Creating M3 Mount Hole for Eagle Library

Welcome to Wing Tech Corner. I recently posted a video detailing how to create an M3 mounting hole component for the Eagle PCB Design software’s library. You can use the embedded video above to go check out the video, which demonstrates how to create the part from scratch.

You can also check out the github repository, where the library and the part in question as well as any future parts, will be published/made available:

Let’s Create!

So fire up your copy of Eagle PCB Design and in the main navigation window, head to the top and expand the “Library” folder. In there, you can create a new folder for your new library files or just store your library file in the Library folder.

At the top of the screen, choose [File], then [New], then [Library]. This will create a new blank Eagle Library which you can then populate.

Once created, you should be presented with the blank open library. If not, double click on the new library you created.

You will want to create a new [Footprint]. And give it a name. Anything will do…

Once you’ve committed to the new name, you can then begin the process of creating the new part:

  • Select Grid/Size
  • Set the units to “mm” and the grid size to “1”.
  • Hit OK to return to the editor.
  • Select the “Hole” or “Drill” tool.
  • Set the Drill Diam to 3.2
  • Place the new hole right in the center at (0,0).

You now have a hole right in the middle of your new part’s footprint entry. Placing a part, like a hole, centered at (0,0) makes it much easier to use when it comes time to place the part on a real board, since most holes’s positions are based on the center of the hole and not the edge of the hole.

The next step would be to add a sort of exclusion zone around your mount hole. This will keep things out, so that screwing a bolt on over the area surrounding the hole will not damage the electrical traces on the board.

  • tRestrict, bRestrict, vRestrict (copper traces, pours, and vias)
  • tStop and bStop (solder resist mask)
  • tKeepout bKeepout (components’ clearance/etc.)

To create a restriction for each of these, you will need to define a space and have a copy on each layer.

  • Change Grid Size to 3mm.
  • Change the Layer to one of the ones mentioned above.
  • Select the circle tool. This will create a solid circle.
  • Create a circle centered at (0,0) and have it go one snap point out, which will be 3mm. This effectively creates a circle with a diameter of 6mm, which works well for quite a number of M3 bolt heads, though not all.
  • Rinse and repeat for each layer.

Once all of the layering is done, you will end up with something like the above. A densely meshed circle. The orange inner ring is the drill hole and the boundary circle. The cross/hash are the different layers’ circles defining a safe zone around your M3 hole.

Once you have it done, save and you will be able to use the part in your next project.

I cover it in the video: Go to Open Library Manager, Add the new library you created by going to “Available”, selecting “Browse”, and browsing to it and adding it. Once added, select the library in the available section and select “Use”. This will make the library show up in “In Use” and you will now be able to find the part when you search for a part to add to your Board design.

Resources and Associated Links

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