gears

[low_delta]

Swing bridge.

Comments

[cynnerth.livejournal.com]

I really like this one.

[pondhopper.livejournal.com]

I'd hang that one on our wall!

[lonewolf2.livejournal.com]

The Engineer in me is curious to know what function these gears serve.

It looks to me that the untoothed sector below the larger gear is a rocker to accommodate thermal expansion/contraction of the moving element of the bridge deck.

[low-delta.livejournal.com]

I'm curious too, to be honest. I didn't look that closely. And I don't usually get to see that side of a swing bridge.

That seems to me to be the shoe that the end of the bridge rests on, to keep it at the proper height, but there doesn't seem to be any marks on it to show that it has been moving... regularly, for a century.

And then there's that lever arm or whatever, sticking out towards the top. It doesn't look like the gear can turn very far. Maybe it simply lifts the shoe upwards, so the bridge can swing?

Maybe I'll have to hang out down there next summer, when the boats are moving through. It stays closed for frequent train traffic, and opens for tour boats (http://www.flickr.com/photos/14542870@N03/5014021394/). Oh, there's a coal tug (http://www.flickr.com/photos/14542870@N03/5309884551/) that goes through there all the time.

[lonewolf2.livejournal.com]

I found this photo of a very similar mechanism attached to the other end of another bridge (or possibly the same bridge) taken by David Haase in 2009 by following the tour boats link in your comment.

http://www.flickr.com/photos/overbythere/3640473201/in/pool-1569898@N20/

You can see in this photo that the lever arm is holding a grease injector over the gear teeth to apply lube to prevent wear. From the grease pattern it looks like the large gear only makes about half a turn - which is just enough to raise the rocker a short distance vertically off the bedplate so that the bridge can swing.

The lifting mechanism is probably a vertical hydraulic jack mounted under the centre of the bridge at its point of balance. The turning ring and its drive gear will be installed around the head of the lifting jack to swing the bridge open and closed. It's very likely that there is a second set of bedplates under the open position of the bridge so that the span can be lowered onto them to lock it against the wind.

[low-delta.livejournal.com]

Ah, a grease injector. This other gear is obviously on the other side or other end, but I'd say it's on the other end. I don't think there are locks for the open position, but I could be wrong. Thanks! Now I'm curious, so I'll have to go back down there and take another look.

This bridge (http://www.flickr.com/photos/14542870@N03/5314044210/) stays open, and is closed only when trains go across. The train engineers change it themselves. There are locks to close it, but the ends hang in space when it's open.

By the way, the pics I linked to are mine, and I own the Movable Bridges group. :-) It's been a while since David Haase added that photo, so I don't recall seeing it.

[lonewolf2.livejournal.com]

I think David's photo is of another bridge since the grease marks on the gear look fairly recent. The relative cleanliness of the deck gratings hint that the bridge is still in regular use and maintained. The bridge in your photo shows no signs of grease and has extensive accumalations of muck on all the visible surfaces, indicating that it doesn't get regular maintenance. Hence that it is rarely swung. The buckled rails in the foreground of your photo tell the same story for the track.

This document:

http://lcweb2.loc.gov/pnp/habshaer/il/il0800/il0842/data/il0842data.pdf

describes Chicago, Milwaukee & St. Paul Railway Bridge Z-6 over the North Branch Chicago River, south of Cortland Street in Chicago, IL. Unfortunately there are no attached photos contrary to the statement on the title page.

Page 10 describes the lifting and turning mechanisms, which appear to be very similar to those on the KK Bridge in Milwaukee.

Bridge Z-6 is described as being unique in its conformation since its turning axis is a very long way from the centre of the bridge span.

[low-delta.livejournal.com]

I believe that bridge is commonly swung, since the coal barge goes through constantly. Better than daily, I would assume. There are only two other similar bridges in the city.

Photos:
http://www.loc.gov/pictures/search/?q=Photograph%3A%20il0842&fi=number&op=PHRASE&st=gallery

Very similar, I would guess.

Video of this bridge, opposite end shown.
http://www.youtube.com/watch?v=vwjr23k_6xA
http://www.youtube.com/watch?v=689YQZlhJ4Y&feature=relmfu