Never Let The Bar Hang Out—And Other Safety Issues
Certain machine shop rules must never be broken. If they are, the results can be disastrous.
Founder and President, CNC Concepts Inc.
Certain machine shop rules must never be broken. If they are, the results can be disastrous. Experienced machinists will seldom break these rules. But we're seeing a large number of newcomers entering the manufacturing environment—people that have had little or no formal training in machine shop practices.
Newcomers to manufacturing are probably used to very safe working environments. Consider, for example, people entering the manufacturing field from high school. Their previous working experience may consist of working in local businesses. While mistakes they've made may have been costly, they probably were not in any real danger. Now, they are in a much more dangerous working situation. If they make mistakes in a manufacturing company, it may result in a personal injury. Here is one specific example.
Many CNC turning centers have a hole through the chuck and all the way through the spindle to accommodate bar feeders. A bar feeder will, of course, send the bar through this hole to provide the raw material to be machined. But if the machine does not have a bar feeder, many companies that have limited bar feed applications will use a bar puller. The puller is mounted to a turret station and draws the bar out at the completion of each workpiece. The bar (raw material) must be of an appropriate length prior to being put in the machine. Under no circumstances, should the bar protrude from the rear end of the spindle (out the back of the machine). If it does, it will be under severe centrifugal force as the spindle runs up to machining speed. At some point, the bar will radically bend to 90 degrees, shredding anything in its way (including the operator).
In one company I know of, CNC turning operators are responsible for cutting their own bars prior to loading them into the turning center. One new operator decided to minimize the number of times the bar was cut to reduce the amount of work he had to do. He was never made aware of how dangerous it would be to let the bar hang out the back end of the machine. Fortunately, when the bar did bend to 90 degrees, this operator was not in close proximity and was not injured. However, the machine's spindle motor was not so lucky.
We sometimes forget how little entry-level people know. Most entry-level people will not even realize that a greater potential for danger even exists in their new job unless you point it out. Most will blindly follow the instructions they've been given. If something out of the ordinary happens—something you haven't warned them about—they won't understand the consequences of making a mistake. And most will simply proceed.
In many cases, we're talking about very basic mistakes. Mistakes that no well-trained CNC person would ever make. What happens when you load a tool into the wrong tool changer position? What if you start the program with the wrong side of a pallet facing the spindle? What if you forget to tighten workholding clamps? What if you run a tool past the point when it gets dull? (How do you tell when a tool is dull?) These are all mistakes that will result in scrap workpieces, damaged tooling and machines, and possibly injury to the operator.
Consider the kind of training you currently supply entry-level people. If you haven't had any catastrophic mistakes, is it because you have worked to make each operator's job fail safe? Or is it because you've been lucky?
Admittedly, people running CNC machines must take on some of the responsibility for their work. In days gone by, people entering the field of manufacturing came from technical schools and apprenticeship programs. They had a firm understanding of machine shop practices before entering the shop. But as we employ people with lesser and lesser previous machine shop experience, we must also take on more of the responsibility for providing safe work environments.
First, we must engineer our processes in a more fail-safe manner. Consider potentially catastrophic mistakes a newcomer can make and eliminate the potential for making them.
Second, we must better educate new people. Make them aware of potentially dangerous situations. Ensure that they understand that if something out of the ordinary occurs, they should notify the person in charge. (They shouldn't simply proceed.)
Third, we may have to better compromise manufacturing aggressiveness with safety. Experienced people have the ability to keep up with aggressive processes. But newcomers may not have the needed skill and won't be able to keep up. In their efforts to keep up, they will be prone to making mistakes.