Drawbar (machine tool)

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A W-type external-thread collet (red) being pulled into its spindle seat (green) with a drawbar (blue), clamping and then releasing a shaft. External thread pull collet action.gif
A W-type external-thread collet (red) being pulled into its spindle seat (green) with a drawbar (blue), clamping and then releasing a shaft.

A drawbar or spindle drawbar is a clamping mechanism for toolholders on machine tools. The toolholder or machine taper itself is held by the draw bar and applies force to the spindle, especially when spinning at low speeds.

Contents

Drawbar Pull

The drawbar pull is an important component that allows the milling machine to keep the tool in place while it’s being used. The force from the drawbar pull supplied to the tool has to be just right because not enough force would cause the tool to wobble leading to inaccuracy, and too much force would apply a lot of stress leading to shorter tool life. Regularly checking the drawbar pull using a drawbar force gauge would ensure that the spindle and tool stay in tune so that your machine stays running efficiently. [1]

Drawbar Materials

Choosing the right material for a drawbar is important because the milling machine needs high durability. Some commonly used materials are High carbon steel, Stress-proof steel, Heat-treated alloy steel, and Black oxide steel.  

Types of Drawbars

Threaded Drawbars

Threaded drawbars are less common in milling machines but still get the job done. This drawbar has a more hands-on approach because it requires the operator to use a wrench and hammer to perform some twisting and tapping so the cutting tool can be removed.

Power Drawbars

Power drawbars are starting to become more popular in milling machines because they are a fully automated version of the drawbar. The way it works is by using compressed air to tighten and loosen the spindle giving the operator an easy way to change tools. [2]

Choosing the right Drawbar

Choosing the right drawbar is important when setting up a milling machine. The right drawbar can be the difference between a good or bad milling machine by affecting its lifespan and efficiency. When choosing a drawbar things to consider are how it fits in the machine, the material of the drawbar, finding a drawbar that is easy to install, and making sure that the drawbar is easy to maintain.

See also

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References

  1. 1 2 "What Is A Drawbar On A Milling Machine?". Lathe Mastery. 6 September 2023.
  2. 1 2 Wilson, Charles (February 28, 2023). "What is a Drawbar on a Milling Machine?". Lathe Matters.