Best Of Scratchbuild Project - CC&F Twin Trailer Flat Car

[cv_acr]

Tim: "Sticky" means it will stick at the top of the list of threads for the time being, so it can be easily found. It won't drift off the first page unless it's made un-sticky.

Nice work so far.

[BCR 570]

Thanks Chris - I always wondered what that term meant.


Problems
I suppose that with any project of this type, one is going to face a few challenges along the way.  I ran into two as I was about to attach the runways; fortunately I discovered them prior, as fixing them after the runways were attached would have been virtually impossible without starting over.

The first problem became apparent when I arranged the two centre sill/bolster beam/diaphragm assemblies together.  I realized that one of the bolster beams was off its mark by several scale inches and did not line up with its counterpart on the other side of the car.  Not only would this be unsightly when viewing the underside of the car, but also it would create major problems later on when adding the remainder of the bolster parts.  Fortunately I was able to very carefully chop the bolster beam away from the centre sill with a #17 blade without damaging the centre sill.  I had a spare on hand which I was able to glue back in place.  I suspect that I might have accidentally shifted the original when putting a square up against it.

The second problem surfaced when I placed the first centre sill assembly upside down on a strip of .010" styrene and attempted to slide the runway underneath the bolster beams and diaphragms - it would not fit.  A dial caliper confirmed that I had cut the runways from .015" instead of .010" styrene.  I suppose I must have put some .015" stock back in the .010" bag at some point.  As the runways had yet to be attached, the solution was simply to cut new parts from .010" x .188" styrene.


Adding The Runways
This is a fairly important and tricky step in the assembly process.  The runways are one scale foot shorter than the centre sill top plate, and must be attached parallel to and centred with it a distance of 8" apart.  In addition, the runway sits on top of the bolster beams and diaphragm plates which are level with the centre sill top plate ie. .010" higher.  The runways effectively comprise the deck of the car and will directly support the trailers, so the joints with the bolster beams and diaphragm plates must be strong.

I devised a controlled assembly arrangement in which the centre sill assembly was placed upside down on a .010" x .080" shim with a .030" x .188" shim in behind.  This was then pushed against a long, hard, straight surface (I used an aluminum track gauge) inside a magnetic gluing tray.  Next I placed .050" shims against the edge of the centre sill top plate to control the distance between it and the runway.  I then pushed the runway against the .050" shims and secured it there with magnets. Finally, I placed angle blocks against the ends of the centre sill top plate, and placed .040" x .040" spacers against the angle blocks to centre the runway within the length of the centre sill top plate.  The assembly was then ready for gluing:




I began by gluing the two bolster beams which were exactly perpendicular to the centre sill.  With everything else held securely in place, the only concern was to make sure that the bolster beams were all the way down onto the underside of the runway.  I then glued the diaphragms.  Because of the thinner attachment point to the centre sill, these were prone to moving around a little bit so I had to make sure that they were perpendicular to the centre sill when glued to the runway.  This was done with a small machinist's square.

I was very pleased with the way these joints turned out.  The runways are mounted securely to the bolsters and diaphragms, they are perfectly parallel to and spaced 8" from the centre sill top plates along their length, and they are centred within the length of the centre sill with a 6" inset at each end for the end sils.  I had a minor problem with glue creeping out from the bolster beams and onto the top surface of the centre sill, but I expect to be able to remove this with fine sandpaper. 

The following photograph shows the centre sill assemblies with runways attached.  The lower pair are resting upside down; the upper pair are right way up:




The next step is to add the cross ties or crossbearers, and the centre sill stiffeners.  There are 32 of these each per car, so I have a lot of new parts to make!


Tim

[BCR 570]

Crossbearers (Part 1)
We now come to the crossbearers which, together with the centre sill stiffeners, are the most numerous part on the car.  There are six on each side located between the centre and outer diaphragms, and another two on each side located either side of the bolster beam for a total of 32 per car.  They are perpendicular to the centre sill and provide intermediate lateral support for the runways on top.

I had hoped to use the smallest size of I-beam from Evergreen for these, which would simply have involved cutting them to length and notching the top flange.  I used the .060" I-beam on the first test section but the crossbearers were a little too large and could be seen extending below the side sills.  To achieve the correct size and the right look, I needed a .050" I-beam.  For the second test section I fabricated my own .050" I-beams from three strips of .010" x .030" styrene.  The look and fit was much better.

However, I was completely unprepared for the length of time it would take to make two sets of 32 crossbearers for two cars!  I spent one evening chopping all the strips, another two evenings assembling the I-beams, another evening squaring up one end, and another two evenings notching the top flange.  I could have built a few and cast them in resin, but that would have taken even more time and would have required the use of ACC, and I really want to stick with styrene as much as possible.  Anyway, they are now done and ready for installation.

