Scratchbuilding a PRR 'FM' 40' flat in HO brass

[jbvb]

Moving this thread over from RR-Line. My first brass scratchbuild, working from John Porter's Oct. 1977 Model Railroader article.  To turn my 7 NMRA AP certificates into 8 plus MMR, I need to scratchbuild 4 cars.  Much more about the prototype in Ted Culotta's blog post:

 https://prototopics.blogspot.com/2018/04/pennsylvania-railroad-fm-flat-car.html

I've got decent soldering equipment and I'd like to be able to operate the car empty, so I decided to do it in brass. Here are the center sills soldered together with one side sill and 4 of 6 connecting plates:

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Here I've got the top flanges correctly centered, and I've started attaching the connecting plates.  Old (Radio Shack) 60/40 rosin core solder and Tix flux using the soldering tweezers of an American Beauty resistance unit:

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Here I've made the side sills and attached the connecting plates to one center sill:



The center sills have been connected and pinned to my soldering pad to attach the crossbearers:

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I'm using 1/32" x 1/16" K&S bar for the webs (the bolster ends are hidden after the sideframes are soldered on). I cut one 45" long piece for each web, another 22" piece for the sloped part. Once they're soldered to the top plate, they're well enough attached that I can file the necessary angle.

The most efficient way I've found to solder them is: Tin all surfaces to be joined, place everything where it will go and hold the top pieces down with the soldering tweezers. Then I help hold it in place with another pair of tweezers and hit the foot switch.

The picture shows a filed bolster at top right, an unfiled bolster center right and the five tinned pieces of the next bolster bottom right.

The bottom sheets of the bolsters get added once I've placed the brake pipes and handbrake rod in slots cut in the bolster webs.

(Previous post edited because I exceeded the character limit. But now one picture is repeated. Above text explains the last picture above)

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Top and bottom of the mostly-complete underframe:

 

Next I had to decide in what order to apply:

- bottom flanges of the crossbearers

- side sills

- end sills

- longitudinal stringers that support the plank deck.

I chose bottom flanges first, then stringers. Next solder the side sills on while the frame is resting on the stringers so the deck is flat, and follow with the end sills.

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Side frames attached to cross bearers and bolsters:





Sorry about the glitches above, this is my first try at posting pictures to the new (to me) Modelers Forum software.  I exceeded the 20,000 character limit, I'm informed.

[jbvb]

I filed down K&S 1/8" brass channel to make the ends.



The upper right corner joint was fixed the next day (March 6, 2021). Resistance soldering tweezers and an insulating soldering pad made this job go a lot faster than I could have managed with my gun and collection of irons.

[jbvb]

I decided I should insulate the trucks from the frame: A high-resistance DCC short could draw 2 amps without tripping a breaker. And there are plenty of 25- and 30-watt soldering irons on the market; they take a minute or two to warm up.



I used Kadee #158 'scale head' couplers. It had been years since I'd assembled a Kadee box. I marked and drilled #50, then tapped 2-56.

I soldered 1/16" brass pads to the bolsters and step-drilled the centers out to 1/8". The photo shows one time the drill found a spot maybe .020 off-center to start; I should have cut my marking lines deeper. I press-fitted 1/8" styrene tube in each hole and adjusted the height of the car. Then I tapped them 2-56. The truck screws expand the tube a bit for a very firm fit.

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After a test run and some adjustments, I applied 1/32" bar stock stringers.

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With the car body mostly complete, I started on the brakes:



I modeled the pipes coming out of the AB valve in two halves. The hand brake rod is installed but I couldn't add the brake staff etc. till the deck was on.

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I finished the brake equipment but decided to leave it off till I finished soldering - not the time to find out how temperature sensitive epoxy is. So I started on the stake pockets. Porter filed a notch into the side of his aluminum XActo miter box to shape the pockets. I used a .0625" slitting saw in my milling machine to make a slot in a piece of steel scrap. The saw wasn't running particularly true, so the notch is a bit wider than 6 scale inches.

Then I cut some 1.75mm strips of .010 brass. I pressed it into the slot with a small file's handle, then snipped each pocket off. I tinned the mounting surfaces of a dozen with my 100W gun. Then I located each (prototype spacing is uneven) and sweat-soldered them by placing one tweezer point on each mounting surface.



