Maintaining Tolerances = Maintaining Your Workholding

As workholding gets more complex, such as these devices for 5-axis machining, proper use and maintenance become even more important.

Workholding comes in many forms, including clamps, chucks, and vises. While the most widely used are vises, which come in numerous shapes, sizes, and styles, all are designed to hold workpieces securely while being machined.

However, no matter what type of system you use, proper care needs to be taken during operation, maintenance, and storage to ensure long life and repeatability.

“The workholding device, no matter what kind, is a mechanical apparatus that requires proper care and maintenance. And, if it’s not properly cared for, it will not perform as desired,” said Mike Chester, technical services representative for Kurt Workholding.

Chester’s advice is simple: Create a maintenance schedule for each device, and stick to it.

“It’s very important to maintain these devices properly because you need them to last,” said Chester. “It’s similar to getting an oil change for your car every 3,000 miles. You cannot expect peak performance levels if you don’t take the time to perform maintenance.”

Know Your Device

Each type of workholding will have its own maintenance needs depending on the movable parts and material composition. Some workholding devices are hardened and some are not. If the device is not hardened, wear can occur from repetitive use only, for example on a screw or jaw plate. When this wear occurs, inconsistencies will begin to appear in the part.

The metallurgical makeup of the part also can affect workholding.

Certain metals can chemically interact with the metal of the workholding device.

“Dissimilar metals interacting with each other can cause wear on your workholding, and when you introduce coolant to the equation, it’s just another negative variable that is attacking the metal of the workholding,” said Chester. “It’s just the nature of the beast.”

The interior of a machine tool is a hostile environment. Coolant and chips will hit — and can become lodged inside — the workholding device. Paying close attention to part tolerances can identify workholding wear before scrap parts are produced.

Workholding comes in many forms, including clamps, chucks, and vises, and proper care needs to be taken during operation, maintenance, and storage to ensure long life and repeatability.

Always treat workholding like it will be used again very soon, said Chester.

“At a bare minimum, when you are done running a part, or even just at the end of a shift, you need to cycle the vise and clean it out,” he said.

Cycling the device simply means operating it at its minimum and maximum capacities.

“Cycling the vise is very important,” said Chester. “This allows you to push out any coolant or chips and make sure the device is working properly for the next job.”

The next steps should be to protect the device by lubricating it, covering it, and storing it where it cannot be damaged.

“Store it with the next user in mind,” said Chester. “The device should be ready to go the minute you take it out of storage. Doing this properly will ensure that the device isn’t full of dust, dirt, and debris when it is needed for the next job.”

Holding Tolerances

The most critical aspect of workholding is creating repeatability. Performing repetitive operations on parts while keeping the necessary tolerances is the function of any workholding device. If tolerances cannot be held, you will be in constant battle with the overall machining process.

The tolerance/repeatability equation can be solved with proper workholding use.

It is a good practice to become familiar with your device’s clamping forces. Too much clamping force could damage parts, and repeatable clamping pressures will help achieve better accuracy.

“If you consistently clamp a part with the exact same amount of pressure, the pressure points are going to wear evenly and you will get longer life from your workholding,” said Chester. “If you don’t have consistent pressure, you will get inconsistencies in your part and inconsistent wear on your tools.”

It’s also wise to avoid certain practices while clamping a part. When tightening a vise, for example, never use a cheater bar or hammer to strike the handle. This can damage the workholding’s internal parts.

One Part of the Whole

Understanding that workholding is a part of the production process as a whole also is important. Using the proper device in the correct way can reduce nonproductive time and chatter, while creating longer, more consistent tool life.

“Whether you are producing five parts or 5,000 parts, the last part that comes off the machine has to be as good as the first one. The ability to be consistent from part to part shows how good the process is and how professional the shop is,” said Chester. “It’s a direct reflection of your ability. If you want to maintain your reputation, you must be able to meet the necessary quality.”

Part of this ability can be augmented by training.

“It’s important to understand the effects that improper use and care of your workholding devices can have on the overall process,” said Chester. “Knowing the device, and learning as much as possible about its operation and care, will have a direct effect on the machining process, and on the company’s bottom line.”