Once you’ve wound a few extension springs, you’re ready to progress to compression springs. Compression springs are widely used in firearms, and being able to make your own opens a lot of doors in your own designs as well as repair and modification of existing firearms.
The basics are the same:
- Determine the form necessary to create the spring, allowing for ‘spring back’.
- Remove any ‘set’ the spring may have from its stock form.
- Bend and/or wind the spring on the desired form.
- Perform any finish steps
- Temper the spring in itsdesired shape.
The difference occurs in step three. Instead of winding a spring where the coils touch, we want to be able to wind a spring where the coils are open and evenly spaced. The easiest way to accomplish this is to use the threading gears on a lathe. Other techniques include custom jigs or simply inserting a shim in between the coils as they are formed.
Always start as if you were winding an extension spring – that is, with the coils touching. This is what you want at the ends of a compression spring. Don’t worry about winding a particular number of turns, you will trim to suit when the spring is done.
Set the threading gear box to the pitch you want for your spring. Make sure you calculate the pitch based on where the center of the wire is – if you set it according to the space you want between coils you will be off by the diameter of the wire. In other words, if you want 1/16″ between coils, you need a courser pitch than 16 TPI. Assume your wire is 0.032″ in diameter (that’s ~1/32″) and you want 1/16″ between coils – you need each turn to be 1/16″ + 1/32″, which is 3/32″ or approximately 11 TPI.
Engage the half-nut and wind the spring. As you get better you might try this under power, but on most lathes it’s possible to rotate the chuck by hand, which makes the process much easier to control, albeit slower.
Continue winding until the desired number of turns, or length (don’t forget to allow for the closing coils) is achieved.
Finish the winding by winding several closing coils in contact with each other. Again, the exact number doesn’t matter, they’ll be trimmed during finishing.
The spring is now ready to remove from the mandrel, and should look something like this:
Complete the forming steps by trimming the closing coils at either end.
If you are winding a spring from relatively thick material (as a hammer mainspring) you may want to grind the end flat, particularly if the spring will go into a ‘seat’ in the final application.
Heat treat the spring as described in Part I and you’re ready to go.