Preparing a Blank for Segmented Turning
At first thought, accurately making segments for a turned segmented bowl seems like a tedious and painful task. That’s not the case, because a special mitre sled simplifies cutting the parts, while some standard supplies and a simple approach are all you need to get the bowl blank assembled and ready for turning.
I have tried just about every method to create segments using mitre saws and disc sanders. Now that I’ve figured out how to create a proper mitre sled for my table saw, I won’t fiddle with any of that stuff anymore. It can’t be done any faster, safer or more accurately than with one of these sleds. Oh, and with less waste. What more could you want?
Attach toggle clamps to the fence to hold the segments safely for cutting.
Don’t panic ... it’s only a test
Cut test pieces out of scrap to check your angle. Mark an “X” on the side where material needs to be removed.
A little pivot
Remove all the screws except for one and fine-tune the angle.
Clamp in place
Your hard work has paid off. Glue it up, clamp it down.
Perfect Mitres – Every time
The possibilities are endless.
The Table Saw
Don’t be overwhelmed when I say we’re going to do this on the table saw. If the jig is made properly, this is the safest way I’ve seen to cut segments. The table saw doesn’t have to be big and fancy, either. I’ve even done this with a jobsite table saw that was worth half as much as my mitre saw.
A mitre sled equipped with toggle clamps not only makes accurate, repeatable cuts, it also makes the task of cutting many tiny segments much safer for two main reasons: (1) There’s much less chance of sending small pieces of wood into the air because the toggle clamps hold both the work piece and the off-cut, and (2) your fingers can stay a safe distance from the blade at all times.
Like many things in life, you must do something the wrong way in order to learn the right way. Please learn from my mistakes and do not make your runners out of wood. The seasonal movement of wooden runners would be enough to cause the sled to bind or slop around in the T-tracks and would defeat the purpose of building the jig.
Make the runners out of UHMW (ultra high molecular weight) plastic or a nylon cutting board. This plastic can be milled in all the same ways wood can. Use a planner to mill the runners to the exact width of the T-tracks of the table saw. The runners should be a snug fit but still slide smoothly. Make the runners slightly less than the maximum height of the T-track.
The Base can be made of anything as long as it is flat; I have had the best luck with MDF. This sled will only be used for cutting small segments, so it doesn’t have to be very big. Cut the base 12″ x 16″.
Attaching the runners
I attach the runners with #8 screws. It’s important to drill the right size pilot holes so the runners do not bulge when the screws go in. An ⅛” pilot hole worked perfectly for my screws. All screws are not the same, so try a few tests in an extra piece of the runner. Try to find a pilot hole that the screws will still get a good bite but not cause the runner to bulge.
With the blade lowered and the runners in the tracks, use the fence to help hold the base square. Drill a pilot hole through the base and into the runner. Be sure to drill your pilot holes as vertical as possible.
Countersink the holes for use with flat head screws. Drive one screw into the runner to keep everything aligned before drilling the rest of the holes. Use a screwdriver instead of a powered driver, to be sure not to torque anything out of place. Use a file or a rotary tool to grind a cutter on the tip of the screw; this will make the screw cut a thread as it goes into the runner.
Now that the runners are attached, your sled should slide smoothly. If it doesn’t, use a card scraper to adjust the runners. The objective is to have the sled slide smoothly but without any slop at all. A little wax on the table as well as in the T-track will help the sled glide with ease.
Attach a piece of hardwood across the front and back of the sled to hold it together once it is passed through the blade. Make these pieces higher than the blade will need to be to cut your segments. I made mine 1 ¾” tall with a second block on top 1 ¼” tall. Attach them with screws from the underside. Just be sure you don’t put any screws in the path of the blade.
Attaching the Fence
Use a protractor or an angle finding tool to draw a line on the sled at the angle you wish to attach your fence. At this time it’s only necessary to attach the fence close to the angle you have chosen. The angle will be adjusted later by cutting test pieces. For eight segments you will need to cut the end of each piece at 22.5°.
The fence is a 3″ wide piece of MDF or plywood. Add a small rabbet to the underside of the fence to ensure your stock will sit flat to the base and tight to the fence and will not be obstructed by wood chips. My favourite method for aligning the fence is to cut a wedge on a mitre saw. Attach the fence with two screws. Since you will probably need to adjust the angle slightly, only use a few screws for now.
You can make this sled with an adjustable fence so it can be adjusted to cut multiple angles if you would like. You will just have to re-set the angle of the fence each time you make a new segmented turning. I prefer to make one sled for each number of segments. I only have a few sleds for my favourite number of segments like 8, 9 and 12. It is extra work to build separate sleds but it allows me to cut my segments perfectly time and time again without fuss.
Fasten toggle clamps to the fence in a position that suits the size of segments you will be cutting. When buying toggle clamps, look for the ones that operate by pushing the handle down instead of forward. Pushing the handle down is safer than pushing the handle forward (towards to blade), for obvious reasons.
Clamp a stop block at whatever length you wish to cut and cut some test pieces from scrap material. When cutting your test pieces, it’s best to cut them out of a wider width because it will better indicate the error of the mitre. If your angle is 22.5°, it’s only necessary to cut four of the segments to conduct a test.
Test your segments along a straight edge.
Unless you got really lucky, you’re probably going to have a gap in one direction or another. Mark one of the segments on the heal or the toe, whichever needs more material to be removed to close the gap. Place the marked segment on the sled and rotate it to see which way the fence needs to be adjusted.
Mark a pencil line at the current fence location so you can see how much you’ve moved the fence. Remove all screws holding the fence except one near the outside. Pivot the fence on this one screw until you think the fence is at the correct angle. Re-attach the fence with the screws in new holes. Putting the screws back into their old holes will just pull the fence into its previous position.
You will most likely have to do a few adjustments and a couple of tests to get the sled cutting the perfect angle. When adjusting the angle of the fence, remember the adjustment is multiplied by the number of segments.
Before cutting into expensive materials it is a good idea to do a test with all of the segments rather than just checking them along a straight edge. Clamp them together with hose clamps. Once you are sure you are cutting the perfect angle, lock the fence in place with a few more screws.
Clamping is Easy
Cut your segments with a combination blade and use hose clamps to assemble the rings. I use Titebond 3 to adhere everything together. I prefer to assemble each layer and glue it down to the base or the previous layer all at the same time. I have had a lot of success and much more faith in this method as opposed to assembling each layer separately and then sanding them flat with a drum sander.
Be sure to begin with a base that is absolutely flat and make sure all the segments in a layer are the same thickness. Take care of these two things and you shouldn’t have a problem clamping each layer down one on top of the next. In between layers, use a scraper, chisel and/or hard sanding block to remove any glue squeeze-out. To help the joints stay together, stagger them on each layer.
This is merely a starting point. Endless possibilities and beautiful turnings await you! Good luck and happy turning!