----- Original Message ----- >
Steve wrote:
>I consulted a couple of ancient, dusty, and dog-earred tomes
> >both of them had good diagrams but lacked sufficient explanatory text
>
Then Harry wrote:
> I usually find the best old ones have such complex theories,
> explanations, and diagrams as to be overwhelmingly tedious. I suppose
you
> could say that an "authority" could simply be someone who has been
able to
> endure the tedium until they at last actually understand the subject.
Now, my turn!
If you can, the best way to begin to understand valve gears, is to sit
along side a model that has the gear in question, and gently move the
locomotive along the tracks, and while it slowly revolves, watch to see
what the different links and lever do! I was lucky, in that back when I
was in Middle School, hidden in a dark corner of a supply closet, was an
ancient cut away model of a Stephenson's Link Motion, as applied to
locomotives. There was one drive whell, with a hand crank on the axle.
As you cranked the model over, you could watch the valve move back and
forth on the valve seat, and as you linked up the reverser, you could
physically see how it shortened the stroke. Not everyone will have
access to such a model today, as I believe that schools no longer feel
it important to teach how anything works, and have removed most "shop"
classes from the choices available! But, you can do the same bytaking
the diagrams in any of the books, and cutting out cardboard bits and
pieces, suing a thumb tack at the pivot points to give you a hands on
way to explore valve gears.
I have come to the point where I now no longer believe that if I build
to a published plan, that the locomotive will automatically run! So, I
take the drawings, and make cardboard or masonite mock ups, at several
times the size of the model, and try the drawn dimensions. Then, you can
physically observe the valve events, and you wouldn't believe how many
times this method has pointed out errors in the published design! (I
won't mention the 3/4" scale Friend's Models Atlantic by name here) But,
it is easier to make changes to cardboard and hard board at an enlarged
scale, than to have to redesign the gear and make all new parts in
steel, when you find the locomotive will only run well in one direction!
(this is from the voise of experience here!) So, get a copy of any of
the valve gear books mentioned, and play around with cardboard mock ups,
it's amazing how quickly it comes to you! Looking at intersection dotted
lines on a drawings, is easily the worst way possible to learn how a
valve gear works. Particularly Baker gear, where one lever sits on top
of another, you begin to forget which line is which part!
Oh well, hope this hasn't confused you even more!
Keith
