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Bernd:
As I mentioned in the Water Cooler section I have a question about expansion/reverse links. I know how it operates. The problem is the drawing on the engine I want to build. This would be Bertha the Steam Engine in the June-July 2000 Modeltech Magazine. There are dimensions missing. Below you'll find two drawings. The first is from the Bertha engine and the second is From Rudy's Steam Launch engine. Note that there are are some crucial dimensions missing, specificly the two holes where the valve rods will be connected.

On Rudy's drawing he gives the distance from the center of the slot to the two holes that the rods will be connected to.


Bertha drawing



Rudy's drawing



Rudy shows the center of the slot to center of the holes to be .281" and from center of slot down .312". The Bertha Steam Engine is missing those dimensions.

Can anybody tell me how you get these. I take it you just don't pull them out of thin air. The Bertha Engine has a stroke if 1" of that will help.

Bernd

Bogstandard:
Bernd,

No need to go to all that trouble, for the Bertha, the figure you require is 2.375" rad from the same rad centre position of the 3" to the centre of the slot.

You work out downwards from the centre of the slot using the dimensions given, to the bottom of the radius around the holes, then come up 3/16" to the hole centres, which means the centre of the holes are 5/8" from the centre line of the slot.

The Rudy's one is calculated out in a totally different way from the Bertha one.


John

Bernd:
Thanks John for that explination. I'll study what you said tomrrow as the brain is a bit foggy tonight.

Bernd

Bogstandard:
Kenneth,

I had totally forgot about that dimension.

Bernd needs to look maybe elsewhere on the plans for that angle of separation, then that should be a fairly easy calculation, as using what is shown, it cannot be determined.

I have also noticed that the third hole has no size or outer rad shown, if those two are missing as well, then difficulties will arise working out where that one should be.


Bogs

Bernd:
John,

Went back and looked at how you described finding the dimension from center of slot down to the two 3/16" holes. Why I didn't see that is beyond me.  :palm:

I went back and looked at the full plans and I can't find anything more, even in the write up there is nothing giving a clue on where to place those holes horizontally . In your opinion do you think one can take what is there and "guesstimate" the horizontal dimensions.? It seems to me all your doing with that link is place the whole works vertically under the valve for a full opening and closing of the valve in the steam chest.

I think I might have a way of getting approximate dimensions. I did this before to find a dimension of an HO scale drawing to be able to determine the size and shape of a part I wanted to create in 1 1/2" scale. What I did was copy the drawing into PDF formate. Then I scaled to a known dimension on the screen and was then able to find the size of the part that was not dimensioned. I'll post my results a soon as I get "round-tuit".

Again thanks for the help John.

Bernd

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