|Project by HokieKen||posted 11-05-2015 09:08 PM||1814 views||12 times favorited||8 comments|
This is my second sled build. I wasn’t happy with some things on the first so I attempted to fix them with this one. So far, so good!
The base of the sled is 1/2” MDF laminated with Formica on both sides. The bottom side is waxed and, let me tell you, waxed formica just glides over cast iron! The front fence is 2 layers of 3/4” plywood I salvaged from an old bookcase. The back fence is red oak I salvage from a coffee table a local business was throwing away.
The base is topped with 1/8 hardboard that is captured in rabbets at the bottom of the fences. The 2 pieces can slide independently as seen in the 3rd photo. This allows me to move the hardboard for different kerf blades, dadoes, and bevel cuts so I always have zero clearance. There is a replaceable insert in the fence that attaches with 1/4” screws into tee nuts in the fence so I always have zero clearance on the back of the cut as well. I put leveling screws under the insert so I can make sure it’s always flush with the fence too.
The rear fence has t-track for a stop block. The stop block is walnut with an hdpe key to prevent rotation. The fence is held to the base with 5 socket head screws that thread into tee nuts in the bottom of the base. The bolts are counterbored and the bolt hole on the left is a tight fit and acts as a pivot. The other holes are drilled oversized for adjustment of the fence. When I squared the fence up, I tightened the left bolt down and snugged the rest. I used the 5-cut method and attached a dial indicator to the base using one of the t-slots. Three 5 cut tests got me to .002 error over a 12” board. I tightened the rest of the bolts down and am very pleased with the accuracy.
The 4th pic shows the bottom of the sled. The runners are oak and are screwed into the base and housed in 1/8” deep dadoes. You can see the bottom side of the T-slots are just shallow 3/4” dadoes. The thru slots are 5/16”. I use tee nuts, like the one in pic 5, that I’ve modified to work with these slots. They’re just regular 4-prong tee nuts with 2 of the prongs ground off. The flange rides in the bottom dado and the 2 remaining prongs catch the sides of the thru slot when tightening down to prevent rotation. I had originally planned on using commercial t-track but I was leery of sinking a 3/8 dado into the 1/2” mdf fearing it might weaken the stiffness of the base too much and allow flex. I don’t know how this type of t-slot will hold up over time but for now it’s working surprisingly well.
I will eventually make a miter bar to use with the t-slots for angled cuts and a right angle miter jig. But, for now the only action the slots have seen is hold-downs.
One final note on the sled construction… I built the sled base in 2 pieces with the runners loose in the slots. After I had the runners installed, I trimmed each piece to final length and shimmed the runners out so they were tight to the outside of the slots. I then installed the front fence to fix the 2 bases in relation to each other. This worked extremely well because it eliminates binding due to both runners being tight to both sides of the slots (overconstrained – an engineering no-no :-)) and gives the HW runners room to expand. But there is almost no slop at all because the runners are in full contact with one edge of the slot. I put my dial indicator on the base using one of the t slots and set it to 0 on the side of the blade and then wiggled the sled as much as I could to measure the slop. The most I could get was ~.0035” with both runners fully engaged. That, obviously, increases when the sled is partially hanging off the front or back of the table. But even then, it’s plenty good enough for woodworking! I was extremely happy with how precise I was able to get this sled. Now if it stands the test of time, I’ll be even happier!
Thanks for looking and questions and comments are always welcomed and appreciated!
-- Kenny, SW VA, Go Hokies!!!