3 1/2" gauge Mabel locomotive valve gear

[bobb]

I have resumed work on this model after a long pause. I have sketched out the Allan valve gear on CAD and frankly the "LBSC" design just doesn't add up. I have looked at a few on-line simulations but can't get my head round them, best one is from the late Charlie Docksteader but it doesn't seem to run in its entirety on Windows 2010 as it's all in DOS? Has anyone else made this model and checked the valve events? Is there a simulation out there which is easy to use on windows?

[millman]

Just googled Docksteader valve gear simulator and reading the blurb it says Windows XP will unzip the files, I don’t know much about computers, or anything else come to that but maybe find someone still using XP.

[uuu]

I run Docksteader on my Windows 10 machine with no problems.

Wilf

[bobb]

Thanks Wilf,
I can get CD to run with Allan gear on Windows 10 but it displays two error messages. I don't think these are of any consequence, however, so I'm going to try to run it. I've set out the gear as I believe it should be on CAD, so will enter the LBSC data and my own and see how it turns out. I might then make a hard model just to be sure.
Bobb

[GWRdriver]

bobb,
My first mentor (ca.1966), a tool & die maker by trade, was building a MABEL when I came under his instruction. He was quite vocal in his opinion of LBSC's "words and music" in that there were errors in dimenisoning which caused him to have to remake much fiddly work and leave holes where no holes should be. At that time neither of us had any experience in the fine old British tradition of never modifying drawings when errors are found, but I digress. One thing he mentioned specifically was that components of the valve gear were incorrectly dimensioned which caused him to have to relocate holes in the frame plates. I can't now recall precisely which holes were affected, or how far they needed to be moved. That may be part of the problem you're having.

[bobb]

Hi all responders,
Thanks for your interest. I have tried to use Dockstader's model for the Allan gear but it is a frustrating programme to manipulate as I can't save the data (it reverts to start up if you try to open a saved application) so I have to take a screen dump and print that off to use when starting again! Also, it is beyond me to understand the layout of his model in terms of the link mechanism dimensions. I think the way forward is to make a physical variable model using aluminum parts. As far as I can determine, the LBSC design does not seem to impart the required valve travel in full gear and the mid gear travel is also incorrect. The mock-up should reveal the correct layout (hope!). Using CAD, I have determined a lot of the key dimensions for the physical model. We shall see, won't us!
Bobb

[uuu]

For the valvegears I've been playing with, I use File-SaveAsDimensions before closing. This creates a .dso file with all the settings - then I use File-OpenDimensions to retrieve them later. This allows me to save multiple versions of the design I'm working on.

Wilf

[brucevoelkerding]

I run the Dockstader Program on Windows 10. Similar to Wilf I am able to save the Dimensions.

I thought about building a Mabel many Years ago and accumulated some Notes.

o on page 714 Model Engineer 19 Aug 1966, I have the 1/2" Dimension from "Top of Frame" to vertical position of the "Rocker Shaft" crossed out and replaced with 5/8". Since I never drew Mabel in CAD, I think I must have read that somewhere.
o I have a Note "appears Valve Centerlines can move inboard, see Model Engineer 16 Aug 1974". I was thinking at the time of the Possibility of making the Saddle more prototypical.
o somewhere I came across a Build Series of Mabel. As I remember it continued up to finishing a running Chassis. Unfortunately, I do not know where it is located.

Bruce

[brucevoelkerding]

there is a short Build Thread here -

www.homemodelenginemachinist.com/threads/3-1-2-gauge-2-4-0-locomotive.4858/

By the way, there is also a Build Thread for the Boiler -

www.homemodelenginemachinist.com/threads/making-a-boiler-for-a-3-1-2-gauge-locomotive.8401/

However, I am sure there is a more complete Build Thread out there, I just can not find it. I think it was done by a Canadian Fellow.

[VGC]

For those who want to know why Dockstader's program works on some PCs from 2010 but not on some others: There are two different ages of the program available on the WWW, see trumpetb.net/loco/

[bobb]

Again, many thanks for your posts. I have now drawn out the LBSC dimensions on CAD and amended them so that they are more or less correct, still a bit of iteration to do before I am satisfied it is as near spot on as is practicable. The main error which he (or the draughtsman) seems to have made, is that the rocking lever changes the direction of travel of the valve spindle, so following the drawings shows an error of 3/32" equivalent to the lap of the valve. I have assumed a positive lead of 0.007" so lap + lead is 0.100". This gives an angle of advance of 11.52 degrees, you need to establish that first and then work backwards from the valve spindle displacement. The rest is a question of iteration. It will be much easier if I can check things out using Dockstader's model, so thanks for the guidance. I hope to be able to solve this conundrum for once and all and if successful will find a way of letting other builders know.
Bobb

[ettingtonliam]

If it works, then put an entry in the 'Errors on Drawings' section