Advanced Router Techniques
Presented by: Derek Roff
Written by Richard Derganc

Albuquerque Woodworkers Association
Meeting Notes
9SEP00

Derek recommended: "Fast, Easy and Accurate Router Jigs", by Pat Warner, as the best of his books, having more new material than his other books. Any of Pat Warner's books are fine, but Derek cautioned that much of this book has been printed in Pat's other books.

Derek's objective was to present Sliding Dovetail cutting, Half Lap joint cutting, Mortise & Tennon cutting and Complementary Curve cutting. And he covered them all!

Making your dovetails slide

Have you ever pondered why the sliding dovetail joint, if suitably tight, can't fit in the dovetail groove all the way? That is why Derek recommends the tapered sliding dovetail joint! At what angle you should immediately ask? Well Derek figured-out that 250::1 produces the appropriate angle, by calculating backward from using four pieces of masking tape, (for a four inch wide piece of lumber), each of which is a mere .004 inch thick. Surprisingly any one who has adjusted their car's points, when cars still had points, has used an automotive feeler gauge. The smallest arm of which is the .001 inch.

So for a board 6 inches wide, use six thicknesses of masking tape each .004" thick on the router guide, to achieve the proper angle on the sliding dovetail. Of course you should only taper one end of each dovetail part! Otherwise you'd have parallel dovetail and groove.

Derek's Router Tips and collected wisdom:

Keep the hole in the fence SMALL, behind the router bit for support!
Route thick stock in MULTIPLE PASSES.
Don't use 2 passes in oak to plow a ¾" rabbet or dado!
Always Use Hearing Protection. Remember you can't hear when you're losing your hearing!
Use earmuff-type and in-ear plugs if you have to, to counter long routing session noise levels.
Muffs have a noise reduction rating of -15 to -32 db; plugs are about -33 db.
How do you know you're very lucky?
If your carbide bits are missing carbide and you're not bleeding, you are very lucky!
To counter uneven work surfaces, cover the table with masonite.
Make adjustments to the height of the insert with tape.
Use a large flat metal plate for an insert if possible.
Make a light scoring pass, when cutting the male end of the dovetail, then increase the depth.

The thickness of the dovetail is variable, but limited by the thickness of the dovetail bit.
Adjustments can be made to the depth of cut using the feeler gauage as follows:
To move .001: place work and .017 shim against fence in position just used.
Hold workpiece, loosen fence, replace shim with .018 shim, reposition fence.
Remove shim, position work against fence. Remember, you're taking wood off both sides, so make very small changes! Derek has observed that most commercial bits are 14°, but 7° to 12° are referenced in the literature, for softwood and hardwood respectively. Derek prefers the narrower angle for both strength and aesthetics.

Use a digital caliper (Mitutoyo, Lee Valley, Veritas, et.al.) available for from $29 to $125.
Some important features are: (digital, metric, English, instant zero, depth and inside diameter).

Use the same guide collar or bushing on the router base plate for all bits (¾" recommended).
Then only one offset and slot size on your jigs is necessary.

Toggle clamps are great for holding the work piece in place while using a pattern cutter bit.

Half the Lap in half the time

First, don't be bashful about using the best tool for the job. Use your table saw to hog-off the extra material, whatever you're doing! So, cut down to near the final height of the lap joint and then carefully approach the mid-point with a good height adjustable router, flat bottomed or pattern bit and a positioning jig which supports the router through the entire cut. Remember, your working stock must be the same thickness for the halves to fit perfectly.

Mortise and Tenon joints x 10 -3

Spiral bits are perfect for mortise and tenon cutting. The up-cutting variety helps to remove wood chips from the mortise. The down-cutting variety helps to keep the finished edge sharp and splinter free. Remember to pre-drill the mortise with an under sized bit 3/16" for a final 1/4" mortise. This is to reduce the stress on the router bit overall.
Mortise first, then cut tenon to fit, approaching the final snug fit in small increments.

Some recommended bits: Whiteside, CMT, Amana, Jesada, Freud and Paso Robles. See Fine Woodworking for a recent article evaluating one size router bit.

Cutting Complementary Curves

What are complementary curves? Curves matching your own curves? Curves that 'say' nice things to you? Curves that are friendly to the touch? Yes, all of the above and more. Derek demonstrated how we might match some existing curve, as in when we want to fit two contrasting pieces of veneer together. This was as much of a mental exercise as a technical one, but one I bet, you just couldn't wait to try for your self at home.

So, Derek made it intuitively obvious to his students, that you just can't cut the same curve from two pieces of veneer and have them fit each other. This due to the size of the router bit itself and the offset resulting from the collar used. But through a complicated three-step process, the halves can be made to fit into a tightly jointed whole.

So, starting with a rectangular piece of material, which we divide with the router in a squiggly line, we produce piece A and piece B, which do not fit each other exactly, And having the objective of cutting two pieces that mate, presumably from contrasting material, from the initial two halves (A and B), call them (A' and B'), having an identical squiggle, so that they will fit together precisely, we do the following:

Using a ¼" spiral bit and a ½" bearing mounted on the bit shank, the relationship is critical, the bit must be ½ of the collar diameter, And using what looks like a circle cutting plate on your router, but is really functioning as an "outboard" or offset means to control the router's motion from a knob or handle 18" or so off the center line of the router's motion, And remembering to pull the router through the cut, do not push the router, so as to keep router bit cutting into the work and therefore preventing bounce-off or bumps on the final work piece,

We make a secondary piece (A' and B') from each of the two initial pieces using the identical bit and collar combination. These two secondary pieces do match and we can make the veneer match.

I assume it is easier to do than to describe and understand.

Let Derek know if you run into difficulty!