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Shortest radius?

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Shortest radius?
Posted by hoofe116 on Saturday, February 23, 2008 8:04 PM

Forgot to add this to the other post.

My RR will be PP. It is early-era steam, with strap-iron track. The biggest engine I forsee running on it will be something like a 0-6-x or possibly a small Shay-type. I will use link and pin couplers.

Sooo... what is the tightest radius I can hope to get away with? And while I'm asking, how is the radius measured, from centerline between the rails of a circle of track, or to the outside rail, or the inside one?

Thanx, Les W.

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Posted by on30francisco on Saturday, February 23, 2008 10:10 PM
Although you should use the largest radius you can, I believe a small loco should negotiate a 24 inch radius. Radii are measured from the centerline between the rails. Link and pin couplers are very forgiving when used on tight curves. If the links are too short for your curves you can substitute a longer link (paper clips work good) so it will negotiate the curve. This is what I do with my rolling stock. I have 39 inch radius curves and by substituting the longer links, my 32 ft piece of rolling stock works nicely - and all my couplers are body-mounted. The spacing may not be prototypical but it works. Better to have 'em running on a layout looking a littly funny (who cares?) than gathering dust on a shelf.
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Posted by cabbage on Sunday, February 24, 2008 4:05 AM
There are quite a few mathematical formulae to tell you what should be the minimum radius curve that your loco will traverse. But -unless like me you are a scratch builder/designer -they are very little used, so I will not give you a run through of "The von Borres" equation... (My father made "quite a few" wheels)

The cornering ability of a wheel depends on the angle of the tyre, normally 20 degrees, the angle on the flange, normally 80 degrees and finally on the sideways movement of the tyre. This the "simplified version" calculation!

For Gauge 1, (assuming a G1MRA wheel), the minimum radius for an axle spacing up to 110mm is 585mm.

For any further increase in axles take fixed length of the wheebase in millimetres divide by 110 multiply by 585 note it down then multiply the noted figure by again by 0.35 (tan 20) and add the two together.

example:

0-6-2 engine fixed wheelbase length 210mm

210 divide 110 = 1.90
1.90 multiply 585 = 1,116
1,116 multiply 0.35 = 390
1,116 plus 390 = 1,506mm

All the above assumes that the wheelbase is fixed any sideways movement in the axle decreases the radius required.

Let us say that the central axle of the loco moves +/- 1.5mm -thus axle movement is 3mm...

210 minus 3 =207 (we run through the maths again)
207 divide 110 =1.88
1.88 multiply 585 = 1,100
1,100 multiply 0.35 = 385
1,100 plus 385 = 1,485mm

When you are working out something as complicated as a Price 16 wheeler then you really do need the von Borres equation...



regards

ralph

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Posted by vsmith on Sunday, February 24, 2008 9:29 AM

 on30francisco wrote:
Although you should use the largest radius you can, I believe a small loco should negotiate a 24 inch radius. Radii are measured from the centerline between the rails. Link and pin couplers are very forgiving when used on tight curves. If the links are too short for your curves you can substitute a longer link (paper clips work good) so it will negotiate the curve. This is what I do with my rolling stock. I have 39 inch radius curves and by substituting the longer links, my 32 ft piece of rolling stock works nicely - and all my couplers are body-mounted. The spacing may not be prototypical but it works. Better to have 'em running on a layout looking a littly funny (who cares?) than gathering dust on a shelf.

Agrees withSign - Ditto [#ditto]

I use links also tad longer than usual ones, curves on the main layout ar R1, I did build a portable loop that is 36" Radius. But I only plan to run short HLW 2-axle stock on it.

   Have fun with your trains

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Posted by vsmith on Sunday, February 24, 2008 9:36 AM

Von who.....???Wink [;)]Big Smile [:D]

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Posted by cabbage on Sunday, February 24, 2008 10:09 AM
Sometimes Vic.....

I know that you are the only other modeller here that has also built a 16 wheeler! A.G Price of Thames had some of the best human computers in the business and sets of 6 figure log tables... I had to work all mine out from scratch and I admit to having a little help from my father. Mine can exceed the 90 feet diameter curves of the original -but by design -rather than by accident...

Oh, Herr August von Borres (1852 to 1906) CME of the Prussian State Railways -the guy who worked out most of the formulae used (still) in modern railway design.

regards

ralph

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Posted by hoofe116 on Sunday, February 24, 2008 11:33 AM

Cabbage,

Whoa, there's some numbers to contemplate! Thanks for the tyre and flange angles, I've been wondering about that very thing, because of the toy engines I've picked up. (I have a lathe.)

Now as the other gentleman from Europe wrote, 24" radii sounds good enough to start with. Since I contemplate using semi-flattened copper wire for track in the initial trial stages, some fiddling won't be difficult. I also forgot to mention I might elect to use a pair of blind drivers. Of course the axles will have a bit of sideplay because of the nature of the stuff I'm learning with. That's fixable if it turns out to be a problem. And most of what I contemplate building and running will be two axle freights and short-wheelbased engines. I have to see what works, and so far I'm not there. I just got a 'model shop', 1/3 of the laundry room with a big workbench. I need to run electric and lights and I'm ready to go, finally. (I exist in the 'inverted pyramid world'.)

