Reclaiming The HOLE-MAKING Process

Modern Machine Shop, June, 2001 by Leo Rakowski

Southbridge Sheet Metal Works, Inc., a metal fabricating shop in Sturbridge, Massachusetts, builds frames made of plate and structural tubing for New England equipment manufacturers. The family-owned shop started in the town for which it is named back in 1934, and president Louis E. (Lou) Colognesi, Jr., can point to many changes that have occurred in the industry over the years.

"Twenty-five years ago, we did a lot of work for builders of machine tools and textile machines," Mr. Colognesi recalls. "Those firms were vertically integrated; they would buy fabricated assemblies from us and do most of the machining and finishing in-house. Many of those companies are gone now. Today, we supply frames and chassis to manufacturers of laser machines, medical equipment, x-ray inspection equipment and similar high-tech products. Our new customers tend to be less vertically integrated; they want components and assemblies that are as complete as possible and ready to go right on the assembly line. To serve our customers' needs and stay competitive, we could no longer simply supply welded assemblies. We had to be able to provide machining and painting of components and assemblies as well."

Over time, Southbridge Sheet Metal added an assortment of hole-making machines that includes drill presses, radial drills... even two CNC machining centers. The machines are fine for drilling and tapping many of the smaller components that go into its assemblies (small pieces of steel plate, square tube and rectangular tube), but they simply cannot accommodate large sections of plate that are used as bases for many of the machine frames. The shop tried to drill and tap the large sections of plate on its radial drills, which were the largest hole-making machines in the shop, but the process was too slow, and repositioning the machine and the workpiece to get at all the hole locations was too time consuming and cumbersome.

To provide the needed drilled and tapped holes, Southbridge farmed out the work to machine shops in the area. One shop machined the large plate sections on a boring mill. Another shop used a large bridge mill. Farming out the work achieved the desired results, but there were drawbacks: "In the first place, having the machining done by a third party is expensive. The machines that were used were large and had high hourly rates to begin with, and the shops naturally tacked on a profit margin that we had to pass through to our customer," Mr. Colognesi explains.

"Having work done on the outside can also affect delivery times," he continues. "The time it takes to get a job done on the outside depends on how busy the shops are. Right now, we can have jobs done quickly. Last summer, shops were quoting 10- to 12-week waits. Another consideration: if your source's machine breaks down, you're dead in the water."

The need to machine large plate sections has been a longstanding concern at Southbridge Sheet Metal. For example, the shop has been supplying fabricated machine frames to one customer at a rate of one to five per week for the last 5 years. The frame has a base made from a 1/2-inch-thick steel plate that measures approximately 6 feet by 10 feet and has 170 holes of various sizes, most of them tapped. The shop outsourced the machining of the base to a machine shop that performed the hole-making operations on a boring mill.

Too Much Machine

Southbridge Sheet Metal wanted to bring the machining in-house to gain more control of costs and scheduling. There were many machines on the market capable of machining large plate sections, but Mr. Colognesi felt they were more machine than he needed for the relatively simple drilling and tapping operations his workpieces required.

The search for a more appropriate machine continued, and while visiting a regional machine tool trade show (EASTEC), Mr. Colognesi found what he was looking for--the VersaDRILL large-format drilling machine made by Vytek Inc. (Littleton, Massachusetts). VersaDRILL is a CNC, gantry-style drilling machine designed for efficient drilling, tapping and light milling of large plate sections. The machine is available in two versions: a smaller-capacity LT series and an HD (heavy duty) series. Southbridge Sheet Metal purchased the heavy duty version.

The HD is available in table sizes ranging from 75 inches by 75 inches to 125 inches by 125 inches, and in weight capacities up to 20,000 pounds. It has an optional automatic tool change capability, enabling the machine to access as many as 20 tools mounted in stationary tool stations at one end of the worktable. (See Figure 1.) The machine provides 16 inches of clearance beneath the gantry, enabling relatively flat, welded subassemblies (and whole assemblies) to be machined as a unit. The machine has a freestanding CNC control with a PC interface. The control is equipped with a Windows-based CAM software.

By purchasing the drilling machine, Mr. Colognesi was able to bring the machining of the bases for his long-running frame job in-house. He found that he is able to machine the base on the VersaDRILL in half the time that it had been taking the machine shop to do the job on its mill. He estimates that if he had purchased the unit 5 years ago, the savings gained by machining the bases in-house for just the one job would have repaid the cost of the machine.