Long Hood – V1

All of the measuring one does only goes so far .. you need to do an initial test print (or at least I do) to finalize basic dimension. A long hood with 3mm radius on the end with the other end to fit the opening in the cab (hopefully) .. the idea is that once I get a good ‘draft’ hood I can then cut openings for things like radiators, doors, fans and so on. Those would be printed separately on a resin printer of sourced from aftermarket parts such as Atlas O scale.

Finished the ‘draft’ print of the long hood. I printed this at .15mm layers since it is just to get the dimensions correct .. still took 7 hrs 29 mins to print. I am pretty happy with it as it stands just a bit proud of the cab .. I think I can simply deepen the notch that fits around the tab at the back of the cab.

You can see that the .. call it the ‘filler flange’ .. *almost* fits .. you can see the same ‘too long’ bit at the end of the hood. I .. *think* I can deepen the notch I show later on to fix this. I won’t bother printing again .. can use an X-Acto knife to tweak the notch and confirm that will work.

Yes, the cab overlaps the ‘b-b’ section a bit .. that is for the battery box appliques to be installed.(Red Caboose GP-9 detail parts)
and a look from the long hood side
The cab is an Atlas O scale U23B part. The tab is made to lock into the Atlas long hood. I may do that .. but for now am just trying for a good fit .. things like locking tabs etc. will be after that fit is done correctly .. or at least .. “good nuff”

Back Walls

Printed off three different .. ummm .. call them “back walls” to the cab. I made the slot that the tab will fit into three different depths .. 2, 2.35 and 2.7 mm. Relatively quick to print so I can tell what works and what doesn’t .. just another example how ‘cool’ to be able to do this

What I am thinking is that I might be able to make tabs that fit on the lower inside of the cab, then a separate piece to fit the inside of the hood. I am trying (for the fun of it I guess) to not glue anything permanently but ‘snap’ everything together.


Darn near a perfect fit with the 2.35mm test print. Sweet.

Back Wall & Connector

With the basic dimensions needed from the last back wall test print I modified the CAD to create this.

  • Red: The back of the cab is open. This will fill part of that opening.
  • Purple: The tab hanging down from the back top center of the cab fits into this slot.
  • Orange: This will act as a stud .. sliding into the inside of the long hood to hold in place
  • Blue: These tabs support the back of the cab rear just under the windows.


The print came out nicely. I still need to make a change .. I just realized that the part labeled “slot for the tab on the cab ” .. in the drawing is purple .. it needs to be lowered to sits flush with the top of the “stud” (orange) .. so the long hood will sit flush against the fill plate (red). While annoying .. beats having this printed somewhere such as Shapeways and that mistake costs $ and time. No biggie, will fix that and re-print.


Like I said above, I realized that I needed to modify the back wall connector a bit so it would fit .. act like a plug .. the inside of the long hood.

I think that if I have to make multiple copies I will cast copies in resin. To do that I would want to simplify the design so I could use a single sided mold .. I changed the design to reflect that.

Long Hood Version 1C

I modified the long hood so that the top curve matches the curve on the Exhaust Stack. All of the pieces shown in blue are Atlas O scale U23B parts

I need to look at the undersides of the cutouts to make sure that the U23B fan blades will fit under the fan covers.

Same view with the headlight assembly, fans and exhaust stack in place.

There are still cutouts on the sides for things like radiators and doors


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