Why I seek to know minimums that might be possible.
Gentleman, please realize that I am trying to build a LOT of railroad into a relatively confined space. This process has me looking for minimums (spaces, curvatures, clearances, etc) that might be utilized.
Sure I would like to just go off and make everything a little bigger so as to not be so concerned about clearances, but I don't necessarily have that luxury,....and often I find that making one thing just a bit bigger, results in having to make an adjoining thing bigger,...and then next the another adjoining thing that much bigger,....and things snowball to the point that it no longer fits in your allowed space.
I do get confused by many of these NMRA specs, and the numerous (and conflicting) postings by many of the forums members.
So I am going to prepare a 'pictorial presentation' of my current clearance issue/question. What do they say,... “a picture is worth a thousand words”. Hopefully this will more fully define why I felt I needed to revisit this subject.
Just recently I was building a new metal 'bridging deck' that would join my external helix track to my subterranean staging tracks inside the main room of the layout. This bridge supports a 3-way turnout that feeds 3 curved sections of track to the 3 staging areas. I had already cut the rectangular hole thru the back wall of the shed. I was replacing my original flat plywood bridge with an alum channel one that would also have 'side fences' on it to protect from derailments falling over the sides of this 'bridge'...
Per my original plans there are to two 24” radii tracks leading off to either side of that 3-way turnout. I had trimmed off a portion of those 2 fences on either side of the alum channel to allow for sideway clearance for cars traveling on those 2 side routes.
BUT as I looked at these clearances (AND those of the cutout in the wall), I began to question if I had provided enough clearance for those very long auto-racks in addition to the long passenger cars?? That's when I decided to come back to this subject and look again at my previous results, and those references supplied by other participants.
I began to look back thru all of discussions, and charts, and other links,...and get more confused by the multiple answers.
I decided to get out the track, and the cars, and the bridge structure and do a full scale mock-up. So here is my bridge with the side fences trimmed in there first configuration
Here are two of the large, long cars I would hope to be able to put down in my staging areas
The question is can they clear the openings I've provided? No questions about height as I've already provided 4"
My first trail was with the AUTO-MAX pair. I figured that this car had its wheel pivot centers at the very ends of the car which would result it it have the greatest overhang to the inside of the curve.
The 24' radius track bending off the 3 way (only tested right hand branch). That little bracket sitting out there will come in handy.
You can see that there is plenty of clearance between the side fences of the deck/bridge and the cars. I forgot to mention that I had already gone ahead and cut an extra 1 inch off of the fences in anticipation of a clearance problem here. It now appears that may not have been necessary, but no matter as I did not require that portion of the fencing.
Moving along down the curve we can now see the that little bracket right up next to the inner side of the Auto-Max. Looks to be 1 1/8” at the very minimum to the centerline of the track. So if I gave it 1.5” that should be plenty!
Brian
My Layout Plan
Interesting new Plan Consideration
Articulated Auto Racks
Next up that nice pair of Atlas auto racks.
Again the very bear minimum clearance
Looks like 1”,...or perhaps 1/16 additional.
Again 1.5” provides plenty of clearance.
Long Modern Passengers Cars
Lets see if my old test proved to be true,...only about 1" overhang to inboard side on 24" radius curve.
Appears to be true. So my provision of 1.5" should be plenty?
Hi Brian,
I know the NMRA Standards and Recommended Practices can be a little daunting so let me try to boil down their recommendations for your particular situation.
RP (Recommended Practise) 7.3 'Curved Track Obstacle Clearances' states that 'modern' (post 1983) equipment should have a minimum clearance of 1 11/16" at a radius of 22 29/32". (The odd radius is a result of converting from a prototypical 35 degree curve or 166' radius).
You have a 24" radius so you can go slightly smaller with the clearance, but the RP suggests that 1 1/2" may not be enough in all cases. It doesn't state what the tolerance is, and your tests suggest that 1 1/2" looks to be plenty of clearance, but if I were you I would increase the clearance to 1 11/16", if that is possible, just to be safe. If you look at the recommendation for a 26 5/8" radius it is 1 5/8", still larger than what you are proposing.
When you compare the amount of work required to do that now vs the amount of work that it will take when everything is together, I'd do it now. I'd rather not see the number of emoticons that you will have to use when you are telling us that something got snagged!
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Just test with your longest and tallest cars and add a margin for just-in-case, and the build. Don't get too bogged down with the minutea of litereature and reseach.
As the Nike ad used to say, "just do it".
Rio Grande. The Action Road - Focus 1977-1983
Perhaps on an ideal layout any type of car can navigate any curve. In reality, many cannot enjoy that level of freedom. If the long cars don't navigate well around the curve, why bother? There's also a large difference between cars navigating around a curve and doing that without altering speed, offering silent prayers, etc.
During my little mock-up here I discovered 2 interesting sidebars: 1) Those long Walthers passenger cars do NOT want to negotiate anything less than 24" radius. Their trucks interfere with the hanging steps. 2) One of my Peco 3-way turnouts that appears totally unmodified from stock condition is TOO TIGHT in its rail gauge in the middle portions of the turnout. It notably slows the cars down that try running thru it, and it even promotes a derailment at times.
I'm going to have to double check all my other Pecos, as this is NOT a detectable flaw visually,...only a barely small difference in track gauge.
