When I made the double sliding router table and table saw fence, I had almost no experience working with a router table. So, after some time using that router fence, I realised that the vertical zero clearance insert I had install to the fence was too thin. The problem is that because it is very thin, when I route the wooden strips head, the zero clearance insert deforms by some millimetres to the inside of the fence. The end result is a crooked routing (I don’t have that problem when I route along the strips). That is why I decided to work in this router table fence improvement. It doesn’t have a zero clearance insert, but I can open or close the opening behind the router bit depending on the router bit I use.
To make this adjustable router table fence, I use a piece of 20 millimetres thick plywood I had in my small woodworking shop. And to hold it against the old one, I use bolts, washers and wingnuts. So, wingnuts will make it easy to loosen and tighten the router fence when I need to set it in a new position.
But to hold the fence with the nuts and the washers I need a T slot, so I route a groove some wider than the washers. And I make that groove some deeper than the bolts head plus the thick of the washers.
Once I decided where to make the groove, I mark the washers width (well, just some more) in the end of the piece of plywood. So, now I have two marks there.
Now, because I don’t have a router bit to route a groove that wide, first I route a groove between both marks and against one mark. And then I route against the other mark. Like this I get the groove I need. And now I glue a piece of 10 millimetres plywood on the first piece of plywood.
With the table saw, I cut the 10 millimetres plywood to get a piece that is exactly as wide as the 20 millimetres thick piece. I pour a very thin layer of carpenters glue on the 20mm piece. I must make sure the glue doesn’t goes into the groove. And I glue the 10mm piece on it. It doesn’t matter if the edges of both pieces don’t fit perfectly. I can trim them later with the table saw.
Now I mark the bolts diameter in the 10mm piece, and I finish cutting the T groove shape. I just have to make a couple of cuts with the table saw.
Now I just need to drill the holes, in the old router table fence, so I can insert the bots to hold the new router fence improvement. The bolts head plus just one washer slides inside the T slot. I pass the tip of the bolts through the holes, and I put a washer and a wingnut in the other side in the old fence.
Now I can move both parts of this improved router table fence depending on the router bits I use. And if I damage too much the opening edges, I can make the “V” cut again with the miter saw. That is why I let this fence protrude as much to each side of the router table.
Now I can make a router tenoning jig to cut tenons to make mortise and tenon joints.