Auxiliary Fence With Renewable Insert
To avoid having to make multiple auxiliary fences (and to avoid never having the configuration I needed handy), I built this thing with a renewable insert at the blade. The image to the left shows that it's 1-1/2" thick (double 1 x 8), with a window for inserts in the half closest to the blade (the rearmost piece of 1x8 is unbroken, full-height.) There's a stack of additional inserts in the right background. For the most part, many inserts can be reserved for specific tasks such as profile machining, etc., and re-used for many cycles while still offering zero-clearance protection.
I chose luan because it tends to be quite stable. The double thickness consists of two pieces from the same board oriented to one another as-grown; then glued and clamped; then trimmed on edges and ends; and made flat (see below.) The fence and inserts are all finished similarly with 2-3 coats of polyurethane.
Because the "window" in the 1x8 closest to the blade is taller than the blade, I chose to rip to get the portion above the blade, then edge-glue two pieces so as to put the window where it was wanted. The surfaces of all wood to be used were flattened and surface-planed in one setting so as to ensure uniform thickness with minimal fiddling after assembly.
Inserts are net 3/4", and are attached in the fence pocket from the back side with four #6 brass flat head wood screws. Inserts exceed height and width of blade at its highest projection, and screws are placed in the surrounding safe arc.
Insert attachment screw pilot holes were jig-drilled for location match, and the fence then through-drilled and countersunk to suit. Through holes are a close fit to help ensure reasonable repetition of alignment.
Although the whole mess was made at the same time, the inserts are intended for individual fitting, in case they might distort non-uniformly over time. Each is planed, scraped, and/or shimmed as needed to get it as nearly flat as possible and flush with the fence surface when its 4 screws are tightened - the same kind of approach that will be needed when any of the original 7 inserts are eventually replaced. (Sounds like a lot of work, but it's fast and takes little time.)
The entire assembly is attached to the working fence with three #12 brass flat head wood screws. (Large screws with deep threads were chosen so the wood threads would hold up to years of assembly/disassembly.) Steel screws would probably be OK, but I'm a little paranoid about hiding anything steel near the saw blade.
Varnished working surfaces were block-sanded down to 800 grit, and kept maintained with a couple of coats of paste wax.
Getting it Right
There are a number of mating surfaces to deal with and still wind up with a face that's continuous, true, and square to the table. Naturally enough, there was a bit of fiddling done to get there! Others may have better ways, but here's how I went about it.
- My working fence is 1x6 poplar made "dead flat" and shimmed to achieve perpendicularity to the table. If the auxiliary fence is also dead flat and its faces are parallel, then it, too, will be perpendicular to the table and parallel to the blade.
- After glueup, I was lucky in that the faces turned out to be pretty much flat. I glued the assembly by clamping it to the saw table with cauls and stretchers, which worked pretty well. For a glueup that didn't quite turn out flat, I'd use a carrier and shims to run it through a surface planer until one side was flat, then plane the opposite side - all at the risk of losing some thickness.
- My trick to ensure flatness (and absence of twist) is to use a 4' aluminum level to check across diagonals, then length. If scraped back and forth lengthwise over the wood, the aluminum will leave black marks on any high spots, which can be worked down with plane, sandpaper, card scraper, etc. Repeated marking and correcting in that fashion will quickly yield a surface whose out-of-flatness is inconsequential.
- I played "rub and scrape" with the aux fence firmly screwed to the working fence, so that surface adjustments were made in the assembled state, with any possible distortions from screw tightening thus accounted for.
- I do check my working fence with some regularity to ensure that it's still flat and perpendicular to the table over its full length, and therefore attach the auxiliary fence with confidence whenever it's needed.
JOHN W. POPP