I was just investigating the cause of a non working VCR, and found the belt had gone rather saggy with age... Fortunately I managed to track down an already sized part, but the thought occurred to me, is there design guide or rule of thumb for rubber belt selection?
Knowing the two pulley sizes and their separation, its easy to work out the circumference of the belt path, but presumably one needs one a bit shorter so that it stretches a little when applied.
Flat belts are sometimes fibre reinforced and have very little stretch. The square belts which ran in V-grooves on tape recorders were pure rubber and more stretchy. I doubt if you would need more than 5% "stretch" on these. The downside of too much tension is both friction and wear in the bearings (often "oilite" porous phosphor bronze).
With cassette decks the wanted tension varies quite a bit, hence the stetch %age does too. I presume the same is true of VHS etc, long time since I played with one.
Ever wanting to push the envelope I ended up sometimes using stationery rubber bands. They can fail, but in nearly all cases they stayed fine for many years, and generally performed as well as the black belts.
NT
Last time I needed an odd-sized poly-V belt for a car, it turned out the stretch was already taken into account on the belt's stated size. i.e. you wrapped a tape measure around your pulleys and bought a belt that was quoted as that length.
No idea if the same holds true for the little ones of course...
Cheers,
Colin.
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