I did save a lot of time by not worrying about the length of these.  During construction of the test sections I learned that I could make them longer than required, install them, and then chop the ends flush with the outer edge of the side sills.  I also did not worry about trying to square up the ends during assembly.  I knew that I only had to worry about squaring up one end as the other would be chopped off after installation, and I could square that end up after assembly much more quickly and accurately. 

The assembly process began with adding the top and bottom flange to the web using a .010" x .020" shim.  With parts this small and relying on capillary action to complete the glue joints, it is very easy to glue the part to the shim!  I countered this tendency by sliding the shim back and forth under the part until it had set up, but with 64 parts to make I went through a few shims!

After assembly I squared up one end with a file and then notched the top flange back at that end.  The crossbearers butt against the centre sill and the top flange of the crossbearer has to be notched back to clear the top flange of the centre sill.  As you might imagine, this took a considerable amount of time.

In the photograph below, the top row illustrates the assembly process, and lower down is a set of 32 crossbearers for one car (actually a set of 36 with four spares):




A few lessons were learned during this stage.  Firstly, depending on the car you are building, there will be steps which really test your patience and resolve, particularly where extensive parts duplication is required, and you just have to persevere.  I can understand those who state that they do not have the patience or are too lazy for this.  During this long process for these parts I alternated the work with continued progress on two current electronics projects and that seemed to help, so I offer that as a possible strategy.


Secondly, I saved a considerable amount of time by not worrying about the length or squared ends while making these parts.  This allowed me to focus solely on achieving a nice perpendicular I-beam profile.  As mentioned, the squaring off and cutting to length could be done later. This type of time saving was a another important lesson in scratchbuilding learned.

The crossbearers are now ready to install, and I hope to be back with info and pictures on that in a few days.


Tim

[BCR 570]

Crossbearers (Part 2)
To install the crossbearers, I placed the centre sill assemblies back in the gluing jig upside down.  I placed .010" shims underneath the centre sill top plate and a .030" shim behind the centre sill web so that the assembly would sit perfectly level.  I fashioned a styrene block to assist in achieving a perpendicular joint with the centre sill.  The block has a .010" shim under the outer end so that it can sit level on top of the runways which were made from .010" styrene.

In the photograph below of an assembly in the jig, you can see the .010" shims under the centre sill top plate and the .030" shim behind.  To the left of the centre diaphragm, the six crossbearers have been installed.  Note that they extend past the outer edge of the runway - these will be trimmed later.  To the right of the centre diaphragm, the six crossbearers are ready for installation.  The styrene block used during installation is also shown:




The installation of this many parts has a fairly significant impact on the eventual quality of the model, so I limited myself to one centre sill assembly each evening and worked slowly and deliberately.  I started with the crossbearers on either side of the centre diaphragm and worked outwards from there.  After tacking each crossbearer into place, I placed the styrene block beside them to ensure that they were perpendicular to the centre sill.  I then applied more glue to fix them in place.

As has been mentioned, the crossbearers were left long intentionally to save time during their manufacture.  This was also true of the bolster beams.  The final step was to trim these flush with the outer edge of the runways so that they will butt up against the side sills.  The crossbearers were cut back with nippers and then dressed with a file.  The file was also used to trim the bolster beams and diaphragms.  The centre sill assemblies now look like this:




The upper pair of assemblies are resting on their inboard side, and the lower pair are resting upside down.

I have now been working on these cars for one month.  A total of eleven evenings were spent assembling and installing the crossbearers, so their completion is a major step forward.  I am glad to have them done.

With the crossbearers in place, the next step will be to fabricate and install the stiffening angles below them.  Unfortunately there are 32 of them per car too; hopefully they will not take quite as long!


Tim

[James Costello]

Looking great Tim - am amazing demonstration of patience too!

[ednadolski]

Fantastic work Tim!!   

Ed

[Coxy]

Tim, Have you considered making RTV rubber molds of the sub assemblies so that additional parts could be cast instead of fabricated?

[BCR 570]

Considered, yes, and rejected.  I ruled out doing any moulding because the introduction of resin parts would mean having to use AC instead of plastic cement.  I like the longer working time with the plastic cement and the ability to tweak parts if necessary.  On two occasions I have had to remove and replace parts, which would have been more difficult with AC.   I also live in a small apartment and space is always an issue, so I did not want to have to acquire and store all the required materials.  I only need two cars, and once past the crossbearer and stiffener stage, the need to replicate parts will no longer exist.