I'd already concluded longer pins would probably (have to) suffice. Since I've made the decision to use strap rail track, everything's sort of fallen into place. Except for somewhere to build the layout. I found I can't use the garage the way I'd first thought. Nor the upstairs, which was mine, all 36x14' of it, because my wife has sort of homesteaded much of it. She's going to decamp, but it'll take a year to do some more remodelling on the house, just small things--furnace/ac plus ducting--that's already cost me a full year. (I work slow and I'm financially challenged).

Now, I went to the microlayout site Vic recommended and it was as a light bulb going off in my head: yes, I can build sort-of working dioramas and fit 'em all together eventually.

Which reminded me that you waxed eloquent about the joys of 16mm narrow gauge, but I'm not so smart as to be able to find that post. Pretty recent, too. What do you use for the power bricks? (The gears 'n wheelsets that actually makes stuff move). Surely, one doesn't cut down existing 45mm gauge? I can see a lot of problems going that way. So what do you use? And what scale does the rolling stock work out to be?

Thanks,

Les W.

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Posted by cabbage on Sunday, February 24, 2008 2:34 PM
Hoofe,

I model in 16mm scale and (now) 13.5mm scale. The first is by far the most common in the UK the latter is by far the most rarest!!!

I can't find the post either(?) but have a look around my home page and I will point you towards a few links here:

http://www.brandbright.co.uk/
http://www.grsuk.com/index.asp?info/welcome.htm
http://www.cambrianmodels.co.uk/16intro.html
http://www.ipengineering.co.uk/
http://www.gaugeone.org/

We either make out own chassis (power bogies) or buy kits... The section on the home page marked "kitchen sink engineering" will give you the run down on how to bolt together a power bogie (total cost £12). I would recommend you seek out Henry Greenlys book "Model Railways" if you cannot find one I will more than willingly scan the required pages for you to work from!!! I am using it to build my Gauge 3 trackwork from -so far it has been faultless... There is an article there on building track work from iron strip.

16mm is bigger than "G" but the track is either 32mm or 45mm.

regards

ralph

PS feel free to e-mail me if you want to ask anything -once a teacher always a teacher -I have found!!!

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Posted by hoofe116 on Sunday, February 24, 2008 5:00 PM

I haven't gotten to build anything yet. Well, I've got a 'power plant' I/W, as soon as it gets nearer complete I'm going to post a pix of it on here and get a reality check. But when I do start actually running, I'm going to eyeball it for 'looks'. I'm not particularly particular about prototypical sizing--up to a point, obviously. I don't have a good mental picture of how this G stuff looks when on tracks. My experience was back in the 70s with Lionel. Wife and I had a pretty big layout in the empty basement. Sigh, an empty basement.....

Les

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Posted by hoofe116 on Sunday, February 24, 2008 5:04 PM

Holy cow! Tongue [:P]

Thanks for the good look at a multi-layer (?) pocket. I'm mentally turning over the issues of building 'em. It'd be a snap if I had a mill.

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Posted by cabbage on Monday, February 25, 2008 1:28 AM
Hoofe,

Now I am confused -what is "a multi layer pocket"? My only power tool (as such) is my £29 pillar drill and £15 compound table. I use this to position holes accurately for drilling. I could use the pillar drill for milling if I fitted a 3mm shank cutter -but it has never appealed to me.

regards

ralph

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Posted by hoofe116 on Monday, February 25, 2008 9:01 PM

Cabbage:

What I meant was, the link pocket on a engine, where the link from the waggon goes in and gets pinned. I don't know the exact name for those, but I think they're called 'coupler pockets'. In the link 'n pin system, as I'm positive you're aware, car coupler pockets apparently can be at different heights above the track, so a switcher(shunter) would have a number of vertically arranged 'slots' in the pocket to accept the different cars/waggons' links. The picture Vic posted shows it perfectly. I've deduced that from what I've read, I've yet to see/hold an actual pocket & link, and probably won't until I make my first one. I'm turning over the notion of casting them from common solder. My wife is an artist and has lots of casting experience, particularly with brass. And I have lots of scrap brass and a forge that is capable of melting small amounts of steel, or reaching welding temperatures..... Lots of work, though.

To digress: remember the exchange of posts where I mis-identified a British loco withthe two nine-foot drivers? I am someday going to build one of those. For that project, I might cast the wheels.

About using your pillar drill for a mill: The way things work in that area is, a 3-jaw chuck just isn't made for milling. You get lots of unwanted movement with all but the lightest cuts. Of course, that's no real problem for the stuff we'd likely do, and I'll probably use my Asian drill press when the time arrives and hog out whatever and finish by hand. But here's a quick test: Extend the quill of your drill to its fullest, grab the chuck and shake. You'll find there's some play. Probably a very few thousandths. That's the tightest tolerance you can hope to hold, not counting the loading on the chuck jaws, which are by no means intended for side loads. (Not that they'll break, they just aren't designed for it). And play means the possibility of 'chatter', which can, on a bad day, make everything worse by grabbing the work or breaking the bit. If you ever do use a side-cutting mill in your drill press-er, pillar drill--by all means crank it up to the highest rpm's.

Les

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