FINISHINGThis section will tell you about a few of the finishing touches you can put on your springs. Some of these are necessary, while others may be called for by the design you have in mind.
TweakingSad to say, your spring may not be exactly what you want. Sometimes not all is lost though - you should know, first, how to correct what's wrong and second, what you can do to "tweak" your springs into shape. First, how to correct what's wrong:
(You'll note that this is the same data you read about in the section on spring design.) Sometimes you'll be able to "tweak" your springs into shape, especially when they're not too far off, and also especially before you've relieved the stress. Here are some techniques you can use: You can open up the diameter a notch or two by grabbing the ends of the wire in your hands and twisting the coil gently in the opposite direction. This works best on short springs with few coils. On longer springs with many coils, you can open the diameter up by simply dropping the spring onto a hard surface (like maybe the floor). Compression springs can be shortened by setting them solid or heat setting them (see the section on compression springs). You can lengthen a compression spring by driving a wedge in between each pair of coils. Be careful to use the same amount of force each time you do this, and also be sure you do it evenly all the way up and down the spring body. Note that when you do this, the diameter of the spring will also open up. Necessary StepsStress reliefSpring wire that gets bent has to have the bending stress relieved. Here are the stress relief guidelines for all common spring wire materials.
PassivatingWorking with stainless steel creates "free iron" contamination on the surface that can later rust and create problems with the part and its working environment. The process of removing this free iron is called passivation: here's how you do it. BEFORE YOU START, find a safe spot to do this. You should do it outdoors, and away from anyplace where animals or other people can get into it.
Don't passivate anything but stainless, by the way: the acid will eat non-stainless steel and ruin the springs. * I have had correspondence from a metallurgist who advises me that muriatic acid is incorrect. He advises nitric acid and has asked me to include a reference to the ASM Metals Handbook on Cleaning and Finishing, for those of you who are interested. Another correspondent advises a 10% solution of citric acid at 66 degrees C. There seems to be some varying opinions on this issue so you may want to consult a metallurgist or materials engineer on this point. Optional StepsDepending on where you want your springs to go, you may want them to look shiny. If you do, you can have them plated after you're finished making them. Plating will not change their dimensions. You can have springs plated with chrome, silver, gold, or any other metal. Springs that are used to make electrical connections are usually plated with silver or gold. If you're not in the plating business yourself, your best bet is to get your springs plated commercially, rather than try to do it yourself. Also depending on the use of the springs you make, you may want to have them painted or dipped in rubber (like if you want to hang something from an extension spring and not let the spring scratch whatever it is that's hanging from it). I personally think that small-wire springs can be beautiful, and although I've never done it myself, there's no reason why someone couldn't make jewelry using them as a starting point. Earrings, for instance. If you want to try this out, go right ahead. Forward to other types of springs that you can make. |
