Quartering HO drivers

What you are talking about is called 'tramming' a steam loco.

In addition to driver quartering, it is CRITICAL that the axle spacing EXACTLY match the siderod hole spacing.

YES, it is important that all the driver axles are parallel, perpendicular to the frame, and precisely spaced in the frame. Real locos have adjustments for this ('shoes and wedges'). Model locos usually do NOT have such adjustments (easily). Hopefully the manufacturer did it right ... if not, you're in for some (careful) precision work (filing, milling, new bearings, shims, etc.).

In addition to 'quartering' (90 degrees is NOT precisely needed, as long as all drivers are alike), the radius of the crankpin locations is also important. Again, they must all be alike.

LOTS of things to get right for smooth operation.

Dan Mitchell ==========

Lungshot1 wrote:

This might help a bit, if you haven't seen it before:

Ptooey

Lungshot1 wrote:

Thanks...I'll look at it closely. I think the major problem was a defect in the axle slot in the frame.

I think I will make a simple, tight frame that will eliminate the shifting of the drivers and start over again quartering the drivers from that point and see how it goes from there.

Thanks for all your suggestions.

Ed

"Quartering" refers to the way the drivers of a steam locomotive are mounted to the axles. The drivers on one side of the locomotive are rotated 90 degrees (a quarter of a revolution and thus "quartering") from the drivers on the other side. This always allows the locomotive to start from a dead stop, and provides more even power from the cylinders to the drivers, with 4 evenly spaced power strokes per driver revolution. If the drivers were not quartered, then if the locomotive stopped with the crankpins all the way forward or all the way back (e.g. the 3:00 or 9:00 positions as on a clock face), then all possible pushing by the pistons could not cause the drives to turn. With quartering, then of the drivers on one side are at 3:00 or

9:00, the drivers on the other side are at 12:00 or 6:00 with the pistons at mid-stroke and able to push or pull on the drives to start them turning. This is the same principle used in automobile engines that the pistons are not all top or bottom dead center at the same time. Gary Q

I'd never thought about that, but it certainly makes sense. Thank you for the clear and consise explanation.

/Carter

I'm missing something! This all makes perfect sense when the pistons drive the wheels, as in a real steam engine. In most models, however, the wheels drive the "pistons", so what possible difference could it make?

MacIndoe

Mac> I'm missing something! This all makes perfect sense when the pistons

It's not so critical for an 0-2-0, but a loco with more than one set of drivers must have all axle/driver sets quartered the same.

Dave

Usually the gears only spin one axle. The others are driven by the side rods, and so you need the phase difference to avoid having the axles try to turn different ways when the pistons are at full stroke.

The wheels of a model locomotive are x units apart. The crankpins on one side are also x units apart and parallel to the rail by y units. If the crankpins on the other side aren't all the same number of degrees [0-180] apart then the distance between the crankpins on the other side won't all be x units apart and the crankpins won't be parallel to the rails. When the geared driver tries to turn the other drivers the the rods will bind. This is because they are in different locations in the crankpin's orbit around the axle. Every degree a crankpin is different from the other makes it larger or smaller than x units apart and at greater height than y units above the rail.

Eric

Mac "I'm missing something! This all makes perfect sense when the pistons drive the wheels, as in a real steam engine. In most models, however, the wheels drive the "pistons", so what possible difference could it make?"

THAT'S what I was missing. I thought that all the drivers would be geared and driven together. If one has to drive another through the connecting rods, then of course they have to be out of phase.

Bill MacIndoe

The european engines tend to be all wheels driven by gears so the need for siderods doing their work is not required and the siderods often have very large holes relative to the crankpins so things don't bind. The American practive is to drive one driver and have the rest of the drivers powered through the siderods. This means that all of the drivers need to be aligned so that the crankpins have the same identical angle between the left and right sides and as close to 90 degrees as practible. Being off by a few degrees won't hurt anything (all drivers at the same angle!) but as you go more, the stress of the rods goes up as there are points in the rotation where the a siderod will have to push the other drivers at a small angle relative to the axle and thus the mechanism will wear faster.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works evevery time it is tried!