Chassis Construction - Counterweights

The next step was to mount the counterweights on the axles.  The key here was to get the counterweights flat and parallel to the plane of the chassis.  After filing each counterweight to remove burrs, I reamed the holes to fit the 1.2mm axles from Aspen.  I then carefully mounted each counterweight and bonded it with CA on the top face and on the bottom around the seal to the axle.  Some holes were not exactly perpendicular to the counterweight face... but for this part you only need to get the counter weight roughly correct - worst case you can file the front - because you really only see the front the counterweight (however the filing causes an aw shucks moment in a few minutes...).  So I mounted the counterweights on one side, and then set the chassis on its side with the counterweights up, I file them flat to each other and parallel to the chassis.  This eliminated some extra CA and generated a lot of brass dust.  The results of the mounting are shown in Photo 6. (Yes the two middle counterweights stick out about 0.010", there is some play in the axles and I didn't make them equal on the backside before taking the photo, which you can see because the wheels are out from the frame as well.).  I think I got the surface parallel to 0.005" without much difficulty.

Mounting note #1:  The K28 has only one large counterweight, it is on the third axle from the front, which you can see in photos or in a larger model.  The K36 has all large counterweights.  Note #2:  When the large portion of the counterweight is pointing up on the fireman's side of the cab, to correctly quarter the drivers, the large portion of the counterweight should point forward on the engineer's side (90degrees different from the fireman's side). Difficult to see that in a photo of only one side, that's where a larger model comes in handy.  The Aw Shucks moment:  it turns out that alcohol doesn't take off paint very easily, but combined with a 3 minute ultrasound soak to remove all the little brass filings, it took off some of the paint on some of the chassis.  This was a surprise to me because I have not had a problem with alcohol before, see Photo 7. 

While painting the counterweights, I touched up the chassis by hand.  I used Floquil engine black for the counterweights since they will be seen more and should match the engine body.  The finished chassis are in Photo 8.

 Chassis Construction - Frames

The Aspen kit comes with flat chassis frames that you need to bend 90 degrees to form the outside frame on the left and right.  I used a bending tool to do the job, but found it very difficult to get the bend exactly the same on both sides.  Getting it 90 degrees isn't hard (keeping it 90 degrees is another story) but if you don't do it exactly on the dividing line then you form a parallelogram and the frame has a little tilt to it...  In reality, the model interface is the flat unbent surface.  So as long as you are pretty close, you won't notice the difference when the model is assembled.  The outside frames could be a little higher on one side and won't see that even in a head on look.   The bent frames then need to have the pilot attached and the cylinder casting attached.  Assembly Note:  The bent frames are easy to unbend, but then are easily bent back.  If you do that more than once, it's easy to tear the brass sheet.  Because there isn't any interference issue, I ran a bead of solder on the inside edge of the bend.  That fillet makes the bends much stronger and after soldering you can visually bend the frames square (check in all directions), the fillet can be seen in Photo 9.

Before assembling, I modified the pilot to be able to take a real coupler.  I cut two of the support rods, bent them to match the existing bent rods (and they can be soldered to a support rod underneath if you really want, and filed down the pocket so that it will accept a Micro Trains coupler, see Photo 10.  I soldered the pilot onto the frame.  This was a little tricky because you need to make sure the pilot is flat and square to the frame.    It was within my soldering skill set (not novice, but not great).  I used a resistance soldering tool, held the pilot in vice with an alligator clip and held the frame using pliers.  It was very fiddly to get the parts to be flat, and square, and centered on the frame, during the heat application, and I had to unsolder/re-solder once or twice, but it worked.  If anyone has a better solution, I would really like to hear it!  Assembly Note:  you need to file the pilot frame to accept the cylinder casting in the next step.  It's not clear you need to do that (and the pilot doesn't extend that far back in the real engine, so you are filing away something that doesn't exist...), but a rectangular chunk of the two rear corners need to be filed - you can see that in the photo of the finished frame assembly below (look at the back corners of the pilot on the chassis that is holding up the chassis being photographed (lower left).  These I didn't make exact, they are hard to see in the model.

The cylinder assembly is pretty easy.  First I filed the back edge of the pilot (resting on the frame) roughly square to the frame, and then mounted with CA.  If the casting doesn't lay flat, you probably didn't file enough of the corner away!  Assembly note:  make sure the cylinder front faces front, don't ask me how I know...  I then added the castings that go in the holes in the rear of the cylinder casting, also with CA.  Make sure that the slit in the top casting is vertical, and make sure that the bottom casting has its two holes lined up vertically, with the smaller whole above, and either right above, or slightly to the inside.  [These parts only approximate the real valve gear linkages and pistons, I think that rotating the hole slightly inside will make valve gear assembly and operation easier, but I tried to assemble them perfectly one over the other.  We'll see later...]  The final chassis parts and frame parts are shown painted in Photo 11.

First Post

There are few blogs/websites that cover the scale Nn3/Nm/Nn2, and many of those are rarely updated.  I am going to give blogging a try, not because I have great modeling skills to share, but because perhaps it will encourage me to spend more time on the hobby and perhaps other Nn3 modelers will start or update their own sites.  I haven't used Blogger before, but it seems pretty straightforward at first try.

