Stretching a Machine’s Reach Without Sacrificing Precision

There are projects that you know can knock out of the park with the resources you have available. And then there are times when you need to ask a little more from your equipment. In those cases, inspection equipment helps you push the boundaries of what is considered “possible.” Over time “possible” becomes an excuse, not a reality.

ENI was faced with such a situation when we won a bid for a project that required precise machining on a long, narrow, fixed-rail assembly, similar to a rail on a gantry crane, but on a much different scale.

The Challenge

The challenge was the sheer size of the part.

At 35', it was too long for the 24' capacity of ENI's milling machine to achieve in a single setup, which is the preferred method. Just 5' wide and between 8" and 10" thick, the metal was not particularly rigid. It was fairly flexible and not especially strong.

The tolerances were unforgiving. A few features required a flatness of 5 thousandths of an inch over the full 35-foot length, including two parallel working surfaces that other components would slide along.

The Journey

Since the surface of the part exceeded our equipment's range of travel, we could not machine the part in a single setup. We would have to machine the portion that was within reach, slide the part down, and then machine the rest.

The problem with that strategy was that it forced us to rely on the accuracy of our equipment to slide the part, pick up on the new location and move on. If there was an error in the equipment, that error would carry over to the second setup and disrupt the extremely tight tolerances that were required for success.

The preferred method of conducting all machining in a single setup was simply not possible, yet sliding the part into a second setup without an independent check from highly calibrated inspection equipment was too risky.

We knew we would have to think outside the box.

The Discovery

This was not the first time we were faced with a part that exceeded a machines' range of travel. But we recognized the challenge from the beginning, and had the foresight to consider the situation early in the manufacturing process. During bidding, we informed the client that we had a machine that was almost big enough, and inspection tools that could help them make up the difference.

Specifically, we would use a FARO brand laser tracker and arm-type portable CMMs.

With these highly calibrated, independent inspection tools, we could detect any errors in equipment and compensate for those errors.

The Solution

The tools enabled us to slide the part enough to allow work on the portion that we weren’t able to reach in the first setup, effectively extending the machine's range of travel.

We built in intermediate features that we treated as reference points when it came time to slide the part. These features could be accessed by the laser tracker at all times so we could ensure we had achieved the necessary consistency between the two setups. This enabled us to create a continuous flat surface that appeared to have been machined all at once. On a different project, we used the same tools and the same strategy to create a continuous hole pattern on a part that was too long for our machines.

The Results

We were ultimately able to produce a part that met all the required tolerances despite the machine travel limitations.

By taking a step back and planning for the setups, we were able to deliver a part that was just as precise but even larger than the machine that was used to make it. We didn’t settle for what was “possible” with the equipment we had. We know we could make our equipment work for us – and we were right.