In the unlikely event that you have an old lathe with plane bearings, you can keep the lathe running smoothly by oiling the bearings on a daily basis. Most lathes today, even those found on the used market, are equipped with ball bearings that are lubricated and “sealed for life.” These bearings don’t require any regular maintenance, but they do need to be replaced every few years.
The sides of ball bearings are generally sealed with plastic, which retains the grease packed into the bearing during assembly. Age and use take their toll on any grease, even in a sealed-for-life bearing. Eventually, the grease fails and the bearing fails shortly thereafter. I’ve always joked that a sealed-for-life bearing is just that: It’s sealed for its life, which is however long it takes for the grease to fail. Fortunately, this is typically a good, long time.
If you use your lathe on a regular basis, you probably won’t notice the gradual loss of bearing performance. If your bearings are more than five years old, however, chances are they’re anemic, if not spent, and it’s time to think about replacing them. A good test for worn bearings is to remove tension from the belt, which leaves the headstock spindle free to turn without resistance. Spin the spindle by placing your hand on the pulley. If the spindle spins freely and the bearings have a “dry” sound and feel, the grease is dry. (If the grease is still good, the spindle will have a slightly dead feel and not want to spin freely.) The first order of business is to remove the offending bearings.
I can’t offer a definite prescription for removing bearings since no two headstock designs are the same. However, understanding how a typical bearing assembly goes together should help you figure out any headstock. The surfaces of the bearings and the bearing seats (the areas on the spindle where the bearings ride and the pockets in the headstock that hold them) are machined to strict tolerances.
There are two types of fit for the bearing seats: a sliding fit and a press fit. In a sliding fit, the two mating surfaces can slide over each other, but there is no radial play. In a press fit, a slightly larger diameter is pressed into a slightly smaller mating diameter. The difference is typically on the order of 0.0005 in. Such assemblies require an arbor press to put them together (see the photo above).
Because the headstock spindle expands as it heats up during use, at least one of the bearing seats must be a slide fit. The bearings are a press fit into the headstock casting, and the front bearing is a press fit against the shoulder on the spindle. (The other side of this shoulder is the shoulder for the nose thread.) The back bearing is a slide fit with the spindle.
Most lathes have additional fittings to hold and cover the bearings. Often, metal rings screw into place with three or more screws around the spindle, and these may contain seals that further protect the bearing. A common design is to have a fine thread on the back of the spindle (the end opposite the nose) on which there are two nuts. The first nut runs up against the inner race of the bearing and is adjusted until there is no play in the assembly. The second nut is then locked against the first.
Sometimes a wavy washer is interposed between the nuts and the bearing as well, its purpose being to remove play from the assembly. This washer should be replaced with the bearings because it invariably takes a set. Snap rings are used extensively today, and there are typically an array of spacers and washers involved. As you disassemble the headstock, make a careful sketch of the order in which you take off all of these parts so that you can reassemble everything correctly.
Once you’ve taken the headstock apart, there are a variety of ways to remove the bearings from the spindle. One method is to use a bearing puller (see the photo on the facing page). A tool of this type would be used for removing the back bearing, and possibly the front, from the typical headstock shown in the illustration above. To remove a press-fit bearing from the spindle, you’ll normally need an arbor press. Often the entire headstock must be placed in a press.
If you have a European-style workbench, it’s not difficult to improvise an arbor press. Using the bench dogs in combination with arbors and support blocks, both turned and fabricated from durable wood, will provide the necessary support and force you need to remove the bearings from the spindle.
Support blocks can be made in one of two ways. One is to nail and glue up a right-angle plate from scrap wood. I used such a plate in the photo essay of replacing the bearings in a Delta headstock. The second way is to mount a square block in a four-jaw chuck and drill a hole through it to a diameter slightly larger than the spindle (11/8 in. for the spindle assembly in the photos). Then scrape a pocket in the support block to accept the bearing.
To make an arbor, turn a hickory or oak billet to a tenon with a shoulder. The tenon diameter should be equal to the inside diameter of the shaft. Clamp the support block to the workbench, insert the tenon into the spindle, then use the tail vise to force the spindle out of the headstock or bearing.
Although it’s tempting to pound the assembly apart using soft-faced mallets and blocks of wood, I strongly urge you not to do this because this practice can ruin the bearings by putting flat spots on the balls. Although it makes no difference in the disassembly, it does in the assembly. Since one is merely the reverse of the other, it’s not a good habit to get into-in my opinion, hammers have no place around bearings. Once the bearings are out, test them by spinning them with your hand. If the grease is dry, the bearing will spin and even coast for a while; if it’s really bad, you’ll feel flat spots in the bearing.
Replacement bearings are easy to obtain. Each bearing will have a shield number on one or both sides, which should be all the information a bearing supplier will need to get you a replacement. For instance, a 2802Z would be a double-row bearing that presses into a 13/8-in. bearing seat and accepts a sis-in. shaft. Bearing suppliers are listed in the Yellow Pages (Bearing Distributors and Technico are two of the better-known companies). It never hurts to take the bearing along with you to the bearing store so you can check the replacement directly against the original. You’ll be amazed at just how inexpensive a new set of bearings is-typically no more than $25.
This method uses a European-style workbench as an arbor press.
Once you have the new bearings for your lathe, reassemble the spindle assembly and headstock in the reverse order that you took it apart. The correct sequence for reinstalling the bearings on a Delta headstock.
In the rare event that you have a very old set of bearings for which replacements are no longer available, you may still be able to salvage the bearings. Such bearings are typically shielded with a metal disk on one side but not sealed. Once you have the bearings out of the headstock, soak them in kerosene or a similar solvent (in a well-ventilated area) to remove the old, dried grease and dirt. Never use compressed air on bearings since it normally ruins them. Using a soft brush and some elbow grease will remove the dirt just fine.
Next, heat up some grease in a metal can by using an electric hot plate. Be most careful of fire-I prefer to do this kind of work outside. Almost any good-quality automotive grease will work, but if you’re a stickler for doing it right, you can get tubes of grease specially formulated for bearings at any bearing store. Drop the bearings in the liquid grease, and let them soak for a while. Once the grease cools, pull the bearings out, remove the excess, and you’re back in business.
Although it’s not a difficult job to replace bearings, not everyone has the proper tools for it. The best alternative to doing it yourself is to take the entire headstock to an automotive machine shop and have the work done for you. Automotive machine shops abound, and they’re well equipped for any work involving bearing removal and replacement. On most lathes, the headstock is a separate piece that can be removed. If the headstock and bed are a one-piece casting, you’ll have to take the entire machine to the shop. If you cannot find an automotive machine shop, check the Yellow Pages and the Internet for “Machinery Repair Companies.”