Friday, 9 February 2018

DB Loco Assembly Tips

Parts List 

In addition to the 3D printed parts, the following parts must be obtained separately by the modeller:
  • Brass wire for handrails, etc. (0.4 mm, 0.6 mm - 3 x 300 mm lengths)
  • Air hoses - e.g. Detail Associates #6206 - 12 required.  (Vacuum brake hoses are included.)
  • Handrail Knobs (4) for uncoupling levers - e.g. Markits 1.5 mm (short) - available from Railwest Models.
  • Handrail Stanchions (optional) - A-Line D1070 or D1071.  Limited quantities available from Marbelup Models.
  • Vi-Trains Class 47 mechanism.  Limited quantities available from Marbelup Models,
  • Hollywood Foundry mechanism, with NorthYard Wheels and Mashima 1833D motor - see below for details.
  • DCC decoder and speaker (both optional)
  • Light Emitting Diodes (LEDs) for headlights 4 x 3 mm (sunny white) and optic fibre (2 mm)
  • LEDs (red and white) and optic fibre, if operating marker lights desired
  • lead or other weighting material
  • Kadee couplers #146 for scale coupler height,  #149 for HO coupler height (see below)
  • Kadee draft gear boxes #262 (supplied)
  • Fixing screws for body, couplers and fuel tank:
    2-56 x 19 mm, 4 required for central body fixing screws
    2-56 x 6 mm, 8 required, for remaining body fixing screws and couplers.
    2-56 x 12 mm, 2 required for fuel tank.
    Kadee #256 nylon screws can be used for the fuel tank, couplers and end body fixing screws.
  • Fixing screws for motor (ViTrains mechanism only) 2-56 x 25 mm (1"), 4 required - to be trimmed to required length.
  • Fixing screws for speaker M1.4 x 6 (slightly longer is OK) - 4 holes are included correct size (1.1 mm) and screws should make their own thread, tapping shouldn't be required.  Suitable screws are available from DCC Concepts - Part No. DCS-PHB156 or in assortment DCS-PHBSet.  Although described as 1.5 mm, the DCC Concepts screws are actually M1.4 thread.
  • Fixing screws for bogie sideframes - self tappers, 1 mm dia. x 3 mm long (8 required).  Suitable screws are available from DCC Concepts - Part No. DCS-PH103
  • Fixing screws for nose - self tappers, 1 mm dia. x 5 mm long (2 required).  Suitable screws are available from DCC Concepts - Part No. DCS-PH105
  • Paint and decals, as desired.

Underframe Preparation

Remove the support structure from the 3D-printed underframe.  Take particular care around areas with delicate detail, including the vacuum hoses and ... (details to be added).

Clean out the indicated holes with a 1.8 mm drill bit and tap with 2-56 thread.  Note that the four holes closest to the motor cutout are for the ViTrains mechanism only.  If desired, the coupler mounting holes can be drilled right through as the top surface of the underframe will be hidden by the loco body.

Underframe Holes to be Tapped 2-56 (viewed from below)
If intending to fit couplers at HO height, file out 1 mm from the bottom of the coupler mounting holes, as per diagram below.  The headstock is only 0.5 mm thick in this region.  Up to 1.25 mm can be removed, if required, to accommodate fine adjustment of coupler height.

Headstock Modification for HO Coupler Height

Bogies and Drive Train

There are two mechanism options: Hollywood Foundry and ViTrains.  The DB loco underframe is specific to each mechanism, so the choice of mechanism must be made at the time of ordering.

See comparison of the mechanism options.

Please refer to the separate assembly tips for:


The coupler height of the DB loco has been set at the correct scale height for WAGR/Westrail narrow gauge rollingstock, i.e. 12.2 mm (above rail height) rather than the HO coupler height (9.9 mm) which is commonly used for most Sn3½ models.  This has been done because the correct height "looks better" for modern locos and rollingstock.  For correct scale coupler height, use Kadee #146 couplers.  

