EMD F7 in SCALE

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Glenn Brooks
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Re: EMD F7 in SCALE

Post by Glenn Brooks »

BDD, I like the way you have modeled your trucks and brake rigging to represent the actual prototype. This is exactly the kind of brake assembly I would like to replicate on my Center cab rebuild.

One thing I missing, and don’t understand fully, is how you would connect your brake cylinder to the brake rigging on both wheels? Do you have a diagram or maybe a photo that shows the complete linkage -brake cylinder arm to each brake shoe assembly? In other words, what ties the two axles to the common brake cylinder?

Thanks much.

Glenn
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NP317
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Re: EMD F7 in SCALE

Post by NP317 »

Glenn:
A close inspection of the completed truck photos shows 4 brake cylinders per truck. Prototypical.
Also, they are non-functional. The actual braking mechanism is the disc brake on one axle per truck.
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Steggy
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Re: EMD F7 in SCALE

Post by Steggy »

Glenn Brooks wrote: Wed Jun 23, 2021 2:34 pm BDD, I like the way you have modeled your trucks and brake rigging to represent the actual prototype. This is exactly the kind of brake assembly I would like to replicate on my Center cab rebuild.
Thanks, but credit should go to Dave Newell for painstakingly modeling the prototype. I understand he spent many months poring over EMD drawings and then recreating the piece-parts and assemblies in CAD.
One thing I missing, and don’t understand fully, is how you would connect your brake cylinder to the brake rigging on both wheels? Do you have a diagram or maybe a photo that shows the complete linkage -brake cylinder arm to each brake shoe assembly? In other words, what ties the two axles to the common brake cylinder?
In my application, I am not using the brake rigging to actually operate the brakes—the disc brake on one of the axles in each truck provides stopping power.

That said, it is possible to make the brake rigging functional. Some friction material would be needed on the shoes and a single-acting, spring-return, double-ended air cylinder would be used to work the rigging. Below is an illustration of the brake rigging for one wheel.

Blomberg 'B' Prototypical Brake Rigging<br />(Dave Newell illustration)
Blomberg 'B' Prototypical Brake Rigging
(Dave Newell illustration)

As you study this assembly, visualize its mirror image to the right of the illustrated assembly—the mirror image would be for the wheel on the other axle. Referring to the illustration, note the inboard brake shoe hanger, which is item 3 on the right. It and the brake shoe are supported from the truck frame by a pivoting link, which is item 2 in the illustration. In the mirror image, item 3 would be to the left.

The aforementioned cylinder would be linked to the tops of the two brake shoe hangers, items 3. Pressurizing the cylinder would cause it to expand and push on both hangers, causing them to drive their respective brake shoes into contact with the wheels. Once the shoes have made contact with the wheels, each hanger would pivot on the brake shoe and support link (item 2) and thus pull on the trunnions, which are item 15 in the illustration. The trunnions, in turn, would pull on the bottom of the outboard brake shoe hanger, item 1 in the illustration, pressing the outboard brake shoe against the wheel tread.

When air is released from the cylinder, its return spring will cause it to pull on the inboard brake shoe hangers, releasing the brakes. Note that the outboard brake shoe hanger is attached to a cross-member (the brake shoe hanger beam) that is a structural part of the truck frame, which acts as the reaction point for the shoe.

Outboard Brake Shoe Hanger Support
Outboard Brake Shoe Hanger Support

The item 2 link acts as the reaction point for the inboard brake shoe.

Inboard Brake Shoe Hanger &amp; Support Link
Inboard Brake Shoe Hanger & Support Link

Although what you see is prototypical and will operate as described, it would not work very well as built. All pivot points ride on machine screw threads—the screws are 316 stainless, which would soon ream the holes. If I were to make the rigging operational, I'd replace the machine screws with stripper bolts to provide a better wearing surface.

NP317 wrote: Wed Jun 23, 2021 10:09 pmGlenn:
A close inspection of the completed truck photos shows 4 brake cylinders per truck. Prototypical. Also, they are non-functional. The actual braking mechanism is the disc brake on one axle per truck.RussN

Correct, and since both axles are linked through the roller chain drive, the one brake on each truck takes care of both axles.

I should note that the brakes on the locomotive are intended to stop the locomotive, not an entire train. The control car that I built to go with the F-unit has a disc brake of the same type on each axle—four brakes total (see below). As an aid to braking, I designed the control car to be quite heavy—about 450 pounds including the trucks—to avoid wheel slide during a full brake application. Adhesion is further improved when a couple of fat-a**es are on board. :D

Control Car Truck w/Brakes
Control Car Truck w/Brakes
Last edited by Steggy on Wed Sep 29, 2021 1:34 am, edited 1 time in total.
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Glenn Brooks
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Re: EMD F7 in SCALE

Post by Glenn Brooks »

BDD, makes sense now. Thanks!

