges that have been unattainable with conventional hydraulic expanding devices.

What needs to be remembered throughout this article is the fact that each application is different. Our engineering staff looks at each application and perhaps recalls common situations or designs that may have similar traits, but each design and job has its own unique element. By looking at each situation independently, we can give our customers the personal touch that many of our competitors don’t have, simply for the reason that our materials used in the conforming process are very complicated and difficult to work with. We take pride in the fact that, with many companies, we are the single-source supplier for this type of application. Whether that operation is turning, grinding, boring, honing, or anything else, we can provide the appropriate design to accommodate the customer’s needs and requests with a Hydra-Lock Conform-A-Arbor or Conform-A-Chuck. We’re confident that, if you have a problem with holding your part or tool, Hydra-Lock will be the company to solve it.

About The Authors

Sean Cresent is the sales engineer at the Hydra-Lock Corporation. To learn more about the company’s capabilities call (800) 634-6973, send e-mail to weholdit@hydralock.com. or visit online at [www.hydralock.com].
Robert Laube is the manufacturing manager at the Hydra-Lock Corporation. To learn more about the company’s capabilities call (800) 634-6973, send e-mail to weholdit@hydralock.com. or visit online at [www.hydralock.com].