I ran into a little problem (two, actually) when cutting half-blind dovetails on my new INCRA LS-25 Wonder Fence System. Other components in use with my LS-25 include:
Incra Mast-R-Lift II router lift, Porter-Cable 75182 router, Whiteside router bits (D14-55 1/2" x 14 degrees dovetail bit, in this case), Wixey digital height guage, Incra Right Angle Fixture, Incra 27" x 43" Offset Router Table, and Incra Router Table Stand.
Problem 1: Carefully following step-by-step instructions, I end up cutting "square" tails (i.e., angular dovetails and rabbet) and pin sockets that are rounded on the inside corners. This sort of creates a square peg (tail) for a round hole (pin socket). I've gone over my two Incra reference books (Master Reference Guide and Template Library, as well as Projects and Techniques, both by Perry McDaniel) and the LS Positioner DVD, but cannot find any guidance for either rounding off the inside corners of the tails or squaring out the inside corners of the pin sockets. In order to get my half-blind dovetails to seat securely, I have had to go at them with a chisel. Am I missing something?
Problem 2: When cutting wide pin sockets (such as with template 27 - DOVP), the series of cuts indicated on the template leave a very irregular, even jagged, cut along the inside edge of the cut. I have been able to partially correct this by making two intermediate cuts between every cut line indicated on the template, but the resulting line is still far from smooth. I even tried standing the pin board on end against the Wonder Fence and Hi-Rise Fence Cap with the router bit inside the pin socket to clean it out and get straight cut line. This has produced a smooth finished cut line, but is a risky procedure: even after carefully setting up stops at both ends of the cut length, the torque of the router bit can sometimes jerk the board out of my hand. Any ideas on how to do this right?
Just to clarify a little, my project called for a tail width of 1-7/8 inches. This required a socket "groove" wide enough to accept the width of the tail, so simply cutting a straight in and out socket with the router bit was not going to do the trick; I needed a socket "groove" several times wider than the bit.
I received the following, somewhat disappointing, reply from INCRA: "Regarding your first question, when you're looking at the end grain of a finished tail board, the ends of the tails will indeed be square. The dovetail-shaped rabbet that's cut across the end of the tail board provides the clearance needed to allow the tail board to cover the radius that's seen at the end of the pin cuts."
INCRA's reply is basically: yes, there will be unsightly scalloping instead of a straight cut at the edge of the pin sockets, but the rabbet on the tail board will cover this defect. For perfectionists like me (and I suspect many of you), hiding a messy cut under a rabbet is not an acceptable solution. Even if nobody else sees it, I'm always going to know that the interior of the joint is very sloppy. So I decided to find my own solution: Laying the pin board cut-side down on the router table, I adjust the fence position and bit height so that the bit fits perfectly inside the pin socket that I had earlier cut per INCRA instructions. With the router still off, I slide the pin board all the way forward with the bit inside the socket groove and secure a stop at the outboard position on the fence. Next, with the router still off, I slide the pin board all the way back with the bit inside the socket groove and secure the right angle fixture at the inboard position on the fence. Finally, with the pin board away from the router bit, turn on the router and SLOWLY slid the pin board forward along the right angle fixture until the spinning dovetail bit enters the pin socket. IMPORTANT: This must be a shallow cut, only chopping away about the first 1/32" of the scalloped edge of the pin socket groove. SLOWLY advance the pin board forward along the fence until the outboard side makes contact with the stop on the opposite side of the router bit. After that, move the fence away from the router bit by not more than 1/16th inch and repeat the cut. Repeat this action as many times as necessary until the unsightly scalloped has been completely cut away and/or the interior bevel of the tail board rabbet and the interior bevel of the pin socket are in contact.
INCRA also provided the following disappointing answer about sliding squared tails into rounded pin sockets: "The square tails don't present a problem, as the tails will only slide into the pins a certain distance before the tails wedge themselves into the place where the radius in the pin cuts begin. This is the same concept that fully rounded tails use, just the "wedging" point is in a different location."
I didn't much care for this solution as it means that only corners of the tails will make contact with the pin sockets, leaving an enormous gap of airspace along all other interior surfaces of the joint. That can't make for a strong joint. I found my own solution to this too: round off the interior corners of the tails to match the radius of the pin sockets (or, with a bit more work, square out the interior corners of the pin sockets with a chisel so that they mate with the square tails) so that all interior surfaces on both the tails and the pin sockets make physical contact.
I'm new to routing and dovetails, so I hope I haven't mangled the terminology too badly. Also, being new to this, I hope somebody will tell me if I am doing anything terribly wrong or dangerously.