I want to build a back fence for my shaper as the Aigner is out of reach for me. I've read some posts in the Knowledge Base of a couple guys that were going to build one out of 80/20 extrusions utilizing their linear bearings much like the workings of a table saw fence, but never saw their approach or finished product.
Has anyone done or seen something like this? I'm on the fence as far as what type to pursue. The Weaver type is probably the easiest but was looking for something I could add a ProScale to for repeatability and ease of setup on new work.
From contributor M:
I canít speak from experience but I can see how a tablesaw style fence could be effective or stiff enough for a back fence with feeder, especially in aggressive situations. Have you searched for some of the shop made parallelogram style fences? They require a bit more projection outbound but look to allow for accurate, repeatable, fence changes. I'm interested to see what comes of this thread as I too have always thought of building one as opposed to my two c clamps and a ply scrap.
I would prefer the parallel (Aigner) style fence but machine shops are few and far between here, and I imagine the location of the pivots would need to be spot on for a fence of this type. So, again I defaulted back to the 80/20 idea.
Remember that the wider the distance from the spindle to the front edge of the aux. top you have, the wider the material you can feed through. I could mill the edges of a full 12" board on my machines (Powermatic model 26 shapers). I used Baltic birch laminated with matt finish white P-LAM both sides. I mounted 80/20 15 series extrusions (rails) #1530 (1-1/2" x 3") which has one T slot on each edge and two on each face, to the underside of each end of the aux. top with flat head machine screws into one T slot on the 3" face, leaving half of the extrusion hanging outside the edge of the aux. top to receive the bearings with flange face facing up.
I used a piece of 1/2" phenolic board 12" wide about 42" long (length relative to aux. top width) as my fence. I used two type 6815 linear bearings at each end of the fence to keep it parallel to the front table edge. Shim and bolt the fence to the bearing flange with flat head machine screws. Now that youíre mounted, you need a method to lock down the fence to the rails. You can buy a bearing already set up for an 80/20 lock knob or do as I did and mount two pneumatic cylinders to each end of the fence, through the bearings into the T slot with a strategically located air switch (I located it under the right side of the fence end where I could flip it with one finger) to lock down your setting. You will need cylinders that when actuated will clamp down on the pull stroke and simply release the pressure when released.
You will not want a cylinder that actually uses air pressure to push back out to release as these types tend to have a stroke longer that the small tolerance inside the T slot. If you really want to make fast work of multiple set-ups go with the pneumatic cylinders. The cylinder will need to have a threaded housing end to mount it to the bearing which I employed a machine shop to drill and tap for me. You will also want a set of shims for the bearing pads to close up any slack in the bearings. Now that the fence is mounted and has a lock system, you will have space on the bottom of the right rail (one T slot) to attach your digital scale. I used an Accurate Technology 250-2 system with a "basic" readout. You will need a 24" lead on the "decoder".
You will also need to accommodate a safe but visible location to mount the readout. I had a heavy gage sheet metal housing made to protect the readout from being bumped and bolted it to the underside of the right fence end so I could see it as I am sliding the fence to a new position then with the flip of the air switch I could lock it in! I was consistently accurate to .005" of the desired material width time after time, all day long running edge jointing, door sticking etc. I had two shapers set-up this way.