Part with used standardized features

Standard features vol. 1

So I thought what was useful knowledge that I gained in parts design that I can forward to you without any complicated explanation. A couple of things popped up in my mind, but this one I think had the most impact.

That is using standard features!

Ok that sounds somewhat underwhelming but let me explain my point.  

Disclosure: Any dimension that wanders into this article will be metric and all standards mentioned are either DIN or ISO, but there are equivalents in other standards so the point is the same

What are stadnard features?

By standard features I am talking about a feature that can be machined into a stock material to provide a function. By this definition of mine, the most easily recognized standard feature is probably a thread. But it is not the only one by any means. There are numerous, and I am going to show a couple of more common ones on an example.

Let’s use a problem to make a point. I need to attach a pneumatic cylinder to a lever. Something like this:

I want the fewest number of parts to accomplish this.

The part will be designed from a hex stock. One part of the stock should be threaded so it can thread into the lever and the other side should be round for attaching a pneumatic cylinder via piston rod attachment. The retaining ring will be used to the restrain the piston rod.The requirements are that the shoulder of the hex stock seat right against lever mating surface, and the same needs to be true for the piston rod attachment.  

So there must be some sort of undercut on both sides, right? But what shape and dimensions of an undercut will be adequate to provide the mating condition on the one side and be easily manufacturable on the other, and introduce the least amount of stress to the part?

Standard features – example

There are standard features that can give you a proven solution to this problem. Let’s look at the designed part:

Every standar feature used to design this part is noted on the picture above.So let’s start from left to right.

The thread is selected for the loads in question and the length of a thread is also not random. There is a DIN 13 standard that defines a minimum length of thread and the depth of corresponding threaded hole. Then next to the shoulder is a relief denoted by DIN 76. This relief is dimensioned primarily as a relief for threading tool.  

On the far right there is a slot for the retaining ring. The dimensions of the slot are defined by DIN 471 standard for retaining rings. The diameter and the shoulder diameter are determined by the standard for rod eye connection. In this case that is a standard ISO 12240-5.

But before the shoulder there is a relief determined by DIN 509 standard. Why is this standard feature used? It is used to provide a relief groove so that the rod eye for the cylinder can lie right up to the shoulder of the hex stock, otherwise there would be a radius that would interfere.  

Standard features – conclusion

So if we analyse the part most of its dimensions are standardized.

If you are new to this and this demoralizes you then wait, it should actually help you.

At first it is not that easy to remember all of this but I got used to it pretty quickly, and so will you. These standards are helpful because they provide a lot of knowledge about usability, manufacturing, assembly and best practises into a schematical recipe that we can implement into our designs. Other benefits are that by using standard features you can speed up design and manufacturing process and be sure that your solutions are optimal.

I hope this was helpful. If you are interested in some details from the article or want more posts like this let me know in the comments.

 

Happy engineering.

Aron

Want to check out the 3D model that I used in this post? Fill in your first name and email to get the download link below:

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