Message Number: 14
From: "VR Bass" <[EMAIL PROTECTED]>
Subject: Re: Wheels
>Harry, you mention a lot of hand work. If I understand it correctly, the
EDM
>method creates spokes without a draft angle
Vance,
Yes, in most cases, but one could certainly use a tapered electrode . .
. The advantage to using EDM would primarily be to get the spoke geometry,
profile, and spacing dead-on and produce corners that only hawk's sight and
a dental drill could do otherwise. The hand work would come in when you
begin to work the rim, spokes, and hub to final shape and couldn't be
avoided. Even if one used a tapered electrode that would result only in
draft. Profiling and rounding off would continue as usual, at least to the
extent it was required.
>This is not necessarily a bad thing in all cases --
True, some locomotive wheels (although mostly UK) did have rectangular
spoke profiles.
>They'll be fine for outside-frame locomotives, where you don't really see
>the wheel except in silhouette.
Yes, but then there goes the Mark Wood approach to wheels out the window
doesn't it. This partly explains why we don't have such products here.
(That and a lesser per capita ratio of compulsive behavior amongst the male
population :-)
>when you work with a caster, be sure to talk about the necessity for
>concentricity,
I understand for some (many?) there is a benefit from wheels that need a
minimum, if not no, machining, but in the model engineering and real worlds
this would be the exception rather than the rule. When either making a
pattern or buying a casting I always assume I'll machine its critical
surfaces.
>I think the lack of a raw material source was what was holding up the
>foundry I work with. Knowing that there are sources of gray iron bar
>means that we could get iron castings without worrying about what's in
that >Ford engine block.
Once upon a time, and maybe still, you couldn't do better than an old
engine block as you could be sure these were done in new iron. Then the
usual source for aluminum for a lot of home foundries has always been
busted up pistons. Admittedly most foundries doing structural or
appearance grade casting in any metal always prefer to use fresh metals for
quality control. (By the way there are companies that do nothing but
supply pure metal in ingots for foundries.) The ones that make "trash"
castings, dead weights, drain grates, manhole covers, and such don't much
care, but in any case it's the foundryman who needs to know what he's
doing. Even new metal needs admixtures, flux, degassifiers and the like,
and careful control of pouring temperature. As you've seen from recent
posts the moulding processes (molds, forms, risers, sprues, etc) are
critical, especially where the sections are small, and ours are tiny. In
the grand scheme of things the metal source seems almost secondary.
Cheers,
Harry
