A Boring bar is a tool used in metalworking and woodworking. Boring is a technique used in many aspects of building. Woodworkers have used boring as a form of drilling for centuries. In woodworking, the boring tool is static in size and used to form circular plunge cuts. In metalworking, boring is slightly different in that it refers to not only the creation of a hole but includes the ability of making a non circular hole. In metal boring you can plunge and drag the tool in the X,Y or Z axis creating a slot or asymmetrical hole or channel. Or, use it in an up and down motion (Z axis) to create a smooth cut perfect circular hole.
Modern boring tools have 3 primary components although many differing designs. The parts include the Body, Bar Holder and Dial Screw (graduated micro screw). The body is made of solid stock has 2 basic parts. The top part will thread or press into the supporting shank. The lower part (bar holder) will be connected via dovetail, T-slots or a smooth notch with an adjustment for bore diameter via the dial screw. As you adjust the dial screw the cutting bit/s will be moved further out creating a larger cut. This also can create some slight distortion if the cutting tool is moved further than the boring head is designed, if there is undue wear in the bearings supporting the tool or if the tool speed is too great for the off-balance effect caused by moving the tool too far from center. This is called unbalanced gyroscope precession.[1] Once the dial screw has been adjusted giving the proper cut a set screw is generally used to prevent any additional movement of the cutting head. The third basic part is the boring tool. Boring tools can be mounted vertically or horizontally in many boring head designs.
Boring can be done on mills, lathes or drill press machines, either with a boring head or just a boring tool. The shorter the distance between the tool holder and the material the less distortion created from reverberation or unbalanced gyroscopic effects. The greater the distance (static or dynamic mounts) the more flex in the tool or an increase in the unbalance of a moving tool. By using a boring head you have increased the mass of the tool holder and decreased the distance. If a reverberation is created it will be at a higher frequency and the deflection of the tool from the desired path will be much smaller and easier to erase through repetitive tool passes. In the case of a dynamic tool (mill or press), you can adjust the balance of the tool with counter weights if the tool is mounted perpendicular to the shaft or decrease the tool length (choke up on the tool).