Cutting a Helix on a CNC Mill

A great feature of a CNC mill is its ability to cut on a helix. Having the cutter travel a helical or “corkscrew” path has several advantages, such as reduced cutting time and smoother operation. Let’s take the cutting of a 1/2″Ø, 1/2″ deep, flat bottomed, blind hole as an example.

A typical approach to this task would be to first drill the hole with an undersized drill to remove most of the material. A simple program could then be written to plunge the cutter in the center of the hole, which will work fine for most of the hole. The problem comes when the cutter approaches the bottom of the hole and the material that was left by the drill point. Normally the feed must be reduced rather drastically in order to avoid damage to the end mill.

A simple helix program avoids the problems with plunging. Most times, depending on the cutter style and size, the hole can be cut without any drilling at all. And if you do drill first, because the tool is constantly moving down in the Z-axis at a shallow angle, the cutter takes care of the material left by the drill point without any frightening noises or chipped teeth. One pass around at a constant Z level will serve to flatten the bottom of the hole.

Many controllers will allow the programming of helical cutter paths (some don’t though). Here is an example of a helical program used on a Haas mill. Of course, the code will likely need to be modified to work in different controllers. The use of variables in the program would make it even easier to program.