Standards in machining
What are machine design standards?
Which to use ISO, DIN, ANSI?
Are there other standards for machining exist?
Machine design standards are a collection of different standards that we use in machine design. ISO, ANSI, DIN and others are the organizations that create these standard for materials, features, dimension, products and processes. These standards completely define the subject in question so that the result of the standard can be replicated. There are a lot of these standards, some of the most well recognized are ISO 9000 and ISO 9001 standards. These are quality managements standards and they will not be discussed here. Here we are talking about these standards for the machine design purpose.
What is the difference between ISO and ANSI and DIN standards?
The difference is in the organization that is issuing the standard. ISO stands for International Organization for Standardization, ANSI – American National Standards Institute and DIN – Deutsches Institut für Normung e.V. (German Institute for Standardization). These organizations are making and improving the standards over time and selling them. There are many other organizations that do the same thing. Most countries have their own standardization organizations. But these are the most well recognized ones.
Concerning machine design and machining, there are standards for numerous machine elements, features, parts, assembly, drawings, annotations, tolerances. Between these standardizing bodies there are little differences among these standards. Most differences are so minute that you will not even pay attention but they are not to be considered the same. The same thing goes for the age of the standard. You should always use the latest standards because there is always some improvement and evolution of the material. When dealing with parties outside your organization always pay close attention to the standard that they are using. Whether the outside party is providing you with documentation for you to machine or they are machining parts from your documentation.
Why use ISO, ANSI, DIN standard?
Simple answer? These standards save time. Some machine design standards like in technical drawings are now so universal that everybody is using them without even thinking about them. In these case standards help us understand each other, shorten the time for explanation and minimize mistakes in the idea transfer phase. There are also components like fasteners and others, that we use all the time and we relay on them being closely up to the standard so that we can implement them.
Besides these obvious examples there are also features that are standardized that can really help and save time in the machine design process. I have mentioned something like this in one of my previous posts. Also thread depth is a good example of this. If you just annotate that thread depths are up to a certain standards then, even if you miss to dimension it on the drawing you have dimensioned it by standard . The holes will be drilled and tapped up to a standard and that is something that you should be doing anyway, for consistency and uniformity sake.
Where can I find standards?
These standards are easy enough to find at organizations website. Like DIN , ISO and ANSI. The problem is that they are not cheap. It is something that is definitely reserved for companies and not even really small operations. You can easily search their websites for the standard that you are interested and buy straight from the source. If you want to check something out first, you can try googling the standard and seeing if something will pop up.
Which standard to use? (A story)
One story to remember how important this is. One of the senior engineers passed this story to me when we started discussing standards. When he was working for another company, they were deigning special train wagons for shipping. One time they found a machine shop in South Korea that can do all the manufacturing for a good price. All of the drawings where done in DIN standard and that was not a problem for the machine shop. After a couple of months when the parts arrived and the assembly started, a lot of pieces could not be assembled. They just couldn’t fit together. After a lot of fighting with the machine shop, plus some language barriers, the problem was figured out. The design firm used a five year old standard for the tolerances and the problem was the nominal size limits for medium tolerance class. The dimensions changed during those 5 years. The machine shop used the latest standard. This caused a lot of re-work and very costly delays.