Introduction: 6 Tips to Building a Better Cross-cut Sled for Your Tablesaw
A cross-cut sled for the table saw is a must have jig for any serious woodworker. More accurate than a miter gauge, it also makes cross-cutting any board easy and safe. However, in order to provide the proper results it must be built with care. I made my first sled last year, following a plan in a popular woodworking magazine. Yet, in a matter of months, the maple runners swelled so much that the sled wouldn't slide in the miter slots. That's when my type "A" personality kicked in and I became determined to learn all I could about the ins and outs of building a cross-cut sled that would last. That research forms the basis for the tips and techniques presented in this instructable. And, while I can't take credit for any of these great ideas, I think you will find the insights of some very talented woodworkers helpful.
Step 1: Tip 1: Milling the Sled Runners
The runners ride in the two miter slots and guide the sled as the workpiece is pushed past the blade. They are most often made from hardwood such as maple or white oak, however, steel, aluminium or plastic runners are also options. Wood runners are more commonly suggested, most likely, because of the moderate cost. The disadvantage of wood runners is that the wood can swell with changes in humidity making smooth travel through the miter slots difficult or impossible.
Tip #1: Since most wood movement is with the grain, mill the sled runners with the grain running vertically as shown in the photo. This will minimize or eliminate side to side expansion of the runner in the miter slot.
Miter slots can vary slightly in size but most are 3/4" wide x 3/8" deep. Most plans call for milling the runners for a snug yet smooth sliding fit with no side to side play (also called slop). However, if the runner width swells too much it can become a problem and, as I mentioned, this is where I ran into trouble with my first sled. The good news: Tip number two allows some wiggle room when milling the runners to width.
Note: The height of the runners should be less than 3/8" so there will be some space under the runner for sawdust debris
Step 2: Tip 2: Building the Sled Base
1/2 " MDF is an excellent and recommended choice for the sled. Base the size of your sled on the size of your table saw and your woodworking requirements but not so large that it is difficult to control.
TIP #2: Build the sled as two separate halves that will be joined together when attaching the fences. Constructing the sled in this manner will guarantee that the sled runners ride tightly along the blade side edges of the miter slots allowing for a less than perfect fit if the runners are milled slightly smaller than the slots.
First, cut the sled base as square as possible, making the length slightly longer than your final dimension (approx. 1/2" or so).
Second, after determining how much of the sled you want on each side of the blade, cut it in two.
Third, measure the distance from the blade to the inside edge of each miter slot and add 1/4" to that dimension. Using those dimensions, cut spacer boards to clamp to the appropriate half of the sled base. These boards will be used to position the runners for mounting to the base.
Fourth, pressing the runners firmly against the spacer boards, glue and nail them in place.
Fifth, after the glue has dried, put one half of the sled base in the appropriate miter slot. It should extend the extra 1/4" or so past the blade. This excess will be trimmed off to create a perfect zero clearance for that half of the sled. Repeat the process for the other half of the sled base.
IMPORTANT: Remember to press the sled base FIRMLY against the blade side edge of the miter slot when trimming off the excess MDF, otherwise the two halves may not join together properly.
The photos show the process for attaching the runners to the base and trimming the base halves for a perfect zero clearance to the blade.
Photo one: A piece of MDF is used as a spacing template. It is cut 1/4" wider than the distance from the saw blade to the corresponding miter slot. Line up the spacer with the edge of the sled base and clamp it to the base and your workbench.
Photo two: Add glue to the runner.
Photo three: Press and hold the runner firmly against the MDF spacer.
Photos four & five: Nail the runner to the base.
Photo six: Set the sled base in the appropriate miter slot and trim off the excess
Photo seven: One half of the sled base after trimming (viewed from the output side of the saw)
Step 3: Tip 3: Building the Fences
The front and rear fences for the sled are most often made of solid hardwood. However, there is no guarantee that the fence will hold it's shape and remain true over time. For this reason, I thought tip number three made sense and was also a really good idea.
Tip #3: Construct the fences like a sandwich with the top and bottom pieces made of 1/2" plywood and several middle layers of 1/2" MDF.
The fences should be at least 3" high and 1 3/4" thick. The length of the front and the rear fences can vary depending on the preference of the user. Since the purpose of the front fence is to simply help hold the sled together, I opted for a shorter fence. This also reduced the total weight of the sled. My rear fence runs the full length of the sled but I noted many examples where the fence was an inch or two shorter on each end of the sled to facilitate angle cuts.
Finally, my fences include additional hardwood support on both the front and rear fences. On the rear fence the support provides both additional height and a dedicated "push block" to keeps my hands a little farther away from the blade. I salvaged these pieces from my original sled since I liked the look and functionality and because my new fences were only 2 1/2" tall without them.
To build the fences:
1) Rip your plywood and MDF pieces to size
2) Glue them up using clamps
3) When dry, scrap off any glue squeeze out
4) Clean up the the faces (and ends if necessary) by using a finishing blade and making a fine cut pass on the table saw
Step 4: Joining the Fence Halves
This step doesn't contain a tip, it merely explains the process for making sure the two sled halves are joined together properly. The photos below provide a summary of the steps. Here is the sequence I followed:
1) Drill countersunk holes through the sled base to attach the fences to the sled (later in this step).
2) Photo #1: Put the sled halves in position on the table saw and lightly clamp them together so the runners are pressing against the blade side of each miter gauge slot. Photo #2 shows how the left runner snugs against the miter slot.
