Below we discuss different topics related to cnc-machining that help understand problems and difficulties related to the process along with potential solutions. Check also our Terminology page for cnc-related slang
As you use a spinning tool (milling bit) to cut out pieces you will get round off corners in inner corners which have a radius equal to the radius of your milling bit. This means there's no way to get a perfect sharp corner when cutting out shapes that will need to slot together like a puzzle.
However, there is a way to make sure you can still put your pieces together: dogbones. Dogbones are adjustments to the corners to make sure the milling bit cuts a bit into the shape such that pieces will be able to slot together. This adjustment is an arc which gets added and has the same radius or higher as the radius of the milling bit. There are 2 different types which just depend on the location of the arc: T-dogbone and a regular dogbone. Have a look at the image below to see the difference between the two.
As you can see, the T-dogbone is more visible than the regular dogbone. So one might ask why would you use them? Well, depending on the way your pieces slot together these actually can become hidden when placed in the correct position, as shown in the image below.
The most expensive design mistake in CNC machining...
Have a look at the image below. Left is drawn with radius equal to milling bit - right is drawn with a radius bigger than the milling bit. Note the changing offset allowance in case your material is not precisely the specified thickness in the way it has been drawn. As the allowance offset increases the corner doesn’t get cleared entirely.
Flat bits mean they create a flat bottom surface when using them to cut and come in a variety of forms. The most commonly used ones at fellesverkstedet are the Upcut, Downcut and Compression bit.