Lowering Micro-Trains depressed-center flat

[nickelplate759]

So, I was cruising along, converting some old Kadee/Micro-Trains cars to body-mount couplers.
I got to an old 50' plug-door NKP car, converted the couplers, put ESMC wheels on the stock (50-ton, solid-bearing) trucks, then started wondering...

I'd never seen a picture of the car in question 84584, and wasn't sure what it really should be. I knew that the prototypes wasn't really a PS1, but didn't know what it was.    So I dug through some NKPHTS material I had on hand - freight car diagrams from 1962. 

Sure enough, there was the series (85475 - 85499).  But...
1.  They are GA-built cars, not Pullman PS1.   OK, I can live with that, given that no one sells a model of the GA car.
<edit>  It turns out that the ancient Bachmann 50' plug-door box is close to the GA car! Maybe a future project!</edit>
2.  They had 50-ton ASF A-3 Ride-Control roller-bearing trucks (MicroTrains sold them with their standard solid-bearing 50-ton truck).

So - now I am
1. replacing the trucks.  But I don't have a 50-ton roller-bearing ASF A-3 ride control truck - I don't think anyone sells 50-ton roller bearing trucks in N scale.  I do have some BLMA 70-ton roller-bearing A-3 ride control trucks.  The wheelbase is too long, but like the GA vs. PS1 compromise, it's as close as I'm going to get.

2. replacing the couplers, again, since the BLMA trucks make the car ride lower (which is a good thing, to be clear).

So -- I've basically had to undo the entire conversion and start over 

Good thing this is fun!

[Missaberoad]

50 ton roller bearing trucks is interesting for sure.

[nkalanaga]

Is the early KD/MT #1030/1032/1033 roller-bearing truck a 50-ton version?

[tehachapifan]

Research is a double-edged sword. On one hand, my spectrum-kissed brain loves it! On the other hand, I've discovered there are a lot more foobies out there than I ever imagined or wanted to know!

[nickelplate759]

Is the early KD/MT #1030/1032/1033 roller-bearing truck a 50-ton version?

Not certain.  Spookshow calls it a 70-ton Symington.   However, I've noticed that MicroTrains oftens fudged the wheelbase on the 70-ton and 100-ton trucks (which generally have a longer wheelbase than a 50-ton truck).         

Anyway, that MicroTrains truck is what I'm using for most places where I want a 50-ton roller-bearing.

[thomasjmdavis]

Just to see what the difference was, I measured  Kato 50 ton ASF A-3 and  BLMA 70 ton ASF A-3 friction bearing versions (both noted here- https://spookshow.net/trucks/asfa3.html ).  I took the outside measurements over the wheel rims, so that flanges don't count. 

Kato A-3 50 ton-   0.620

BLMA A-3 70 ton- 0.6225

You may get something different, depending on how much play there is in the 'journals' (ie- little bitty holes).  Or how much the plastic may have shrunk or swollen due to age, temperature, low humidity, etc.

The difference is .0025 

.0025 x 160 =  0.4  which is to say, 4/10 of an inch. 

My guess?  The Kato may be a little oversized, and or the BLMA a little undersize.  My recollection is in the real world, the difference is 2 or 3 inches between 50 t and 70 t trucks of the same type - that is, in scale, under 1/50 of an inch, which... well, I can't tell the difference without a magnifier.

[nickelplate759]

Interesting.
From the NKP equipment diagrams, the 50-ton ASF A-3 (roller bearing) has a 5'6" wheelbase.
The 70-ton ASF A-3 and 70-ton Barber S-2-C (both also roller bearing) trucks both have a 5'8" wheelbase.   So a .0125" difference (actual) in an N-scale model.

[thomasjmdavis]

Interesting.
From the NKP equipment diagrams, the 50-ton ASF A-3 (roller bearing) has a 5'6" wheelbase.
The 70-ton ASF A-3 and 70-ton Barber S-2-C (both also roller bearing) trucks both have a 5'8" wheelbase.   So a .0125" difference (actual) in an N-scale model.

I took a look at my C&EI diagrams, and see the same thing.  I think 5'6" was (is?) the AAR standard for 50 ton trucks- all the 50 ton trucks in C&EI diagrams- from old work cars to their last boxcars, had 5'6" wheelbases, with either 'solid' (aka friction) or roller bearings..

[nickelplate759]

Taking my own advice for once...

Before trying to repaint a Micro-Trains depressed center flatcar for NKP 2093  (NKP's one and only such car), I looked at the NKP equipment diagrams available from the NKP Historical Society.  A few interesting things caught my attention:

First, the floor of the depressed center part of the car is only 24" above the railhead, and the bottom of that car is a mere 7 3/8" inches (about .045" in N-scale).  The Micro-trains flat is going to need a scale foot of lowering to get there - I don't think I can get it quite that low, but some reduction is definitely called for.

Second - the 6-wheel trucks have 30" wheels!     The two other NKP heavy duty flats with 6-wheel trucks also have 30" wheels.   I've never come across 30" wheels before - how  common were they?    And second, Anyone got any ideas on how to model them in N-scale?  I've never seen them offered, and don't want to pay what it would cost to have NWSL to make a set.     ESMC has 33" and 28" wheels - my first thought is to stick with 33", as I think 28" will look positively dainty, especially since the car is almost certainly going to ride a little high even after lowering, but the reduction in ride-height from the 28" wheels is 2.5"

[nkalanaga]

I'd go with the 28 inch in this case, but that's just my opinion.  If you know someone with a lathe, they could probably make you a set of 30 inch wheels, just give them a pair of 33 inch and tell them to match everything except the diameter.  You'd have to scrap the larger ones to get the insulators, but it could be done.

