Finally Made The Jig I've Needed To Make

The bottleneck in the window project, aside from all the repointing -- and there's no way around that -- has been cutting the curved sash pieces. Long story short, I'd been cobbling together a Frankenjig to cut the interior curves, adding pieces and drilling new holes as needed for different radii and material thicknesses. It worked, but it always took forrrrrrrrrever to setup. 

Why?

Because there weren't enough fixed or easily adjustable points. Everything was a custom setup, and that usually meant way too much measuring, drilling, driving screws, chopping parts off, adding parts on, etc. 

So I finally made a jig that should speed things up tremendously. 

I started with 1/2" plywood, 30" wide and 60" long. It sits on a simple 2x4 frame, with the 2x4s jointed and planed to get everything flat, square, and straight.

On one end, I screwed down a milled 2x4; this provides a flat, straight, square reference surface to rest the work pieces against. In the previous jig I'd get the workpiece centered on the rest piece and then drive some screws, through the meat that gets cut off in future milling, to hold it in place. I'll keep doing that for now; in the future, I'll make this adjustable as well. 

On the other end I added a 1/2" drill bit to serve as the sled shaft. 1/2" is a pretty good size for this setup; it's big and solid, and makes the math I have to do when setting up the jig pretty easy. The Frankenjig had something random, like a 5/16" drill bit, which made the math not so simple. If I'd have had a piece of 1/2" diameter steel laying around I'd have used it, but I didn't; the drill bit works just as well.

That was the easy part. The sled took a little more effort and thought. 

The sled is another piece of 1/2" plywood. It spins on the shaft at one end, and the router sits at the other end. The router has to stay firmly in place on that end of the sled, so I cut a couple strips out of some scrap OSB and screwed them down, making a snug cradle for the router base.

That gave me the sled table and the sled. If I was cutting the same radius in the same sized work piece over and over and over, this would have been fine. 

But all my cuts are different due to slight variations in window size. The whole point of this jig was for it to be adjustable; with the shaft fixed at one end, the sled length needed to be changed, and easily. Enter the sliding dovetails. ​

The plywood piece that the router sits on (yellow), its undercarriage (green + orange) is where the adjustability lies. Without getting into the weeds of woodworking terminology, the green pieces got wedge-shaped slots cut in their sides, and the orange pieces, rails really, were milled to have an identically wedge-shaped piece protruding from one side. Long story short, this allows the green pieces to slide along the orange pieces (or the orange pieces to slide along the green pieces). Adjustability. 

​By fastening the orange pieces to the green piece on the router end, and with the other green piece pinned in place by the shaft (the drill bit), the router end assembly can slide closer to, or farther away from, the shaft. Cutting a slot in the yellow piece, which goes on top of this assembly, prevents the protruding shaft from getting in the way.

Everything's a little too snug, but some light sanding should take care of that. I don't want the movable parts to be all loosey-goosey, but I need fine adjustments to be made easily...right now, it takes some force. 

You might be thinking to yourself "but if the sled adjustments are easily made, what will keep that setup locked in place during router work?". Fair question. 

​It might be tricky to explain, but I'll give it a go.

Referencing the colorful design above, I drilled a hole through the green piece nearest the shaft and installed a threaded insert on its bottom, where the piece slides across the table. 

I had a screw and knob assembly (carriage bolt + plywood star-shaped knob) leftover from the router table project, and I cut a circular washer out of OSB. Luckily, the carriage bolt was the exact right length to fit through the washer, through the slot I cut in the sled, through the piece of wood that moves around the shaft, and can be threaded snugly into the threaded insert. 

Long story short, I can get the sled set to whatever length (radius) I need and them a few turns of the knob locks the adjustable section to the piece that's fixed to the shaft.  ​

That's the setup. I still need to come up with a way to make the work piece position adjustable and I need to add a couple stabilizer wings to the sled (she's a little top heavy with the router in it), but for now, this simple setup alone should speed things up quite a bit. Kinda hoping I get to use it for a storm window build tomorrow.