Provision has been made in the underframe design to lower the couplers to match the HO coupler height by using Kadee #149 couplers which have an "overset" shank together with a spacer approx. 1 mm thick between the coupler box and mounting pad.  The bottom of the coupler openings in the headstocks is only 0.5 mm thick, and this thin section needs to be filed 1 mm deeper to allow for the lower coupler mounting height.

The #146 and #149 couplers are both "long shank" style which avoids the problem of the "glad hand" on opposing couplers from fouling the cowcatcher.  The suggested draft gear boxes are Kadee #262 (supplied).  Kadee suggest assembling the coupler so that the main part of the draft gear box is on the bottom and the lid is on top.  The draft gear boxes simply snap together.  

Due to the length of the DB loco and long end overhang, coupling of 4-wheel wagons next to the loco is not recommended on curves of 850 mm radius or less.  The loco itself will operate on curves of 700 mm radius, or slightly less, but the coupler overhang is probably the limiting factor.

Underframe Details

There are four large air pipes to be added to the air reservoirs on the underframe, as highlighted in yellow below.

Underframe Air Piping (viewed from below).
These can be formed from 0.8 mm brass wire, and glued into the holes provided in the air reservoirs and underframe.  

Approx. dimensions for the L-shaped pipes are as follows:
  • Front left: 5 mm + 8.5 mm
  • Front right: 13 mm + 8.5 mm
  • Rear left and right: 34 mm + 8.5 mm.
Note that the front right pipe should have a gentle upwards bend, about midway along the longer part, to match the height of the hold in the underframe.

DCC and Sound

The underframe is specially designed to accept a 23 mm square high-bass speaker (Soundtraxx 810129 or equivalent) if a sound decoder is to be installed.  The speaker faces downwards on a "sound duct" which has a "tunnel" through it for the front drive shaft.  

The underframe speaker mount include four holes, nominally 1.1 mm diameter, which are suitable for M1.4 fixing screws, 6-8 mm long.  Ideally, the holes should be tapped with a M1.4 thread, but the screws can be inserted without tapping.  (DCC Concepts sell suitable screws - part number DCS-NB14x6 or as part of an assortment DCS-Nbset.)

The recommended sound decoder is the Soundtraxx Tsunami EMD 645 Non-Turbo.  The Tsunami "AT" style decoder model 828048 is suitable and slightly cheaper than the TSU-1000 style model 827109.  More recent equivalents are also available in the Soundtraxx Econami and Tsunami 2 ranges.

Note: The above links are for the SoundTraxx web site.  SoundTraxx do not sell direct but their products are available from many retailers.

Body Preparation and Details

Take care when removing the support structure from the body, especially around the cab windows to avoid damaging the vertical dividers between the windows.  

Once the body has been "cleaned up", it is also necessary to remove the two temporary braces which link the fixing posts near the centre of the body, as highlighted in yellow below, as well as another one just behind the cab.  These have been included to protect the body during production and shipping, and must be cut away to provide clearance for the motor, etc.  These can be cut with a fine-toothed razor saw or a cutting disk in a rotary tool, at low speed.  

The ten fixing holes in the body shell and nose should be tapped with a 2-56 thread.  If necessary, clean out the holes prior to tapping using a 1.8 mm drill bit.

Nose Assembly

The nose is a separate 3D-printed part.  This has been done to avoid stepping on the sloping top surface of the nose from the 3D printing process.  Once the supports have been removed from the nose, a light sanding may be required on the bottom surface to remove the slight stepping present there.

Small holes have been provided to secure the nose to the cab with small screws, e.g. 1 mm dia. x 5 mm long.  The screws should be inserted from inside the cab, into the nose.  The holes are angled so there is some hope of reaching them with a small screwdriver.

Once satisfied with the fit of the nose, it can be superglued onto the cab, preferably from the inside to avoid traces of glue on the visible surfaces.

