We all work with industry standards and conventional methods. Usually, the standards are developed by organizations and/or professional societies. The motivations for the standards are public safety and industrial efficiency. One of the early applications was the establishment of the American Society of Mechanical Engineers (ASME) concerning the safety of pressure vessels; specifically steam boilers in the 19th century. A locomotive or a ship’s boiler exploding was a bad thing.The Society of Automotive Engineers (SAE) established standards for fasteners and other automotive and mechanical components. For fasteners, three standards evolved: SAE, British Whitworth and Metric.
The adoption of these standards allowed for the fully automated production of fasteners which lead to high quality and low-cost fasteners.Sometimes industry leaders establish their own in-house standards. The aerospace companies have done this.The industrial machine design and manufacturing industry has adopted standards from several organizations and developed some also. One standard, is tool mounting internal and external tapers. Tapers are covered in the Machinery’s handbook. The 30th edition is about 4000 pages long.I visited a long-time customer a while back and was able to talk to one of the technicians whos’ job it is to recondition lens molds. She has been working there for over 30 years.
She uses a hand procedure utilizing our beveling machines. These machines are supplied with 0 Morse tapered (0MT) spindles. I asked how things were going and she mentioned that the tools they make did not fit right on the spindles. We have been supplying machines to this customer for over thirty years and this is the first time that the taper fit has been an issue. I checked several tools on several spindles and they all fit the same. So, at least the tools and the spindles were precisely made; but not accurate.
Tapers are not easy to measure and validate without specialized tools. One device for measuring angle is the taper micrometer. It has a bar with the cylinders spaced at 1” (25.4 mm). A .0001” (.00254 mm) graduated micrometer is mounted in the frame and the stem contacts one of the cylinders. With this instrument, you can set the micrometer to the desired taper or fit the bars of the instrument over a taper and adjust the micrometer so that the bars are in full contact with the taper.
Figure 1 shows a taper micrometer with a #1 Morse taper reamer in the jaws. It is difficult to see, but the micrometer reading is just under .050 inches. The specified taper for a #1 Morse taper is .04899 inches/inch. Thus, the reamer is accurate. I did not have a taper micrometer with me during the visit, but more importantly, neither did the customer’s tooling shop. I asked about the specification of the tool taper and the tool engineer had an apprentice bring in the shop print he was working from.
The taper specification was listed as two diameters at a certain distance. This a good way to specify a taper and the angle can be calculated. However, the physical procedure to validate the specification is difficult without a taper micrometer. This is where is gets dicey: The tool engineer was “Very Sure” of his specifications and I had the Machinery’s Handbook (M/H) as a reference. So, we were in an uncomfortable situation. Clearly, the tools and the spindles did not match. From the tool engineer’s point of view, I was calling into question his company’s’ long-time adherence to the specification on the print. From my point of view, I was relying on the M/H. There are two solutions:
1. Send a sample tool to us and have us make spindles to fit the customer’s tools (and charge a special fee, which we do).
2. Measure the taper with a taper micrometer or make their tools with a standard taper reamer so the customer can provide the actual standard taper specification to the us and we can supply the custom spindles. By now you may be thinking that taper identification is more difficult than it needs to be. Tapered spindles and tools/arbors have been around for a long time. This does not change the fact that the standards for the tapers are not always known or adhered to. Because of this, we usually ask for a sample taper (internal or external) to match our spindles to. In the case above, I assumed the company had an accurate taper that matched the standard, but it does not always work out that way.