Whether for machining bulky workpieces, or in projects that require precision finishing in a production process or machining center, hydraulic vises and similar workholding systems offer a highly flexible and stable fixturing solution that speeds up work cycles and cuts down on waste.

In many situations, a machine shop simply cannot afford to apply traditional mechanical vises and other clamping devices to hold workpieces in place. Examples include tasks involving heavy and/or oversized workpieces that are difficult to mount manually, and to apply the necessary clamping pressure evenly and consistently, thereby risking movement or vibrations that result in scrap.

“In the past, one machine shop was having some difficulties machining welded beams that were perfectly straight – using a mechanical vise setup,” said Larry Johnson, president of Special Machined Components, a shop in Mason, Ohio. “Due to the size of the workpieces, mechanical vises were tough to load and control. I understand that they had to scrap quite a few of the beams during the first two or three months of production, perhaps 50 of them.

“However, at our shop, thanks to our hydraulic workholding system, I don’t think we’ve had to scrap 10 workpieces over a 12-year period, certainly a huge improvement over the mechanical vises.”

Special Machined Components began machining beams for heavy-duty vertical lifting systems in 2001. The lifting systems — which normally use four or six of these beams — are used to raise heavy vehicles like trucks, buses, and fire trucks overhead, for maintenance. Naturally, consistently precise machine finishing was required for every beam, each one of which needed to support from approximately 15,000 to 40,000 lbs., providing a total lifting capacity of 160,000 lbs.

The hydraulic workholding system that Johnson’s company installed in 2001 was a six-vise, stacked ProHold model manufactured by Planet Products. Some job shops use it for welding and riveting as well as machining operations.

One of the problems of using a mechanical vise for large or heavy workpieces, such as those that are machined by Special Machined Components, is that it is difficult to set up the machine for consistent clamping. For example, if a powerful, 225-lb. operator is working the first shift is followed on the second shift by a much smaller man, there is likely to be a difference in the clamping power between the two shifts.

Also, over-clamping, or clamping a vise too hard, can create workpiece distortions, which results in wasted material and production time.