?: What's your preferred thickness for plywood for subroadbed-clearance issues

[DigitalGriffin]

So I was doing a little math:

20'2" is the minimum clearance for a double stack (per CSX)

20'2"/87 = 2.78"

2.78 + .083 code rail = 2.86"

2.86 + .10 = 2.96" (tie thickness)

2.96 + .1875  = 3.152 (roadbed thickness)

3.152 + 3/8" plywood = 3.52....and you are over your limit of 3.5"

1/4" ply is too flimsy for most uses (unless you are doing a helix with lots of supports.)

 

 

[selector]

Is their any reason you couldn't mount  your cleared item, tunnel portal, or whatever, a bit higher than whichever roadbed you elect to use?  I have pared the bottoms of cast portals because I thought they looked too high, particularly for my Naigara which was originally designed to be safe with the NYC's lower clearances.  If I had to, I think I'd put a stone base, carved plaster or hydrocal, under their feet to get another foot or so of scale clearance.

I think you can get flimsy with roadbed, but if you support it with several pillars closely spaced, even masonite should serve well.  The key is what is below it and how frequent.

Also, if you have radiused crowns on the portals, will your stacks clear at their outer edges?  Quite a few older tunnels have had 'shoulders' carved into them so that double-stacks would not be in danger of snagging on tunnel ceilings. 

If we are talking about a roadway overpass or a girder bridge, can that be shaved or sanded to get you a bit more clearance, maybe carved?  I'm fishing because I don't really know what you're dealing with as a potential obstacle in the way of height.

Would it be at all possible to have the line dipping just a fraction before the juncture so that you can make up some needed clearance that way?  If all you need is maybe 1/4", that would be a potential solution.  If you practically need a fair bit more because of the shoulders of the stacks, then it could be the only solution.

Crandell

[gandydancer19]

one-half inch.

[Mark R.]

My layout is a mixture of solid top and open grid - everything is cut from 3/4" plywood.

I've seen too many layouts in my time where the owner skimped on the materials during construction only to have sagging issues down the road. I also have a number of deep scenes on my layout which may at times require leaning on the benchwork to reach something .... no concerns of anything flexing or moving here !

Mark.

[DigitalGriffin]

Hey Crandell

I think my point in making this post is that the old addage of 3.5" track head to track head will allow you to squeeze any size car through (double stack being the tallest known).  

3.5" may not be enough if you have moderately thick piece plywood for a subroadbed.

You could drop the cork roadbed and get what you need for clearance. 

But for mainlines going into a tunnel on a city scene, this might be subopitmal as you have to cut it down before you enter, and then build it up again as you exit the portal.

The difference in grade is minimal for 1/8" more.  I think of it more of a cavaet emptor on clearance when designing your layout and that statement "3.5" between railheads" needs a little star by it.

 

 

 

 

[cuyama]

I'd say your rule-of-thumb is what is off. Where did you see 3.5" recommended for HO for railhead-to-railhead spacing? Most folks I know use 4", but that's only a general guideline and changes a lot depending on the circumstances (such as angle of crossing, access to the lower track, distance the lower track is hidden, etc., etc.)

Where tracks cross at an angle closer to 90 degrees, the crossing itself is short and the roadbed can be thinner just where it crosses the lower track

Byron

[doctorwayne]

If you're speaking of overhead clearances for a helix, and can afford to close either the inside or outside face of it, you should be able to get away with 1/8" Masonite for your track support.  Use construction cement to attach the edge of the Masonite track support  to a continuous Masonite panel, similar to a fascia.  Oh yeah, skip the roadbed, too.  You may want to add some vertical support strips on the open-side edge of the track-supporting Masonite, too, again using construction adhesive. 

The helix would look sorta like this, although without the risers and with more levels of track:

 

Total height of the track and its support would be only .288", plus whatever the thickness of the caulk holding the track in place.

My minimum mainline clearance is just under 20', low enough to prevent me from operating gondolas loaded with vertically-positioned auto frames (I'm modelling the late '30s, so no double stacks).  Since these loads were acquired after the layout was constructed, I simply don't run them through the restricted areas - adds operating interest when not everything can go anywhere. 

Similarly, access to a turning wye is limited by an 18' clearance under another track:  excess height rolling stock that requires turning needs to be sent elsewhere. 

 

In your case, though, I suspect that the helix is an integral part of the mainline and can't be by-passed or ignored.

 

Wayne

 

 

[tomikawaTT]

Where clearance is an issue I have elected to get creative with steel stud material.  Total thickness, from the top of the code 100 Atlas flex rail to the underside of the dimple-pattern stud is on the order of a quarter of an inch.

The flex is caulked to the steel with latex caulk.  On curves (and the one helix I've built so far) I stitch the ties to the stud with bare #22 wire run through holes drilled in the ties and the steel - just in case.

In other places, the usual roadbed is cookie-cut 3/8 inch ply, 10mm of fan-fold underlayment and a layer of card stock track template.  Risers average 16 inches apart, and the plywood has been stiffened where necessary with steel angle iron.

Chuck (Modeling Central Japan in September, 1964)

[cv_acr]

DigitalGriffin

So I was doing a little math:

20'2" is the minimum clearance for a double stack (per CSX)

20'2"/87 = 2.78"

2.78 + .083 code rail = 2.86"

2.86 + .10 = 2.96" (tie thickness)

2.96 + .1875  = 3.152 (roadbed thickness)

3.152 + 3/8" plywood = 3.52....and you are over your limit of 3.5"

What "limit"? I don't really understand you there. Clearances are dealt in _minimums_, and clearance is railhead-bottom of obstruction.

You could have a 3 foot railhead to railhead distance, but that doesn't help if the thickness of the roadbed, bridge beam or whatever is 2'11". If it's only 3/8" thick, then it can hardly even be considered as having any relation to the lower track.

Recommended minimum is 3", railhead to _bottom_ of obstruction (bridge, helix roadbed, etc.) If it's a hidden staging yard or connecting track, then more is always better for access, but if it's a helix then minimizing the vertical distance between levels will lessen the grade, at the cost of less room for fingers for fixing problems.