Reaction Wood

■ I recently ripped a lot of 4" to 6"-uride pieces ofcherry. As I ripped them, some pieces bent away from the blade, and some didn't. Why did this happen, a nd is there a way to prevent it?

James Clark Garland. Texas I've had a similar problem in the Woodsmith shop. As I ripped the wood, the kerf closed up and started to bind on the blade, or it opened up like a wishbone. From the way the wood bent, I knew I'd run into what's known as "reaction wood."

abnormal growth. 'ITie reason some pieces develop a "crook" or "edge bend" and others don't has to do with the the tree thev were cut from.

Your wood (and mine) was cut from a leaning tree, like one that grew out over a river, or got knocked partly over by the wind.

As the tree grew, it had to adjust or react to gravity trying to pull it down. So it developed some special cells in the trunk to keep itself standing. I"he wood that contains these special cells is called reaction wood.

reaction wood. For some unknown reason, reaction wood is formed differently in hardwoods than in softwoods. When a leaning softwood tree reacts to gravity, the cells on the lower side of the trunk are compressed.

This compression wood is usually harder—but more brittle — than normal. (You mav have come across a hard spot when nailing or cutting pine or fir.)

Reaction wood in hardwoods is called tension wood. fhis is because hardwoods' abnormal cells form on the top side of the trunk. They are "stretched" holding the tree up against the pull of gravity .

Tension wood is usually stronger than normal, so it's difficult to machine. And when cut. it often leaves a "woolly" surface that creates a blotchy finish.

abnormal shrinkage. There's another peculiarity to reaction wood. I'nlike normal wood which shrinks mostly across the grain, reaction wood also shrinks with the grain — 10 to 20 times more than normal wood. .And it shrinks unevenly. So even il you joint the edge straight, over time the edge is likely to bend again.

using reaction wood. Should you avoid using the other boards that came from the same log? Not necessarily. 'ITie severity of reaction w ood varies from board to board. So if the rest of the wood seems normal, use it.

Can you avoid buying it? Probably not. Once logs are cut into boards, it's hard to tell if they contain reaction wood. Fven a reputable lumber dealer won't know if he's selling you reaction wood. So if you do run into some, it's best not to use it, or else cut it into very short pieces for small projects—or your firewood pile.

fence note: rout roman ogee on edge to produce ogee shape roman ogee

ogee bit

OGEE VS. ROMAN OGEE

fence note:

using ogee bit, rout edge with workpiece flat on table

roman ogee bit

roman ogee bit has convex curve at bearing

ogee bit has concave curve at bearing ogee bit and the earlier Woodsmith jig have a similar drawback — the width of the workpiece is limited (by the saw fence on yours: by the jig's second fence on ours). But on the latest Woodsmith miter jig the fences are removable so it doesn't have this limitation. see photo above.

extra control The second reason for building the latest miter jig iscontrol. If you've ever had a workpiece "creep" when cutting a miter, you'll know why

I like the extra control lhat you get with the new jig.

Having a fence on the back side of a radial arm miter jig counters the pull on a workpiece from the spinning blade. On jigs with an inside guide (like yours) you have to hold the workpiece very tightly to prevent the spinning blade from pulling the piece away from the guide.

The higher, narrower fence on the latest jig makes the work-piece easier to grasp. And that means less force is needed to counter the pull of the blade. This makes cutting miters with the radial arm saw more accurate — and safer.

There's one last benefit. You can add a long fence to the new jig. With that and a stop block, you can cut longer identical miters than with a jig that has a fixed support.

OGEE VS. ROMAN OGEE

■ 1 routed an S-shaped profile on the drawer fronts, top molding, and kickboard of the File Cabinet shown on page 6 of this issue.

Selecting the bit to rout that profile can be confusing since there are two S-shaped router bits that look very much alike, the ogee and the Roman ogee.

how to teij_ Here's how to tell them apart. Hie Roman ogee bit hasa con rex curve next to the Ix'aring, see Fig. 1. An ogee bit has a conca ve curve coming off the pilot bearing, see Fig. 2. So an ogee bit cuts the reverse of the profile cut by the Roman ogee.

Because the bits cut reverse profile s, they are theoretically interchangeable — you could use the more common Roman ogee to form an ogee profile. But to do this, you must hold the workpiece vertically on the router table, see Fig. 3. And this can result in chipout on the face when cutting across the grain.

i se the right bit. The recommended (and safest) way to rout an ogee is the traditional way — with an ogee bit, see Fig. 4. You can rout the workpiece flat on the router table or hold the router freehand. 'ITiis way you have better control and get a cleaner cut. (For sources of ogee bits, see Alternate Catalog Sources on page 31.)

RADIAL ARM MITER JIGS

roman ogee bit felt about our earlier radial arm miter jig shown in Woodsm ith No. 60. see Fig. 2. That jig consists of a pair of narrow fences screwed to the base, sec Fig. 2.

The only difference between your jig and our earlier jig is in the placement of the workpiece when cutting the miter. On your jig. you pull the workpiece against the outside edge of the triangular guide. On the earlier Woodsm Hh jig. the workpiece is pressed against the inside edge of the fence.

Since they both work, why build a more complicated jig like the one from Woodsmitli No. 72? (Refer lo pholo above.) Two reasons — versatility and control.

versatility. 1 think your jig roman ogee bit has convex curve at bearing

■ Thirty years ago. I made a radial arm miter jig that's similar to the one you described in Woodsmith No. 72. But my jig consists of a simple triangular guide screwed onto a plywood base. What's the advantage of the extra guides, removable fences, and locking wing nuts?

W. P. Westlake East Dorset, Vermont Your question brings up what may be one of the most basic facts about woodworking — there's seldom only one right way to do anything. Your miter jig will work perfectly well for cutting miters with a radial arm saw. see Fig. 1. If it does what you need it to do — don't change.

For a long time, that's how I

note: rout roman ogee on edge to produce ogee shape roman ogee fence note:

using ogee bit, rout edge with workpiece flat on table fence

SHOP TIPS CONTEST

Woodworking Tools and Installation Tips

Woodworking Tools and Installation Tips

There are a lot of things that either needs to be repaired, or put together when youre a homeowner. If youre a new homeowner, and have just gotten out of apartment style living, you might want to take this list with you to the hardware store. From remolding jobs to putting together furniture you can use these 5 power tools to get your stuff together. Dont forget too that youll need a few extra tools for other jobs around the house.

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