What is a Dogbone and how to make it with your CNC machine ?

Whenever you want to joint 2 pieces using mortises and tenons, you will encounter a problem: your mill is round and can’t make square holes. To get around this problem, we use a technique called “dogbone”.

In the world of CNC milling, a dogbone is simply a way of deforming a square to fit another square in it.

The most basic model of dogbones is: drilled circles of the diameter of your end mill on the corners of your piece. But this requires a separate operation to drill them, as the rectangle's tool path can't reach such shallow regions.

The true optimal dogbone solution is to make them a little more discreet and integrated in the contour/pocket operations of the shape for that they need to be done like this :

A circle of the diameter of your mill that is offset by half the endmill diameter, on a 45 or 135° angle, but they take more time to draw.

For those of you who are working in Fusion 360, there is a super handy free Add-In we advise you to download, that creates dogbone automatically ! 

It adds a new function in Fusion that works like this. 

1. Make your design with regular edges and without thinking of dogbones. 
2. In the design tab, click on the dogbone icon. 
3. Select the edges you want to become dog bones, and enter the parameters according to the tool you are going to use, and the Radial offset you desire. 
4. It will automatically create dog bones on all the corners you've specified.

You can download it directly here.
And find all the information about it on this GitHub repository.

If you are using a lot of dogbones in your designs, we also recommend this more advanced Add-on : Nifty Dogbone. It is not very expensive and will manage updatable dogbones on any complex designs