Steam wagon "Meg" advice, please.

As you do, my mind is thinking about the next project, or possibly the one after that. I rather fancy revisiting Barrie Neville's 1 inch scale "Meg" steam wagon. I have the copies of Engineering in Miniature in which it was serialised some 30 years ago but the author doesn't give the details of the gears, sprockets and chain used in the transmission, beyond the diameter.

Is there anyone who has a set of drawings and can tell me the tooth count and dp for the gears and the tooth count and pitch for the chain, please? I do know that these came from Bonds o' Euston Road and later of Midhurst. I've a s/h Bonds gear catalogue on its way and will attempt to reverse engineer the info if I must but would prefer the genuine information, if possible.

Has anyone on here built this wagon and is there anything that I should be aware of?

Thanks in anticipation.

Mike

Is Barrie Neville still with us? I have a contemporary address for him but can find nothing online to suggest present whereabouts.

From the information in the March 1990 issue it looks to be about 1/4 in chain so nowadays you would probably have to go for a metric 10mm pitch and probably module 1 gears are going to be the most readily available. Have you googled it? there have been a couple of threads on this forum which might give clues to who has built it.

Edited By Bazyle on 21/06/2020 11:14:48

I would have said 04B (6mm pitch) chain would be a better substitute for 1/4"

If you have the diameter of the gears in the article and can count the number of teeth in a photo then should be easy enough to work out

Thank you Bazyle and Jason

6mm and 1/4inch pitch chains and sprockets are both available from HPC, amongst others, as is 4mm pitch at over 5 times the price per unit length. I'm stumping up the price of 4mm for another project but definitely going cheaper for the wagon ( it's a much longer chain for one thing!).

The drawing gives the shaft centres as 1 1/2 inches so taken together with the outside diameters an educated guess for the dp is certainly possible helped by counting teeth in the photos. This last will be an approximation as I don't think the full gear is visible anywhere so it'll be count what looks like a 90° segment and multiply.

To confuse the issue still more, I'm more at home with metric these days so am toying with upscaling at 2mm to 1/16". It's not as if the castings are still available, beyond the set Station Road Steam had a year or three back.

Mike

I feel the essence of twittedness coming on.

Re-reading the articles when fully awake, rather than just before sleep, I can see that it is not the o.d. that is given but the pcd. That provides the ratio outright and it simplifies to deciding on a suitable dp or module. I'd assume the original was dp but, if you read the previous post, I'm looking to go metric, in which case module will fit in better.

Off into the workshop for a bit now but I'll do some rough figuring this evening.

Mike

Coming back to this, between the articles and the Bonds catalogue, things become clearer.

First, the Bonds' chain was 5mm pitch. Given my plans to upscale, I'll almost certainly use modern, easily available 6mm pitch. You'd have to peer under the body to see it, anyway.

The gears in the original design must have been 32dp. I'm inferring this from the comment in the article that they need thinning from 1/4". The only gears in the catalogue that are this thickness are the 32dp ones. Again with the desire to upscale, the nearest metric gears would be mod1.

As an aid, I've laser cut the gears in 3mm acrylic, to both mod 1 and mod 1.25, reducing the tooth count appropriately for the latter. At the moment, the larger teeth seem to look better but I wont buy the steel gears until the wagon has progressed enough for me to try the acrylic gears in place and see which looks best then. Looking at photos of full size wagons online, the mod1 tooth count is certainly closer for the crankshaft gears. Ho, hum......

A last question, for now, that I hope one of our boiler experts can advise on. The cylinder block will be a two part fabrication, comprising the block and the saddle, silver soldered together. I have a piece of 2-1/2 inch bronze bar for the block (£2.50 more years ago than I care to remember). Given it's going on top of a boiler, should I get a piece of bronze sheet for the saddle or will brass be acceptable. Volume 2 of the boiler test code requires no brass in the structure of the boiler, other than lock nuts on screwed stays, but accepts brass fittings. Does the cylinder block count as fitting or structure? Obviously it's above the water level and there would need to be a serious amount of dezincification before it could cut loose.

Mike

I don't know about the rules but I would suggest that the cylinder is a structural component because it sustains mechanical load as well as pressure.

Mike,

Thats a really good question and like so many difficult to answer definitively. Several ways to look at it, one being if you build the boiler without drilling for the cylinder studs or steam take off (which many commercial TE boilers are supplied as for obvious reasons, you can do the 2 X WP initial shell test and argue your boiler is structurally sound. Therefore the cylinder is a fitting and not part of the boiler structure (when considering the pressure system). However the PER requires that the pressure system is tested - hence the 1.5 hydraulic after fittings are added. Technically superheaters on a loco are part of the pressure system and should be included in the 1.5 test. Normally with a TE boiler the cylinder will be included with the 1.5 test as it is directly connected to the pressure system and is often steam jacketed. Someone will no doubt argue that by drilling the stud holes and steam take off you are materially altering the boiler from its previous condition although as the original design allows for that this is often overlooked and I think largely irrelevant. The one exception to this would be that any structure like a doubler or adaptor that is soldered to the boiler below the bolted joint for the cylinder is pert of the boiler structure (take the Avelling pressed cylinder mount for example).

So my answer would be your cylinder is a boiler fitting and not part of the boiler structure per se so brass should not be an issue. Niether do I think you will be steaming this 7 days a week so the corrosion issue is a very minor and if it did corrode the effect would most likely be porosity rather than out and out catastrophic failure, so on a risk and rules basis I wouldn't have a problem with the brass flange. Other inspectors may well argue / view the situation differently though so imay we'll be worth asking the question of whoever is going to certify your boiler. Under the model code it is difficult to challange your inspectors decision. Once you have had a certificate though you do have an argument that it was previously tested successfully in the as presented condition and therefore acceptable. In that circumstance the new inspector can only refuse to test it, not fail it (as long as it is not corroded and leaking) and you are free to seek another opinion!

Paul.