This blog post is translated from German with DeepL.
What is ISO GPS 8015?
ISO GPS 8015 has been the valid superordinate drawing standard (GPS = Geometric Product Specification) since 2011. It does not itself contain any information on how something is drawn or measured, but only defines the principle, i.e. the “philosophy” of drawing and measurement.
How something is entered is regulated in various standards increasingly subordinate to ISO GPS, such as ISO 2768 (SN EN 22768) for general tolerances, ISO 1101 for geometric tolerancing, ISO 1302 for surface finish, ISO 3601 for O-ring recesses, to name just a few examples.
Principle of ISO GPS
To explain ISO GPS 8015 in a single tip is not easy. It is not without reason that even the first basic training courses on the subject take three days, such as the course offered by VAKB (Verband Ausbildung Konstrukteure Bern). Nevertheless, we would like to try to explain the basics here and provide an overview.
The principle of ISO GPS 8015 is: “the drawing should be complete and unambiguous”. At first glance, this sounds plausible and simple.
But behind it is a fundamentally different way of thinking than before: taking into account globalization and the omnipresent price pressure, ISO GPS assumes that the part must be able to perform its function in any case, no matter where in the world and with which manufacturing process the part is produced. This is done without any supplementary explanations or information (which could be misunderstood or not understood at all due to language barriers, for example) and without any assumptions.
A few examples:
- Are you aware that the squareness general tolerance according to ISO 2768 of tolerance class (m)K for the range 0-100mm is 0.4mm? With this awareness, even with a “simple” rectangular plate, I have to ask myself if the plate would still work with this angular deviation. If not, I have to tolerate the plate more accurately with a shape tolerance “squareness”. We find the same problem with the subject of perpendicularity of a bore axis to (which of the two) base surfaces (See Figure 1).
- A similar example is symmetry: in the tolerance class mentioned, the symmetry general tolerance for 0-100mm is 0.6mm. The fact that under this consideration, for example, the function of a keyway is anything but guaranteed without additional symmetry tolerance suddenly appears logical (See Figure 2).
- Depending on the manufacturer or manufacturing process, I cannot assume that a cylinder head counterbore is made in one clamping. This means that the counterbore could be produced completely independently of the throughbore. Based on this “independence principle = each form element is to be considered independently”, the question arises whether my screw will fit if the two bores exhaust their respective permissible tolerances in opposite directions. With the highest probability I come to the conclusion under this consideration that the counterbore must be dimensioned concentrically to the throughbore (See Figure 3).
Often controversial: when I see a bolt circle with 6 holes, I assume that all 6 holes are equal and the distribution is 6×60°. Since assumptions are not unambiguous and defined, I must therefore measure the angle with 6×60° and also write 6x in advance when measuring the hole diameter (e.g. 6xØ8). Now it is clear and complete.
In our company it is usual and clear that all dimensions are in mm. But if I don’t write this on the drawing, it is not clear and depending on the country of manufacture, I could suddenly get a part that is too big by a factor of 25.4 (inches), for example.
These examples show on the basis of supposedly simple geometries how the view and principles of ISO GPS lead to a partly completely new way of looking at drawings and masses.
ISO GPS 8015 for quality assurance
A clear and complete drawing naturally also includes a clear definition of how the masses and tolerances are measured.
Using the example of a bore-shaft fit: the diameter is measured with a caliper or micrometer (two-point measurement), with a limit plug gauge or ring gauge (pen/envelope), with a 3D measuring machine (depending on the setting, gauss, pen, envelope, circumference or area). Accordingly, both the measured diameter and the center determined by it may be different.
A “new” solution to this is the so-called enveloping principle: the addition of a circled “E” to the dimensional tolerance. This means that for a bore, the lower tolerance limit is measured with limit plug gauge and the upper tolerance limit – if relevant – with 2-point gauge, and for a shaft vice versa. This ensures that the appropriate clearance is present for clearance and transition fits. At the same time, the tolerance is then valid as a cylindrical form (in return, a non-enveloped tolerance is only a local measurement, which must be correct only locally without a corresponding form tolerance).
But be careful: to measure correctly with limit plug gauge / limit ring gauge, the gauge must be present and at least as long as the toleranced area. Reason: otherwise the measurement could theoretically be correct only locally, but the entire shape could be banana-shaped, for example.