Here’s a couple of photos I took last month unit in Hawaii, when I was studying brake systems, these are a brake system on a Whitcomb 44 toner center cab. Although in this case there Is only one brake shoe per wheel each side, not two, I suppose because the Whitcomb is a smaller engine than the F7.. Looks like the key is that brake hangers pivot off the wheels to draw opposite sides together...

Glenn
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rkcarguy
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Re: EMD F7 in SCALE

Post by rkcarguy »

I may replicate and laser cut the parts for the brake linkage and shoes for my S-12, but only for looks. We'll let the disc brakes do the real work.
The linkage for adjusting the brake shoe position is jewelry-like in scale and prone to damage in handling or derailments otherwise, and I think there will be a tendency for the linkage to try to "rack" when pushing on the taper of the wheel.
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Steggy
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Re: EMD F7 in SCALE

Post by Steggy »

EMD F7 in SCALE
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BODY CONSTRUCTION: Revisiting the Latches, Part I

Many pages back, I described the latches that keep the body closed. Without some kind of latching mechanism, the gas springs will try to open the body, not good when you are at speed. :shock: If you've ever had a car's hood fly open while making time on the expressway you know what I didn't want happening.

Anyhow, my first design was to use a miniature toggle lock, one per side.

First Design Body Lock
First Design Body Lock

These toggle locks worked very well—as long as the locomotive was stationary. :? They didn't cope well with vibration when barrelling down the track and after several instances of one or the other unlatching itself, I decided to go back to the metaphoric drawing board and devise something else. Some cogitating—always a dangerous activity for me, as well as lots of aimless scribbling on my sketch pad, resulted in a totally different design that I was sure would do the job.

The “totally different design” involves a spring-loaded plunger engaging a striker attached to the body. The plunger is mounted into a bracket assembly that is attached to something structural on the frame. A tab attached to the plunger makes it possible to unlock the body. Nothing to it!

Once I had a somewhat-focused idea as to how I would make this new-and-improved body lock, I went to work doing a layout and piece-part drawings. Here's the “worksheet” I did my layout on.

Second Design Body Lock CAD Layout
Second Design Body Lock CAD Layout

The new design worked flawlessly in CAD, so it was time to cut some metal. The striker is an assembly of a formed bracket with an elongated hole to engage the locking pin, and a perforated mounting plate to which the bracket is welded. The size and shape of the mounting plate was chosen to present plenty of area for bonding the striker to the body's Alumilite nose casting with epoxy. Perforating it meant epoxy could envelope the plate to produce a strong joint.

Here's a pic of the strikers after welding and cleanup:

Striker Assemblies
Striker Assemblies

The striker bracket is formed from 304L steel, the mounting plate is 1018 CR steel. I welded the assembly with stainless steel wire and 75/25 shielding gas. I chose stainless for the striker bracket so I wouldn't have to worry about corrosion of the exposed surface that would be in contact with the plunger.

Speaking of the plunger, I had to fabricate both it and the bracket assembly that would mount it. The latter is made from a piece of rectangular tube that after some drilling and reaming, was welded to a mounting tab made from CR steel. The tab's mounting holes are elongated to provide necessary adjustment. The bracket assembly is bolted to a removable part of the frame called the “tray,” whose primary function is to mount the electrical control assembly that is the “brains” of the locomotive. The tray is formed from 3/16 inch HR steel, so it is strong and rigid.

Meanwhile, the plunger started out as a round piece of 1/2 inch diameter naval brass, which is a good material for this application. Here's the drawing for the pin:

Plunger in CAD
Plunger in CAD

Here's a photo of the plunger undergoing machining:

Plunger in the Lathe
Plunger in the Lathe

I elected to single-point the threads, mainly because I could better-control the fit between the plunger and the nut that would be attached to it. I wanted that fit as unsloppy as I could make it.

Next was to make the release tab that would be part of the plunger assembly. Some CR steel, drilling and a little grinding here and there was all it took. Here's a photo of the plunger, tab and the hex nut that secures the tab to the plunger:

Plunger Assembly Parts
Plunger Assembly Parts

Continued in the next post...
Last edited by Steggy on Mon Dec 13, 2021 4:36 am, edited 1 time in total.
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Steggy
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Re: EMD F7 in SCALE

Post by Steggy »

EMD F7 in SCALE
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BODY CONSTRUCTION: Revisiting the Latches, Part II

Continuing from the previous post, here's how the plunger and tab fit together:

Plunger &amp; Release Tab
Plunger & Release Tab


I assembled the plunger assemblies to see how things fit:

Latch Assembly
Latch Assembly

Everything looked hunky-dory, so I mounted the latch assembly to the frame's “tray” so I could check it against the part of the body where the strikers would be mounted:

Latch Assembly on Tray
Latch Assembly on Tray

The two capscrews that secure the latch assembly to the tray pass through the side of the tray and thread into a tapping pad. This arrangement facilitates moving the latch assembly around to get the proper adjustment. It also give the mating parts lots of surface area to keep things from drifting out of place.

