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Adam New wood lathe belt
June 4th, 2005 07:59 PM
I've been playing with the one returned to my PMT shop and have talked to another maintenance technician who's done this before.

You need to unscrew the top 3mm allen socketed round-head screw holding the red plastic hinged cover closed, unscrew the remaining four top screws holding the black top tray in-place and last, but not least, removed the four flat-head screws (2 front/ 2 back) holding the whole black cover and red hinged cover onto the lathe's headstock.

Once this is done you should have the same marvelous view of basic mechanics I have in my PMT shop.

The top pulley assembly (driving the lathe's spindle assembly) consists of the spring-loaded "follower" split pulleys. All that is keeping this unit functioning is the spring inside the sheetmetal protective cup to the left of the pulleys and the smooth running of the moving pulley half. DO NOT remove the snap ring. It is not necessary to dissassemble this subassembly to replace the drive belt.

If you have, post back and we'll go over another "really..." fun procedure in reassembling the spring-loaded assembly.

A little bit of oil on the pulley shaft (outside pulley sides, no excess oil on the inner pulley sides please) will help keep things "following" properly.

The bottom assembly is the little engineering masterpiece. It appears to have less moving parts and be more robust than either a Delta variable speed drill press or my Shop Smith's mechanism.

Rotating the speed change dial, turns a threaded shaft that cause a 90 degree angled yolk to move the bottom pulley's right side in and out, effectively changing drive pulley diameters.

The follower pulley above compensates for increase or decrease in belt tension by literally changing (spring-loaded) its diameter.

All this happen while the machine is rotating. Otherwise, the yolk would be subject to a great deal of stress, with no change in effective pulley diameter to relieve it and most likely break.

Now, to see this you have to have the safety covers off. So, standard safety procedures dictate; safety glasses, no loose clothing, no tie (don't laugh, they used to wear them in the shop?) and in my case my bolo is tucked inside my shirt and Sears ID badge is firmly lodged in my breast pocket.

Changing the speeds on your lathe, while watching the two pulleys give and take may be a unique experience for you. Enjoy.

When you're ready to proceed, dial your lathe speed control (with the lathe turned on) to the lowest speed. Even if you old belt is "elsewhere", this will set your pulley ratios where you'll need them later.

The proceding involves working with drive components. UNPLUG your lathe.

To get a new belt on, you're going to need to remove the bottom bracket assembly (four 5mm allen cap screws). The end plate will come off very easily.

There is just barely enough room to slip off your old worn belt. With the belt out of the way, check the split pulleys' inside surfaces to make sure no belt material (or other foreign substance) is present. It there is, remove with a solvent (Goop off). No oil here please. The new belt will be traveling back and forth through the whole range enough times to make rusting concerns just about moot.

Slide the new belt over the bottom pulley and immediately replace the bottom bracket (with the four cap screws).

Your new pulley is set to go and all you need to do now is gently "roll" it onto (and into) the top pulley assembly. Bear in mind, your top pulley assembly is going to be snapped closed in the beginning. So, part of this rolling effort is going to involve gentle hand turning the spindle (large faceplate would be of help here) while you're rolling the new belt in place.

Once you've got the belt on. Immediately plug the machine back in and do a trial speed range run to make sure any stresses are removed from the installation procedure and to verify your lathe is now fully functional.

Bingo! You just saved $110.
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