Tim

[DKS]

Tim, one thing to tuck in the back of the mind... styrene has this nasty habit of occasionally warping over time (sometimes over a period of months), especially when it's been exposed to plastic solvent repeatedly. I recall you mentioned using a metal weight down the middle? If it were me, I'd rely on this weight to help fight any possible warp. I'd think in terms of having the weight precisely fit the space between the two assemblies, so that the plastic can be bonded directly to it. Just a thought...

[BCR 570]

styrene has this nasty habit of occasionally warping over time (sometimes over a period of months), especially when it's been exposed to plastic solvent repeatedly

Yikes!  During the build I have been constantly focused on keeping everything perpendicular and square - warpage would be a shame after all the time spent on this.  The assemblies have really started to firm up following installation of the crossbearers and stiffeners, and once the two halves go together and the side sills go on the opportunity for warpage should be limited.  The two test assemblies are very rigid and strong.  Where warpage is likely to occur is at the ends of the car where the centre sill top plates extend past the centre sill web.  These will be quite vulnerable until I have installed the coupler boxes and end sills.

Yes, the metal weights have been designed to fit precisely between the centre sills.  There will be six of them occupying the spaces between the bolster beams and diaphragms.  All will be machined to a thickness of 070" and laminated to the inside surfaces of the centre sill webs, so hopefully that will help avoid lateral warpage as you suggest.

I appreciate your suggestion.

Tim

[BCR 570]

Centre Sill Stiffeners
Well they didn't take quite as long!  Simpler assembly, less finicky installation and a long weekend have got me through this step sooner than I had hoped for.

I have been referring to these parts as centre sill stiffeners, but I would surmise that their primary function is to reinforce the butt joint between the centre sill web and the crossbearers above.  The stiffeners are made from angle stock and are located vertically on the centre sill beneath each crossbearer.  They extend down to the bottom flange of the centre sill, and likely reinforce that joint as well.

I assembled and installed the stiffeners for the first test section after completing the centre sill with the bottom plate installed, so each stiffener had to be cut and filed precisely to length to fit between the crossbearer and the bottom plate.  On a test section with a few stiffeners this was not too onerous, but on the full model with 32 stiffeners, an easier approach was required.  For the second test section I left the centre sill bottom plate off, left the stiffeners long, and trimmed them after installation and prior to adding the bottom plate.  Much easier.

The stiffeners were estimated to be four inch angle stock, so I assembled them from a strip of .010" x .020" styrene and a strip of .010" x .030" styrene.  The .030" wide strip was stood on edge against an angle block, the .020" wide strip was slid into position against it, and the joint was then glued.  When they were dry I chopped and filed one end square.  This end will go up underneath the crossbearer; the other end will be chopped off and discarded.

The photograph below shows the assembly sequence at top, and below is a set of 32 stiffening angles (actually 36 with four spare) for one car:




To install the stiffeners, the centre sill assemblies went back into the gluing tray, this time resting on their side with a .030" shim underneath and a .010" shim behind so they would sit level.  I made a styrene block to help keep them perpendicular during installation.  The block was fitted with a .050" shim underneath at the outer end so that it would sit level on the centre sill web.  The parts were then primed with glue and slid into position with the block beside them to act as a guide.

In the photograph below, you can see the stiffeners installed to the left of the centre diaphragm plate.  Note that they have been left long and they extend past the bottom of the centre sill.  On the right you can see that I am halfway through installing the stiffeners, and the remaining three are visible in the foreground.  The styrene block is in place up against the third stiffener.  Another centre sill assembly with stiffeners already installed is perched on top as a guide to remind me which way the angles should face:




After installation the assemblies were left alone for an evening to finishing curing.  The next day I placed them in turn on a steel block and trimmed all of the stiffeners flush with the bottom edge of the centre sill.  I then used a file to ensure that they were completely flush and would not interfere with the mounting of the centre sill bottom plates.

Here are the assemblies after installation and trimming of the centre sill stiffeners:




I am very pleased to reach this stage of construction prior to the end of the long weekend.  The new school year starts in earnest tomorrow and my modelling time in the evenings will now be less than it was.  The assembly and installation of the crossbearers and stiffeners is a major step forward with 64 parts added to the models.

The next step will be to install the centre sill bottom plates.


Tim

[BCR 570]

Centre Sill Bottom Plates
Now that the crossbearers and stiffeners have been installed, the centre sill bottom plates can finally be added to complete the centre sills.  The bottom plates were cut to length from strips of .010" x .080" styrene to match the top plates.

Prior to installation of the bottom plates, the bolster stiffeners were added to the outside of the centre sill web.  These blocks were made from .030" x .060" styrene and were needed to help ensure that the centre sill bottom plates remained clear of the notch for the centre bearing plates.  The bolster stiffeners extend up past the bottom of the centre sill web slightly, which meant that they could be used as a stop when locating the centre sill bottom plates on either side of the bolster.

