Since I originally created this elbow in HO scale it seems reasonable to discuss it a bit before re-creating it in O scale.
This is a solid elbow and I am not going to get into the actual process of creating it .. that’s simply application of CAD design. Instead I want to focus on the “why” of the dimensions – keeping in mind that these are mostly specific to the HO version.
This represents a Class 150 24-inch elbow.
I uploaded a single elbow to Shapeways:
Cost: FUD $7.33 – FXD $9.01 – From that you have to understand that $5 is for ‘handling’. If you have one elbow printed or 100 .. you have the $5 handling charge. I normally add a 10% markup so the cost for FUD would jump to $7.33 + $.73 = $8.06. Shipping is a flat rate $5. That means ordering ONE elbow in FUD would be $8.06 + $5 = $13.06 .. OUCH!!
The way to get around that is to order in quantity. If you had nine friends (optimistic) who each wanted 10 of these as you did and then you had me put 100 elbows into a mesh the price changes quite a bit. For FUD then you would have a cost of $238.00 + $5 shipping for a grand total of $243.00 .. which means that now the cost per part drops to $2.43 each
Is there a better way? Yep. Rework the elbow so it is in two parts .. like you would get in a plastic kit complete with locating pins/holes .. and use these as masters to make an RTV mold and then cast the things in resin.
There is a famous saying .. “There’s no such thing as a free lunch“. That still applies!