Tip #53
Shopsmith Ovararm Pin Router
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Under-Table Operations

Many of the operations that have been explained in the overarm operations section of this chapter can be performed with equal ease in the under-table mode.

However, because the rotating bit is not always in plain view during under-table routing, extra care should be taken at all times when in the under-table mode.

Warning: Whenever possible, use piloted bits, fence, fence extensions, miter gauge or other guiding devices during under-table routing. NEVER press directly down on top of your workpiece during under-table routing. If your workpiece should break, your hand could slip into the rotating bit, causing serious injury. ALWAYS use a push block, push stick, feather board or other safety device to exert downward pressure on the workpiece during operations. The bit is often not visible during under-table operations, therefore extreme caution is necessary.

Edging
Although most of the same rules apply to both overarm and under-table edging, the bit is often not visible during under-table routing and therefore, it's even more important that you always use the fence, fence extensions, miter gauge and/or guiding device during under-table operations.

In addition, keep in mind that during under-table routing, the bit is rotating in the opposite direction as during overarm operations. Warning: The stock must always be fed from right-to-left during under-table routing.

Full Edge Removal-Since full edge removal requires the use of an unpiloted bit, under-table edging should be restricted to straight-edged or round workpieces. Either of these can be handled safely with the aid of a fence, miter gauge, or other guiding device.

However, since odd-shaped workpieces cannot be controlled with fences or other devices and the operator cannot always see the cut as it's being made, full edge removal on odd-shaped workpieces should be performed only in the overarm mode and with a proper guiding device. Warning: Do not use the under-table mode to remove the full edge from an odd-shaped workpiece.

Partial Edge Removal-Because of limited bit visibility during operations, partial edge removal in the under-table mode should always be performed with piloted bits or with the aid of a fence, miter gauge, or other guiding device to control the depth-of-cut.

When performing operations on straight-edged or round work-pieces, use a fence, V-shaped fence faces or piloted bits. When working with odd-shaped project components, always use piloted bits to control your depth-of-cut.

Decorative Surface Cuts
If your decorative surface cuts are to be made in a straight line and will go all the way across a work-piece from one side to the other (no stopped cuts), they can be performed in the under-table

mode with the aid of a fence, miter gauge or other guiding device.

Because of limited visibility, making decorative stopped cuts in the surfaces of workpieces is not advised in the under-table mode of operation. These cuts are best performed in the overarm mode, where the workpiece and bit can both be kept in plain view at all times.

Moldings
The process of making moldings in the under-table mode is very similar to that discussed earlier in this chapter for the overarm mode, with a couple of important exceptions:

First, remember that with under-table operations, the bit pushes up on the workpiece instead of down. Therefore, when cutting straight moldings, the use of feather boards is essential (Figure 22-53). To use feather boards, you will have to construct hold-down fences (Figure 22-16). Warning: Be sure your stock is held firmly down against the table surface and inward, against the hold-down fences. With small work-pieces, be sure to use shop-made wooden push sticks for added safety. Because the bit is not always in plain view, when making Irregular-shaped curved moldings in the under-table mode, always use piloted bits.

If your curved moldings are round, use V-shaped fence faces like those shown in Figure 22-14.

When making curved moldings, proceed as you would for overarm routing. First, form the edges on an oversized piece of stock. Then, cut your molding away with a scroll saw or bandsaw and sand the sawn edges smooth.

Joinery
With the exception of mortise and tenon joints, virtually all of the structural joints shown in Figure 22-27 can be formed with the routing system in the under-table mode. In fact, some of these joints (such as tongue and groove and splined joints) are actually easier and safer to form in the under-table mode than they are in the overarm mode.

Beyond the basic joints, under-table routing provides the ability to form two very unique joints that would be difficult (if not almost impossible) to form with any other machine. These joints are the false dovetail and the false finger-lap.

Both of these joints are formed by gluing your project together, cutting grooves for contrasting wood “keys” in the corners and gluing the keys into position. Once completed, the corners of your project have the look of dovetails or finger-lap joints.

To cut these unique joints, begin by building a false dovetail fixture like the one shown in Figure 22-54. Note that the dimensions for this fixture are based on 1/2" dovetails spaced 1" apart. If your dovetails will be larger, smaller, and/or spaced differently, you will have to adjust your fixture accordingly.

Before you can cut the dovetail slots (or square slots, if you're making finger-lap joints), you must first assemble your project with 45° mitered corners and glue it together. Warning: Clamp and let glued-up stock dry for at least 24 hours prior to routing.

After the glue has dried, begin by positioning your project in the fixture with its side against the spacer bar. Turn on the router. Move the miter gauge (with fixture attached and project in position) into the bit to make the first cut (Figure 22-55). Turn off the router.

Return the miter gauge to its starting position. Move the project to the right in the fixture and drop the slot you just cut over the spacer bar (Figure 22-56). Move the miter gauge into the bit again to make the second cut. Repeat the above procedure for all subsequent slots on each corner of your project (Figure 22-57).

Next, make the dovetail “keys” that will slip into the grooves you've cut. Begin by choosing a piece of contrasting stock, approximately 3/4" thick x 3" wide.

Set up the hold-down fences (Figure 22-16) and feather boards, and adjust the bit's depth-of-cut equal to the depth you cut in your project. Begin by making the first pass on one side of your key stock (Figure 22-58). Now, flip the stock over and make the second pass on the other side (Figure 22-59).

Check to see if the key fits into the slot you've cut in the corners of your project. If it's too snug, adjust your fence to make a slightly deeper cut in your key stock (which will create a narrower key). Keep working with this until the key fits snugly in the slots you have cut.

Next, saw the full-length keys off your key stock, and discard the scrap in the center. Then, cut the keys to about 1" to 1-1/4" long.

Spread glue on each side of the keys and insert them into the slots in the corners of your project (Figure 22-60). After they have dried, sand the keys flush with the project (Figure 22-61).

This same process will work for finger-lap joints. Instead of using a dovetail cutter, use a straight 1/4", 3/8" or 1/2" un-piloted bit.

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