Minimum clearance for 00 running on the straight

[spikey]

I need to build a removable, non-scenic "bridge" linking two baseboards which are one metre apart, and for this I'll be using extruded aluminium channel.  Problem is, this needs to be as narrow as possible.

 

I'm told that for 00, the accepted minimum distance between obstructions is 50mm, that being 25mm either side of the track centreline - but could I get away with less? 

 

I can't arrive at the answer myself for the simple reason that I don't yet have an outside-cylindered loco to measure, so the question is - what's a realistic minimum safe distance between straight bridge sides for something like a Bachmann 2MT or a Crab?

 

 

[LNER4479]

The prototype minimum distance is 11ft 2ins which works out as a tad under 45mm in 4mm scale. This is perfectly OK for straight track with modern RTR (but do remember to open it out on curves!)

[spikey]

Cheers mister.  That's all well and good if a Bachmann 2MT or a Crab is actually scale across the cylinders, but unfortunately to me right now that's a big unknown.

 

Reason this matters to me is that (shock! horror!) I might have to buy the extrusion, and if 45mm between walls is in fact safe, that's significantly cheaper than the next one up over 50mm

[28XX]

Very little uk rolling stock is more than 9 feet 3 inches wide, which is 37mm in 1:76. Its unlikely that any recent models cheat by as much as 4mm per side.

[LNER4479]

Certainly, I've run a Bachmann Crab round a layout with 45mm track spacings with no ill effect. That was my reference to 'modern RTR' - these days they're typically CAD designed based on laser scans of surviving prototypes and therefore scale out pretty much 'spot on'. My logic was that if 11' 2" was good enough for the full size things then 45mm should be good enough for accurate models. The traditional 50mm spacing allows for cruder models which were more of an approximation to the real thing.

 

Reading your post above again and thinking about that 45mm channel, it'll be tight as you might have as little as 2mm breathing space either side for a 'tight to gauge' item of rolling stock... I can measure a Crab across the cylinders (no sniggering at the back!) when I get home this evening if you like?

Edited June 14, 2017 by LNER4479

[34theletterbetweenB&D]

...That's all well and good if a Bachmann 2MT or a Crab is actually scale across the cylinders, but unfortunately to me right now that's a big unknown.

The post from 28XX is correct, but it's not just the static dimension, it's the dynamic envelope you need to consider. Any yawing action while the loco is running increases the effective width, however relatively small engines like a Crab won't go the 4mm extra, A pacific though...

 

I would cover the walls of the extrusion with a slippy tape, self adhesive PTFE or similar if you can get it, just in case

[spikey]

Good points there, chaps.  Thank you.  So are we agreed then that 45mm should be OK if the loco isn't waddling like clapped-out J94s used to when running light, particluarly if I can find something slippy to line the sides?

 

... I can measure a Crab across the cylinders (no sniggering at the back!) when I get home this evening if you like?

 

May I please take you up on that if it's not too much trouble?

[Dunsignalling]

If you want to check clearance, use a Bachmann 08.

 

Of all my locos, they are the only ones I've had clout anything.

 

John

[spikey]

If you want to check clearance, use a Bachmann 08.

 

Hmmm.  All well and good if you have a Bachmann 08

Edited June 14, 2017 by spikey

[mightbe]

You'll have zero issues with 45 mm centers. If you want to eliminate hunting, tighten the gauge to 16.2 mm. (Seriously)

 

Quentin

Edited June 15, 2017 by mightbe

[Memphis32]

Don't forget it's internal dimensions you want to be 45mm - not outside. With ali extrusion you may have 1mm+ wall thickness

[LNER4479]

May I please take you up on that if it's not too much trouble?

 

There you go ...

 

 

Seemed like the easiest way of doing it

[Colin_McLeod]

 

Reason this matters to me is that (shock! horror!) I might have to buy the extrusion, and if 45mm between walls is in fact safe, that's significantly cheaper than the next one up over 50mm

http://m.ebay.co.uk/itm/302324868418?varId=601160934970

 

Price for a 2m length of 45mm is £19.50

 

Price for a 2m length of 50mm is £33.00

 

Difference is only £13.50 so why not play safe and get the 50mm?

[Dungrange]

http://m.ebay.co.uk/itm/302324868418?varId=601160934970

 

Price for a 2m length of 45mm is £19.50

 

Price for a 2m length of 50mm is £33.00

 

Difference is only £13.50 so why not play safe and get the 50mm?

 

That's nearly 70% more expensive!!  However, looking at these, the 45 or 50 mm is the outside dimension.  The 45 mm channel has a 2.5 mm wall thickness, which means that the internal dimension is only 40 mm.  The 50 mm channel has a 4 mm wall thickness, which means that the internal dimension is still only 42 mm.  That's probably okay, but I wouldn't want to go less.  The more expensive channel is therefore the one to go for.

