On Oct 1, 8:22 pm, "dennis@home"
wrote:
"Matty F" wrote in message

...



On Oct 1, 7:21 pm, (Andrew Gabriel) wrote:
In article
,
Matty F writes:

I've been making devices to keep tram rail points to one side or the
other by means of a spring.
Here's the finished points changer:
http://i38.tinypic.com/8yf4ld.jpg

Looks impressive.

Just wondering if you considered an over-centre toggle mechanism?
I think that would have a similar force profile, but no centre dead
spot.

That sounds interesting. I've had a bit of a Google for one but I
can't find a decent picture.

This is another type of points mechanism. But it has almost no force
around the centre point, and definitely doesn't work as well as the
ones that I have made:
http://i36.tinypic.com/skxmpt.jpg

Thats an over centre toggle AFAICS.
It should be almost impossible to get it to stop in the centre if the joints
are free.

But there is a lot of friction when the rail is moved sideways. The
rail rests on a flat steel surface that gets rusty, and there are lots
of leaves and dirt and other crud all around, even though they are
cleaned out and greased every week.
So I can make that rail stop at at almost any point.