First loco scratchbuild: tips for outside frames?

[Lacathedrale]

I would like to scratch-build the chassis of a locomotive in 4mm to see if I can do it.  I have access to a mill and a lathe, and I can do a bit of soldering. Building victorian locomotives means picking the least difficult, rather than the most easy, but I figure if I can do this, I can do anything. I would like to build a 2-4-0T with outside frames (4mm coupling rod throw).

 

The target is this lovely loco here:

 

It seems there are really only two areas that are going to complicate things mechanically:

 

Outside Frames:

Since I am happy with those outside frames being functional, I assume that I can simply treat them as if they were normal inside frames using high-level hornblocks, etc. - albeit with some rivet head detail.

Is there a standard for how wide outside-frames should be?

 

Cranks

My thought for the cranks was to sweat together some fairly substantial brass sheeting (1/16"?) and then drill and file together.

After separating, I would look to soldering rod through the drilled holes for fixing to the axles and as coupling rod pins (where washers would be used as retainers)

For fixing the cranks into the axles, their ends would be drilled, and I would look to use loctite retainer for fixing one side, and solder for the other.

 

Any thoughts much appreciated.

 

[garethashenden]

The only outside frame engines I've built so far have been Great Western which are actually double framed. Is that the case with this one as well or are the outside frames the only frames? With double framed engines its common to build the inside frames functional and the outside just cosmetic. You can do what you propose, but most of the commercially available hornblocks aren't really visually right. It would probably be easiest to have the indie frames functional and then have something along for the ride on the outside frame that looks right. This would let you have any springing/compensation out of sight.

 

What gauge are you working to? Generally the outside frames should be to scale regardless of gauge. Which wheels are you using? Gibson and Markits both do extended axles with outside cranks for some of their wheels, and it should be possible to mix and match things to get something to work. There are also etched cranks from Finney/Brassmasters and probably others.

[Lacathedrale]

I'm working to EM gauge. I can't find any information of whether they are double or outside framed conclusively, I'm happy to go with what works well.

 

I didn't realise AG did outside cranks, it may be worth a look. It seems they do two outside-crank wheels, either 20.5mm or 22.5mm - probably better to err on the smaller side, eh?

[garethashenden]

I count 5 outside crank steam wheels and three diesel wheels in the catalogue, Obviously most will be the wrong size. Do you know the prototype size? 

[MarkC]

If you're going to use AG wheels and functional outside frames with proprietary axleboxes, then life is a little easier for you, because AG use extended 1/8" axles. Romford/Markits' axle extensions are 10BA, so you'd have to modify the axleboxes or make your own.

 

If building outside frame locos then I too use normal inside frames, with the outside ones being cosmetic. It also makes life easier for dismantling locos for servicing.

[Izzy]

I have found that building a normal inside frame chassis and treating the outside ones as purely cosmetic easier and more practical for several reasons. Most O/F locos like the one you propose to make seem to have a 'wavy' footplate and need firmly attatching to the outside frames for strength and rigidity. It's also easier to give the carry wheel split-axle current collection and allow all the axles a bit of sideplay for getting around curves. Making sure the outside cranks/rods aren't overwidth and clout the platforms is another aspect that gets nip & tuck as the wider gauges are used and stout/thick working outside frames might prove an issue here. If you use the latter then how to attach the rest of the body becomes an issue to be overcome. It would need to be removable to allow access to the motor/gears etc.

 

Bob

[pete_mcfarlane]

I've not built an outside framed loco, but I have done some diesels with jack shaft axles. The flycranks were made as per the method you suggested with no problems. 

 

I countersunk the rear of the crank to take the Alan Gibson crankpin screws then treated them as per a driving wheel with Gibson crankpins bushes and retaining screws. Since there was no plastic wheel to melt I had no problems soldering both cranks on (having quartered them by eye). I think people have soldered cranks in place near plastic wheels by putting the chassis on it's side in a plastic tub and filling it with water to just above the top of the wheels. The water stops the plastic from melting. 

