Small High Precision Lathes

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Small high precision lathes have numerous adjustments that can be made to significantly improve accuracy in finished products. These are all things to keep an eye out for when purchasing a new, or even a used high precision lathe:

• The saddle, cross-slide and compound should have a bare minimum of play. Grasp the compound and twist it from side to side. A properly adjusted lathe should allow very little movement.

• Check the gibs, the metal strips that sit to one side of a dovetail slide (such as the cross slide and compound). A properly adjusted gib with good gib screws should be adjustable so that the dovetail slide is very smooth and snug.

• Look at the faces of the gib. These are often fairly rough, although they can be polished and lapped for a smoother finish. Is the face of the gib lubricated with white lithium grease?

• Grasp the cross-slide at its end and see if it will slide back and forth. There should be movement of about .100 inches. With proper adjustment, this movement can be reduced to about .020 or less.

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... When you turn the carriage handwheel by hand, the saddle should move along the ways with no binding or sticking, but should also be tight enough to allow very little slop or play. Move the carriage about halfway along the ways, then grasp it and see if you can rock it back and forth. If everythings properly adjusted, it should allow very little movement. Too much play or slop will cause chatter while cutting, making a smooth, clean cut difficult or impossible.

• Remember that the metal strips are brittle and can easily crack around the position of the set screws if excessive force is used. Be sure to inspect this (and dont crack them yourself in the process of inspecting the machine).

• Check the lathes motor and drive belts. Typically, a lathe will have a toothed automotive-style belt for its main drive. Is the belt in good shape? Is it cracked or does it have teeth missing? Is there slop or deflection in the belt? Is it aligned properly between the lower and upper pulleys? A properly aligned belt should not touch any part of the lathe other than the two drive pulleys themselves. A slightly off-kilter belt can be corrected, though, by slight adjustments of the position of the motor itself.

• Have a look at the headstocks internal parts. A properly maintained headstock should have lithium grease on the gears, shafts and levers. Neglecting this maintenance can lead to the Hi/Lo lever seizing up, or other problems.

• The main bearings and spindle need to be properly aligned. This is essential to the accuracy of the lathe. Check the alignment with whatever tools are needed.

• If you remove the headstock for inspection, be careful when reinstalling it. The headstock will have a V-groove which mates with the ways for proper alignment. Make sure that no chips or grit are present on the base of the headstock when it is time to reinstall it.