9 Aug
2006
9 Aug
'06
8:41 p.m.
Tony Duell wrote:
You're lucky to have a local electronics shop, and it sounds like you
have more than one.
Ha! No, I live in a "backwater" :-( In *that* sense, I *am*
lucky to have a local electronics shop! :< There are two,
maybe two and a half (or, maybe one and two-halves?) located
within a few blocks of each other. But, *combined* they don't
amount to a *good* shop.
OTOH, one has to be thankful for whatever is available.
The supply of belts (and vacuum tubes) was really quite
unexpected.
But, I can't rely on them for a variety of *components*.
Those have to be obtained via mail-order. Which seriously
impacts how you do things.
Other places that I have lived were more metropolitan and
finding disti's with open door policies was pretty easy.
Yes, there are places that will do that. And, most manufacturers
will sell kits for not-too-outrageous prices. But, since you
usually only have to replace *one* belt (at a time), having to buy
a whole set can *appear* costly.
Problem is finding out how to contact manufacturers directly
to gain access to those things. Again, certain localities
are considerably nicer in that regard (e.g., when I lived in
Chicagoland, I walked into Jensen and got photocopies of
old spec sheets, speaker cabinet plans, etc.)
Can you recomend any places to start looking (usual
disclaimers, of
course). I collect names of companies that sell useful stuff for
hacking/restoration.
I just go to one of the local electronic stores. They have
a wall display
of assorted belts, each individually packaged
(to justify the price? :< ). Of course, they have no information
as to *applications* so it is wise to know what you are looking
for before walking in.
Again, you're lucky. Over here, there are companies who sell 'belt kits'
for particular models of VCR, with no information as to the sizes of the belts each kit contains. Great if you want to fix that
machine, not so
good if you want a belt for something else. I don't know of any place in
London that will let you match up a belt (or who will supply a belt by
dimensions).
Sure. But doesn't that imply that the centreline of the belt lies on the
circumference of the pulley? Which means that said program would
calculate the correct size of belt (assuming it's measured around the
centreline).
I'm not sure what the "norm" is for measurement. Note that
2 pulleys of dia's A & B at a center-to-center distance of C
could end up using a belt only *slightly* different than
pulleys of dia's A' & B' at a distance C'. I.e. matching
up belts is not trivial -- each time I have done it, it has
been a trial and error process: "How does *this* one look?
Any better than that LAST one??"
And, of course, when you find the right belt, you buy *two*
AND save the packaging of the one belt that you actually
*use* (with annotations so you don't go through the same
mess next time).
FWIW,
there's a program in the HP67 Mechanical Engineering Pac (which
will also run on the HP41 series with a card reader) that calculates belt
length given the diameters of the pulleys and the coordinates of their
shafts. It assumes the belt goes round the outside of all the pulleys, it
gets the wrong answer if one pulley is outside the belt (which would be
done if that pulley needs to turn the opposite way)[1].
The problem with many of
these belts is they usually ride in
a groove cut in the circumfrence of the pulleys. It seems
like the depth of that groove is typically half the "diagonal"
thickness of the belt (assuming a square cross section) In any case, for the sort of belt we're talking
about here, there should
be enough 'stretch' to get it to fit.
I've only seen problems with "rubber feet" -- especially on
Sun gear -- disintegrating. And, they end up messier than
a wad of chewing gum that has been sitting in the summer
Sun for a day... :-(
Unfortunately, they are always oddball shapes/sizes so replacement
is a chore.
And, *never* set a bit of kit on a piece of *furniture* -- lest
you later discover a disintegrated foot and find yourself trying
to HIDE that fact from The Powers That Be! ;-)
So, one more bit of math involved. It's
often easiest to bring
an old belt -- even if broken -- since the packages are
I've had blets turn to a sticky rubber blob (like the rollers in the
other thread), then you can't match it up.