EMD F7 in SCALE

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Steggy
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Re: EMD F7 in SCALE

Post by Steggy »

rkcarguy wrote: Mon Jun 14, 2021 3:43 pmVery Nice BDD.
Thanks!
Food for thought. I put valve springs on my bolster pins (3/4" bolts), such that they keep a constant pressure on the "anti-roll bearings" so no shims are needed and there will be no click-clack if they are left a bit loose.
Way back when I was developing this design, I looked at several ways of "preloading" the anti-roll bearings, and settled on shimming. There's obviously some trial-and-error required to get the correct shimming, but once done, doesn't have to be monkeyed with anymore. I'm just careful when I detach the trucks to not get the shims and center bearings mixed up.
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Re: EMD F7 in SCALE

Post by rkcarguy »

Any more details on the disc brake rotors? That's one of my last things to tackle for my trucks....aside from getting my locomotives wheels on the lathe.
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Steggy
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Re: EMD F7 in SCALE

Post by Steggy »

rkcarguy wrote: Tue Jun 15, 2021 4:55 pmAny more details on the disc brake rotors? That's one of my last things to tackle for my trucks....aside from getting my locomotives wheels on the lathe.
What would you like to know? All I did with the rotors was reduced their diameter and drill/tap setscrew holes. They came with keyways.

The rotor I originally used came from Northern Tool, but is no longer carried by them. This site has what appears to be a suitable substitute. Scroll down to see SKU 1827.
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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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Re: EMD F7 in SCALE

Post by rkcarguy »

I've seen that rotor but they are only 1/8" thick, I was looking for something about 3/8" thick. Being I'm looking at 2-tons of train that's really going to want to go downhill on my 2-3% grades, I've got to have more robust brakes. I'm leaning towards using Honda Civic rear calipers which spec a minimum disc thickness of 8.2mm. These give me options of air over hydraulic and mechanical brakes via the e-brake lever arms.
I may have to just laser cut some discs, weld them to hubs and turn them, but it would be nice to be able to use an off the shelf part instead
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Steggy
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Re: EMD F7 in SCALE

Post by Steggy »

rkcarguy wrote: Wed Jun 16, 2021 12:04 pmI've seen that rotor but they are only 1/8" thick, I was looking for something about 3/8" thick.
Tolomatic offers rotors up to 1/2 inch thick in a variety of diameters, many of which are available with keyed hubs. They, of course, also have the calipers to go with those rotors.

I see no reason why you couldn't use straight air to the calipers and avoid the hassle of an air-over-hydraulic system. As always, KISS.
Last edited by Steggy on Wed Sep 29, 2021 1:16 am, 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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Re: EMD F7 in SCALE

Post by rkcarguy »

BigDumbDinosaur wrote: Wed Jun 16, 2021 12:42 pm
rkcarguy wrote: Wed Jun 16, 2021 12:04 pmI've seen that rotor but they are only 1/8" thick, I was looking for something about 3/8" thick.
Tolomatic offers rotors up to 1/2 inch thick in a variety of diameters, many of which are available with keyed hubs. They, of course, also have the calipers to with those rotors.

I see no reason why you couldn't use straight air to the calipers and avoid the hassle of an air-over-hydraulic system. As always, KISS.
Good to know on the Tolomatic calipers and discs, I'll have a look. I always worry about stuff like that though, because to many times I've gotten 5 years down the road and need another one, and they have changed or are no longer available. Use popular car parts and you can always get them for decades to come.
Regarding the calipers, what I was really wanting to do was flip the e-brake arms around so that they were sprung "on" (appears possible by swapping the springs from left to right and vice versa) and then use an air cylinder to release the brakes. I will have locomotive and whole train brakes, so no need to adjust pressure once I get the spring rate right. I'd either plumb up the hydraulic as a backup or just put some fluid in them to keep them lubricated and plug the brake line hole.
Regarding straight air to hydraulic calipers, I'd be concerned about lubrication and moisture in the air freezing up the caliper. One of Glenn's projects came with GM drum brake cylinders that used air to spread the shoes apart between the wheelsets, and they were corroded and frozen solid inside.
I already have a bunch of Parker air cylinders that are stainless bodies with HDPE seals which should work quite well and won't have any corrosion issues.
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Re: EMD F7 in SCALE

Post by Steggy »

EMD F7 in SCALE
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THE F-UNIT GETS NEW TRUCKS: Part VII

With the truck frames, bolster assemblies and wheelsets made, it was time to try assembling a truck and find out what wouldn't fit, or what had to be modified.

truck_assy_1end01.jpg
truck_assy_1end02.jpg

Above is one truck fully assembled, sitting on the erecting stand. Everything fit without any problem.

truck_inverted01.jpg

Above is a view of the truck's underside with the roller chains fitted. With this view, it should be clear why I had to be careful with my parts layout—there's not much room for error. Things got more crowded after installing the brake rigging.

