Hello Mike….Welcome to the discussion.
Yes indeed, I agree wholeheartedly with your sentiments! However, there is light at the end of the tunnel! After a great deal of searching I did find a suitable “hybrid” cutter: you are absolutely correct; the design calls for a non-standard radius, that is, it does not fall within industry standards. That said, you would be right to increase the size of the section to permit selection and use of a “standard” cutter. Problem is, due to the collective (knock-on) effect this would have on the final build of the toy it would mean, in order to retain the integrity of the concept, a complete redesign of the toy: a huge challenge in itself so late in the day. So far, most of the toy has been made: the cone (tower) is complete as is the base. The rings are well advanced: 8 waiting to have the edges rounded and two with some turning work yet to be completed. Because of this, I persevered with my search for a cutter with an appropriate radius. Although successful, eventually, it is still a compromise as it has a cutting radius of 7.8mm ( I won’t translate to imperial as there is no simple equivalent): the design actually calls for a 7.5mm cutter radius - the rings/hoops being 15mm thick or in other words have a cross-section equal to 15mm diameter.
Just for the record, I failed to appreciate the implications of this when I took on the challenge - something I now regret! There is a reason for this: until I retired some years ago I was actively engaged in 3D CAD technology in the aircraft industry and indeed spent over 20 years using advanced CAD drafting programmes. Had I spotted the design flaws in this designer’s toy design I not only have the capability, I have the tools (a suitable computer programme, i.e. Sketchup 2017), experience and, indeed, the skill to redesign the toy to ”fit” within the tooling available, routinely, within the industry. But, as I say, back tracking would mean scrapping all that has already been made and obtaining a fresh supply of suitable material: demanding, costly and with personal health issues to contend with, impractical.
Mind you, purely as “an exercise in design” I did reproduce the designer’s design on my computer snd made some interesting discoveries, which enabled me to determine how much leeway there was for tweaking the section radius.That is how it came about that the cutter I found will meet the assembly criteria imposed by the peculiarities of this design.
With over 40 years as a Design Engineer (20+ years on the drawing board and 20 years on CAD system) my view of this design tells me that the designer - at the time he/she created this toy design - did so without the benefit of a background in any commercial enterprise involved in, engineering type, functional design: more than likely, he/she is a talented university undergraduate or an ‘A’ level student at a college for Advanced Education creating a project for course-work assessment.
Regrettable though it has been, I did miss the chance to do a completely remodelling of the design to make it, not only easier to manufacture, but compatible with accepted, industry standards for design and manufacture.
As I recorded elsewhere on the forum, a milling machine would make life easier: I am waiting on news in this case as a machine, currently out of commission in need of a new part - an internal power trip device - may be serviced in the near future - however, no rotary table is an issue as these can be very costly ( equivalent to around $500 US) which is, frankly, more than my personal resources can stretch to, especially as I would have no further use for it once the rings are finished.
”Back to the drawing board” is sadly, not an option. Just hope I can get there anyway even if it will mean using a good deal of ingenuity …….and, dare I say, luck!