How to start Walschaerts Design as a beginner?

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Old Bill
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Re: How to start Walschaerts Design as a beginner?

Post by Old Bill »

"I can't imagine the original designers of the LE locomotives or RRSC mikado etc went to quite this length of charting valve movements when designing the gear on their locomotives."

It is only thanks to Charlie Dockstader's software that I can produce these charts. The difficult bit is understanding what they mean! My thanks for all of the assistance in that respect.

I have now started to draw it out on the board from a mechanical perspective and have found that the crosshead contacts the piston rod gland! I have shortened the connecting rod by 1/4" and made other adjustments to keep it all functioning. Fortunately, another run of the software has shown it to be OK. There is always something!

Steve :)
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Bill Shields
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Re: How to start Walschaerts Design as a beginner?

Post by Bill Shields »

Ah...now it comes down to interference checking.. :shock:

Valve Gear designing is a very iterative process.
Too many things going on to bother listing them.
VGC
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Re: How to start Walschaerts Design as a beginner?

Post by VGC »

@Steve: I did not thank you for your reply including the image https://i.postimg.cc/K4XKsNW6/004-Oval- ... -Steps.png yet, so many thanks late!
Is this your own result, or is the valve gear behind this diagram downsized exactly from a real (original sized) valve gear?
If not, does anyone here have a backwards diagram from original Baker valve gears? I would be glad to have something to compare with the diagram of another type of valve gear.
Old Bill
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Re: How to start Walschaerts Design as a beginner?

Post by Old Bill »

I have an erecting drawing for the Walschaerts version of the loco so that gives the main dimensions. I have bought the long-frame Baker gear castings from Roger Goldmann so I am using his dimensions for the basic mechanism and the cylinders I have were poured for Henry Greenly's 4-8-4 somewhere around 1970, I think, so the port sizes have been set by the castings. I have put all three together on the board to get it to look right and then followed on from there using Charlie Dockstader's software to see what I have got. As you say Bill, an iterative process with some help from my friends!

Steve :)
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Bill Shields
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Re: How to start Walschaerts Design as a beginner?

Post by Bill Shields »

Port dimensions are (should be) independent of valve gear driving the valves.

I have often toyed with the idea of building a loco with baker on one cylinder and walschaerys on the other. .and waiting for someone at a club to ask the poignant question.

Current project uses Southern but is using valve and port dimensions from a loco designed to run on Stephenson gear.
Too many things going on to bother listing them.
Berkman
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Re: How to start Walschaerts Design as a beginner?

Post by Berkman »

what did you go off of to design the SOU VG?
Would love to see a pic

I've always thought a RMI 2-6-2 or something would be neat with SOU VG
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Bill Shields
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Re: How to start Walschaerts Design as a beginner?

Post by Bill Shields »

Description in STEAM LOCOMOTIVE STUDY COURSE and original patent design and other pieced together sources

There are many things not clearly defined in either...hence the iterative design approach

Once worked out works fine...as long as the driver to which the crank is attached does not have any vertical movement

Vertical motion of the wheel changes timing of events.
Too many things going on to bother listing them.
Moron
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Re: How to start Walschaerts Design as a beginner?

Post by Moron »

Bill Shields wrote: Fri May 28, 2021 10:30 pm Description in STEAM LOCOMOTIVE STUDY COURSE and original patent design and other pieced together sources

There are many things not clearly defined in either...hence the iterative design approach

Once worked out works fine...as long as the driver to which the crank is attached does not have any vertical movement

Vertical motion of the wheel changes timing of events.

Southern is awesome, a mix of walschaerts and Baker. You probably already know this but I’ll put in what I know anyway as maybe it’ll help simplify the gear for someone. Hopefully I have this right (feel free to correct if I’m wrong)

All Southern has an “all square” layout. The eccentric circle controls valve travel, the lap and lead is controlled by the ratio between the 2 pins at the end of the eccentric rod. The link radius is the same as the distance between the die block (in center) to the eccentric pin when the engine is in dead center (similar to walschaerts) creating an exact radius so that no movement is imparted on the valve (constant lead) and the biggest Secret, the degree of angle on the bell crank acts in the same manner as backset in walschaerts, allowing to adjust/create equal movement on each extreme of the valve from center. Southern was popular due to the fact that it had virtually no valve gear “kick”, and in the days of Johnson bars, this meant hooking up the gear with ease thus saving money. It did not like lateral travel too much apparently.
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Bill Shields
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Re: How to start Walschaerts Design as a beginner?

Post by Bill Shields »

From a broad description point of view...you are absolutely correct...

I would substitute your term of 'lateral', for vertical.

Getting it to work is another matter since many of the important dimensions and relationships between components are not spelled out in documents and must be learned the hard way (make many parts that cannot be used.).

I have seen only a few southern geared model locos in my life and most have "adjustments" built into what would be fixed length links in the full size locos...with the exception of the gear on George Thomas' Nellie..and he ended up building a mechanical simulator (1960 era) to get it right.

I have no idea how many parts he made before he got it correct...but I do know that I have 5 sets of VG drawings for that loco and none are the same.. and none agree with the running model.

Anyone who wants the descriptions I used can email me direct and I will PDF them over. Bshields at mehrs dot com.

As I said.. the model I am using as my guide sits on vertical travel stops once the boiler is attached and totally prohibits axle box travel unless the loco should go airborne and totally unload the springs.
Too many things going on to bother listing them.
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LVRR2095
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Re: How to start Walschaerts Design as a beginner?

Post by LVRR2095 »

Southern Valve gear can work very well in our scales.
Attached is a photo of the Southern gear built by the late Lewis Bullock from New York State.
It is on a 3 - 1/2” gauge 4-6-2 Lehigh Valley RR locomotive.
Carl Purinton was also fond of Southern Gear and used it on several of his locomotives.
On Southern gear there is no die block slip as you get with Walschaerts gear.

Keith
3/4” scale Southern Valve Gea
3/4” scale Southern Valve Gea
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