Boring on the Lathe - 2: Boring bars
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
The oldest style of boring bar is the round shank with a hole through one end and a set screw in the tip to keep a high speed tool bit in place. This is the style shown in the animation on the first page (above) and the image on the left.
The most common boring bar in the shop would probably be the brazed carbide type. These are steel bars with a carbide tool bit brazed into the tip. They usually come in sets like the photo on the right. The sets come in various holder diameters to fit the tool holder being used. However the tools in each set are all the same holder diameter. The sets vary in length and shank diameter to suit the needs of the machinist.
The photo on the left shows two brazed carbide boring tools of the same length. One is a large diameter and the other is skinny in diameter therefore one is sturdy without much flexure and the other will flex quite a bit.

As a rule never use a tool smaller than you have to or longer than you have to. Keep things rigid.

Still another type of boring bar is the carbide insert style shown on the right.
If you chose to you could mount an adjustable milling machine boring head in the tail stock of the lathe and use the quill to feed into the part. In this case diameter is controlled by offsetting the adjustable boring head. The carriage is not used at all.

I have actually seen this setup run once. It was a long part that reached further than the carriage could be rolled out. The part was turning in a steady rest and the boring was accomplished as explained above R.S.
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label: lahte boring, broing bars, setup, controll, cross slide boring