12" working railroad

Discuss park gauge trains and large scale miniature railways having track gauges from 8" to 24" gauge and designed at scales of 2" to the foot or greater - whether modeled for personal use, or purpose built for amusement park operation or private railroading.

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Topics may include: antique park gauge train restoration, preservation, and history; building new grand scale equipment from scratch; large scale miniature railway construction, maintenance, and safe operation; fallen flags; track, gauge, and equipment standards; grand scale vendor offerings; and, compiling an on-line motive power roster.
rkcarguy
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Re: 12" working railroad

Post by rkcarguy » Thu Dec 07, 2017 3:33 pm

The square steel unfortunately has rounded corners, not good for the upper exposed corner of the locomotive deck. I could only get aluminum in sharp corner tube which I don't really want to use. Channel is also too wide by the time I get up to a flange that is in the 2-1/2" range.
Probably what I'm looking at is to use the 1/4" thick angle for the perimeter frame, and then make a 4' long sub-frame out of square tube to provide the additional support to the center, out to the truck pivot points(which are 3'-9") apart in 1/6th scale.
In fact, now that I think about it, If I bolt the sub frame to the perimeter frame, and then the "fuel tank" (muffler) and air tanks bolt to the underside of the sub frame, this will allow me a modular construction that will be easier to work on and/or replace as the years pass by.

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BigDumbDinosaur
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Re: 12" working railroad

Post by BigDumbDinosaur » Thu Dec 07, 2017 4:56 pm

Angle is a poor choice for building a locomotive frame, as it is the weakest of the common structural shapes.

A locomotive frame can be treated as a simple beam with the load focused in the center and the supports on two infinitely small pointss (the juncture of the truck bolsters with the frame). Hence the frame must be very rigid relative to its expected load-bearing requirements if bending is to be avoided. Angle, unfortunately, doesn't provide a lot of bending modulus, and has poor torsional resistance, which means unless the vertical dimension of the angle is large the frame will twist and sag, an effect often seen in Backyard Rails locomotives, whose frames were fabricated with angle.

My choice if I were building your locomotive would be to use ship-and-car channel for the longitudinal structural members, which has a significantly higher bending modulus than angle of the same general dimensions. Rectangular tubing would be even better (and easier to fabricate with), if the "sharp corner" requirement weren't cast in concrete.
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rkcarguy
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Re: 12" working railroad

Post by rkcarguy » Thu Dec 07, 2017 8:18 pm

I'm thinking I will do an angle perimeter frame over a tube steel one. Yes you make a good point BDD, I don't want flex or sagging between the truck pivot points and the bolsters so the structure will need to extend to the ends and be tied in with the coupler bolsters.
With the 2-1/2" leg vertical, 3-1/2" leg horizontal though, and 1/4" thickness, I'm expecting it to be fairly stiff. After I miter weld the corners I'll have to test it with my fat butt and see what happens.
MC4 dimensionally would work but at 13.8 # per foot it's far too heavy, that would give me almost a 280# empty frame.
What thickness angle are you seeing in backyard rails loco's? I know some of the pictures I've seen just appear to be sheet metal uni-body type frames which is far from what I'm building.
I am trying to avoid a few things so this will last along time. Any lap joints, long continuous welds(will warp the frame), and hollow voids that can't be finished and will eventually rust, like inside a steel tube.

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BigDumbDinosaur
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Re: 12" working railroad

Post by BigDumbDinosaur » Fri Dec 08, 2017 12:38 am

rkcarguy wrote:I'm thinking I will do an angle perimeter frame over a tube steel one. Yes you make a good point BDD, I don't want flex or sagging between the truck pivot points and the bolsters so the structure will need to extend to the ends and be tied in with the coupler bolsters.
With the 2-1/2" leg vertical, 3-1/2" leg horizontal though, and 1/4" thickness, I'm expecting it to be fairly stiff. After I miter weld the corners I'll have to test it with my fat butt and see what happens.
You will also have to check for torsional stiffness, the lack of which can result in a derailment-prone locomotive, as well as structural problems with the body. Plus, you have to be careful when you jig your frame that you don't accidentally build a twist into it.
MC4 dimensionally would work but at 13.8 # per foot it's far too heavy, that would give me almost a 280# empty frame.
I disagree. A 280 pound frame would be commensurate with the size and general characteristics of a 12 inch gauge locomotive. Weight is your friend in a locomotive, and a rigid frame is a good place to have it. Also consider that only the center sill (if used) and outer sills need to be that size. Crossmembers can less substantial material.
What thickness angle are you seeing in backyard rails loco's? I know some of the pictures I've seen just appear to be sheet metal uni-body type frames which is far from what I'm building.
The three BYR locos with which I am familiar used 1/4 inch thick angle. One of them is a GP50 that has a noticeable swayback to its frame. The others are F7s, which being shorter are not as prone to frame sag, but exhibit a little of it.

In designing load-bearing structures, "beam" (an abstract word for any structural shape) thickness is less important than "beam" height. In a "beam" supporting a focused load, deflection approximately varies inversely with material thickness. In the same "beam," deflection approximately varies inversely with the cube of the height. For example, if a "beam" of 2 inches height can support a focused load of P, a "beam" of 3 inches height can support a focused load of P × 3.375. This is why shapes such as H- and I-beams are much used in structures.