With the latch assemblies mounted to the frame, the next step was to verify the fitup between the strikers and latches:

Striker Fitup Check
Striker Fitup Check
Striker Fitup Check
Striker Fitup Check

The fit looked okay, so it was time to thoroughly clean the body area where the strikers would be bonded and mix some epoxy. I chose a JB Weld product for this application. Although not as strong as PC-7, the epoxy I used for joining the nose to the steel part of the body, JB Weld is more than adequate for this purpose and unlike PC-7, doesn't need a 24 hour cure to achieve full strength.

Since it was imperative that the strikers not end up in the wrong place, I secured them to the body with some tiny drive screws. The holes in the striker mounting plates are very slightly smaller in diameter than the drive screws, which interference fit retains them while handling the striker. The mating holes in the body are very slightly larger than the screws so the striker can be set into place without have to beat and pound on anything. There is no harm in the drive screws remaining—they are entombed in epoxy.

Needless to say, I wasn't taking any photos while I was busy gluing things together—cameras and epoxies are not drinking buddies. :D In fact, I somehow neglected to take photos of the strikers after they had been installed. I will get them next time the body is laying on its side, which will be very soon.
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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Steggy
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EMD F7 in SCALE

Post by Steggy »

EMD F7 in SCALE
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BODY CONSTRUCTION: Slappin' On Some Paint

With the new body latch project put to bed and some other mundane-but-necessary body work completed, it was time to get out the paint. Actually, there were still some other body details that needed attention, but they could wait.

First step was to blast the body clean. It's essential to “profile” the surfaces of the Alumilite parts before any primer is applied. If not properly done, the primer will literally fall off the Alumilite—it will not bond. Steel, of course, also benefits from the profiling effect of blasting. Here's the body after being blasted.

Nekkid Body
Nekkid Body

Next, epoxy primer was applied inside and out.

Primed Body
Primed Body

With those steps completed, it was time to topcoat it.

Making paint look good is not a highly-developed skill of mine. My painting abilities are adequate for everyday parts, especially parts that will be out of sight, but are not at the level that would be required to give my F-unit a good appearance. Plus my vision has deteriorated in recent years, so I was confident that if I undertook to do the finish paint it would turn out terrible. :roll:

With that in mind, I elected to have the finishing handled by an auto body shop whose proprietor and his daughter are very good at what they do. We went over photos I have of no. 401 in its 1950s livery and when they felt confident they could duplicate the original's paint scheme, they went to work. I also had them paint the interior of the body with my favorite shade of machinery grey (no photos of that—if you've seen anything in machinery grey you've seen the body's interior :D).

In addition to painting the body itself, they took care of grab irons, ladders, fan grilles, and other small external parts. These were all done from the same batches of paint to avoid obvious tint mismatches.

Anyhow, here is what the body looked like after some quality time in the spray booth, which is where these photos were taken.

Body in Paint
Body in Paint
Body in Paint
Body in Paint
Body in Paint
Body in Paint

Interestingly, the cost of the paint used was much greater than the labor, nearly twice as much, in fact. I recall when it was the labor that was the big number. Thank you, tree-huggers, for unnecessarily driving up the cost of everything.
Last edited by Steggy on Mon Dec 13, 2021 4:45 pm, edited 1 time in total.
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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makinsmoke
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Re: EMD F7 in SCALE

Post by makinsmoke »

That’s a really beautiful F unit.
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NP317
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Re: EMD F7 in SCALE

Post by NP317 »

A drooler of a paint job.
Matches the quality of your work.
I'll take it!
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Steggy
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Re: EMD F7 in SCALE

Post by Steggy »

makinsmoke wrote: Mon Dec 13, 2021 7:58 amThat’s a really beautiful F unit.

Thanks!

NP317 wrote: Mon Dec 13, 2021 1:38 pmA drooler of a paint job.
Matches the quality of your work.
I'll take it!

Thanks as well! I, of course, can't take credit for the paint job. All I did was do some planning.
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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Steggy
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EMD F7 in SCALE: Let’s see what she looks like!

Post by Steggy »

Here are a couple of photos of the freshly-painted body mounted on the chassis. There’s still more cosmetic work to be done, e.g., mounting grab irons and ladders. Also, the unit’s final electrical system isn't done.

f7_es01_rs.jpg
f7_fs01_rs.jpg
f7_fs02_rs.jpg

I'll be updating some more on body construction details in following posts.
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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