Best Sled for Cutting Bowl Segments

At the recent bowl Segmented Bowl Turner's Symposium, there was a lot of discussion regarding sleds for cutting bowl segments. After listening to everything that was said, I still think that my current design is the best.

Here is how to build one - step by step:

• Cut  a nice piece of hardwood so that the thickness is the exact width of the miter slot in the bed of your table saw. I did this by using my planer and taking off 1/128 of an inch during each pass until the board just fit into the slot. I then cut a slice off the board that was the exact depth of the slot (or very slightly less). Use a Forstner bit to counter-sink a couple of places for sheet metal screws to hold  this to the bottom of the sled board. You do NOT want wedge shaped counter-sink which could cause this board to spread as screws are tightened. This is why you will use sheet metal screws. I call this the miter slot board. Note that you want this to be long enough to extend the entire length of the miter slot over the full travel of the sled board. This will lessen the effect of any slop in the width of the board.
• Next you need an absolutely perfectly rectangular piece of wood for the base. I used 1/2 in Baltic plywood. I call this the sled board.
• Lower the blade below the table saw surface. Place the miter slot board from step one into the miter slot and place the sled board onto the table saw surface and align the side of the sled board exactly against the edge of the table saw. Use the rip fence to align the other side of the sled board. Of course, these two alignments are redundant to each other.
• Drive a couple of short screws through the sled board into the miter slot board. These are temporary.
• Turn the whole thing over and attach the miter slot board to the sled board using sheet metal screws. I originally tried to use 4 screws, but I found that my tolerances were tight enough so that doing so caused the sled to bind slightly. I ended up using only two screws.
• At this point, I had a sled board with edges perfectly aligned to the blade – either parallel or perpendicular.
• I raised the blade and cut 60% of the way through. This amount is not critical.
• Now you want to position the fence. I used a pivot knob, but I don’t think this is necessary. The important thing is drawing a perfect line. See the following diagram:

• Assuming that everything is square, you want to draw a line such that it crosses the kerf and has the desired angle. You want the left distance minus the right distance, divided by the width to equal the tangent of the angle.  I suggest doing this in mm, since my mm rulers tend to be more finely marked than for inches – unless you have a ruler marked in 64ths.
• Here is how to do this. Place the fence board at about the correct angle from the blade – in this case about 75 degrees where you will want it to end up. The important thing here is to make sure it intersects the kerf. Place a small mark where it crosses the right side of the sled board. Measure this. I suggest adjusting it slightly to have it on an exact mm or ruler mark. Next measure the width of the sled board. Multiply this by the tangent of 15 degrees (0.26795). Add this to the Right Distance. This will give you the Left Distance. Mark this and draw a very fine line from this mark to the mark you made on the right side. You probably want to get the fence board out of the way until after you have the line. Then align the fence board along this line and screw it into position. I used 1” drywall screws for this.
• Left Distance = Right Distance + [Width x Tangent(15 degrees)]
• When I did this, I had the advantage / disadvantage of the Pivot Knob. With this, I could not select my Right Distance arbitrarily, and I had to draw the Line along the fence board, but once I had the fence at the right angle, I could tighten the Pivot Knob and then drive in the drywall screws to secure the fence at the correct angle. This prevented the screwing from moving the fence.
• You see the clamps. These go through the fence board to a T-nut that is counter-sunk into the bottom of the fence board. It is important to put in a couple of drywall screws to hold the fence board down against the slide board. Otherwise, the clamp will lift the fence board off of the slide board.
• For other angles, I don’t see any reason that I can’t use the same fence board. This was my original reason for putting in the pivot knob. But so far, I have cut only segments for a 12 sided bowl.   

Additional Improvements:

Here is what I learned subsequent to doing the write-up above:

• The pivot knob is not necessary.
• I have replaced the clamp that holds down the piece being cut with a quick release clamp. 
• Note that the two clamps on the right hold a spacing block and that this block is cut at the same angle as the piece being cut. I now think that the spacing block should be square. The angle allows the piece being cut to work its way up onto the block, thus introducing a small error. 
• Since building my sled, I have noticed that most sled plans have the fence going at the other angle. In other words, if you my sled has the fence at 15 degrees, most other designs have it at minus 15 degrees. I like my design better because blade pressure against the piece being cut tends to force the segment against the stopping block. Setting the fence at the other angle would tend to move it away from the stopping block and if this were to happen, it would introduce an error. 
• I mounted a piece of plywood at the far end of the sled to keep the two halves of the sled aligned. After some months, I found that the two sides were not both lying flat on the saw table. 
• I will try to add a photo of the improved version below.