Titanium jewellery can be a challenge. Making a titanium ring is not too difficult - you will not be able to use normal goldsmith techniques. Your best approach is that of light engineering. A lathe, a power saw and a powerful polishing machine will make it a lot easier. Most titanium ring manufacturers start with round bar. Some manufacturers may use titanium tube, but this usually has a seam - which makes it difficult to machine. Titanium solid bar, grade 5 and grade 2 titanium is easily available from most titanium suppliers. You can buy titanium solid bar in various sizes - 25mm or 1 inch diameter bar will cover most ring sizes.
Your first step would be to cut a 150mm section off of the length - this will easily fit in most small lathes. Set the cut section into the lathe with a tungsten carbide drill bit - or a concrete drill bit. (you will have to re-sharpen the bit to get a good cut). Start with an 8mm drill and then step it up to just under the ring size you need. This is called boring and is basically taking out the center of the round bar. Once the section is drilled out to the right side you can take the drill out and put the bar into the chuck. True the ring bar in the chuck - then use a tungsten carbide cutter. Depending on what profile you want (half round, soft D shape or flat). Take the thickness of the tube down to the thickness you want the ring to be when it will be finished (Work on 2mm - 2.2mm), then profile the outside of the ring.Your cutter can be sharpened to the shape you want - use a grinder, and lots of water so the cutter does not burn when grinding. To get curves for D shape profiles I use a hand held air grinder with shaped grinding stones.
If you are going to add grooves as a pattern, or grooves to inlay gold or silver now is the time. All of the drill speeds and cut feed should be very slow when cutting titanium - if you spin the piece too fast you will only burn the cutter - or worse the scarf (off cuts from the cut) will ignite. Use a cutting fluid when make deep cuts - my suggestion is "slowly slowly". Sharpen your cutter regularly. If you are going to inlay the titanium ring the walls of the cut should be 90 degrees. They should be at least 1.4mm deep to hold the gold or silver.
Once the profile is cut, and the grooves cut you can pair off the ring - if you are making several rings do not pair off until all the outside detail is complete. If you are working on one ring only you could pair the shank off before the detail is put in - you will need to make a tapered spindle or triplet to mount the ring onto afterwards. If you are going to engrave a pattern into the outside of the titanium ring using a triplet or spindle is very useful - you can take it off the lathe and place the triplet and ring directly onto your engraving machine. It also helps if you are going to hammer precious metal into the grooves - this inlay work can be done whilst on the bench, holding the triplet with one hand and hammering the gold in with the other.
Once the gold or silver has been hammered (inlaid) into the grooves take the ring off of the spindle. You can then solder the joins using hard solder. Don't worry if the titanium discolors - this will be removed later. When all the solder work is done you can remount the ring on the triplet - make sure when you place the triplet back in the lathe that it is true - use a block of brass up against the edge of the ring once it is spinning on the lathe. You can also push the ring tightly onto the spindle while doing this. Find the profiled cutter you used to make the cross section and scrape off the excess gold or silver. If you are good with a lathe you could also have inlaid the ring whilst it was flat, and at this stage put the profile in - cut slowly or you will tear rhe silver out of the groove.
Next the ring comes off the triplet and is placed directly into the lathe chuck - you will need a right shaped cutter to put the comfort fit into the shank - when one side is done flip the ring around and do the other side. All you sandpapering can be done while the ring is on the spindle - and the inside can be doen on the bench with a hand held air grinder. Next you can polish the outside and the inside of the ring - a normal Goldsmith's polishing machine will do it - although a poerfull polsiser is a lot easier. Again - don't rush - the surface of the titanium should have been sanded gradually from P120 right down to P1200 grit - use water if needed. When polishing try and concentrate on the titanium bits, and avoid the precious metal inlay - the gold or silver is much softer than the titanium and you will polish grooves into the gold or silver. Change the direction of the polish regularly. Grade 5 will give you a beautiful polished surface - while grade 2 titanium (pure titanium) will never polish to a mirror finish. The ring can then be sent to the ring engraving machine for hallmarks and carat stamp. If you are going to be stamping your hallmarks in with a hand stamp you should do it before you inlay.