 

The minimum 11'2" track centre dimension (~45 mm) LNER4479 quoted in post #2 includes something like 18" (6 mm) clearance between vehicles travelling in opposite directions and I think that distance is measured between the kinematic envelopes.  The stock itself will probably be around 37 mm wide as 28XX has stated in post #4.  Scaling down the prototypes kinematic envelope will add around 1 mm either side of the stock when stationary, which increases the minimum width of your channel to 39 mm (ie the stock will effectively be around 2 mm wider when moving).  There is then the need for a prototype clearance, which I think can be as little as a couple of inches, but that's still another 1 mm each side, which increases the minimum distance to between the walls of the channel to approximately 41 mm.   

 

However, I will echo mightbe's suggestion in post #10 to narrow the track gauge to 16.2 mm (ie 00-SF of 4-SF standard).  The reason for this is that there is quite a lot of 'slop' with 16.5 mm track gauge and standard 14.5 mm back-to-back and this is the reason why some stock has a tendency to wobble.  Narrowing the gauge by 0.3 mm (which you won't notice) helps to reduce the amount by which any rolling stock can move from side to side, thus helping to keep it within the scaled down kinetic envelope of the prototype.

 

The important point is that you understand whether whatever supplier you are looking at is quoting internal of external dimensions.

[spikey]

LLNER4479 thank you very much indeed. 

 

Next time I see Betty Windsor, we'll see what we can do about a knighthood.

[ejstubbs]

 

http://m.ebay.co.uk/itm/302324868418?varId=601160934970

 

Price for a 2m length of 45mm is £19.50

 

Price for a 2m length of 50mm is £33.00

 

Difference is only £13.50 so why not play safe and get the 50mm?

 

That's nearly 70% more expensive!

 

The cross-sectional area of the 45mm channel is 225 sq mm.  For the 50mm channel, being thicker and with higher sides, it's 408 sq mm.  So you actually get 80% more aluminium in the 50mm, which means that only 70% higher cost is actually a bargain!!!  (Well, maybe not really, but it helps to explain the difference.)

[melmerby]

Can't you use two pieces of right-angle fixed to thick plywood?

The RA will brace the ply so it stays reasonably flat over the distance

That way you can make the clearance what you want and the ply will make a good track base to work with.

 

Keith

Edited June 15, 2017 by melmerby

[spikey]

Can't you use two pieces of right-angle fixed to thick plywood?

The RA will brace the ply so it stays reasonably flat over the distance

That way you can make the clearance what you want and the ply will make a good track base to work with.

 

Keith

 

Yes I could, Keith, but I'd still have to order the extrusion and pay carriage on it, I don't have a suitable bit of ply to hand (and even if I did, I only have a handsaw to cut it with which isn't much fun on account of the arthritis), and I don't need a good track base to work with.  Hence my wish to use ally channel

[ejstubbs]

You can buy aluminium angle from the DIY sheds.  Just be sure to steer clear of the anodised or laquered kinds if you want to use them as running rails (which would save the cost of track, but may require you to use thicker and thus more expensive ally angle).

 

For example, Wickes currently do 18 x 18 x 2440 ally angle for £8.49.  Two of those, plus a length of say 9mm ply to form the base (which Wickes should be able to cut for you when you buy a sheet) works out cheaper than the 50mm channel for one track.  The second track wouldn't need any more ply - you could just get Wickes to make two cuts off the sheet of 9mm - so would work out cheaper than the 45mm channel.

 

And you'd have complete flexibility over the actual width of the base for each track, rather than having to run with minimal clearance simply because a bigger extrusion costs more.

[spikey]

Thank you for pointing out the alternative approaches, gentlemen.  I am now sorted.

 

Well, at least as far as this aspect of the current build is concerned ...

Edited June 15, 2017 by spikey

[DCB]

Thank you for pointing out the alternative approaches, gentlemen.  I am now sorted.

 

Well, at least as far as this aspect of the current build is concerned ...

Don't keep us in suspense, what size did you use?   I used some galvanised channel for a 00 branch line across a door which can't have been much over 40mm inside and once I changed the flexitrack for 26" set track straights it was fine, but I couldn't keep the flexi from snaking and causing trains to rub the sides.

[spikey]

Haven't sourced the extrusion yet, but as regards fixing the track to it, double-sided sticky tape is the biz.

[The Johnster]

To go back to the point about static and dynamic widths. I would suggest having a screen wall of anything thin, smooth, and rigid enough, halfway between the track in the '6 foot, like a motorway central reservation crash barrier.  That way, even if any of your stock does foul it, it'll simply slide harmlessly along it without coming into contact with anything coming the other way on the opposite track.  This will still work even if two trains which are both capable of fouling each other, the worst case scenario, pass each other on this section.

 

Did somebody say something about knighthoods?