Build a dado sled for long panels
Most smaller panels don’t need a dedicated sled, but if you’re machining dadoes on longer panels this jig will give you accurate results with ease and allow you to create large projects in virtually no time.
If you shy away from making larger cabinet or storage projects because machining long workpieces scares you, this sled might help ease your fears. Large panels are harder to work with, but the right shop-made jigs, coupled with a bit of knowledge, will make larger projects enjoyable and successful.
A router can easily be used to rout a dado across a workpiece with the help of a very simple 90° jig. A router isn’t as fast as a table saw, and it often tears out the material more than a table saw, but there are ways around this. My main challenge with routing dadoes is that I can’t dial in the exact width of the dado like I can with my dado stack and some spacers on my table saw, yet still machine the dado in one pass. Sheet goods are rarely their stated thickness, and to get a good fit takes a bit of patience. It’s also possible to machine a narrower dado with a router, then machine shallow rabbets on the face to produce a tenon that fits the narrower routed dado, but that’s not always the easiest or quickest approach.
When I’m machining dadoes on my table saw I can often just use the fence to reference the edges of the workpieces off of. The only time this doesn’t work is when the workpiece is on the longer, narrower side. I recently made a wall cabinet to store 11″ × 14″ baskets, and the gables were 84″ high × 12″ wide. This meant I had to keep this long, narrow workpiece square to the fence while machining dadoes for a fixed shelf near the centre of the gables. It was 50/50 whether I could create these joints properly, and those weren’t good odds.
Add Some Wax
Brown adds a bit of wax to the areas on either side of each mitre gauge groove. This helps protect the table’s surface from glue squeeze-out while attaching the runners to the base panel.
Protect Your Table Saw
Masking tape will further protect your table saw’s surface from glue squeeze-out while gluing the runners to the base panel. Here, Brown is ready to place the base panel on the runners and add some weight before hand planing the runners to their final height so they don’t bottom out in the mitre gauge slots.
A Nice Fit
A few passes with a shoulder plane will have the runners and base sliding nicely in the slots. Be sure not to remove too much material. Wax on the runners will help them move more freely.
Glue Up a Fence
Although solid wood would work nicely, Brown didn’t have an appropriately sized piece on hand, so he used a few layers of Baltic birch for the second fence. When he glued them up he ensured they were perfectly flat.
Add the First Screw
A carpenter’s square will bring the fence close to its final location while you attach the first screw from underneath the base panel. This is done with the help of two spacers cut the exact width of the kerf. The fence can then be rotated slightly to ensure it’s square to the kerf before the other screws are added.
Cut a Kerf
With the runners fitting nicely, and the stiffener secured to the distant portion of the base, make a cut in the base panel that runs no more than 3/4 of the way across the base. This will give you a line of travel to set the fence perpendicular to.
Time for Glue
With the few screw holes bored from the underside of the base panel, Brown adds glue, followed by the screws, then adds a few more clamps to ensure the joint is strong.
Add Some Strength
A cleat between the fence and base will add extra strength to the sled’s main working parts.
Nearly There
Once the glue has cured, machine a wider kerf in the base panel. This will give you one edge to reference off of for all the cuts. Which edge that is depends on what type of table saw you have. A right-tilt saw will have the same right edge of the kerf for each dado, no matter how wide the dado is, and vice versa.
Start with the base
Plywood is strong and durable, but it’s not always very flat. MDF and particleboard, on the other hand, remain quite flat over their lifespan, but aren’t as durable. Since I’m the only person who will use this jig, and I can be pretty gentle on my jigs, I opted for 3/4″ MDF. It also happened to be what I had on hand.
First, I trimmed it to size. You’ll have to make sure this jig is sized for the work you do and the comfort level you have with machining different awkward dimensions of workpieces against a rip fence. I find 24″ wide workpieces are much easier to register against a fence, even if they are on the long side, though I rarely work with long 24″ wide panels. Workpieces that are 16″ wide are somewhat common, so that’s what I chose to focus on. Any narrower widths would also be easy to machine with this sled. When all was said and done, I could machine about 17-1/2″ wide workpieces with this sled.
The length of the jig is also up to you. The longer it is, the better it will machine longer workpieces, but there are diminishing returns, too, as it eventually becomes heavy and hard to handle. I opted for a length of 48″, as this provides me with a decent amount of support to keep long workpieces sturdy while in use, but it’s not so long that it’s hard to store when not in use. I broke the base out to 48″ × 22″.
The runners
I used quarter cut, even-grained hardwood for the runners, as this would be durable and stable. I machined the runners square, then dressed them to width, sneaking up on the final dimension so as to get a perfect fit. I opted for a fit that was ever so slightly snug, as I was going to use a shoulder plane to refine the fit once the runners were attached to the base. You could also machine them so they fit nicely before installing them if you don’t have a shoulder plane. I also machined them slightly thicker than the mitre gauge slots are deep. This ensured their upper faces were proud of my table saw’s surface when I glued them to the base. I would reduce their thickness with a hand plane after they were attached to the base.
