February 11, 2023

Replica B-17 Bomb Release Switch

(Sorry Files are not available for this project… maybe in the future.)

This is a Replica of a B-17 Bomb Release Switch. This is part of a much larger wall art project that I am working on. (more on that in the future.)

All of the dimension were taking straight from the original plans from the B-17 so its pretty accurate (as far as I can tell to the real thing) although some dimensions were changed slightly to make it easier to 3D print. The larger project that I am working is modeled after the B-17G but these releases where used on Model E,F and (I think) early G models too. Although from my research there was also a thinner taller shield assembly box used on some planes.

Here is the design in Fusion 360.

Here are all of the 3D printed parts (before finishing).

Hardware for the release consists of a grommet, (4) 8-32 Round Head Screws, (2) 6-32 Flat Head Screws, and (4) 2-56 screws that where used in place of rivets (just in case I had to change out pieces from wear)

I started with a smaller switch but ended up using a larger 6 Pin Momentary 3 Way Switch that I found on Amazon.

It was totally unnecessary because it will never be seen but I modeled the inside of the box exactly like the original one so these Nut Plates are separate.

After sanding all of the pieces with 80 & 220 grit sand paper to begin assembly… the Nut Plates are aligned with filament pins and then glued to the box with CA (superglue).

The filament pins are trimmed on the outside with just a nub left and simulated rivet heads are glued on to cover them up. I used this method so it was easier to sand the box.

Here are the finished Rivets just like on the original box. After this step the box could be painted. (not shown)

Next the Spring Latches are attached with the 2-56 screws. These spring latches are for the indents in the handle and are actually functioning.  In case I ever had to change them I used screws instead of actual rivets. These are one of the things that are a little thicker than the real ones because they are plastic not metal.

Spacers are then inserted into the guard handle. (These spacers allow the mounting bolts to be tightened fully without binding the guards movement.)

The handle is then secured to the box with (2) of the 8-32 bolts.  You can also see how the spring latches work with the indents of the Guard.

I did add a recess to the box cover for the printed Decal. (The original cover would just be flat.)

The switch is then just force tapped into the cover.

These are the simulated Decals. The top one was printed in Red with a color change to white for the Text. It didn’t come out as well as I hoped (especially the E) so I printed another one in white filament,  painted it Red, then just sanded of the paint from the lettering. This is the one I used on the final build.

The decal is actually glue in place and the 6-32 screws are just for show. These screws originally held the switch in place.

The cover is then screws to the box with the other (2) 8-32 screws.

The switch tip extension is then just pressed onto the switch. Funny enough some 80 years later you can still find these for sale…. that is if you want to spend $39.  I didn’t so I printed one and hope it stays on.

A quick test of the handle and everything looks great so far.

One last detail was to print a decal and apply it to the handle.  The lettering is suppose to be white but I forgot the lettering on the actual decal would be clear so I should have painted under the decal white before applying it.

After installing the grommet the Bomb Release Switch is pretty much complete. (except of the mounting bracket shown in the beginning but that will come in to play later.

I should point out I purposely distressed everything to make it look old and used. I think the original overall finish of the box may have been black but I liked the OD green better. I’ve actually seen it both ways on B-17’s in museums so who knows. Finishes was one aspect I couldn’t find a definitive answer on in my 100’s of hours of research into this project.

The only thing missing is a spring for the Guard handle to return it to the upright position. (I still have to find or make one.)

I still might have to distress the screws a bit more as they stand out.

Overall this came out better than I could have imagined when I started this project.

Now that this part of the project is complete I still have a 100 or so hours to go on the rest of it.

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