Turn radius and side clearances for biggest trains?

@Will Wilkin posted:

If a cardboard rectangle shows the car footprint and overhangs wherever I lay it on the track (actually, on 5.5" wide track shelves, center line equals center rail), then:

1) What should be my biggest rectangle (top view)?

2) How long a wheelbase (defined here as length between front and back pivot points along center rail)?

3) How much swing-out in front of that wheelbase, when making my tightest turns?

The pic below shows that a 26" wheelbase of a 3"W car has a significant overhang beyond the walls of my O-60 curve.  Would my real brass steam engine (or diesel, whichever is bigger) really have such a long wheelbase?

Also, would 6" clearance above rails be high enough for (almost) everything?  It's okay to exclude double-stacked containers on flat cars, I'm not gonna run those.  Besides those, what would be the highest thing I need that tunnel to fit?  Not to seem stingy in height but there will be CD shelves built up the wall above the track and starting the first shelf an inch higher might cost me a full row of CDs no longer fitting on the top shelf.

Some O scale brass has a minimum  has a minimum of 48"r or O 96  But not Lionels.  My pass. cars are 20" or 80 scale feet.  and work fine , on O72 but overhang like your sample , it works but is toyish a lager Radius is always better

John Armstrong's Track Planning for Realistic Operation book give you a chart for calculating all your clearances and other vital stats you might not have thought of. IMHO, every layout builder should create the chart for their layout and follow it as they build. Otherwise, you may live to regret some of your decisions about curves and track spacing.

Good luck!

Don Merz

Thanks Dave, the side clearances are very important because this track will run high in a cathedral space over my ground-floor kitchen table, and therefore will have (transparent Lexan?) guardrails, hopefully the 5.5" corridor width will be wide enough?  Also there will be 2 tunnels through a wall.

So hard width and height tolerances need to get built in now, by me an inexperienced returnee to RR modeling who has already cut holes in the wall for this track and doesn't even have a train yet to jam into all these spaces for a dry fit....

Will,

Your geometric template you built is a good approach, but you need to know where the pivot point of the trucks are, not necessarily the overall length of the car. As the distance between the trucks decreases, the overhang on the outside of the radius increases.  It looks like you've aligned the center of the extreme ends of the car with the centerline of the radius.  Thus will give you a conservative estimate to the inside of the curve, but an inadequate clearance to the outside.

And for engines, the scale duplex steamers have a more complicated geometry that depends on more than the length and width of the engine, since so much of the detail parts are not on the fixed boiler.

Best to have someone who runs a scale Big-boy give you maximum overhang from centerline to both sides of various curve diameters to be safe.  I think @gunrunnerjohn has talked about this in one of his posts a while back.

Good luck!

I think this is the thread Jeff refers to, several pictures show the pivot point versus overhang point he notes.  This is about a LC + 2.0, I can imagine a scale unit!

Thanks Jeff and Hokie, I followed the link to that other discussion of turns and side clearances, and after reading it I am going to adopt the priciples as here written by gunrunner John:

https://ogrforum.com/...6#156701992339487326

Personally, I'd recommend a minimum of O72, at least on any mainlines.  If you do O72, 3.5" clearance from the track centerline, and at least 5.5" separation of concentric curves, you'll eliminate most of the contention issues.  This will also allow you run virtually any O-scale locomotive or car, scale or semi-scale.  The only remaining parameter is the clearance height, so far 5.5" above the railhead seems to be sufficient for all the cars and locomotives I've tried.

This might mean abandoning the 1 x 6 (5.5" actual) shelves and moving up to 1 x 8 boards (0.75" x 7.25" actual)!  That would be 1/8" wider on each side than the 3.5" John recommends.  I could keep the straightaways at 5.5 but then would need a neat transition to the 7" wide curve boards.

But will O-72 even fit the tight tunnel space I have?  Time to cut that plywood curve and make the dry fit!

Assuming O72 curves, the widest swing I have is the MTH scale Big Boy at about 3.25" from the track centerline.  I think backing up the cab may swing out that far as well.  My Vision Line Big Boy has 3.0" from the centerline clearance.  I have no idea why the MTH scale model has a wider swing, I would have thought they'd be pretty much the same.

Now that I've actually cut it out and shoved it through the wall...I see these O-90 curves are BIG!!!

Maybe too big for the tunnel.  What else have I got?  My O-60 curve shelf was already cut at 5.5" wide, but today's conversation made me re-draw the O-90 and O-72 so each is 7.25" wide.  That moves the center-line of the board 7/8" in so my O-90 is now an O-88 (at center rail, anyway).  And it moves my O-72 board center out by 7/8" so my O-72 is now about an O-73+.  I'll be able to cut 2 of each of those curves per sheet, giving me the 2 circles I need.  Here below is a pic of that O-72 in dry fit, the unpainted curve ballasted by the saw (so the board doesn't fall into the kitchen).

But now it seems the kick guard "retaining wall" on the bedroom floor will be set at 16.5" out from the wall.  Inches further than I was hoping!  Of course, nowadays I stand plenty further back than that from shelves to read my titles, but my eyes worked different a few years ago.  I'm just gonna have to go on the assumption that wider turns will increase the house value more than tighter turns...  Everything argues against the practicality of O-60 curves despite the tight space.

I love these philosophical moments where choices reflect deepest values.

@Don Merz 070317 posted:

John Armstrong's Track Planning for Realistic Operation book give you a chart for calculating all your clearances and other vital stats you might not have thought of. IMHO, every layout builder should create the chart for their layout and follow it as they build. Otherwise, you may live to regret some of your decisions about curves and track spacing.

Good luck!

Don Merz

Don, I ordered the Track Planning for Realistic Operation book on your recommendation.  Based on reviews, it looks essential and fascinating.

I will just say one thing.  You'll never regret making the curves wider, but you may well regret not making them wide enough!  Another bonus of the wider curves, the overhang of big articulated locomotives isn't as great the wider the curves are.