Or, maybe, if they're to-scale, Z scale diesel wheels?  They'd have to be regauged, which would probably require new axles, but they should be very close to 30 inches in N scale.

[nickelplate759]

OK, decided to test 28" wheels.

On the right are NWSL 28" wheels (of which I had exactly 3 pairs handy, not enough for the whole car).  On the left are the original 33" Micro-Trains pizza-cutters.



I'm gonna go with 28".  Looks good to me!

Regarding lowering the car - I'm thinking that I'll go with however much will get MT 2004 (underslung) couplers to the right height.  It'll still be way too high, but better than it is now.   Getting the height right would involve moving the truck bolsters a little closer to the ends and machining out a good deal of the cast-metal underframe.    The car is just an approximation of NKP 2093 in any event, and I'm not going for five nines of accuracy here.

Here's the 28" wheels (on the right) vs. 33" pizza cutters on another car (different side-frame style though).

[nickelplate759]

I've decided to go ahead and lower a Micro-Trains depressed center-flat, to model NKP's one and only such car (NKP 2093).

 I started a thread back in Crew Lounge last month ( https://www.therailwire.net/forum/index.php?topic=60721.msg837392#msg837392 ) but think it'd would be better to continue here.

To recap, the car sits far too high.  It's not a perfect match for the NKP car, but it's close.   I've decided to lower it enough to take MT 2004 offset-shank couplers.  They mount at .220".   That still won't be nearly as low as the prototype, but is likely as close as I can get without pretty much machining a new frame, and the car is about 90% frame.

To get to that goal, I need to lower the car about .060".   I can get about .015" by swapping the original 33" wheels for 28" wheels - note that the prototype car had 30" wheels, so 28" is closer anyway.   

Here's a picture of the car before starting, but with 28" wheels on the car end to the right of the picture.  You can see that the smaller wheels already help the appearance a little.


The question is how to achieve the remaining .045".

Here a couple of photos
MT Commonwealth 6-wheel truck (coupler removed already, ESMC 28" wheels installed):


MT underframe (bottom view):


Note that the truck has a significantly raised bolster, which is about .068" thick ( I measured ).
Note also that the underframe has a boss at the kingpin location (call this "body bolster").  It's just a tad over .030" thick, maybe .035" (hard to measure).
So, between the truck bolster and the body bolster I've got enough material to remove the needed .045" or so.  The question is how to go about it.

At the present time, both the car frame and the trucks are made of unobtainium, so I don't have the luxury of starting over if I screw this up too badly.

As I see it, options are:

1.  File the body bolster flat - that'll get me .035" lower, and I can probably get the rest by filing about .010" off the truck bolster.
2.  Drill out the truck bolster so it fits over (around) the body bolster.    Same result as option 1.  The body bolster is .173" in diameter, but since it's a little shallow there may be a challenge in securing the truck.  Also, the truck bolster is only .230" wide, so that leaves only about .030" of material on either side of the bolster (left & right) after the  hole is enlarged, which seems like it'll be fragile.
3.  Leave the body bolster alone, and file a channel in the truck bolster (lengthwise) about .045" deep.

Probably need a combination of either 1&3 or 2&3 to get all the way there.

Anyone have experience to share, or some better ideas?

[Chris333]

I chopped the truck bolster down a bit:

https://photos.app.goo.gl/dbt9niaAR3mCzPZz6

https://photos.app.goo.gl/N3vB9YzB64w7vCpMA

Pretty sure I filed the bottom of the metal frame perfectly flat.

https://www.rr-fallenflags.org/el/frt/erie-f7210jwa.jpg
https://www.rr-fallenflags.org/el/frt/erie-f7268.jpg
https://www.rr-fallenflags.org/el/frt/el7260alb.jpg
https://www.rr-fallenflags.org/el/frt/el-7201.jpg
https://www.rr-fallenflags.org/el/frt/highwide.jpg
https://www.rr-fallenflags.org/el/frt/el007285m20a.jpg

[Mark5]

Why'd you post that in crew? I belongs here. 

I have one of these for N&W. The first thing that struck me about the model (aside from ride height) is that the trucks need to be closer to the ends (at least for N&W this is so, haven't been able to find a pic of the NKP proto).

Mark

[mmagliaro]

Can you show a photo or prototype drawing?   I ask because it looks to me like the trucks are quite inboard on the model.  In your other thread, you mention moving them outboard a little, and I think that is a good idea and probably necessary.  If you take them up another .045", it looks like they will hit the underside of the body where it curves over and down to the depressed section.   You might have to change the couplers to something more compact to allow for this.  Maybe Z scale couplers.  This depends on your minimum radius requirements. 

Other than that, I think I would do what you're thinking - file down the body and truck bolsters as much as you can, and put a single
.005" PTFE washer in between them for smooth pivoting.   If the wheels start hitting the underside of the car, you might have to Dremel away on the underside to make cavities for the wheels to clear.

As far as "experience" with this, all I can say is that filing that underside can be done, but it's going to be a pain.  It's hard to get a file in there and really draw it flat against the underside.  This is a perfect job for a milling machine, where you can clamp that puppy under the head and just machine off everything in sight until you make the underside a completely flat, THIN surface, with nothing protruding to hit the truck.