 

One challenge you'll have with having cosmetic frames as part of the body is the underhung springs, which will be in the way when you try to remove the body, from the chassis. I guess they could be made removeable. 

 

Those LCDR tanks are very nice....

[Michael Edge]

14 hours ago, MarkC said:

 Romford/Markits' axle extensions are 10BA, so you'd have to modify the axleboxes or make your own.

 

If building outside frame locos then I too use normal inside frames, with the outside ones being cosmetic. It also makes life easier for dismantling locos for servicing.

These are the old Romford extended axles, Markits now produce an extended axle with machined cranks fitting with a screw on a smaller square at the end. These are available for 00 and EM gauges but you may have to move the outside frames a bit further apart in EM since Markits wheels are overscale width at this gauge.

I think for this loco with very prominent underhung springs I would use the outside frames and split the body under the footplate.

[MarkC]

2 hours ago, Michael Edge said:

These are the old Romford extended axles, Markits now produce an extended axle with machined cranks fitting with a screw on a smaller square at the end. These are available for 00 and EM gauges but you may have to move the outside frames a bit further apart in EM since Markits wheels are overscale width at this gauge.

I think for this loco with very prominent underhung springs I would use the outside frames and split the body under the footplate.

Thanks for that, Michael - I'm still using old stock here.

 

Regarding the OP's loco - your solution sounds good, given your comment about the prominent springs. Not straightforward when compared to a conventional chassis, & dare I say, possibly not an ideal first scratchbuilt loco, but definitely a good solution.

 

Mark

[burgundy]

I would echo MarkC's suggestion that the best way to scratchbuild an outside framed loco is to build an inside framed one first. 

I have similar ambitions and have been progressing from etched kits, through scratchbuilder aids and recently completed the first genuine scratchbuild. It was the simplest loco that I could find - an inside framed 2-4-0 tank!  

The next step from there will be an outside framed 2-4-0 from a scratch builder etch which is currently in hand. 

I have seen the problem of underhung springs solved by making them detachable. Make the hangers out of very small diameter tube and attach wire at the end of the spring that is a close fit to the tube. This is enough to keep the spring in place under normal circumstances but is easily detachable. 

Best wishes 

Eric 

 

 

[Siberian Snooper]

The Martin Finney outside frame cosmetic axleboxes are half etched and fold 180° which with a bit of fettling slide up and down nicely. If you're building the loco with removable wheels you could easily attach the springs to the cosmetic axleboxes.

 

 

[Lacathedrale]

I'm certainly open to being convinced in making an inside-frame chassis, but It is not clear to me how cosmetic outside hornblocks would work? how do they stay aligned to the horns?

 

If the 2-4-0T outside frame really is going to be a pig, would an inside frame 0-4-2T with a radial axle be any better? Both are on the list but I figured they were both as annoying as each other!

 

 

I could feasibly

[Siberian Snooper]

If I remember tomorrow, I will take a couple of snaps of a partially complete Aberdare chassis, it still only has the inside frames, until I complete preliminary running trials, which will hopefully commence in the morning, the outer axleboxes are fitted to the axles and the cranks fitted to one side and the rear two on the other side and it runs reasonably as 2-4-0. Tomorrow's task is to quarter the final crank and give it a run in both directions, I can then fit the outside frames.

 

When I fettled the outside axleboxes, I marked each so that I could fit it on it's correct axle and side. The chassis is built as a CSB ( continuous spring beam), so it's all a bit floppy at the moment.

 

 

[Siberian Snooper]

See my reply here

 

[andrewnummelin]

I like the look of the SECR loco - should be a fun build!

Looking at the sizes of the springs it may be seen that the rear one has more plates than the centre one: this is common and came from having the inside frames terminating before the firebox so the rear one carries the full load, the centre driven axle had bearings & springs fitted to both inside and outside frames so the springs have fewer plates than those of the rear wheels. The front axle probably carried less weight than the driven ones and probably only had the visible spring that looks as though it may have been intermediate in size between the those on the driven axles.

 

See https://www.scalefour.org/forum/viewtopic.php?f=19&t=7927#p88936 for a discussion on the topic.