Handrails on Body

Starter holes are provided on the body for three handrails which can be formed from brass wire (e.g. 0.3 or 0.4 mm).  The starter holes should be drilled out slightly larger, e.g 0.05 mm larger than the wire size.

One handrail is inside the topmost recessed step on the left side of the loco, next to the radiator grilles.  The spacing between the holes is 3.5 mm (centre-to-centre).

Photo by G Stallard
The other two handrails are on the roof, adjacent to the recessed steps.  The spacing between the holes is 8.5 mm.  Photos indicated that the bends in the top handrails should have a radius of approx. 1.5 mm.  Radiussed corners can be formed by bending the wire around the shank of a drill bit, or using special pliers with round jaws made for wire forming.

Photo by G Stallard
Starter holes are also provided on the sides of the long hood for the handrails for the rear steps, and on the nose for the front handrails. - see below.

Handrails on Cab Front

Two handrails either side of central window:
  • Right side: 7.5 mm between hole centres
  • Left side: 7.5 mm + 12 mm between hole centres, with 65 degree bend between straight segments to match slope on nose.

Handrails on Top of Nose

  • Left side, on top step notch: 4 mm between hole centres
  • Left side, on sloping section: 8.75 mm between hole centres
  • Right side, on sloping section: 11 mm between hole centres*
* Front hole for this handrail is missing from some nose prints, but can be easily be marked and drilled.

Handrails on Front of Nose

See diagram below for the handrail shapes.  DB1581-1584 had straight handrails.  1585 originally had unique "curly" handrails but the hole positions are the same as for the straight ones, and it was later fitted with straight ones.  1586-1593 had angled handrails.

Handrails on Underframe

The 3D-printed chassis incorporates holes approx. 0.6 mm diameter to house the vertical handrail posts, typically cut from 0.6 mm brass wire.  There are also starter holes on the rear steps, and on the headstocks, for the end handrails.

One option for the long handrails is to solder each section of handrails from 0.6 mm brass wire.  Marbelup Models has developed a PDF template for the handrails which can be downloaded and printed.  Ensure it is printed at 100% size - check the scale on the bottom of the template to ensure the scaling is correct.
Handrail Diagram - Download PDF for Accurate Dimensions

Handrail Diagram (PDF)

On the real locos, the rear handrails and the rear end of the long side handrails have 2 fixing points near the rear steps.  Holes been provided in the underframe for the additional fixing points, if desired, which would entail soldering additional short lengths of wire to the respective handrails.  The vertical spacing between the upper and lower fixing points is 8 mm.

Use of A-Line Handrail Stanchions

An alternative, which is potentially easier than soldering, is to use preformed steel handrail stanchions available from A-Line (Division of Proto-Power West, USA).  These are available from various online hobby shops and/or eBay.  (Marbelup Models has limited stocks of these stanchions available at $15 per pack of 35 stanchions.  Each loco requires 16 stanchions.)

A-Line Handrail Stanchions
Although these stanchions are intended for HO locos, the two longest sizes are sufficiently long to be trimmed to the correct length for the DB .  The A-line part numbers are D1070 (extra long) and D1071 (long).  The stanchions should be trimmed at the bottom.  After trimming, file off any rough edges from the cut end.  

The number and lengths of stanchions required are as follows:

  • 21 mm long, 8 required - left side
  • 18.5 mm long, 7 required - right side
  • 16.75 mm long, 1 required - right side, rearmost stanchion.
Note that the length should be measured from the top of the "loop".  When installed, the bottom of each stanchion should be flush with the bottom of the running boards.

The holes in the 3D-printed chassis should be carefully drilled out to accommodate the stanchions (suggested drill size: 0.75 mm  - test on some scrap plastic first).  

After preforming the long handrails as per the PDF template, test fit each handrail without stanchions.  Once satisfied with the fit, remove each handrail and thread on the 8 stanchions.  It is suggested to orient all stanchions the same way, e.g. with the open side of the top loop inwards.  For the right side handrail, ensure the single, short stanchion is at the rear.

