A friend of mine who I had taken a woodturning course led by Petr Bakeš in Hradec Králové asked me to show him deep hollowing and undercut. I have been using a simple and extremely efficient deep hollowing tool Brother System 2 from Henry Taylor Tools. https://www.henrytaylortools.co.uk/brother_system_deep_hollowing_tool.html,
It works very well with fresh wood and with dry wood the ring has to be set properly and correct revs have to be used to avoid clogging. Nevertheless, it sometimes happens. This heavy duty tool allows hollowing as deep as 33 cm and with a swan shaft it handles any undercut. The diameter of the ring is 13 mm and the shaft is either 13 or 16 mm. I use the latter one. The 16 mm ring was also available in the past but the producer stopped making it as the 13 mm one is sufficient for any project.
Thos system is suitable for turning from either side and is used for spindle turning as well. The producer recommends setting the ring for 11 o’clock, but it can be set as required. The advantage of this design is that a thickness of a shaving can be set. The ring is easy to sharpen with the original accessory and a stone.
There are tools with a similar design e.g. https://www.robert-sorby.co.uk/sov16s-ults-ultima-hollowing-system, http://www.crownhandtools.ltd.uk/page120.html or https://www.dictum.com/en/combination-tools-bagd/wiedemann-ring-cutter-702350.
I sued this tool for turning the walnut bowl. The wood comes from the other half of the log see the news before. The diameter of the bowl is 30 cm and it is 18 cm tall. The thickness of the shaving was set to 0.7 mm. I set the cutting ring to 11, 12 and 1 o’clock. You can see deep hollowing in the video (starting time 16:53) https://www.youtube.com/watch?v=BAf60cXJQE8&feature=emb_logo.
Thank you for reading and if you have any question, do not hesitate and write or call. Good luck with turning!