Sign my
GuestBook

NS class 5000

Chassis construction

The first cut, I declare this project for STARTED!!

Generally it is recommended to cut etched parts out of a fret by cutting the tabs with a sharp knife on a hard surface. You will see me do that later in this build. This applies to the most common form of etched frets: 0.5 mm sheet with half-etched tabs, so 0.25 mm. This fret however is no less than 0.9 mm thick and the tabs are not half-etched. I did not even attempt cutting them with a knife but got out my jeweller's saw which made short work of the strong tabs. The discolouration of the brass sheet show its age.

 

A trail assembly to get a feel how every ting goes together.

All but one cleaned and de-cusped. The right hand frame plate was left unchanged to show the huge impact of a bit of sanding of the sides on 1200 emery paper.

I filed all cusps off all around. Technically it is not necessary but I hate to see cusps, remainders of the etching process. It is sloppy work of lazy builders. So I removed them. I also did this on all sides of the spacers. This was a bit of a miscalculation. The cusps on the recessed sides (red lines) have been calculated into the width of the etched spacers. A little bit of filing would have made them fit perfectly but filing the cusps away completely to obtain a a flat side was a bit too much. The spacers now have a bit of play loosing much of their function as, well, spacer. I will have to adjust the frame carefully before soldering.

 

A trial fit of the middle axle bearing. I did not fit, as expected. Well designed kit have such holes a bit undersized. Etching is an inaccurate process and it is better to have them bit undersize than too big. It is up to modeller to open them up with a bit of reaming to get a perfect fit.

Much to my surprise I needed only a few turns to get a perfect press-fit of the bearing. I marked the reamer so I could quickly replicate the width of the bearing hole on the opposite side.

I will give three bearings an accurate position without play beforehand:

  • the two middle axle bearings, to fixate the lateral position of the frame
  • one bearing on the front axle; to fixate the longitudinal position of the frame

So the holes of these bearings are reamed to press-fit the bearing. They will also be soldered straight away into the frame plates. The remaining seven holes will be reamed more liberally giving all other bearings a play of say 0.5 mm.

Once I hook up the frame in the jig with the witness axles in place the loco frame will be fixated by the three bearings already soldered in place and the witness axles will have some liberty to move the seven other bearings to algin them correctly. Once the coupling rods are in place they force the witness axles to take the right position relative to the axle centres. Then I know all bearings are in once level and they are also in line with axle centres.

 

But before I start with that I will first address another issue. The model has a very ancient motor and gear. I will replace these with a good can motor and a 1:50 gearbox.

Frame, running board and motor loosely assembled...

...to determine the dimensions of the needed motor and gearbox.

I don't like the motor and transmission supplied with the  kit so I want to buy a High Level Kits Gearbox.

Choosing the combination of motor and gearbox depends on mainly two factors

  • will motor and gearbox fit in the loco
  • will the motor's max rev. and the gearbox' transmission ratio lead to the a prototypical top speed.

These two interdepencies need some iterations to choose a suitable combination. I quickly aimed at Mashima 1424, with a max rev of 15,000 rpm

Driver diameter 1,435 mm
Driver circumference 4,508 mm
Loc max. speed 65 km/h
Driver rpm

65,000,000 / 4,508 / 60 = 240 rpm

Motor rpm 15,000
Gearbox ratio 15,000:240 = 62:1

The suitable gearbox in terms of size would be a LoadHauler+ with a gear ratio of 60:1

I downloaded the gearbox profile sheet, printed it, cut out the appropriate gearbox and motor profiles and glued the profiles on styrene sheet.

I cut the sheet to size and drilled an axle hole.

 

This is how the LoadHauler+ with a Mashima 1424 would fit.

With the running board in place, still okay.

And with the boiler placed, still okay, although it will be visible. The motor end on the cab side will be a tight fit

But it wil do

The motor profile will fit easily into the firebox