Locating spiral spring pins

I work as an Tooling Engineer and I love to use spiral spring pins (DIN 7343). But I have not found its 3D printed equivalent. So I decided to make them. 

 Advantages over regular pins:

• Do not need precise hole diameter so no matter your printer setting these will fit great (the holes can differ up to 0,6 mm in the 12 mm diameter variant)

• Are retained in parts by radial tension

• Have uniform strength and flexibility after insertion

• Distribute static and dynamic loads equally throughout its cross section without a specific point of stress concentration

• Its flexibility and shear strength are unaffected by the direction of the applied load

• Are designed to remain flexible after installation and are an active component within the assembly

• Ability to dampen shock/impact loads and vibration prevents hole damage and ultimately prolongs the useful life of an assembly

• Do not need to have perfectly round holes 

• Firmly hold both mating surfaces with uneven hole diameter

• Use less material than normal pins

          (Source: Spirol.com)

Disadvantages are: 

• The need for additional fastening method e.g. bolts and nuts or glue. (The pins hold themselves in the hole but have no axial retention method)

• Possibly wasted filament when using brim or raft

• Need to be printed vertically so they have ridges and worse strength than horizontal pins

In 3D printing they are great for:

• Joining two parts together e.g. for gluing or assembly when you need precise alignment without

 precise holes 

• Strong connection that can withstand shear forces and dynamic load  

• Sliding connection that has no clearance 

For my needs I designed them in three fits.

• Free fit meaning that they can be inserted into the part without any tools. Thanks to the flexing they still do not wiggle in the hole but can be taken out and in repeatedly. Used in often disassembled parts or sliding parts. Even when the hole in sliding parts wears out a little the flexibility still removes all the wiggle

• Medium fit is good to start with to see if you would like it to be more or less tight

• Tight fit meaning you will need to use vice or hammer to push it in. Ideal for glue ups or permanent assemblies.

Printing:

• PETG, ASA, ABS are the best choice for these. But I tested PLA spiral pins and they still performed great

• No infill just ≥ 2 perimeters 

• The use of brim or raft might be necessary if the bed adhesion is not ideal. For these I prefer 2 layers of raft because you can easily peel them of

• Might consider raising the nozzle temperature in order to have better layer adhesion and shear strength.

• Ideal printing orientation is 45°. So you can cut it under 45° and print it angled.

What's in the files?

In the files there are diameters 6, 8, 10, 12 with several lengths each. If you would like some more sizes just hit me up or use a upscale function in your slicer. There is also a hole test which you can print to test the clearances. There are holes with exactly 6, 8, 10, 12 mm.

Using Prusaslicer cut method:

In Prusaslicer is this great feature that lets you cut your part in pieces. I want to use spiral pin 8x20. You choose the cut button on the left menu - decide your dividing plane - add connectors - choose dowel type - circle shape - depth 10,3 mm, just to be sure, with 0 tolerance - size 8 mm without tolerances.

Than you confirm connectors - add at least 2 holes - place your cut results as you need on the bed - and perform cut. 

After that, despite the warning label, you delete the default connectors and use spiral pins.

And that's all. Hope you fall in love with these guys as much as I did and they save you some headaches and ruined parts because of bad tolerances.