bridges

[RobSWR]

Hi my name is Rob, I'm new to the forum. I am building a model 00 gauge railway on an 8' x 4' table top in my loft for my grandson when he comes to visit.

 I would like to incorporate a bridge. My query is what height is required for a loco  to clear going under the bridge, and what incline ratio would I need be for my 30 year old diesel electric loco pulling 3 x coaches? I have seen some reports of a ratio 1:30, I think I could make it 1:50 would this be better for the slope!

[atom3624]

Don't forget, what goes up ....

Don't want things coming down too quickly either!!

The 'more gentle' the better.

You could trial a few slopes yourself to see which best suits you.

 

Al.

[walkingthedog]

For a bridge I have 2 1/2 inches clearance from the top of the rails. Looks and is about right.  The shallower a gradient the better it is but as Atom said if it goes up it has to go down again. So 1:30 means 5ft to rise 2 inches. Curved gradients need to be shallower. 

[Chrissaf]

Another alternative is to create a valley by cutting away a section of the baseboard for the bridge to traverse. That way the track can remain level. The cut-out is then lined with any suitable lightweight material** to create a valley floor and sloping sides under the bridge. The valley floor could be a canal or a road that exits and enters a tunnel entrance thereby keeping the valley fairly short in length. Or of course you could make it longer and go right across the baseboard so that you end up with two bridges (one each side of the layout in different styles ***) for additional scenic interest.

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Note** for example foam or cardboard covered in scenic 'plaster cloth'. The framing under the baseboard at the valley location then needs to be extra deep to allow the cut-out, but at the same time keeping the baseboard rigid and strong.

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Note*** say the far side (distant) being a girder bridge with a curved top (bit like the Tyne bridge) with the nearest side being say a brick pillar bridge with arches.

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8ft x 4ft is going to be fraught with issues implementing a workable up and down gradient. I know from personal experience that it is difficult to attain better than 1:30 in such a tight small space. At the design stage and prior to build start, it is so much easier to 'design-in' my valley idea. This is definitely the way I would have gone with my folded over figure 8 layout design [8ft x 6ft] if I could start over and do it again. As others have said, putting gradients in curved sections significantly increases rolling stock drag forces. I would be surprised if you could achieve 1:50 both up and down in just 8ft x 4ft and still have points and siding in the design. It might just be doable with two basic loops, but that detracts from the playability factor.

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See also – further TIPs on how to get the best user experience from this forum.

https://www.hornby.com/uk-en/forum/tips-on-using-the-forum/

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[walkingthedog]

Bit like this.

/media/tinymce_upload/7d6d5462d64ba0afbe7b601a8961339e.jpg

This is the bridge clearance

 

/media/tinymce_upload/a50c2afd829ece5966bd163d41b5bfe4.jpg

[96RAF]

From my understanding you want one line to cross over another (or the same) line.

One way of doing this akin to what Chris has said about digging into the baseboard but keeping the line level is you take the under line down half the clearance depth and the over line up half the clearance depth, which effectively halves the gradient.

 

Imagine a figure of eight. The lower line at the crossing dives down say 1-1/4” and the upper line climbs 1-1/4” to give 2-1/2” overall clearance at the bridge.

 

You can make good use of this by setting the lower line at the bridge crossing right on the baseboard level and building the rest of the lines up above the board, rising to 1-1/4” then to 2-1/2” over the hump, thus giving ample scope for undulating scenery.