Is it Possible that you have never known how to make Seamless Mylar Belts ? Because I do !

During the 1970s, I was employed as a Technical Assistant to all the Technicians of a Company who manufactured Flight Data Recording Equipments here in the UK.

Royston Instruments (The Designers) and Royston Engineering (The Manufacturers) made two recorders, one a Maintenance Recorder which recorded 144 sets of data onto one inch tape, and an Aircraft Crash Recorder.

My remit was to keep Engineers and Draughtspersons up to date with developments in all areas which were of interest to them. As a result of that I sourced Catalogues, Periodicals and Documents etc. from Libraries, Manufacturers etc.

One most important to us at that time was a 'Technical Note' I discovered from NASA, referred to the Tape recorders designed for use in the early Meteorological Satellites called Tiros (sometimes called Tyros).

This document as I recall was either stamped Unclassified or Declassified, also my memory told me it was a D**** however ; the only related reference I can find now, is to the following.....

Licht,J.H.,and White,A.,"Polyester-FilmBelts,"Mach.Des.32(22):137-143, October27,1960; also NASA Technical Note D-668,May1961

(Mach.Des. Is for Machine Design).

The strange thing is that I cannot locate either document.

Nevertheless and for those of you who are interested, here are the basic details behind the 'endless belt'.....

Someone had realized that a large washer, proportioned like the letter 'O' cut or stamped out of a sheet of mylar (DuPont's polyester film) if stretched between rollers, does indeed become a seamless belt, albeit of wedge shape.

Further development of the belt by heat treatment was also carried out and barrelled rollers were designed which induced the belts to centralize on the rollers so that the belt did not 'run off'.

I understand mylar belts are available today but none of which is seamless and therefore I assume and logically, they must be inferior.

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would it be due to advances in joining materials, like adhesives etc? if you can glue something to the same strength what's easiest- cost effective to manufacture at that point.
Elizabeth gives a good  reason for suggesting that large diameters might be difficult to cut, but I don't see the necessity to make a belt any larger than say 15CM diameter and even by hand* that should be easily achievable. In a production process, there would be little problem indeed in making a press to stamp them out.The question really is whether you need a seamless belt made of a vastly stable material, which would almost never need replacing and one that is not affected by considerable extremes of environmenal abuse.The post by another of course is irrelevant because the point of this post is to show how to produce a belt which does not have joins, joins that will always affect the Recording and Playback of the medium to some degree. *Two centered metal disks of the required diameter can be used to cut around using a scalpel blade (Cutting the larger diameter first of course).
My deck (Artemis SA-1) uses 1/4" magnetic tape for a belt and has a tensioning roller which is the only part effected by the splice. This will of course inject energy into the plinth on each revolution of the tape but the DC motor injects more, I can sometimes hear that when next to the deck when there's no record playing, none of it gets through to the stylus when there is. There was a reason it's designer didn't use leader tape, he said as much when I cornered him at Munich last year but he didn't say what it was. I suspect the coating adds a bit of damping to the tape. I have some leader tape but haven't got around to experimenting with it, it's time will come. I'm probably not going to attempt turning a polyester ring into a belt but if the right sized belt were available it would be an experiment worth trying. I quite like being self sufficient for belts, if it breaks i just splice another together and I have a centimetre or so tolerance to play with so any improvement would have to weigh against this.