Every farm shop has an assortment of small cans, jars and tubes of concoctions designed to help with repairs around the farm. Some of these products work great, some work sometimes and some never seem to live up to the promises on their label. The trick is to use the right goop or glop in the right place in the right way.
Pipe thread sealant. Known as "pipe dope," this sealant comes in several formulations. Old-style pipe dope is a paste-type sealant that’s prone to dry out over time, which increases the chance of leaks if the pipe fittings are subject to vibration and makes disassembly difficult when it comes time to repair or replace the fittings.
Modern pipe dope that contains Teflon offers the lubrication of Teflon combined with a flexible, low-strength thread-locking compound. Representatives of 3M say that pipe dope with Teflon will seal fittings against low pressure (household water pressure) upon assembly and cure within 24 hours to produce a semi-flexible bond that matches the burst pressure of most water pipes.
Teflon thread tape. This isn’t a goop or glop, but it offers a less messy alternative to Teflon pipe dope. Wrap thread tape onto male pipe threads clockwise, as if threading a nut onto those threads. Two complete "wraps" around the fitting provides an adequate seal.
Because Teflon tape dramatically reduces friction during assembly, it’s easy to overtighten fittings. Merely "snug" fittings with a wrench, then do one more turn. Tightening until you can’t turn it anymore can strip threads or crack fittings.
Use Teflon tape only on tapered pipe threads, never on straight-thread O-ring or flat-face O-ring fittings. The thickness of the tape wedged between the nut and straight-cut threads of the fitting can create tremendous pressure when tightened, damaging the nut and threads and causing the fitting’s seal to fail.
Retaining compounds. Used in the assembly of press-fitted cylindrical metal components (such as shafts inside sprockets, bearings onto shafts, etc.), these make a tight fit even tighter, which is generally a good thing.
Coat a shaft with retaining compound before installing a bearing, sheave or pulley, and those components are cemented together so well that future disassembly will require the use of a torch to melt the compound.
Retaining compound will fill voids of 0.005" to 0.010" and can theoretically be used to repair a shaft that has been slightly worn by a "spun" bearing. Mechanics consider such use a temporary, emergency repair, only to be used to get a field finished or until complete repairs can be made.
If a fingernail catches on the groove in a worn shaft or an audible "click" is heard when the bearing or sprocket is wobbled on the shaft, it is best to replace all damaged parts.
Epoxy. This is the generic name for a thermosetting resin. Epoxies are sold in kits with ingredients that, when mixed, undergo a heat-producing chemical reaction to "cold weld" cracks and holes in metal, plastic and fiberglass. Once cured, epoxies can be sanded and painted.
The secret to using an epoxy is to apply it to clean, bare, unpainted surfaces and to follow directions. Adding more hardener to make it cure "faster" or extra resin to make it "stronger" can dramatically weaken the final product. That’s why many epoxy manufacturers now package their products in double syringes that squeeze out properly proportioned amounts of hardener and resin.
Epoxies mixed at the proper ratio will bridge holes and cracks up to ½" wide. Larger holes might require reinforcement with fiberglass netting, metal netting, etc. Allow 24 hours to cure. Properly mixed epoxy is often stronger than the surrounding metal, plastic or wood.
Cool Tool of the Month
"Air-in-a-can" technically isn’t a tool like a wrench or hammer, but it can be just as useful as those toolbox standards. It’s faster and easier to use air-in-a-can than to drag out an air hose and fire up the air compressor to clear away a little dust in a circuit box or dry a surface prior to
applying epoxy or retaining compound.
- Mid-February 2012