LBSC's Doris

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Erection Drawing of Doris

Jim Mullner

February 2022

Drawing Corrections

The information given in the Model Engineer articles is general pretty good but there appear to be issues in a few spots. Namely things will interfere if built to the dimensions shown. Here are a few of those areas that I was able to discern by modeling Doris in Solidworks.

If you are actually going to build an LBSC design make sure to layout the entire project using 2d or preferably 3d CAD software to avoid nasty surprises during real assembly and testing.

Please use the 3d model files presented here to check your work and review the details provided in the Model Engineer magazine articles. I recommend reviewing the original instructions and then reviewing the 3d model to confirm.

Buffer beam and frame

If angle is used to connect the buffer beams to the frames, recenter the rivets and also be aware using the angles will cause interferences later. But these are minor.

Leading and Trailing Coupling Rods

The thickness needs to be 15/64 inch not 1/4 inch. This resets the 3/16 inch dimension to 1/64th inch less too.

Coupling Rod Thickness

This rod also should be 15/64 inch thick instead of 1/4 inch.


After making the changes above, the crankpins need adjusted. The driving crankpin needs the 5/8 inch dimension to be 19/32 inch.

Feed Pump

If the brakes are built into the model, the lower fitting on the feed pump needs to be a right angle.


The brakes will interfere with the axle boxes and hornstays if the brake shaft is not shortened to 2-5/32 inches from 2.5 inches.

Middle Brake Beam

The Middle Brake Beam should be 2-1/16 inches wide, not 2.75 inches, to accommodate the above changes. See 3d model for details.

Drain Cocks

There were two issues here. First the handle on the tapered plug and the handle on the shaft must have the same distance between centers – use 1/4 inch. Second, the shape of the connecting rod had to be altered to let the shaft go through the approximate location in the bogie given without hitting and screws (almost flipped its profile) – the hole in the connecting rod should probably be slotted. See 3d model for details.


By lowering the connecting rod shaft for the drain cocks you need to put a clearance cut in the bogie bolster. See 3d model for details.


There are a number of issues here but the biggest is the vertical pitch of the firetubes. It really must be 3/8 inch (not 7/16 BARE). This will setup the upper features correctly.


The 5/16-40 tapped holes in the backhead should be at 1.25 inch not 1-3/16 inch from the top.

Regulator Lever

The center regulator lever needs to have its lower 7/16 inch dimension changed to 3/8 inch.



External Resources