EMD F7 in SCALE

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BigDumbDinosaur
Posts: 360
Joined: Tue Jun 28, 2011 9:19 pm
Location: USA

EMD F7 in SCALE

Postby BigDumbDinosaur » Fri Dec 02, 2016 5:20 pm

EMD F7 in SCALE
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BODY CONSTRUCTION: Part II

Once I had all materials in hand and had worked out a general plan of attack for building up the body I went to work. As earlier described, the body's skeleton handles the important task of maintaining rigidity and panel alignment. Since the body components other than the nose and number two end bulkhead are steel, welding the parts to the skeleton was practical and would produce a strong assembly.

The first step was to attach the number two end bulkhead panel, which as previously described, is made from Alumilite. This item is secured to the rear of the skeleton with 10-24 stainless steel machine screws that extend through the skeleton and are secured with stainless KEPS nuts. Also, when the vestibule diaphragm faceplate assembly is installed, the screws that secure it pass through the skeleton framework, thus capturing the bulkhead and adding more support.

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Number Two End Bulkhead attachment: Outside

The above picture shows the attachment of the bulkhead from outside the body. Later on, the screw heads were permanently concealed by applying a small amount of PC-7 epoxy and sanding it smooth. Due to the tendency for PC-7 to entrain tiny air bubbles during mixing, causing a bit of surface porosity, a dab of Bondo® is used to achieve the final appearance.

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Number Two End Bulkhead attachment: Inside

The above picture shows the attachment of the bulkhead from inside the body. Once the side sheets are in place the attachment hardware is concealed from view, but accessible from the inside. Theoretically, the bulkhead could be removed, but I decided to use PC-7 to blend it into the side panels, making it decidedly non-removable. :D

It was necessary to attach the bulkhead to the skeleton before anything else, as the bulkhead implicitly sets the fore-and-aft positioning of the roof crown and side sheets.

Next came the attachment of the roof crown sheet. As received from Dave Newell, the roof crown was rolled very close to the correct contour, such that only minor adjustments were needed to get it correctly positioned. Careful positioning of the roof crown was essential, as its position determines the vertical position of the body side sheets.

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Skeleton w/Roof & Number Two Bulkhead Attached

The above picture was taken after the roof crown had been attached to the skeleton. Note the curved wooden blocks used to produce a stable support for the assembly. Working with the body inverted greatly simplified the built-up process.

The next step was to attach the fireman's side side sheet. The top edge of the sheet abuts the bottom edge of the roof crown, with the junction between the two being concealed by the roof line batten and the air intake grill when attached. The procedure was to simply set the side sheet into place, resting on the edge of the roof crown, and then secure everything with C-clamps. I used a rubber mallet to "lightly adjust" the side sheet into alignment with the roof.

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Skeleton w/Side Sheet Jigged: Fireman's Side

In the above picture, the side sheet is in place, ready for welding. C-clamps are like money: you will never have enough. :D Note the shop rag attached to the end of the bottom edge batten. The rag is there so I don't run into the batten and poke a hole in myself, bend up the batten—or both. :lol:

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Skeleton w/Side Sheet Welded: Fireman's Side: Inside View

In the above picture, the side sheet has been secured. There are many small welds rather than a few larger ones, both to assure that panels don't vibrate and to minimize the distortion that is endemic to sheet metal welding. To make all these welds, I used 0.025" wire in my MIG unit, with the voltage set low enough to produce one wire diameter's worth of penetration. The body panels are all fabricated from 16 gauge steel, which is also the wall thickness of the rectangular tubing used to build the skeleton. So there was a need to limit penetration to prevent localized cosmetic disturbance of the panels.

Incidentally, I use 75/25 shielding gas at 15 SCF/H for most of my steel MIG welding. 75/25 produces a less aggressive arc than straight carbon dioxide, making for smoother and more attractive welds.

More photos follow in the next post.
Science makes it known. Engineering makes it work.

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BigDumbDinosaur
Posts: 360
Joined: Tue Jun 28, 2011 9:19 pm
Location: USA

EMD F7 in SCALE

Postby BigDumbDinosaur » Fri Dec 02, 2016 5:20 pm

EMD F7 in SCALE
————————————————
BODY CONSTRUCTION: Part II cont'd

Here are some more photos and commentary.

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Skeleton w/Side Sheet Welded: Fireman's Side: Outside View

The above is what the fireman's side side sheet looked like after being welded to the skeleton. I should note that prior to welding, I prime all parts to eliminate potential corrosion problems in areas into which paint can't be gotten after welding. The particular primer I used is "ruddy brown" spray primer sold at Ace Hardware.

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Skeleton w/Side Sheet Jigged: Engineer's Side

In the above, the side sheet for the engineer's side is jigged and ready for welding. I no doubt could have used a few more C-clamps. :shock:

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Skeleton w/Side Sheet Welded: Engineer's Side: Outside View

Above is how the body looked after the side sheet for the engineer's side had been welded.


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Inside View of Body Structure
Above is an interior view of the body after welding. The wiring tubes that run through the outboard ends of the skeleton arches are not yet installed.

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Nose Casting Attachment Brackets

In the above, the wiring tubes have been installed into the skeleton arches, and the brackets that will eventually secure the nose casting to the main part of the body have been welded in place. Once the nose has been mounted these brackets will be bonded to the casting with a liberal amount of PC-7 epoxy, producing a structurally sound joint.

With all of the above structural work completed the next step was to attach the nose casting. I'll cover that in the next post.
Science makes it known. Engineering makes it work.

Andrew Pugh
Posts: 177
Joined: Wed Jul 12, 2006 9:22 pm
Location: British Columbia, Canada

Re: EMD F7 in SCALE

Postby Andrew Pugh » Thu Jun 15, 2017 11:13 am

I would love to read more regarding the mechanicals and control system when you get around to it BDD. I fully understand if further updates aren't a priority for you, just wanted to let you know I (and I'm sure others) haven't lost interest in your build thread.

AP

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BigDumbDinosaur
Posts: 360
Joined: Tue Jun 28, 2011 9:19 pm
Location: USA

Re: EMD F7 in SCALE

Postby BigDumbDinosaur » Sun Jun 18, 2017 1:22 am

Andrew Pugh wrote:I would love to read more regarding the mechanicals and control system when you get around to it BDD. I fully understand if further updates aren't a priority for you, just wanted to let you know I (and I'm sure others) haven't lost interest in your build thread.

I get back to it sooner or later. Too much to do and not enough time in which to do it.
Science makes it known. Engineering makes it work.


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