My current project involves resurrecting and building Apsen K series Nn3 locomotives. There is already an excellent article on building the Aspen K-28 in the Nn3 Handbook, written by Tom Knapp, so I will focus on some of my key learning experiences.  As is the case with a relatively new modeler like myself, there is sometimes a lot of technique (and the experienced modelers must have some really cool jigs...) between one picture and the next.

Locomotive Erecting Facility

My Aspen models were a mix of kits that I saved for and Ebay purchases that I got more cheaply over the past several years because they didn't run (two were dead and one would move, a little, and then stop).  Through a lot of trial, error, and testing, I've found that "Some fiddling was required" is an understatement with the Aspen valve gear.  I think in all of the built up cases the gear bound up and in at least one case that burned out the motor when the operator just cranked up the voltage.  One of the models had relatively smooth running valve gear, so I built up a K-28 chassis in an attempt to duplicate that gear set.  Note that without a "live" set of gear to look at, I never would have seen what was supposed to go where from the drawing in the instructions, or any photos.  Much of the gear needs to be bent, soldered or glued, typically in directions that are somewhat prototypical but not nearly what I expected.   That attempt, using the kit chassis that has the axle weights already installed by Aspen, ended only partially successful.  I could get it working, but not well.  In the end I stripped all three locomotives down, and totally tore the chassis down to parts.  I have left a couple of superstructures the same, but I also stripped a couple down to bare brass as well.  The locomotive parts, some partially reassembled, are in Photo 1.  Kind of looks like the erecting shop in a steam locomotive factory

The reason that I stripped everything down (I did leave the one example chassis, I will strip it later) was not to clean everything (a nice byproduct) but to re-align everything on the chassis from the ground up.  From a practical standpoint, once I had to remove the burned out motor on one unit, I found that I could easily check out the valve gear operation manually.  So my first recommendation to anyone working with an Aspen kit or fix is to take the motor out so that you can look at the drive train and run it by hand.  Fix it that way, because if you can't run it like a Brio engine on test track, the 8V motor sure won't.  I just used a superglue debonder and it came right off, just have to be careful not to get any near the motor seams.

 From my first attempt, I found three main root causes of drive train issues:  (1) fiddly is an understatement, the design is very fiddly, with a number of bends required to move various rods and levers around each other and these can get bent easily with handling or derailments; (2) the axles should extend equal distances on both sides of the chassis, with the correct wheel to wheel gap, equal side to side play (gears on the axles are centered in the mechanical gaps) and (3) the preinstalled counterweights on the axle ends were attached to the axles with seemingly random distance from the outside plane of the counterweight to the chassis - which makes it hard to cleanly put on valve gear and connecting rods.  I didn't take pictures in advance to illustrate, but I was disappointed that the kit chassis came misaligned straight from the factory.  As a result, I have spent parts of the last 5-6 weekends tearing down all of the chassis, stripping them of paint and getting ready for re-assembly.  The parts of chassis (still without valve gear) are shown in Photo 2.  I stripped with laquer thinner (brake fluid sort of worked, was very slow) and then primed with Tamiya clear metal primer (recommended by my local hobby shop) and then I used Floquil grimy black on the chassis (it's behind the outside frame so any black would work).

In the top left of the photo is a scrap of PC board with a thin brass shim soldered to it.  After using a caliper unsuccessfully, I made this jig to set the wheel height.  The axles are 0.510" end to end, by the time you subtract the wheel width, the correct 0.212" back to back wheel spacing and divide by two, I needed a 0.088" gauge that if put on the tire, would allow me to easily see the correct distance from outside of the tire to the axle end.  I would love to watch an experienced solderer at work and see the jigs they use in this scale.... getting a large flat surface wasn't easy ... but it allows me to see all four wheels on a side at once after each one is set individually.  After setting the correct spacings, and checking with a Republic Locomotive Works gauge, the chassis are shown in various states of assembly in Photo 3. 

In that photo, the two chassis on the left are complete, one shown from the top and the other from the bottom.  The third has everything but engineers side wheels installed, the fourth has the internal gears set, and the fifth is still bare.  The parts are shown on the right.  If you are doing this yourself, a couple of notes:  (1) There are six grey gears that are completely alike, except, two have smaller axles (and smaller axle holes); (2) The middle gear in the right of the photo has some bosses on it to keep it from rubbing on the wall, on two chassis those have been sanded down a bit (not by me) to fit the gap without binding (I am not sure why, except for length they look identical with K26 chassis); (3) one axle was longer in my chassis, not sure why, I used it on the worm gear, will move or file it down if it is an interference issue later.  I also placed Kapton tap around part of the structure to prevent shorts later, now is the time to install it (Photo 4).

The five completed chassis are shown in Photo 5, drying.  I used superglue to set the wheels on the axles - it won't prevent a determined push, but will help handle some mis-handling after the engines are completed.  I originally used it on the inside of the wheel, but ended up using it on the outside because it will be pretty hidden by the counterweights, and if on the inside the bead can interfere with the side to side play of the axles needed for good operation (there is only 0.020" on each side to begin with...).  I have never found a superglue applicator that I like, I always get too big a bead (even with a pin).  For this fine application I used a "syringe type" applicator tip, but dipped into the glue - I've never found the trick of using them to dispense CA glue.  I also like the small Loctite superglue tubes (like miniature toothpaste tubes) they stay sealed pretty well l- much less mess than bottles.

Well, this has taken a lot longer to write than I expected, so that is all for now.  Hope you found this interesting, write if you have tips/tricks for the assembly or see anything wrong.