Greetings,
I have a 2-6-6-2 that I removed both sets of gear covers in order to clean & re-lube the gears. Once the gear covers are removed the axle is free to rotate.
After I started cleaning and re-lubing the gears, the thought occurred to me that I had neglected to note the orientation of each set of side rods. Am I correct to assume that they are 90o to one another? If so, are the side rods for the front set of drivers 90o ahead or behind the rear set of drivers?
The following photo of a C&O 2-6-6-2 seems to indicate that the front driver side rods are 90o behind the rear drivers - at least in the forward direction. These would be reversed if the locomotive were backing up.
Thanks,
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
As on a conventional duplex-drive locomotive like a PRR T1 or Q2, there is no fixed phasing between the two engines of a Mallet or simple articulated at all. They can assume any relation to each other on the 'real thing'.
In practice, a combination of slipping and back pressure usually brings the two sets into phase with each other over time ... until something like differential driver wear puts them out again.
Of course, the drivers in each engine have to be quartered precisely to keep a double-acting two-cylinder engine in proper time. In a model, that requirement is relaxed because the wheels are being externally driven: they need not be at precisely 90 degrees, or even particularly close to it, but on a given engine (Mallets and simple articulateds have two 'engines') all the drivers must be at precisely the same DEGREE of quarter. Or the rods will cause trouble.
(Incidentally, on a Deem-conjugated duplex, my preference is to phase the two engines at 135 degrees; that gives the best compromise between moving the running gear mutually opposed, as in a Withuhn conjugated duplex, and having eight instead of four power pulses per revolution (the overlap making for extremely smooth running even at comparatively short cutoff). In an engine using zero overbalance for high speed this configuration is useful. This would nominally be true for an unconjugated duplex, of course, and by extension to Mallets, so if you are setting up a fixed driveline to both engines that's where I'd phase it if possible...)
Correct except for Rivarossi, 88.5°. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
Yes, the rod sets on either side of the boiler are meant to be at 90 degrees from each other. It needn't be precisely 90 deg, as Overmod says. Do the best you can.
Please do have the rod sets on each side of the boiler offset from each other a bit. Makes it more realistic.
I have seen film of a DMIR Yellowstone with the siderods on both sets of drivers perfectly matched to each other, but I think most folks agree our models look better if the front and rear sets of drivers are off from each other. On a "simple" articulated, you might want to make the front and rear drivers not-quite quartered, so the "chuff-chuff....chuff-chuff" sound decoder sound would accurately match the drivers.
Let me repeat: there is no "quartering" between the forward and back engines of a Mallet or simple articulated.
The only 'quartering' is from side to side, as for any two-cylinder double-acting reciprocating locomotive.
Theoretically you could conjugate the two engines, with a Cardan shaft with universal at the hinge point of the forward engine, and some way to traverse the rear engine's cylinder saddle. (Note how similar this is to the way 'electric' Mallets drive both sets of wheels from one motor...) There is little point to conjugating a Mallet because any slip and spin of the forward (more likely to slip) engine rapidly causes it to run out of steam and stop -- and it will likely be in some phase with the HP through the receiver when it does. So no shaft, and no coordinated or detented phasing between engines ... and no fixed relation in angle between the two engines' main pins...
135 degrees is: with one engine rods-down, the other will be advanced 90 degrees + 45 degrees, clockwise looking at the engineer's side.
OvermodLet me repeat: there is no "quartering" between the forward and back engines of a Mallet or simple articulated. The only 'quartering' is from side to side, as for any two-cylinder double-acting reciprocating locomotive.
Right, and I don't think anyone's saying anything to the contrary? On a real engine, drivers slip so the front and back drivers change their relationship over time. However most model articulateds have the front drivers off from the rear by 90 degrees, because most folks feel that looks better than having say the front and back drivers in unison. Since many model railroaders like to use the "articulated" sound option on their sound decoder - the double "chuff-chuff...chuff-chuff", it would be more accurate to that sound if the front and rear drivers were not quartered, but were close - off by say 10 pct. or so.
wjstixSince many model railroaders like to use the "articulated" sound option on their sound decoder - the double "chuff-chuff...chuff-chuff", it would be more accurate to that sound if the front and rear drivers were not quartered, but were close - off by say 10 pct. or so.
All of my duplex and articulated steamers have come factory-assembled with the driver's side cranks matched for clock-face angle. If the ones on the right side of the boiler are at BDC, the cranks on the other side are rearward at 90 deg, or 0900 hrs, looking at the boiler from that side. Or, it's the other way around, meaning the cranks on the firing side of the boiler trail those on the right by 90 deg, I forget which it is. I don't like the look, even if the prototype is likely to be in synch a great deal of the time because I know it often isn't in synch, also much of the time. So, I remove the cover plate and lift one of the driver axles' gear clear of the other and slip that set a couple of teeth.
Overmod wjstix Since many model railroaders like to use the "articulated" sound option on their sound decoder - the double "chuff-chuff...chuff-chuff", it would be more accurate to that sound if the front and rear drivers were not quartered, but were close - off by say 10 pct. or so. Except that his locomotive is a Mallet, a true compound, and except at starting that type doesn't have the double licks. All you hear is the low and comparatively long rush of the LP exhaust when running...
wjstix Since many model railroaders like to use the "articulated" sound option on their sound decoder - the double "chuff-chuff...chuff-chuff", it would be more accurate to that sound if the front and rear drivers were not quartered, but were close - off by say 10 pct. or so.
Except that his locomotive is a Mallet, a true compound, and except at starting that type doesn't have the double licks. All you hear is the low and comparatively long rush of the LP exhaust when running...
I didn't say it was correct, just that a lot of modellers like to set it up that way.
tstage If so, are the side rods for the front set of drivers 90o ahead or behind the rear set of drivers?
Tom, I know the answer to this one!
Relationship of siderods between the front and rear engines of an articulated (or duplex) locomotive does not matter.
If it did, everytime the locomotive had wheel slip, the crew would need to get out and check the relationship again.
-Kevin
Living the dream.
Reading these replys is interesting but using the term "quartering" applied to articulated front and rear engines isn't right and I think that is what is confusing many of the readers.
The engines are independent of each other whether simple or compound. There is no physical connection between them other than the drawbar/pin connecting their frames.
Quartering refers to the side rod pins on each wheel being in alignment with each other. The left to right relationship is basically 90*. This is so both sides won't be full forward vs full aft which could cause the engine to lock up during starting. Having them quartered at 90* allows one side to be at full stroke and the opposite side in mid stroke so there's always steam admitted and working that particular piston.
Each engine works independently and can and will be in the same relative position with rods up, down, fwd or aft at any given time. As previously said one engine or another will slip periodically and so the rod position will change front to rear. Most folks like seeing them not in the smae position on their artics as it looks cooler.
I have read that with simple artics it was normal for them when running at higher speeds to have them become syncronized with each other due to the draft or steam flow or something like that. I have seen that with N&W 1218. OVERMOD can probably explain that better.
We need to think syncronized more than quartered when discussing the artics.
Just my 2¢.
oldline1
Well, and I think people may really be talking / thinking about the sound of the chuffs being synchronized, not the relationship of the front driver's siderods to the rear drivers. With a simple (non-compound) engine, an engine going slowly when starting will have a more distinct separation of the exhaust chuffs of the front and rear drivers. As the engine speeds up and chuffs become closer together in time, eventually the individual chuff sounds merge to make a sound more like a non-articulated four chuffs per revolution engine.