The next step was to blast and paint all the parts, followed by final assembly.

truck_assy03.jpg
truck_assy04.jpg

In the above photos, the brake rigging has yet to be installed. Doing so was next on the list.

The brake rigging has a lot of "fiddly" parts that are a challenge for an old guy whose hands aren't quite as agile as they were when he was in his thirties. :roll: Ergo I started by contemplating the drawings I have of the pieces to make sure I understood what got attached to what. In the process, I concluded assembly would be easier with the trucks inverted. Below is a truck upside down in the vise, awaiting brake rigging.

truck_inverted02.jpg

Continued in the next post...
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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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Re: EMD F7 in SCALE

Post by Steggy »

EMD F7 in SCALE
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THE F-UNIT GETS NEW TRUCKS: Part VII, cont'd

Continuing with the brake rigging, I found it advantageous to assemble the inboard and outboard brake shoe hangers to the trunnions (the links that join the bottom ends of the hangers), since that is where most of the fiddly stuff is located. The below illustration was my working drawing, courtesy of Dave Newell.

brake_rigging_assy.jpg

I deviated slightly from the assembly drawing, in that I reversed the screws holding everything together so the nuts were facing outward. Doing so gave me much-needed clearance around the roller chains, which are very close to the brake rigging.

Below are some pictures of the truck—still inverted—with the brake rigging installed.

truck_brake_rigging03.jpg
truck_brake_rigging04.jpg

Below are some close-ups of some of the brake shoes, taken after the truck had been righted and placed back on the erecting stand.

brake_shoe_hanger02.jpg
brake_shoe_hanger04.jpg

After installing the brake rigging, the next procedure was to assemble and mount the brake cylinders, which are Precision Steel Car (PSC) parts. The end caps are attached to the cylinder body with 2-56 hex-head brass screws and nuts. Handling dinky parts like that is not something I can do very well, so I got some help in putting the cylinders together. I completed the cylinder assembly with linkage parts also sold by PSC. All parts were primed with an etching primer to assure a solid bond, followed by multiple coats of gloss black. I gave the paint three days to fully harden before handling the cylinders.

Assembling and painting the cylinders was one thing. Attaching them to the truck frames was another. This proved to be quite a challenge due to minimal working clearances and the size of the fasteners. The screws I had gotten with the trucks for mounting the cylinders were 2-56 × 1/8 inch hex heads, which proved to be impossible to use, one reason being the screw holes in the cylinders' mounting feet are partially obscured by the cylinder's body, preventing the use of a nut driver. Even with a miniature open-end wrench and a lot of patience, I could not get the screws started into the tapped holes on the truck frame.

Assessing the situation, I concluded the mounting screws were not long enough—only two threads protruded through the mounting feet, not quite enough to pick up the threads in the tapped mounting holes in the truck frame. Unfortunately, the next length available in a hex-head was 1/4 inch, which I determined would be too long for the depth of the mounting holes. I needed screws that were 3/16 inch long, but could not find a source that had them in hex head.

The solution to the problem was to use 2-56 × 3/16 inch socket-head capscrews, with split lock washers to take up a little length and to avoid having the screw head in direct contact with the cylinder's relatively-soft brass foot. While socket screws are not to prototype, they made it possible to complete the assembly.

The screws and washers I obtained are black-passivated, stainless steel, which are relatively unobtrusive. I was able to start and tighten these screws with a ball-end hex driver, although I was glad I had more screws than needed to mount all cylinders, as one or two found their way to the floor—naturally, never to be seen again. :D Mounting the cylinders was a laborious process, requiring several hours to complete both trucks.

Below is a photo of one of the cylinders after being mounted on a truck.

brake_cylinder.jpg

Continued in the next post...
Last edited by Steggy on Wed Sep 15, 2021 3:09 am, 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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Steggy
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Re: EMD F7 in SCALE

Post by Steggy »

EMD F7 in SCALE
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THE F-UNIT GETS NEW TRUCKS: Part VII, cont'd

With the brake cylinders mounted, the brake rigging was done and the trucks were ready for use. Here are a few more photos.
finished_trucks01.jpg
finished_trucks02.jpg
disc_brake01.jpg

In the below photo, I mounted the body on the chassis to get a better perspective on my handiwork. Being made to the same scale as the rest of the locomotive, the new trucks look like they belong.

body_on_frame_on_trucks01.jpg
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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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Dick_Morris
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Re: EMD F7 in SCALE

Post by Dick_Morris »

Nice!
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NP317
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Re: EMD F7 in SCALE

Post by NP317 »

Remarkable achievement making those two trucks!
They look perfect.
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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.
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