Quartering?

[Dakguy201]

A slightly different question -- on an engine such as the Challenger (4-6-6-4) is there any ideal relationship between the position of the front and back set of drivers?  If so, could it be maintained over any period of time or would wheel slip make it a hit and miss proposition? 

[tomikawaTT]

Dakguy201

A slightly different question -- on an engine such as the Challenger (4-6-6-4) is there any ideal relationship between the position of the front and back set of drivers?  If so, could it be maintained over any period of time or would wheel slip make it a hit and miss proposition? 

Since there is no mechanical connection between the engines (an engine being a set of drivers powered by a set of cylinders) the two engines of a simple semi-articulated like the Challenger (or N&W A, or Alleghany...) had no reason to stay in synch with each other, and they didn't.

Likewise, since the high pressure engine of a Mallet exhausts to a receiver, rather than one high-pressure cylinder exhausting through two pipes to the ends of one low pressure cylinder, there was no reason for the engines under a N&W Y or a C&O H to take and hold any fixed relationship.

It was quite usual to have one engine slip while the other gripped - the PRR T-1 was notorious for it.  As soon as that happened, all suggestion of synchronization would be lost.

Chuck

[The Dude With The Hair]

 Would that cause problems if somehow you managed to dead center one set of drivers, and the other didn't have enough power by itself to start the train? Or was that not even possible?

[BigJim]

 Would that cause problems if somehow you managed to dead center one set of drivers, and the other didn't have enough power by itself to start the train? Or was that not even possible?

Dude,
Have you been following along in this entire conversation?

[Paul Milenkovic]

BigJim

 Would that cause problems if somehow you managed to dead center one set of drivers, and the other didn't have enough power by itself to start the train? Or was that not even possible?

Dude,
Have you been following along in this entire conversation?

Yeah, when they were double-heading K-4s on those Pennsy name trains, there were these rare instances when they dead-centered both engines and the crews had to get these long crowbars out of racks underneath the tenders.  They would have four men standing on top of a lineside water tower pushing on one of those crow bars  . . .

Seriously though, what quartering gains for you is that when you dead center one side, the other side is at maximum mechanical advantage and hence starting is not a problem.  You could have both sets of drivers, either on a double-headed consist, an articulated, or a duplex, at dead center on one side, but each set of drivers is then off dead center on the other side.

[Deggesty]

tomikawaTT

Admittedly, I'm late to this party.  Two things:

1. There was a thread over on the Model Railroader General Discussion forums that cleared up the 'why' aspect without resorting to engineering treatises and higher mathematics.
2. Three cylinder locos (SP 4-10-2, UP 4-12-2, JNR C52 and C53 class 4-6-2s...) were 'thirded,' not quartered.  The rods don't have to have a 90 degree lead angle, just al long as they are the same on all axles.

Unlike model locos, 1:1 scale siderod sets are not rigid in a vertical direction - they have to allow for the vertical movement of equalized driver axles.  Therefore, they can only deliver force parallel to the rod, never perpendicular to it.  As for expecting rail friction to prevent the piston-driven wheel from slipping and getting out of sync with the rod-connected wheels....

There was one occasion that saw a seriously wounded N&W J returned to Roanoke on a single cylinder, with the other main rod disconnected and chained up.  The siderods on the 'dead' side had to remain in place to preserve proper quartering...

Chuck

When that J (#600) was returned to Roanoke from Bristol, it had to be stopped on a downgrade when it met #45 so that it could be be started again if it had stopped at the end of a stroke. No quartering was possible, since it was running on only one cylinder; the left siderod was left on to minimize imbalance on that side. Since learning of this, I have marveled that the counterweight to the main rod did not cause problems, because the main rod, along with what was left of the valve gear, was taken off in Bristol. After the meet with the southbound Tennessean the engineer got it up to eighty miles an hour for a short distance. Clyde Taylor, the Road Foreman of Engines who was on board, said, "I figured it would rock and raise h___, but no...it ran just fine. You wouldn't believe how well it ran. It was smooth as silk." Of course, it was running light. Incidentally, the engineer of #45 the day the 600 went back to Roanoke was the father of the engineer who was running her. See the March, 1999, issue of Trains.

Johnny