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Quartering a Locomotive – What is it?
Jim C posted this question:
“I overheard someone at the train show taking about “quartering the wheels of a locomotive”, but didn’t get the chance to find out what he meant. I’m just curious on what quartering is, how is it done, and if its worthwhile? From what I overheard, I gather it has something to do stopping a loco from swaying back and forth, but I’m not sure?”
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6 Responses to Quartering a Locomotive – What is it?
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If you haven’t removed the driving wheels from their axles you should have no problems. Quartering ensures that when the driving rods on one side are at the top (or bottom) of their circle of travel, the driving rod on the other side is in line with all the axle ends.ie a quarter of a rotation difference. It is important that all the driving wheelsets have the same difference of rotation. If you scroll to the very bottom of this page and enter “quartering” in the search box, you will come across a previous post of mine dated Dec 23rd 2012 explaining how it can be done.
Robert
I don’t think the 90° angle (quarter of a circle) found on 2-cylinder & most 4-cylinder engines will be correct for a 3-cylinder simple-expansion engine; to get a more or less even torque, the 3 cranks are set @ 120° to each other, I believe. 4-cylinder engines are usually 90° + 180° + 90° +180° – yes, I know that adds up to 720°, but that’s because the cylinders are double-acting; the outside piston on one side goes in the opposite direction to the inside piston on the same side, each being on the power stroke at the same time, of course. Please don’t ask me to explain Richard Maunsell’s Lord Nelson Class, however – at least one of them gave 8 exhaust beats per revolution of the wheels instead of the 4 we’re used to from other 4-cylinder engines (with all wheels coupled together, i.e. not duplex,Mallet, Kitson-Meyer, Beyer-Garratt, etc.).
The reason real steam locomotive drivers are quartered is, if they were exactly the same, or at 180 degrees, and the engine stopped with the rod at exactly 3:00 or 9:00, you wouldn’t be able to start the locomotive. If they are at 90 degrees, no matter where it stopped, at least 1 piston would be able to exert pressure on the wheel to make it move.
On an electric model(as opposed to live steam), this is irrelevant. It is also impossible to see both sides of the model at once without a mirror, so unless the model is being built to be a contest entry, no one will notice if they’re quartered. BUT, if you are putting wheels on the axle, why not do it right? But if you have a model where they aren’t perfect, and don’t want to take the wheels off the axle, it will still run, as long as ALL the wheels are exactly the same. If one is slightly off, the side rod will bind.
When the linkage on a locomotive converts the reciprocal motion of the steam engine to the circular motion of the wheels, every 180 degrees there is a point at which the lines of force go directly through the center of the axle. If the pressure on the linkage were applied at that point, nothing would move. If there is only one steam engine and one wheel, the wheel would have to be turned manually until the push or pull is no longer through the center of the axle. Then the force from the engine can accomplish something. On a locomotive there are at least two engines, one on each side. Because the wheels are connected from one side to another, they are built so that the wheel on one side of the locomotive is rotated 90 degrees from the wheel on the other side – one quarter turn. That way, when the linkage on one side is at dead center, the linkage on the other side is at its most efficient angle, and because the wheels are locked together, the force on the other side turns the first wheel past dead center and steam can be sent to the piston in the engine. Because most locomotive steam engines apply force in both directions, for each revolution of the wheel there are four applications of force and four “chuffs” as unused steam is released, two for each side, alternating from side to side.
Once the wheel is moving, inertia can usually carry it through the dead center position, but if a locomotive is stopped with one side at dead center, the other side can get things moving.
In an electric model locomotive, where the wheels are turned by electric motors via gears, the linkage on a locomotive does not have to be quartered to enable it to move, but it would not correctly represent how things are on the prototype.
On locomotives with compound engines (with both a high and a low pressure cylinder) both cylinders work in phase as if they were one engine. Locomotives with two or more sets of driving wheels do not have to have wheels of one set coordinated with those of the other and there can be 8 or 12 chuffs per revolution of the wheels, but within each set of drivers the wheels need to be quartered from side to side.
When more than one wheel on a side provides driving force to the tracks, only one of them is connected directly to the steam engine. The others are connected to each other by a strong rod to make sure all the driving wheels on the same side stay aligned with each other and to transfer the driving force to all the driving wheels.
If your locos run smoothly, no problem. If they do need quartering properly, you need a special jig or the services of a model engineer.
I would like help quartering a 3 1/2″ Rob Roy loco