It took a while to work out the best technique for using my jig: hold the free end of the strip down with the blade of a screwdriver while pressing the file handle down. And a couple appear to have gotten pinched by the tweezers. But with solder, a re-do is usually possible.

I had the next dozen made.  Rope staples (4), grabs ( and drop steps (4) will come after

Footnote: My modeling caliper is a 1970-vintage Craftsman vernier with english & metric scales. The easiest way for me to use it for HO scale feet and fractions is to measure 3.5mm, 1.75mm, .875mm etc.

[jbvb]

After all 24 stake pockets were installed, I changed to Tix low-temperature solder and installed the end grabs.  Next I did the side grab irons, also with low-temp solder. I find the American Beauty likes this job best when set to about 80 watts.




The grabs are bent from Tichy 0.0125" phosphor bronze. There are two handednesses of side grabs. All 4 end grabs are identical, but all 8 need 4 bends each. This is because I didn't think I had enough #80 drills to drill 16 holes in .015 brass.

Next step (excuse my pun) is bending drop steps from DA .010 x .018 brass strip. I made the bonding surfaces as large as possible, but the Tix solder is fairly strong. Finally, 4 roping staples next to the bolsters.

Those were the last soldered parts. I cleaned the soldered assembly, epoxyed the brake gear in place and airbrushed the body. I blackened the projecting steps, grabs and stake pockets. I didn't have enough blackener on hand to dip the whole thing, and would be a bit concerned about corroding joints loose even if I did.

Were I doing this again, I would make the necessary jigs and silver solder at least the flanges to the side and center frame members. Maybe the bolster sub-assemblies too. I've made those parts shift a bit several times while applying coupler mounts, floor stringers and stake pockets.

[jbvb]

I decided to emulate the prototype's drop steps, where the steel strap was twisted 90 degrees at the top, using DA .015 x .024 strip. This mounting also avoided crossing the slight offset visible between the bottom of the side frame and the bottom of the end channel:



Happily, my flat-jaw pliers are about 15 HO scale inches wide. I first made 4 90 degree bends, making a 15" square shape with a gap at the top. Then I used the soldering tweezers at 80 watts to heat-anneal the brass mounting Ls. Then I twisted the Ls at the top 90 degrees with two pairs of pliers, tinned and sweated the step into place. Only two of the corner grabs came off while doing this, and they went right back on.

I also got a little clever with the roping staples (cable loops, possibly other names) next to the bolsters: To save myself holes, I used round-jaw pliers to bend a 180 degree J shape on the end of .0125" wire. Then I drilled a single #75 hole right above the corner joint of the side frame. I passed the wire through, touched it with flux and heated the bottom flange of the side frame over the hole. The solder from that joint flowed onto the wire, securing it. Then I cut off the extra wire inside the frame.

When the drill got dull doing the 2nd hole, I was really channeling model railroading from the B&W era: I picked up a fine stone, put the thickest lenses in my binocular magnifier and sharpened the drill. Took me about 5 tries to get a decent point, but it finished the job.

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Old MRs have shown me reasons to use brass; several figured in this project. Small metal details are much more durable than most other materials. An example is the Carmer Cut Lever. The Pennsy thought highly of them but they vanished before I started hanging around the tracks in the late 60s. There are etched versions but none match the pivot location and depth on the FM flats:



Heating brass wire red hot anneals or re-anneals it. First I annealed all but the ends and bent it to the basic offset shape:

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I heated it a bit more thoroughly than I planned, but I'm within the range in pictures:
 


I re-annealed the S-bend in the middle and punched a hole through the center with a steel pin. I didn't drill because I didn't want to remove material from something hanging off the end of an operating car. Pete Magoun gave me Cir-Kit Concepts 1/8" brass brads for doorknobs. But I hammered one through the small hole in the lever. Then I drilled the end sill channel. I tinned just the tip of the brad with Tix low-temp, touched the hole with flux and slipped the brad through. I put the tips of the tweezers on the ends of the brad at 70 watts for a few seconds:
 


The lever moves on the pivot. Getting the S-bend wide enough to punch is necessary, but doesn't always happen. Maybe a smaller hammer?