I created a Tee, 90° elbow and a union to fit Evergreen tubing. This is ‘close to scale’ pipe in HO. I put that in quotes as 14 inches and down pipe is ‘nominal’ in size. Originally those NPS values were set to the same ID based on wall thicknesses standard at the time but as wall thicknesses changed the ID started to vary. Pipe 14 inches and larger have the same ID though.

(Fig 1)

Modeling Pipe in Scale
Evergreen tubing is widely available and relatively constant in size (nominal) so I use that to represent pipe in scale – see ‘
Evergreen No. 229 tubing has a 0.281″/7,1mm OD and 0.225″/5,7mm ID. This where we get into the “close to scale”. 12 inch pipe is 12.7 inches diameter. This means that Evergreen No. 229 tubing is 3/4″ undersized in scale. In HO that 3/4″ is only a bit over 0.008 inch .. so imy opiniion .. ‘Close Nuff’.

What I do is make short studs on the pipe fittings that slide into the ID of the tubing. In this case the stud will be 5,6 mm OD to fit the (nominal) 5,7 mm ID of the No. 229 tubing. The stud is 2 mm long .. enough to center the fitting for gluing the fitting and tubing together and the walls are 0.7 mm thick .. about as thin as you want for 3D printing. That the shape is curved helps.. The sectional view (Fig 1) shows this.


I have a gate valve, 90° elbow, Tee, Union and Flange designed. I had got this far when I stopped. I could add a 45° and 22-1/2° elbow if there is any interest.

Gate Valve

90° Elbow

It took a while to convert the elbow from my old CAD as I ended up using he old work as a guide and rebuilt the thing from scratch.




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