From when is ISO GPS 8015 valid?
Even if the standard is still unknown or new for many, it has been valid for all drawings since 2011. Therefore, the mention “Tolerancing according to ISO 8015” as suggested in the SNV standard excerpt 2018 is not necessary. However, this can be useful so that, for example, it is clear within the company that this drawing has already been revised according to the new standard.
How do I implement ISO GPS 8015?
Changes are part of the changing times and that you have to keep up with the times is clear and recurring for everyone in our industry. But implementing ISO GPS 8015 is a bit more complex than other adaptations.
For example, over the last 16 years, most plants have updated surface specifications from the old “N7…” designations to the Ra value specification. This could be done “top down”: the development department introduced the new designations and the manufacturing department (after obtaining a new standards extract) only had to look and get used to them.
If this approach were taken with ISO GPS 8015, the introduction would likely be met with opposition from manufacturing and additional effort and cost would be expected.
This is because if manufacturing and inspection do not understand the standard and are not trained, considerable opposition can be expected and, at least in the case of external manufacturing, the price of the parts will most likely increase, even if the quality effectively required is no different than the quality previously manufactured.
The following example of a drawing according to “previously usual” (left) and “new” according to ISO GPS (right) shows how much more complex the drawing looks, which logically quickly becomes more expensive to offer.
Thus, the implementation needs professional support and must start with training of the quality/measurement engineering department and manufacturing. Only when these departments (or suppliers) are prepared, the development can change to ISO GPS.
As preparation, it is recommended that the “key players” complete an introduction to ISO GPS 8015 in order to be able to assess the scope. These key players could be e.g. head of development, head of production and head of quality assurance. The course could be e.g. the introduction ISO GPS from VAKB. This three-day course is about what the standard contains and building understanding. In order to be able to introduce the system in the company, depending on the size of the company, specialists are still needed to support the company (ideally from other companies that have already converted).
What does ISO GPS mean for us as a service provider?
For us as a development service provider there are two consequences:
- During the quotation phase, we have to clarify with the customer whether he wants drawings according to ISO GPS 8015 or “according to the old standard”.
- If the customer changes over, we have to be ready “know-how-wise” to apply the standard. We initialized this process at Gimelli Engineering AG in 2017.
Is the introduction of ISO GPS 8015 mandatory?
Basically, the standard applies and sooner or later all drawings will be implemented accordingly. But of course the conversion also means a considerable effort for a company and so it is important to weigh up what effort there is and what advantage the company has from it. Because drawings according to the previous standard can still work very well. They are just not clearly defined according to ISO GPS and leave room for maneuver. If one is aware of this leeway and can deal with it, the risk may be very small. Accordingly, it may well be that the time of introduction is postponed for some time.
Reasons for switching:
- If your customers are converting, you won’t be able to avoid dealing with it.
- If your industry sets the standard, you may need to adopt it to continue to deliver (e.g., security, automotive, etc.).
- If your buyers are increasingly looking for the cheapest solutions and changing suppliers, the risk of receiving parts that don’t work but are within tolerance increases. So you bear the consequences for this.
- The same applies to internal personnel changes: if your long-time employee retires, possibly a younger, ISO GPS-trained employee could produce parts correctly according to drawings that then no longer work.
Reasons not to change:
- If you produce internally and the same employees always produce the parts or the know-how transfer for new employees works out well, the risk of having problems with previous drawings will be relatively small.
- The same is true if you stay with your regular suppliers and they have deep personnel fluctuations.
Consequences for vocational training
Vocational trainers must be aware that the standard is trained in the design engineer training and required in the partial examination. This means that the apprentice designers must have ISO GPS under control in the 2nd year. We must therefore support them in this, i.e. the vocational trainers must know ISO GPS (e.g. attend the VAKB course mentioned).
From the 3rd year of apprenticeship, they can then work according to the company standard.
ISO GPS in the standards excerpt
Since May 2018, the latest edition of the SNV standards excerpt is available. In contrast to the 2014 SNV standards excerpt, most of the chapters and example drawings have been consistently adapted in accordance with ISO GPS 2018. It is therefore definitely worthwhile to purchase the new standards excerpt.