Process of making any segmented turning starts with strips of flat dimensioned stock. The more horizontal the curve on the turning is to be the wider the stock needs to be. Wouldn’t recommend any less than an inch for pretty much anything. Lengths up to about four foot are more manageable, contrasting colours are attractive and it should be calculated before hand what percentage of your wood needs to be which colour.
Once you’ve got your stock, you’re ready to start cutting segments. People do this in several ways, a chop saw is a common choice and I have seen people successfully use a bandsaw with some nifty jigs, though mine never seems to yield good enough results for this. My choice is always the table saw, set up with a blade of 60 or more teeth for a smooth finish on the end grain. The best way I’ve found so far to repeatedly cut segments fast (roughly 400 per hour) is a mitre gauge with a sacrificial fence fastened to it that includes a small horizontal step for the lumber to sit on, a zero clearance blade guard with a small wooden ramp glued to it, somewhere around 10 degrees and waxed. I use a wide block of wood, 4 inches or more, clamped to the foremost part of my fence, off which I reference the outside edge of each segment before sliding the mitre gauge forward to cut it off from the stock. The mitre gauge needs to be set at the specific angle for the number of segments you wish per ring. For example 15 degrees for 12 segments, 15 x 12 = 180, but there are two faces meeting at every juncture so the 180 is doubled, to make the required 360 circle. Charts like this are available all over the net to download.
With the mitre gauge set cut the end off the stock at the desired angle, rotate the stock 180 degrees (I mean roll it over to expose the underneath) then you will be able to get a specific measurement that your segments will be cut at. I usually do several different sizes and glue those rings together in a form appropriate/pleasing afterward.
Now just keep rolling and cutting, rolling and cutting until you have a massive pile or segments ready to be glued together. DO NOT let them build up on the right hand side of the table saw blade past 5 or 6 as vibration will cause them to get near the blade again, it’s rare for them to be launched at you but very common for them to be damaged although both are highly possible!
Now we’re onto the glue up. Play with the segments for a while first and choose a pattern you like before you get the glue out.
If your mitre gauge is out by half a degree then that will show as more than 20 degrees if you put all the pieces together. Mine seems really close but still results in a 2 or 3 degree accumulated error over 14 or 16 segments. This is not tolerable as any gap on glued faces on end grain not only looks awful but is likely to cause a small wooden explosion on the lathe at a later time! My favourite way to get around this problem is to glue them together in two steps. First into two half rings, separated by wooden dowels on which they can pivot to ensure good contact on glue faces, then to sand each mating edge of the half rings on a good flat surface or well set up sanding station. Then the two half rings can be successfully glued together with all error removed.
I’ve only ever used modern glues for this work and so clamps are a necessary evil unless using super glue with accelerator, though I don’t recommend this as it just isn’t as strong and makes a right mess. So the answer is band clamps. These are not that expensive, starting at about £6 and working upwards, but most commercial ones are quite bulky and clumsy and have very wide bands that aren’t glue proof. Add to that the fact that you’ll probably want 10 or more in your arsenal and making your own looks very attractive! Mine are a simple design, plywood outer and a wedge inside that jambs a standard packaging band readily available from all manner of large boxed things, like domestic appliances etc. These are perfect as they are very flexible, resist glue completely and you can swing off them if you’re brave enough!
Gluing can be tedious, particularly if you need to be tidy about it, so do yourself a favour and get a nice wipe clean board like an old kitchen door etc and think mess! I start with a small plate onto which I squirt a liberal amount of standard PVA glue and dip every adjoining face into it, wiping off the excess on the edge. Less here is not more, you do want glue to squeeze out from everywhere so you can be confident that the end grain hasn’t soaked it all up. Once you’ve got them all glued and clamped together in a ring wipe off the excess with a damp cloth or sponge from both the ring and your work surface. In no time at all you’ll have a pile of rings which no matter how good you are will not have flat enough tops or bottoms to be glued to another ring successfully. The next trick is to sand them flat. I paid a trip to the local tile store who supplied me with a 2 foot by 2 foot travertine style floor tile which is as flat as a pancake, onto which I glue or double sided tape, strips of sand paper in two rows, one half 60 grit the other half 120 grit. Much smoother than this and they won’t stick together as well. When all the tops and bottoms are flat and consistent then you can glue them together. Again, with the glue less is not more, you still want tons of squeeze out but without having applied so much pressure you’ve squeezed all the glue out. Excess is no problem here and with most woods tools require sharpening several times while turning something and I haven’t personally found the glue to dull tools quicker than pine let alone oak or utile. People glue them together in lots of ways. I normally jamb one board on top and one on the bottom and use three of more large F-clamps to apply even pressure. Others have the same board technique but with threaded bar and nuts. Let the glue dry at least overnight, bottles that claim 10 minutes success are full of lies and inevitably peril on the lathe!
You are now ready to turn your project, whatever it may be. For segmented turnings bowl gouges 3/8ths of an inch or heavier seem most successful, whatever tool you use needs to me extremely sharp. Much sharper than turning between centres or just regular bowl work as a dull tool will try to catch on the edge of every single segment resulting in tear out of the would fibres and often a few missed heart beats. Difference in wood species can require delicate sanding if their densities vary or you’ll end up with a do-decagon instead of a cylinder. I hope this inspires you to have a go, if you have a workshop, or if not, then to consider buying one I’ll make for you! Thanks for reading.