From: ericb@microsoft.com (Eric Brown)
Subject: Re: Sliding Dovetail Question
Date: 14 Dec 92 22:04:58 GMT
Organization: Microsoft Corp

HUNTRESS GARY B <HUNTRESS@NPT.NUSC.NAVY.MIL> writes:
|I have dreams of building a "Governor Winthrop" slant front
|desk.  The plans from a recent magazine article call for a couple
|of sliding dovetails that are the width of the entire piece.
|
|[NOTE:  not knowing which is which, I'll refer to the female
|part as the tail and the male part as the pin]
|
|I'm quite certain that I can make the tail properly.  I'm equally
|certain that I'll have trouble getting the pin right.  I'm
|envisioning trying to hold a large maple panel perfectly vertical
|while running it across my little router table.
|
|A sliding dovetail appears to be a "binary joint", it'll either
|fit or it won't.  As opposed to the mortise and tenons that i've
|made, they're "analog joints" and seem to have degrees of fitness
|:-))
|
|So, is there any wisdom regarding construction of the pins?
|
|Gary Huntress
|huntress@npt.nusc.navy.mil

Another poster reccommends clamping the board in a stationary position
and using a router fixture.  You can also consider fastening a tall (say,
12") accessory fence to your router table fence.  If you do the latter,
use a feather board to hold the panel to the fence.

In either case, you need to carefully check the thickness of your panels
to see if it varies *at all*!  If the thickness varies more than a few
thousanths (both between panels and over the length of a panel), then
more effort is needed to produce consistent width parts (I seem to recall
this part being the tail, but I could be wrong).  Typically, one would
run the board one way through the router table, then turn the board
around and run it through the other way (same principle applies to hand
held router).  Thus, if the panel thickness varies, so will your machined
tail (or is it pin...).  This is due to the fence being placed on both
sides of the work piece.  The solution (other than planing to
a precise thickness), is to use two router setups; one with the dovetail
bit in the fence, the other with the dovetail bit ~half inch away from
the fence (exact dimension determined by trial and error fits into the
groove; you make the grooves first).  This way the fence stays on the
same side of the work piece for both cuts.

Make sure you have scrap pieces the same thichness as your panels and
do your adjusting/fitting using these scraps.  Only when you are convinced
that you have it correct do you run the actual panels through the router.
And repeat the testing with a scrap piece after resetting the router
for the second pass.

One last note: the second pass with the router bit on the opposite side
of the workpiece from the fence is somewhat dangerous.  If the board
pulls away from the fence, it will make a mess of things.  This is why
feather boards or some other types of hold downs are very important to
keep the work securely against the fence.
 
-- 
    Eric
               Microsoft Systems, Advanced Systems Development
            {sun, uw-beaver, apple, uunet, fluke}!microsoft!ericb 
                       internet: ericb@microsoft.com
Newsgroups: rec.woodworking