BB Section?

As good a name as any for now. It stands for ‘Battery Box Section’ – meaning the area above the frame and below the cab.

Version 4A – 1mm Radius

Waking up this morning I was looking at photographs of GP-7 locomotives and having my first cup of coffee and realized that the radius used on the hoods was not crazy excessive. With that in mind I changed the radius on the corners of the BB section from .3mm to .1mm – full size that would be from about 5-5/8″ radius to a 1-7/8 radius.

I have gone back and forth on this .. I suppose it really depends on the individual and who builds the locomotive (a made up world perhaps but even a fantasy has to follow some rules!)

Note the four rectangular slots around the opening. These were made to let the tabs on the bottom of the cab (Atlas U23B O scale) to lock in place. It worked fine and the cab locked in place nicely.

Version 4b – 3mm Radius

I separated the BB-section into Upper and Lower parts. This was to facilitate printing on an FDM to eliminate supports. Guide pins on the upper part snap into holes on the lower part to align the two.

I added the weight wells in this version. There is plenty of apace to add weights inside these wells. The biggest problem I see is having access to them. I recessed around the openings 1mm side and .040″ deep (hey .. cheap readily available .040″ polystyrene) for a lid. This required me to fill in the top of these wells which changed the rectangular slots to rectangular wells. The cab still locked in place so all was well with that change.

The major change is the addition of the EZ Lok FL-256-HI bushings. These are designed to be inserted using a soldering iron to press them into place, melting the plastic to secure them. The 256 in the name stands for the 2-56 machine screw threads they contain. This should allow be to secure the frame to the BB-section and allow later access to the wells to add or remove weight.

I placed an order for the FL-256-HI bushings with and they shipped the same day. Sweet. I have noticed that they usually give a”worse case” on the shipping – many times it is much faster.
Just a side note. The faces you see on the upper and lower parts of the ‘BB-section’ facing down .. were actually printed with those faces up. This enabled me to print the BB-section without any supports needed.

Here’s a look at how the frame and mechanism fit the BB-section. I added guide pins on the lower BB-section part with matching holes on the frame to align those parts. The screws will of course hold in place. The one thing I will need to do is drill/countersink holes in the mechanism frame for four of the screws but .. I will put that off until much, much later.
A closer look at where the countersunk holes will need to be (ok .. call it ‘approximately’ .. seems the best way to locate them would be to use a transfer punch to locate the holes. The biggest problem there is as to how to do this without screwing up the mechanism. Seems like removing the trucks would make the most sense.

Leave a Reply

Your email address will not be published. Required fields are marked *

The maximum upload file size: 100 MB.
You can upload: image, audio, video, document, spreadsheet, interactive, other.
Links to YouTube, Facebook, Twitter and other services inserted in the comment text will be automatically embedded.