Square or rectangular tubing produces load-bearing characteristics similar to those seen with an H- or I-beam, but is easier to use in structures in which crossmembers will be present. This is because parallelogram-shaped elements present continuous surfaces for making welded joints. I've done much structural work with rectangular tubing and can tell you the only real downside is material cost.
I am trying to avoid a few things so this will last along time. Any lap joints, long continuous welds(will warp the frame), and hollow voids that can't be finished and will eventually rust, like inside a steel tube.
Most of that is a matter of good design. In the case of lap joints, an anti-corrosion step I take before the actual fit-up and welding is to clean the mating surfaces of scale, rust, oil and grease, and prime them with a bare metal primer (like this stuff). After the primer has thoroughly dried (8 hours minimum recommended), fit up your pieces and weld. Only the primer in the fusion zone will burn away and it will not interfere with the weld. I've used this technique for years with good results.

Tubing will not rust out if the interior is not exposed. That's a matter of how you arrange your structure.
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Glenn Brooks
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Re: 12" working railroad

Post by Glenn Brooks » Fri Dec 08, 2017 12:52 am

Rick,

It might be of interest to you to look back one or two years in the Chaski build forum for a recent diesel outline road engine thread in 7 1/2”gauge. What I remember as intriguing was the builder posted several photos of his body, hinged at one end. This allowed him to tilt the whole body off the frame at one end, for maintenance - much like the hood of a car. I seem to remember the photos and write up also discussed frame build, and arrangement of his power plant. Some of these 1.6” scale loco’s approach 1000#. So lots of similarities with what your doing.

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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rkcarguy
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Re: 12" working railroad

Post by rkcarguy » Fri Dec 08, 2017 12:44 pm

Glenn, I viewed that thread last night, that is BDD's F-7. The members on it aren't that heavy, but he's got a lot of braced frame work there that makes it very stiff.
BDD, thank you for the update on the member sizes and such, I thought that the L3-1/2x2-1/2x1/4 would be more than adequate. I wish they made that in 3/16 wall actually, and then I'd infill it with a more substantial frame. I was hoping to avoid having an internal frame that went up inside the body, as it will really limit space for the fuel and hydraulic tank. I was also hoping to make things more lightweight yet very "structural", and then bolt on plate to the area's behind the coupler boxes as needed for additional weight. This would allow me to remove it and lighten things up if I had to, during transport or working on the locomotive.
BDD, I've built several trailers, utility and car haulers, and found that rust is a problem inside the tubes. What happens is, the air inside condenses and evaporates as the weather changes, and you have this mini-environment of cyclic moisture in there. I have to consider this as I will operate in 90* summer as well as below zero weather, rain and snow. When I made some modifications to my 2nd trailer, it was only a couple years old and I found some considerable scale inside the tubes despite the welds being sealed(I did the cutting on a hot day and it "purged" air when the saw passed through the wall of the tube).
The last one I built I did use HSS, but I dumped a quart of used oil into each frame rail and then welded the end caps on!
The frame is by no means just going to be an open center perimeter of steel, I will be using either channel or HSS 2x3 cross braces at 6 locations to pick up the pivot pins for the trucks, both ends of the fuel tank(muffler-which is a massive rectangle tube 8x6x3/8 @ 15" long), and also at each end just behind the stairs. I could also add a strip of vertical material to the inside of the perimeter angle frame, such that it would be sort of Z-shaped and stick up 2" inside the body. This would take the vertical height of this member up to 4-1/2", and it would not protrude upward beyond the 2" aluminum channel inside the bottom edge of the body, so no space lost there.

As for not having warping or twisting, I'm planning to cut and tack the frame on our steel layout table at work, then weld it out at home in addition to adding all the tabs mounting plates tapped holes and such for everything. The welds that show will be ground smooth, so it's just a matter of jumping around with the welder to keep the heat even to minimize warping. Like you BDD, I'm picky and don't like zip ties around frame members to secure hoses wiring and such. It ends up being very time consuming, because I end up tacking everything, check fit by installing all the components, then remove all the components and weld out everything. Then coatings and finally assembly.

rkcarguy
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Re: 12" working railroad

Post by rkcarguy » Fri Dec 08, 2017 1:51 pm

I formed and installed the grille into the opening atop the body last night, it looks really good. Having issues with my pictures not showing up on image shack, hoping it's resolved soon, I did upload current pics so hope they get it figured out.

rkcarguy
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Re: 12" working railroad

Post by rkcarguy » Fri Dec 08, 2017 2:37 pm

Hopefully this picture will work.
train.jpg

rkcarguy
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Re: 12" working railroad

Post by rkcarguy » Fri Dec 08, 2017 2:42 pm

train2.jpeg

rkcarguy
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Re: 12" working railroad

Post by rkcarguy » Fri Dec 08, 2017 2:43 pm

Haha, ok if I save the pictures on facebook it resizes them, then save them back to my phone and I can post them!

Glenn Brooks
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Re: 12" working railroad

Post by Glenn Brooks » Sat Dec 09, 2017 2:43 pm

Hey Rick, lookin good! Glad you found a way to resize and post photos.

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

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BigDumbDinosaur
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Re: 12" working railroad

Post by BigDumbDinosaur » Sat Dec 09, 2017 3:10 pm

rkcarguy wrote:Haha, ok if I save the pictures on facebook it resizes them, then save them back to my phone and I can post them!
Gotta get yourself a real camera :D and some photo editing software. The photo editing software that came with my camera (a Fuji Finepix SLR) was lame, not that I expected it to be all that good. My editing preference is ACDSee, which can do just about anything you could imagine with digital photos. All of the pictures I have posted in my F7 build series were massaged in ACDSee to make them meet the forum's requirements, as well as fix exposure and contrast issues, framing, etc. Also, I use ACDSee to convert photos from the JPEG format produced by my camera to more compact GIF to make files smaller with no loss of detail.

One thing I've learned about photo editing software is the free stuff is usually limited and lame, and cheapware is only slightly less limited and lame. As always, you never get more than what you paid.
Science makes it known. Engineering makes it work.

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