When the lab meets reality, part 2

So, last time we looked at some of the issues you face when taking measurements outside the machine. Now, let’s see what happens when you do the same thing, but from inside. If you’re thinking this will be easier, you’d be wrong. Up to a point, the good news is that things do get better. But the bad news is, they also get worse! Measuring accuracy is never “plug and play”! Let’s see why.

The most important and obvious change when you go inside the machine is that you lose most of the person-dependent variables that existed outside (remember, in the last blog we discussed the impact of the technician him- or her-self on measuring). Also, the degree of efficiency you’ll achieve will be superior any time a measurement process is automated. That’s the good news.

On the other hand (drum roll: bad news incoming), go inside the machine and you find yourself working in the nightmare of the machine’s environment. Once again, let’s use a practical illustration to make the point. Imagine that you have a contact-style tool setter that you use to touch off the tools you’re working on. The upper-tier tool setters have around 1.0µm repeatability – at least in theory.

Contact style tool setters

A simple process follows, right? Think again. If you want to achieve accuracy, you probably want to think about using a high-quality tool setter with carbide plates, and preferably a blower mounted to clean the plate between touch-offs.  Then remember to rotate the tool while measuring (by the way, make sure that you are not milling the probe while you’re doing it). Plus, don’t forget to adapt the probe speed to your machine’s reaction time (and in the process, contact your probe supplier to make sure that it’s adjusted correctly).

Laser tool setters

Another well-known option is the laser tool-setter, which works much in the same way as a contact tool-setter but offers measurements of radius and length. These are very accurate instruments when mounted correctly. But, remember to align your laser with the axis of your machine. With these devices, you must make sure that you measure off-center, as the spindle speed will affect the measurement if you put them at the center. As stated by the manufacturers, you must also make sure you have a clean tool before measurement, as fluid films might be as large as 100µm, and a laser tool setter has no way of telling you if it is measuring the tool with or without the fingerprint you left on it.

There’s also the reality that when using the laser tool setter in an automated environment where you might make a measurement multiple times that you cannot guarantee the level of dirt on the tool, so you must take the approach of the micrometer – taking several measurements to ensure accuracy. Experienced operators in a demanding environment repeat the measurement process 20 times over, to make sure that they get a good reading.

Camera-based measurement systems

What about a third option, the camera-based tool measurement system? Made for measuring tools in a demanding environment, these still require preparation to get closer to the results you’d get from the lab. Unlike the other tool-setters, camera-based technology can also help you when the tools are dirty – provided that you can create a reference measurement of the milling cutter.

Of course, alignment is vital when mounting the unit. The camera can help you find the correct alignment, a one-time task when installing the system, so take your time and do it properly. Also, you should take care to have clean tools before starting the reference recording. After the reference recording is done, you can keep machining and measure again as often as you like. A good tool preparation routine can help you with this. Remember, the system can also reject tools that are too dirty and set them aside for manual cleaning while the sister tool does its job.

Measurement takes skill, effort, and understanding

In these two blogs, we’ve described use cases for various tool measurement scenarios taking place both inside and outside the machine. In both, we see repetitive processes taking place on the workshop floor. If there’s a general takeaway regardless of the context, you should always take your time to familiarize yourself with the measurement tools you are using and learn how to use them properly. Measurement equipment is an investment, and your goal is to maximize your return. There are no shortcuts to accuracy, and a lot of parameters to consider if you want to achieve it.

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