Carefully insert each stanchion vertically into the drilled holes.    It is probably best to insert the stanchions part way initially, then go along and press them down to the full depth, and also insert the ends of the handrails into the holes in the underframe.  Make sure the bottom of each stanchion is level with the underside of the running boards.

Once all the stanchions are in place and the long handrails threaded through, check that all the stanchions are vertical and make any necessary adjustments.  Then, the stanchions can be glued into the holes in the running boards and the handrails glued into the holes in the underframe.  It is optional whether to glue the handrails where they pass through the loops in the stanchions.

Separately form the U-shaped handrails on the side, and the end handrails from 0.6 mm wire, as per the template.  Install and glue the U-shaped handrails into the underframe.

Temporarily fit the loco body to the underframe in order to test fit the end handrails, the top ends of which locate into holes in the loco body.  Only glue the bottom end of the end handrails, to allow for future removal of the body.  It is suggested that the top end of the handrails should protrude approx. 1 mm into the body, to allow them to be sprung out slightly when the body is removed.


Four horns are included as part of the 3D-printed underframe.  Carefully remove them from the underframe, leaving the spigots attached to the horns intact as much as possible.  Only two are required, with two spares.

(Alternate horns can be source from detail parts suppliers e.g. in brass, if greater robustness is desired.)

Starter holes are provided for the horns on the front wall of the cab (right side) and on the left side of the long hood, just behind the vestibule door.  Consult photos appropriate to the era being modelled to determine correct horn placement.

Drill out the starter holes to suit the diameter of the spigot on the back end of the horns.  Carefully trim the unwanted spigot (projecting sideways or lengthways) from the horns.


The holes provided in the body shell for headlights are nominally 1.8 mm diameter, but typically slightly undersize due to the 3D printing process.  The headlights should be 2 mm in diameter, so drill the holes out to 2 mm taking care not damage the thin surround around the hole.

(The holes are deliberately undersize because the thin surround would not print otherwise, as the minimum detail thickness is 0.5 mm. and the outside diameter of the surround is 2.8 mm.)

One method of lighting the headlights is to use a short length of optic fibre together with a 3 mm LED (Light Emitting Diode).

The DB locos had "sealed beam" headlights for which "sunny white" LEDs are a suitable approximation.  (Many older locos had larger diameter headlights with replaceable bulbs which tended to have a more yellow appearance, similar to "golden yellow" LEDs.)

Note: Incandescent (filament) lamps are not recommended due to their high operating temperature which may damage the 3D print material.

To attach the LED to the optic fibre, 3 mm black heatshink tubing is recommended.  With the use of a hot air gun, the heatshrink tubing will shrink to form a snug fit over the optic fibre.  However, the hot air may well be hot enough to melt the plastic optic fibre, so the trick is to shrink the tubing over the shank of a 2 mm drill bit, them slide the drill bit out and slide in the optic fibre.

Typical steps are:

  1. Cut heatshrink tubing to length, e.g. 8-10 mm.
  2. Hold 3 mm LED in a small vice by its legs, with the clear lens uppermost.
  3. Push the cut length of heatshrink tubing over the clear lens of the LED.
  4. Hold the shank of a 2 mm drill bit inside the heatshrink tubing while applying heat from a hot air gun.
  5. When it has cooled, withdraw the drill bit and insert the desired length of optic fibre.  For the rear of the loco, you will probably have to feed the non-flared end of the optic fibre through the curved hole provided (from the outside) and attached the LED with attached heatshrink tubing on the inside.
CAUTION: Do not used the hot air gun or other heat source to shrink the heatshrink tubing in close proximity to the loco body or other 3D printed parts as they may distort due to the heat.

For the dual headlights, it is simplest to wire the two LED in series as this reduces the wiring and avoids the need for two separate resistors.  A resistor of around 2K2 (2,200 ohms) is a suggested starting point for LEDs powered from DCC decoders.

Marker lights can also be drilled out and illuminated if desired.