Lathes are a mainstay of professional and amateur machine shops around the world. They range from industrial, fully-automated CNC lathes to amateur woodworking or metalworking lathes. Maintenance on most lathes doesn’t require a lot of extra work, but it is important to know some of the basics.

Aligning a lathe tailstock isn’t just necessary for the overall maintenance of the lathe, it’s also a way to perform some advanced cutting techniques. In this article, we’ll review the function of the tailstock on a lathe and several methods for aligning it.

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The function of a tailstock in a lathe

The lathe headstock holds the workpiece in place and has a live center to turn the workpiece. The tailstock doesn’t always need to be used – smaller workpieces, particularly wider and shallower ones, may not require the extra support that a tailstock provides.

Typically, you’ll use a tailstock for supporting a longer, thinner, and/or heavier workpiece. The dead center in the tailstock allows a workpiece to spin freely while still being supported. A workpiece mounted in this way is said to be turned “between centers”.

At other times the tailstock can be used to mount a drill bit or other tool. The tailstock is then advanced slowly into the workpiece, creating a hole in the center. When properly aligned, a tool mounted on the tailstock can produce a perfectly dead-center hole in the workpiece. 

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Aligning a tailstock

There are a number of ways to align a tailstock. Some are quite complicated, some are quick and easy. Which method you choose will depend on what you have the time and patience for, and how accurate you need your results to be.

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Method #1 – Commercial Precision Alignment Bar

One of the easiest ways to align your tailstock is to purchase a pre-made alignment bar. This is mounted between centers, and the test indicator is mounted on the lathe saddle.

At this point, alignment itself is easy. The dial indicator is moved along the length of the bar, and any misalignment between centers will be shown on the indicator. Mounted the same way, the dial indicator can also be used to detect and correct vertical alignment as well as horizontal.

Pros:

• Easy to set up
• Quick process
• Intentional misalignment can be measured and set to make a tapered cut

Cons:

• For best accuracy, requires the lathe center to run true, with no wobble or misalignment on the headstock
• Requires a highly accurate alignment bar

Method #2 – Test Bar

With a test bar mounted between centers, a series of cuts can be made the length of the bar, and measurements taken of each diameter after each cut. Any misalignment will be reflected in the difference between diameters, and the tailstock can be adjusted until the dimensions match.

Pros:

• Uses easy-to-find material
• Doesn’t require a “true” center

Cons:

• More time-consuming
• Wastes material (the test bar)

Method #3 – Indicator Mounted to Headstock

A simple but quick method, this approach requires mounting the test indicator to a fixture which itself is attached directly to the center of the headstock. The dial indicator rotates freely along the axis of the lathe, as a normal workpiece would.

A simple parallel bar is mounted on the tailstock, and then advanced until the test dial rests against the bar. At this point, the dial indicator can be zeroed in an original position, and then slowly rotated along the circumference of the parallel bar. Measurements can be taken in three or four positions (top, bottom, and sides of the bar) which will show if and how much the headstock is out of alignment.

Pros:

• Needs only a dial indicator and a parallel bar

Cons:

• May need to fabricate a special fixture for the dial indicator

Conclusion

Aligning a tailstock isn’t an impossible task, although finding a method that gives the desired accuracy might take some trial and error. There are nearly as many different methods to align a lathe as there are machinists to run them, so experiment with the ones that work for you until you find one you like.