Drive pulleys and belts can cause a good deal of trouble, even in new lathes. If a lathe has “as cast” die-cast pulleys (which are common on economy lathes), chances are that they are neither perfectly concentric nor round. Since V-belts grip on the flanks of the pulley groove, a dial indicator is of little or no use in checking accuracy. The best method is to turn the pulleys over by hand with a pointer held stationary in the groove. You can clamp a pointed object such as a scriber in a suitable place near the pulley. Any radial or side-to-side runout will be apparent through care full observation. Concentricity tolerances for pulleys are quite loose typically 0.005-in. to 0.006-in. minimum runout. If the runout is excessive (more than 0.010 in.) and your lathe is having vibration problems, the pulley is the likely culprit.
VIBRATION IS A PROBLEM that can cause great consternation, since turning is difficult if the machine and work are moving around. Vibration tends to be speed related-most lathes have a bit of vibration, usually at one or two specific speeds. This is one of the reasons I like variable speed. If the work itself is causing the vibration, tweaking the speed up or down a bit is an instant cure.
Pulleys and belts are the most common sources of vibration, so these are the first things to inspect. Check for worn belts and out-of-true pulleys. If these are in good shape, next check the dynamic balance of the rotating parts. The motor may even be out of balance; although this isn’t a common problem, it does happen.
Vibration is often a problem on lathes that have sheet-metal stands. Pouring sand into the stand can work wonders, but you have to make sure that the sand doesn’t get into the motor, pulleys, and other moving parts. (If you’re pouring sand into the stand, make sure you leave some air space below the motor for cooling purposes.) Placing sand bags in the base of the machine will often do the trick. Stamped-metal legs can be reinforced by adding wood cross braces, and vibration can be dampened by draping sand bags over the cross members. Another alternative is to build a replacement plywood box stand for your lathe and fill the legs with sand.
Truing Die-Cast Pulleys in a Wood Lathe
If you have a lathe available while your lathe is apart, this is a good way to true a pulley.
What you should do about pulleys that are out of true will depend largely on how much money you want to spend and how much trouble you’re willing to go to. The best solution is to replace the defective pulleys with machined cast-iron models, which should last as long as your lathe. High-quality pulleys to fit most spindles are available at most bearing stores, but they’ll be expensive ($30 to $60 each) and will have to be special-ordered. If your headstock spindle is an odd size, you may still have to have the arbor hole in the pulley bored out and a new keyway roached.
Another remedy is to have the pulleys machined by a local machine shop. I’ve also mounted die-cast pulleys in a wood lathe and machined the sides of the grooves with a scraper. I mount a suitable square of wood in a four-jaw scroll chuck such as the Nova or the Oneway. I then tum the end to a short stub arbor that’s a press fit with the pulley. I push the pulley on the arbor and lock it there with the setscrew in the pulley, as shown in the photo essay on the facing page. I further support the pulley by bringing the tailstock up close and engaging a live center with a 60° point into the bore of the pulley. I now start the lathe and scrape the offending groove flanks true. It’s really quite simple. However, since your lathe is apart there are some technical problems to overcome-you’ll either have to do the work on a second lathe, or temporarily substitute a simple one-groove pulley for the one you’re scraping.
Sometimes dirt and rubber from the belt will build up in the pulley grooves and cause the belt to make a “klunking” sound as it runs. This buildup can usually be removed with solvent, but sometimes it will require sanding or filing. Again, mounting the pulley on a stub arbor can help in this task. Finally, a pulley greatly out of balance can cause excessive vibration. Many automotive machine shops have dynamic balancing machines and can remedy the problem for you. For the headstock pulley, have both the spindle and the pulley balanced as a unit.
Belts are much like tires, ranging greatly in price and quality. The difference between discount-store belts and good belts is like the difference between bias-ply tires and radial tires. A cheap belt will be stiff and uneven in cross section and will often cause noise and vibration. You can obtain a high-quality replacement belt from a bearing store for less than $20; Gates Green Belts is a reliable brand. It’s good shop practice to replace the belt whenever you replace the bearings and vice versa. Normally, you can expect to get two to five years of use out of a good belt, but less if your lathe has a variable-width pulley speed control.
The motor that powers your lathe may sometimes require attention. When faced with a motor that won’t run, you have two options: repair it or replace it. Your nose will usually tell you if the motor is burned out-it will have a distinct electrical-fire smell. Unless the motor is underpowered to begin with, rewinding is typically a good option. A motor rewinder (look in the Yellow Pages or on the Internet) can rebuild the motor for $100 to $ 1 50. A rewinder can also help with other motor ills. Common problems with single-phase induction motors are burned-out starting winding, problems with the centrifugal starting switch, and a bad capacitor.