Introduction: Accurized/Incremental Tablesaw Fence
I really like the Unifence on my tablesaw. But watching this video, I got inspired, especially when I saw what it can do for instant box joints. It turns out to be amazingly handy to have your saw fence always snap to 1/16" increments. But I thought, why make a whole new fence? Why not just add incremental capability to my existing fence? And for those times that you want infinite adjustment, I'll make it so the incremental mode can be disengaged. It was surprisingly easy to do on my fence, your mileage will vary with how exactly your fence is constructed. With incremental mode engaged, running a 1/8" kerf sawblade, I can make amazingly quick finger joints. Read on to see how you can do it too.
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Step 1: What You'll Need
You'll need a length of 16 tpi threaded rod (I used 3/8).
A threaded butt connector to match the rod (essentially an extra long nut).
A piece of wood that will bolt underneath you fence's front rail, slotted to receive the rod. (i used a piece of oak flooring). **This slotted piece of wood is henceforth known as the "rod carrier"
Some fasteners to attach the wood to the rail (I used 1/4" threaded rod).
A toggle clamp (mine was salvaged off of a piece of office equipment).
And a piece of spring steel(I found this clip in the electrical/conduit aisle at home depot)
Step 2: Attach the Rod Carrier to the Front Rail
To make the rod carrier, I used my tablesaw to cut a slot in the wood plank to receive the threaded rod as a snug fit. The rod carrier holds the threaded rod in position so that the half nut can engage it. The threaded rod is a little longer than the wood, and has nuts on both ends which are used to adjust the rod left or right, thereby adjusting the fence left or right when the half nut is engaged.
Next it's time to attach the rod carrier to the underside of the saw's front fence rail. Mine is flat and made of aluminum, so it was fairly easy. But Instead of drilling and tapping the aluminum I decided to make a strip of blind nuts and slide that into the hollow part of my front rail. To make the blind nut strip I cut a strip of sheet metal to length and marked where I wanted the nuts to be, and then drilled 3/32 pilot holes in the strip. Before I proceeded any further, I clamped the strip in place and used the 3/32 holes as guides for where to center punch bottom side of the front rail, and then the top side of the rod carrier. That ensured that, later when those center punch marks are used for drilling the 1/4" holes in the front rail and rod carrier, that all the holes would be properly aligned with each other. Then I proceeded to drill out the pilot holes in the strip to their final 1/4" dimension.
I then welded 1/4" nuts to the metal strip. it was tricky getting a good weld without burning through the thin sheet metal. I found it helped a lot when I sanded the zinc off the nuts and the face of the metal strip in the spots where the weld was going to be.
Then I drilled the 1/4" holes in the rail and wood strip at the center punched points. I slid the blind nut strip in place and threaded a 2" piece of 1/4" all-thread up into each blind nut. Then I put the rod carrier in place and bolted it in. The alignment of the holes was pretty good, but I had to auger out a couple of the holes in the wood to get it to go in place. Then I carefully positioned it and tightened it down.
Careful positioning is necessary here, because it's critical that the face of the threaded rod be exactly parallel with the face of the front rail. Depending on your fence's design, the face of the rod could conceivably be in front of -- or behind -- or flush with -- the face of your front rail. (Mine was about 3/16 behind the face of the front rail) But it has to be parallel, so that the half nut will engage the threads at a consistent depth throughout the range of the fence's left/right travel.
Step 3: Make the Half Nut Assembly
The 3/8-16 butt connector(long nut) will be sawed in half to become the half nut. This is the piece that will engage the threaded rod. I used a hacksaw to cut it in half lengthwise. Then I welded a couple of 10-32 nuts to the backside of it. After I cut off the unneeded parts of of my spring steel, I drilled holes in the spring steel and attached it to the half nut with 10-32 socket head screws. I made sure to have a tight fit with no play between the spring steel and the half nut. In order to make the overall fence position precisely align with the position of the threaded rot, it's critical that the half nut has no play in relation to the spring steel, and that the spring steel have no play in relation to the fence.
A tip for drilling high-carbon or other hard steel: You'll burn up the tip of a regular drill bit and hardly even put a dent in high carbon steel. You could go buy an expensive cobalt bit. But I've found that a sharp carbide tipped masonry bit (even one of those cheap zinc-coated ones!) cuts through most hard steels like butter. But the carbide tip has to be sharp, so either use a brand new bit or one that's been sharpened on a diamond grinding wheel. Harbor Freight has diamond sharpening wheels for about $10.
Step 4: Attach the Half Nut Assembly to the Inside Face of the Fence's T-square
The half nut needs to be lined up parallel with the threaded rod (not cocked) and at the proper height. In order to get the proper alignment, I cut a template out of plywood so that I could clamp my threaded rod to the t-square. Then I clamped my half nut assembly to the threaded rod with a C clamp. With the half nut clamped in place I then drilled for and inserted roll pins to keep the half nut assembly registered precisely in place. If I had used screws or bolts, the half nut assemply might have been able to slide or rattle back and forth, which would have defeated the whole purpose of the project.
Step 5: Attach the Toggle Clamp and Adjust
When the toggle clamp is locked, it pushes the half nut forward, causing it to engage the threads of the threaded rod.
You could use any method you wish, but for me the toggle clamp was perfect. Initially I thought I'd have the clamp going straight vertical (first picture) but I realized later that having it angled was going to work better. I used countersunk machine screws to bolt it in place. I then installed a longer screw in the hoop of the toggle clamp in order to extend its reach down to the backside of the half nut assembly. I then adjusted that longer screw so that the half nut is engaged when the clamp is locked. When the clamp is unlocked the half nut springs back such that it doesn't touch the threaded rod, and the fence is infinitely adjustable. The final three photos are finished state.
The very final step, not pictured, is adjusting the threaded rod. As I mentioned, there are nuts on both ends of the threaded rod. With the half nut engaged, I installed the fence near the 1" mark on the measuring rule. I then used the nuts on the threaded rod to move the rod left or right as necessary to get it to line up precisely with the 1" mark. That way the 1/16" fence increments fall precisely on the inch, 1/2inch, 1/4 inch, 1/8 inch, and 1/16 inch marks, not somewhere in between.