3) Photo #3: Clamp the front fence in position and drill holes in the fence using the pre-drilled holes in the sled base as a guide.
4) Photos #4 & #5: Add glue, clamp the front fence to the sled and drive 2" screws into the countersunk holes. Allow an hour or two to dry.
5) Remove the clamp on the front fence and reposition the sled on the saw to attach the rear fence (you may need to remove and reattach the clamp holding the two halves together).
6) With the rear fence clamped in position, drill a single hole through the fence (first hole on the left end) using the predrilled hole in the sled as a guide. Drive a screw into the hole and remove the clamps.
7) The next step will square the fence to the blade.
Step 5: Tip 4: Squaring the Fence to the Blade
The only way to get an accurate cut is to have the rear fence perfectly square (at a 90 degree angle) to the saw blade. Most often a single square is set against the blade and the fence to determine the proper fence position. There is nothing really wrong with this approach but I think the next tip makes the process all the more foolproof.
Tip #4: Use two 90 degree drafting triangles, one on each side of the blade, to assure finding the correct position to secure the rear fence.
The reason I like this method is that, if your fence isn't perfectly straight, your blade is warped or out of alignment on the saw, then getting both triangles square to the fence and blade at the same time isn't going to happen.
Note: I have a moderately priced contractor style table saw and, after this exercise, I came to the conclusion that my blade was just a hair off (maybe half a hair). Since I wasn't about to take the saw apart I decided to finish the sled and see if the results were acceptable. They were, so I'll leave perfection to those of you with better equipment than mine.
After finding the proper position for the fence, strike a reference line on the sled using a very sharp pencil.
Step 6: Final Assembly
Next, you have two choices. You can either:
(1) Clamp the fence to the sled at the reference line and shoot a small nail through the underside of the sled (on the end of the fence opposite the screwed end). Next, with the fence now secured to the sled, remove the clamp and make a test cut* to check if square. If the fence is out of square, tap the fence with a mallet to slightly adjust the angle of the fence, then make a second test cut and check again**. Repeat this procedure until you obtain a satisfactory result. Now, with the fence square to the blade, reclamp and drill holes in the fence using the pre-drilled holes in the sled base as a guide. Finally, screw down the fence with 2" long wood screws.
or, as I did...
(2) If you have confidence in the accuracy of the reference line, clamp down the fence, drill a hole for a set screw on the end of the sled and screw down the fence. Make a test cut and check. If you like the results, reclamp the fence to the sled and finish drilling the mounting holes in the fence. Complete the assembly by securing the fence with 2" long wood screws.
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*HOW TO DO A TEST CUT:
A test cut is a foolproof way to see if the sled is set up correctly. Simply rip a good size piece of scrap (making sure it has straight, parallel edges). Press the workpiece against the fence and cut into two pieces. Slide the cut edges together to see if they fit together without any noticeable gaps. If all looks good, take one piece and flip it over (front to back) and check the fit again. Any error in the cut not visible on your first inspection will now be doubled and be much more obvious. As shown in the photos, if the edges butt together firmly with no gaps then the fence and blade are aligned correctly.
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** Determining which direction to adjust the fence: If the gap in the test piece is at the rear fence, move the fence back. If at the front fence move the fence forward.
Step 7: Tip 5: Increase the Sled's Versatility With a Layer of Hardboard
Since a zero clearance kerf is necessary to avoid chipout when making any kind of cut, this next tip will dramatically improve the versatility of your sled.
Tip #5: Cut pieces of 1/4" hardboard and attach them to the fence and sled base with carpet tape. Then, with a regular blade, cut a kerf in the hardboard. At this point the hardboard is simply duplicating the kerf of the sled in providing the zero clearance necessary for a clean cut. However, eventually you may want to make wider cuts using a dado blade or with the saw blade set for an angle cut. These cuts will forever change the kerf size of the sled and fence. However, by simply replacing the hardboard when switching back to a regular blade set to zero degrees, you can easily return the sled to zero clearance cutting.
Step 8: Tip #6: How to Guarantee a Smooth Sliding Sled
If your sled glides over your table saw's surface from day one that's great. However it may not and, eventually, it pays to employ this last tip:
Tip # 6: Apply a light coat of Johnson's paste wax to the sled bottom and runners, then buff when dry. This should reduce any friction and make the sled slide much more smoothly. Alternately, you can apply the wax to the top of your saw and miter slots, or to both the sled and saw top if you like.
Note: Wax used on the table saw top will not affect your workpieces once the dried wax residue has been buffed off.
Step 9: If You Are an "A" Type Personality
Accuracy and precision are key components to good woodworking. So, if you are an "A" type personality like I tend to be, you may find this website both intriguing and maddening at the same time:
http://wnwoodworkingschool.com/5-cuts-to-a-perfect-cross-cut-sled/
On his website, William Ng has a fascinating video on how to test your cross-cut sled for accuracy and adjust it to within one thousandth of an inch of a perfectly square cut! Needless to say my sled didn't pass his test but it was fun to give it a try. In any case, since my test cuts look good and fit together well, I'm more than satisfied and confident my new sled will do everything I need it to do.
I hope you find these tips helpful if you plan on building a cross-cut sled. If you get yours to within .001 of a degree accuracy I'll be a little jealous but glad I may have helped in some small way.