The first pieces of the centre sill bottom plate to be installed were the sections at each end.  These extend from the end of the centre sill web to the outside edge of the bolster.  The centre sill assemblies went back into the gluing tray on their sides with a .010" shim behind and a .030" shim underneath.  The centre sill bottom plate end sections were then stood on edge and glued in place:




The styrene block was used to push against the bottom plate sections while gluing in place.  Once they were dry, the centre portion of the bottom plate was added.  This part was longer than my largest angle block, so I used a long strip of heavy styrene strip between the part and the angle block to hold it in place while gluing:




In the photograph above we are looking down between the steel blocks and the assembly is upside down with the bottom plate in place.  You can see that the stiffening angles extend all the way down to the bottom plate and provide additional material for the bottom plate to bond to.

The last sections of the bottom plate to be added extend along the taper from the inside edge of the bolsters to the outer diaphragms.  The outer end of these sections was placed against the bolster stiffener, and the inner end of these sections was cut to length and bevelled slightly to mate with the centre portion of the bottom plate.  Here is a closeup of this section after installation:




When these sections had set, the joint between the centre and tapered sections was filed smooth.  The outer end of the end sections was sanded flush with the ends of the centre sill web.  The centre sill now has its full I-beam profile and is complete.


First Stage Of Assembly Complete!
With the centre sill assemblies now complete, some time was taken to clean them up, including minor filing and sanding away of irregularities, and erasing of pencil marks.  There were several gaps where the diaphragms bottom plates meet the centre sill bottom plate, and I was able to insert some styrene fillets and sand the joints smooth.  The bolster stiffeners, having done their job in helping to locate the centre sill bottom plates, were filed down level with the centre sill web.

Here are the completed assemblies, with one pair upside down and the other showing their inboard and outboard profiles:




This marks the completion of the first stage of construction for these models.  The existing assemblies now comprise 103 individual pieces of styrene, and they have reached the stage where they are now ready to be joined together.  That will have to wait for arrival of the custom tungsten weights which will go between the centre sills, and they are not due to arrive for another month.

Fortunately, there are other parts which I can work on in the interim.  I will turn my attention next to the side sill assemblies.  I am really pleased to reach this stage of the build, and it will be a nice change of pace to set these assemblies aside for a while and work on some new parts. 


More soon,

Tim

[DKS]

An impressive display of craftsmanship... and patience.

[BCR 570]

Welcome Back
This project was set aside for a few months to wait for manufacture of some custom tungsten weights.  I had planned to work on some other parts in the interim, but instead got busy finishing the benchwork and first phase of wiring on the layout, and more recently have been focused on finishing some equipment projects.

The custom weights arrived late last year, and with other projects reaching completion, I am looking forward to getting back to work on this project.


Tungsten Weights
One of the challenges with an 85 foot flatcar, or any flatcar for that matter, is incorporating sufficient weight.  My effort to duplicate the prototypical construction of these cars makes that even more difficult.  Fortunately the double centre sill design provides a space in between in which to conceal weight.

The width between the centre sill webs is .070".  Between the bolsters there is space for a weight 4.5" long with a depth of .185".  This centre weight would have to be tapered at each end to fit inside the centre sills.  In addition there was space at each end between the bolsters and the couplers for a weight .425" long and .080" high.  Having had prior experience with ordering custom weights manufactured in 99.99% pure tungsten, I ordered two sets of weights for these cars.  They are manufactured in China. 

During this project I have been making use of the nearest thing available in N Scale, which is the Minitrix 85 foot flatcar.  I actually obtained one with the intent of kitbashing it, but there were too many differences.  It has been very useful, however, for engineering my model, and will shortly be used for different coupler trials.

The Minitrix model is the same length as the car I am building, and comes with two steel bars which fit into a cavity in the centre sill.  These two weights add up to 0.314 ounces or 8.90 grams.  Here is the Minitrix car with the two weights removed:




In comparison, the tungsten weights for my scratchbuilt car add up to 1.229 ounces or 34.84 grams.  Here is my car in its present form with the three tungsten weights which will go inside:




The NMRA's RP20.1 Car Weight Formula specifies a weight of 1.4375 ounces or 40.75 grams for an 85 foot car in N Scale.  My scratchbuilt model with its tungsten weights will come in at about 85% of this recommended weight, but significantly heavier than the Minitrix model.  With metal wheels the car will reach 90%, and with brass castings for the brake equipment and etched metal hitches, we might be just about there in terms of desired weight.

So it is now time to move on to the second phase of assembly, which will see the two halves of the car joined together with the weights in between.  This project will then begin to resemble something like an actual freight car.


Tim

[SirTainly]

Outstanding work as ever Tim, good to see you back on this project!