Simply test all clearances with your longest car, then add 1/4 inch. Is there more to it than that?
- Douglas
DoughlessSimply test all clearances with your longest car, then add 1/4 inch. Is there more to it than that?
That is one way to do it for sure, but it doesn't take into account future acquisitions. As I suggested, why not give yourself the maximum clearances now when things are under construction. If other elements of the layout construction prevent building to the maximum clearances, then Brian will have to live with whatever clearance he can build.
I think the important point is that he is testing as he goes.
railandsailThose long Walthers passenger cars do NOT want to negotiate anything less than 24" radius.
Just to give you an idea of how far you are pushing the envelope here, the work done by the LDSIG published in MRH identified 2.5 X car length as the point where "most equipment will track reliably if everything is of similar length". For 85' cars, that would be a 29.3" radius. The 24" radius fits in the "some equipment may track reliably, but 2x is generally considered pushing it" category.
I have the right to remain silent. By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.
carl425Just to give you an idea of how far you are pushing the envelope here, the work done by the LDSIG published in MRH identified 2.5 X car length as the point where "most equipment will track reliably if everything is of similar length". For 85' cars, that would be a 29.3" radius. The 24" radius fits in the "some equipment may track reliably, but 2x is generally considered pushing it" category.
Carl,
You make a good point. Perhaps the clearances on the curves are the least of Brian's problems. Maximizing the clearances so that future equipment can clear the obstructions is a waste of time if the rolling stock won't go around the curves reliably to begin with.
Maybe Brian needs to change his era. Just sayin.
I don't really have a set era, just sort a mix of steam and diesel transistion, but also including modern cars. Those 3 examples, the auto racks and the long passenger cars, are VERY likely the largest/longest cars I will ever wish to run. And I can do without the auto-racks if necessary.
I definitely want double stack container cars to fit, and I think if that AUTO-MAX car fits then the double stacks will??
I do realize that the 24" radius is pushing things, but because of my 'condensed layout plan' I had to put a number of such curves in there for yard and staging areas. I thought most of these modern cars would negotiate those radii physically, even while not looking so good. And I may have to trim/shave-down a few under carraige items to make them work (I'm not a rivet counter....ha...ha).
hon30critter Doughless Simply test all clearances with your longest car, then add 1/4 inch. Is there more to it than that? That is one way to do it for sure, but it doesn't take into account future acquisitions. As I suggested, why not give yourself the maximum clearances now when things are under construction. If other elements of the layout construction prevent building to the maximum clearances, then Brian will have to live with whatever clearance he can build. I think the important point is that he is testing as he goes. Dave
Doughless Simply test all clearances with your longest car, then add 1/4 inch. Is there more to it than that?
I think Brian is running 85' passenger cars and 89' autoracks. It doesn't get much longer than that.
Tape a pencil to the middle of the side of a car and run it over the smallest radius curve he will run it on (I think he said 24 inches), so that the pencil makes a line on the surface.
The pencil should make a slight parabolic shaped line along the inside of the curve. Measure along the curve, then add 1/4 inch (or even 1/8th of an inch since the pencil tip will already be proud of the car.)
He only needs to do this once for 24 inch radius curves, and once again for whatever long car he will run on tighter radii.
Also, on the outside corner of the car because of overhang in that direction.
railandsail I don't really have a set era, just sort a mix of steam and diesel transistion, but also including modern cars. Those 3 examples, the auto racks and the long passenger cars, are VERY likely the largest/longest cars I will ever wish to run. And I can do without the auto-racks if necessary. I definitely want double stack container cars to fit, and I think if that AUTO-MAX car fits then the double stacks will?? I do realize that the 24" radius is pushing things, but because of my 'condensed layout plan' I had to put a number of such curves in there for yard and staging areas. I thought most of these modern cars would negotiate those radii physically, even while not looking so good. And I may have to trim/shave-down a few under carraige items to make them work (I'm not a rivet counter....ha...ha).
As far as the inside clearance figure goes I figured its the postion of the truck centers that matter most. the farther apart they are the more the car will overhang on the inside dimension.
Negotiating the curves is a different matter. The couplers, their lengths, and the overhangs of the ends of the cars all effect the need for clearances on the outside of these cars.
BTW, how about this old Ambroid craftsman kit of a Hogshead Tobacco car. I have one of these in a partially completed condition,...I picked up long ago at the Timoium train show in those early days when the unusual and long car fancy was forefront in my mind.
http://southern.railfan.net/ties/1962/62-6/hog.html
HogsHead Tobacco Car
Advertised in November 1965, this is a model of 92' car built for the Southern Railway. It is said to be one of the world's longest cars. With 10,000 cubic feet of space, the car's interior is 84 feet long, 9 1/2 feet wide and nearly 12 feet high and it has carried 100 hogsheads of tobacco (that's 105,000 pounds of tobacco, or about 80 acres of tobacco). See the Southern Railfan's web site for information (where you also can find some amazing prototype photos of this car.
The complete kit with hardware, decals, coupler pockets, but without trucks, sold for $5.25
So, what is a Hogshead? Besides being something with which the Scandinavians used to decorate the Christmas food table, it is also a measurement of volume; a barrel, sort of. But since I don't know the exact volume (in gallons), I leave it like this for now.
This car was later sold by Northeastern as kit B-8.