15 - Sliding Table, страница 14

15 - Sliding Table, страница 14

IN THE SHOP

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Epoxy Systems

For years the only type of epoxy I

used was the "five minute" variety sold at most hardware stores. It was great for quick repairs — to mend a cracked plate or fix a broken toy.

It wasn't until I discovered epoxy "systems" that I realized how

useful epoxy can be for -

woodworking. It's extremely strong, virtually waterproof, and doesn't shrink at all.

two parts. Like the five -

minute varieties, an epoxy system comes in two separate parts: a resin and a hardener. When the two parts are mixed together, a chemical reaction occurs that hardens or "cures" the epoxy.

What makes an epoxy system special is you can vary the curing time by choosing the type of

hardener. Fast hardeners cure in

Epoxy 5yeteme Tipe

Use an epoxy system when you need a bond that's strong, waterproof, or won't shrink. Select a hardener to provide the working time you'll need (slow, medium, or fast). Measure out only what you'll need. Mix thoroughly, scraping the container often. Add sanding dust (if desired) to make a filler. No clamps required, just immobilize the parts. Remove any squeeze-out before epoxy cures. Heating up epoxy causes it to cure faster. Cooling down epoxy causes it to cure slower.

about ten minutes. Slow hardeners offer a much longer assembly time — up to an hour. This makes it the perfect choice whenever you need to glue up a project that has a lot of parts.

In addition to this, epoxy does some things other glues can't. It can bond dissimilar materials together — like metal to wood. I often use it to glue a bolt in a jig. Or to repair a stripped-out screw.

And since epoxy only requires

It ivasn't until I discovered epoxy "systems" that I realized how useful epoxy can be.

that the parts touch each other for a good bond, it's the perfect solution for those awkward situations where you just can't get a clamp onto something.

customize. But the thing that I like best about epoxy systems is they allow you to customize the epoxy to fit your application. By varying the mix ratio on some

_ systems, you can change

the curing time. Other systems provide a variety of fillers that can be used to change the consistency of the epoxy. (For more on this see the box on page 15.)

drawbacks. The only drawback to using epoxy systems is they can be expensive. And since they come in two parts, they're not as convenient as pre-mixed glues. (Epoxy systems can be found at some wood

working stores. Or they can be mail ordered, see Sources on page 31.)

three steps. There are three basic steps to working with any epoxy system: measuring out the two parts, mixing them together, and applying the mixture.

HIEASURINQ

By far the most important step to working with an epoxy system is measuring. When measuring out

- the parts, make sure you

follow the directions.

Some manufacturers allow you to vary the mix ratios. Others don't, and they - warn that an improper ratio can result in a mix that won't cure (what a mess), or one that is weakened if it does cure.

The most typical mix ratio is two parts resin to one part hardener. But depending on the product, it can vary up to five parts resin to one part hardener.

One trick that I discovered when measuring out epoxy is to only measure out what you'll need — you can't save the leftovers. (If you're working on a large job, it's best to use several smaller batches.)

As you measure out the parts, it saves clean-up time if you pour them into a disposable container (such as a plastic yogurt cup or a small can). Just keep in mind that as soon as the two parts are combined, a chemical reaction begins and the epoxy mixture will get hot. So don't use Styrofoam cups — they can melt.

safety tips. There are a couple other things to keep in mind

14

ShopNotes

No. 15

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