Lathe Maintenance

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Just a few noteworthy items on lathes or any machine tool with ways.

A lot of people worry about being able to operate a lathe or other precision machine tool in a manner that will be consistent to produce a fine finish to a given tolerance. Many think that learning to operate it efficiently is all you need to know.

For any precision tool to operate with precision and to maintain that precision over time it must be MAINTAINED PROPERLY, just like an automobile. It needs to be lubricated at regular intervals with the proper lubricants, to be cleaned to protect its finish and its tires and spark plugs need to be changed when worn or damaged.

Most older lathes and precision machines do not have roller bearings in them but rather use either brass or babbit bearings which if kept properly lubricated will wear very little over the life span of the machine. Ball bearings in precision machines are not your normal off the shelf industrial bearing, but precision bearings made especially for precision machines, and must also be maintained to keep their precision.

For most things where a brass or babbit bearing is used, a .003 clearance is needed for an oil fit, and .005 for a grease fit. to allow the lubricant to coat the surfaces and do their job. Because of the close tolerance that must be maintained with a precision machine tool, these lubrication tolerances must me less in a machine tool to maintain its precision. This can make the bearings heat up quicker and also wear much faster if not lubricated at frequent intervals with a proper lubricant. In my years in the field of smithing, welding and machining, and visits to different shops I have seen many different opinions and many different lubricants used to maintain these precision machines.

Roller bearings are the easiest to maintain as there are recommended lubricants for use with them.

Brass and Babbit one the other hand require a totally different approach and lubricants. The lubricating medium that has shown the most useful for the headstock bearings (the part that rotates the chuck), in my opinion is a mixture of 8 parts 10W non detergent motor oil and 2 parts of a product called Slick 50, that was originally designed as an additive for airplane engines. A normal lubrication schedule is an application before use and every two hours of use. With a constant vigal of the bearings by feel for heat build up. Heat build up will make the spindle expand in size, and create friction and heat from especially high speed use. The bearing is in a more or less massive housing that will limit the expansion of the bearing, then the combination of friction and heat will decrease the area for the lubricant to flow and may end up galling and seizing the spindle and bearing together.

The most important part of a lathe or other precision machine tool is its WAYS, the highly precision machined and ground runners that the Apron (the part that moves back and forth) move on. Once these are damaged or worn precision just went out the window so to speak. Older machinists or those who have been long time machinists can often still maintain precision cuts by knowing how to position the cutting tool in the proper location to compensate for this wear. Thur the years the best lubricating medium I have come across other than WAY BED OIL is a mixture of 9 parts hydraulic oil and 1 part Marvel Mystery Oil. Hydraulic oil has anti corrosion additives and is made to lubricate the very small tolerances that are necessary in hydraulic pumps and motors. A normal lubrication schedule is to clean the ways before use and apply a light coat of lubricant before use.

THE WORST ENEMY of a lathe is DUST. As you know it is in the air all the time and has a tendency to settle on everything. When it settles on the oily ways of a lathe it mixes with the oil and if not cleaned off completely it forms an abrasive compound that will destroy the precision of the ways.

NEVER use gasoline to clean any bearing surface as it leaves behind an unseen residue that breaks up the film of oil necessary to lubricate. Mineral spirits is a good cleaner and easily obtained.

The best way to prevent dust from building up on precision machines is to COVER them with a COTTON BED SHEET. It will breath, thus preventing any moisture build up under it such as would happen with a plastic cover or tarp, moisture is in the air all the time and it rises with the air from below and if trapped under the cover will condense on the lathe parts and quickly rust the exposed parts.

Another important maintenance item is keeping the cuttings cleaned up so they don't get forced under the Apron as it traverses toward the chuck. A paint brush is good for this. I use air pressure to blow the shaving away, but the old timers would frown on this procedure. If you do use air pressure make sure not to blow the shavings into the gears of the lathe as it may cause the gears to shear teeth and cause excess wear. I make simple sheet metal pans to prevent a build up of cuttings.

As most lathe work is close to the chuck, this is the area of greatest wear to the ways on a lathe.

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9 inch SB tray.


old 18 inch tray.

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To quickly check the amount of wear on a lathe you are looking at, just use your fingernail on the inside of the way nearest close to the headstock as this is where the most wear will be. You can determine the amount of wear by the ridge near the top of the way as shown below. You can see it from the backside in this picture. Although this lathe has seen some use and a little lack of maintenance it can still do the work by careful setting of the tool point.

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The easiest way to set the tool height for a lathe is to use a 6 inch steel rule with the lathe tool point tight against the work and rule so that it doesn't slip down and adjust the point so that the rule is up and down as shown below.



If you take a small cut over the whole length of the piece and then measure the ends and it is not cutting true, their can be several things wrong. First check the tail stock to be sure the tail stock is lined up with the headstock if you are turning between centers (it is adjustable side to side). If its due to wear, and its larger at the chuck end, the lathe apron is either dropping or moving toward you because of wear in the ways. Move the tool bit a little higher to compensate. If it is smaller move the tool point down a little to compensate, then take another small cut to check it. Remember it doesn't take much up and down movement to make a big difference in the outcome of the cut.