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Baker Valve Gear Advice Please


Old Bill:
Hello friends!

Please may I ask for some advice? Now that my launch engine is complete, I have gone back to my locomotive and am in the process of laying out the Baker valve gear for a 1 1/2" scale 4-8-2. I have downloaded the software created by the late Mr  Dockstader and, in combination with my drawing board have come up with a potential solution. The question now is what constitutes a good solution? What are good valve events so what am I trying to achieve? Everything I have read tells me how to lay it out but not quite what I am aiming at so I would value your opinions very highly.

 I want about 1/64" of lead so in mid-gear I get this:

The lead is fine and, although the laps are different, I can make the valve to suit. Here is the Sine chart as well.

I set up the steam chart for nine reverser positions from mid to full forward gear and get this.

The chart doesn't tell me a lot but comparing the cut-offs between front of cylinder on the right and rear on the left, they are not identical but almost match my 75% cut-off target in full gear. (Don Ashton's recommendation). They do diverge in the mid-range so my question is, is this significant and will it matter?

As you can see below for the same set-up but in reverse, they differ more significantly and you can see the bias in the shape of the chart.

I just don't have a feel for what are 'good' valve events and how sensitive it will be so I would very much appreciate some views.


Steve   :thinking:

Knowing that a total symmetry of the steam distribution between the 2 ends of the cylinder is not possible, I think that you have to tend towards it... for the regularity of the running and mainly in forward running, (except for a shunting loco!).
in my opinion the oval diagram allows more easily to appreciate this symmetry at each position of the reverse arm.

I would say that as presented, your distribution looks close to the ideal !

With my personal tests with these programs with my gauge 1 locos, the final adjustments were a few microns on the position of a pivot or the length of a lever, really insignificant...except for the fun and the personal satisfaction to get spot on !

Old Bill:

Thank you so much for your thoughts. I really appreciate them. The guys who did this originally worked with other people and could count on a lot of experience. As I only want to make this once I am relying on my friends here to keep me right!

Here are the oval diagrams for forward gear:

pic host

To my eye, they look quite even so thank you for your comments. I am working on the board this morning to create a full-size layout and design the components. I will post pictures of the bits in due course!

Steve   :)

You may be quite satisfied with this solution, I cannot see how it can be better !
you have to cut the gears to these dimensions for a great running loco !

Old Bill:
Thank you. I will have a go!

Steve   :)


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