Once the runners fit the mitre gauge slots, I added a bit of paste wax to my table saw’s surface, directly beside each of the mitre gauge slots, followed by masking tape, to further protect my table saw from glue squeeze-out.
A narrow bead of glue on top of the runners is all that’s needed. Place the base on top of the runners and add some weight to the base. Let this dry for at least an hour, then remove the assembly and tape and clean up any glue squeeze-out on the table saw.
At this stage I used my shoulder plane to dial in the fit of the runners.
Attach the stiffener
I made the stiffener that’s distant from the user from solid poplar. This part needs to be fairly strong so it keeps the far end of the jig’s base fixed together. Remember, you’ll also cut through a portion of the stiffener’s height, so don’t skimp on size.
Mill up the stiffener and ensure one edge is straight. The other faces aren’t overly important, as they will never be used to reference any workpiece. I eased all the edges of the stiffener that would be visible in the final assembly before applying glue and screwing up through the base into the stiffener. Ensure the screwheads are countersunk above the lower surface of the base.
The main fence
This is the most important part of this sled, as it needs to be straight, square to the direction of travel and strong enough to last. I cut two pieces of Baltic birch plywood to about 3″ wide and about the same length as my base panel. Exact dimensions aren’t important. I glued them together face-to-face, using a flat surface (my jointer’s infeed surface) to clamp them against to ensure they were flat. When dry, I cleaned up the two long edges of the fence and trimmed the fence to length, slightly shorter than the overall length of the base panel.
Because the most important part of locating this base is to ensure it’s square to the direction of travel, I put the jig assembly into the mitre gauge slots on my table saw and made a cut in the base. I stopped the cut about 3/4 of the way along the base before I cut the base panel into two parts. I then machined two pieces of scrap that fit into the kerf with a friction fit and slid them into place in that kerf. I could now use my carpenter’s square against the two scraps to give me a line perpendicular to the direction of travel. This is what I used to position my second fence.
I countersunk one hole in the underside of the base and drove one screw up into the fence, making sure to drill a pilot hole in the fence first. I kept the fence’s trailing face about 1″ away from the rear edge of the base panel. At this point, I could rotate the fence until it was perfectly square to the kerf with the help of my square and drive in a few more screws. Ensure no screws are added near where the blade will cut through the fence while this jig is in use. Once I was sure the hole locations secured the fence perpendicular to the kerf, I removed the screws, added glue to the underside of the fence and reinstalled the screws for good. I added a few clamps and cauls along the length of the fence to ensure a good connection between the fence and base panel. When it was dry, I added a 7/8″ square cleat the length of the fence between the rear face of the fence and the base to add strength to the fence.
To make the sled easier to carry, I added a simple handle to the stiffener. Depending on how you want to store it, you might want to add a few holes in the base so you can hang it on the wall where it won’t get damaged.
Put it to work
At this point you’re ready to cut dadoes. I have a right-tilt table saw which means the right edge of my dado stack, no matter how thick I have it set, will always be at the same point. This assists me when aligning the workpieces for machining. If I’m making one cut I’ll usually mark the location of the dado directly on the edge of the workpiece, adjust the workpiece until it’s in line with the right side of the kerf and make the cut. If I’m machining multiple pieces alike, I will use a stop block or extension stick, both clamped to the fence closest to me when the jig is in use. To speed up the process of adding stop blocks, you can even add a line for each inch mark on the fence, though I find it’s rarely needed. Everyone works differently, though.
The base on my sled is 48″ wide. Further, my base extends 27″ to the left of my dado set. This provides a fair bit of support for longer stock, but if you need extra support I strongly suggest you use a support of some kind to keep the workpiece flat when you’re machining. I place a sawhorse, complete with a flat, smooth surface on its top, to not only provide me with support, but also a low-friction surface that allows the distant end of the workpiece to slide easily. To check if the height of the sawhorse is in line with the height of the sled’s upper surface, stand near the sawhorse (or whatever support you’re using), kneel down so your eyes are at the same level as the workpiece and look down the workpiece. It doesn’t need to be perfect, as the workpiece can often be flexed slightly into place, but it should be very close.
I almost never clamp a workpiece in place, though there’s nothing saying you can’t. The weight of the workpiece is usually somewhat substantial, and as long as I hold it firmly in place it stays put. There’s nothing wrong with adding some adhesive-backed sandpaper to the working face of the main fence in order to keep the workpieces from sliding. While on the topic of the workpiece moving while in use, a coat of finish may look nice on a sled like this, but it also reduces friction between the sled and the workpiece, increasing the chances of it moving during use. I left my sled unfinished. I also lightly sanded the MDF with some 100-grit paper to add a bit of extra tooth for the workpiece to grip onto.
In use, I always make the pass, lift up the workpiece, then return the sled to its starting position. Dragging the workpiece over the blade a second time is only going to make the dado wider, decreasing the accuracy of the joint.
Rob is a studio furniture maker and the editor at Canadian Woodworking & Home Improvement. Instagram at @RobBrownTeaches