AB Loco Assembly Tips - Draft: More Details to be Added.
These instructions are preliminary and further information will be added as time permits. Please do not hesitate to contact Marbelup Models if you find any missing information as this will prompt updates to this page.
Parts List
3D-Printed Parts
- Underframe
- Fuel Tank
- Body - cab and short hood
- Body - long hood
- Parts sprue containing motor mounts, drive shafts, and coupler shims.
- Bogie Sideframes.
Mechanical Parts
- # North Yard (NZ) drive bogies for WAGR A Class with 2 mm diameter worm shafts.
- # Motor - Auscision part no. SP-1. Includes twin brass flywheels.
- # Drive cups to suit 2 mm diameter shaft. (2 required). Four drive cups are included in North West Short Line (NWSL) U-Joint set 489-6.
- # Brass Strip 6 x 1 mm, 2 required. ( K&S part 9843 contains 3 strips.)
- Fixing screws for body, couplers and fuel tank:
# 2-56 x 11 mm, 10 required for 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 mounts - self tappers, 1.5 mm dia. x 6 mm long (4 required).
For items above marked with #, Marbelup Models has a limited quantity available for sale.
Miscellaneous Parts
- # 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 (30) (optional) - A-Line D1070 or D1071. .
- Brass wire for handrails, etc. (0.4 mm - 1 x 300 mm length, 0.6 mm - 3 x 300 mm lengths)
- Kadee couplers #146 for scale coupler height, #149 for HO coupler height (see below)
- Kadee draft gear boxes #242 (supplied as standard with Whisker couplers)
- Scrap styrene sheet, 0.25 mm thick (preferably black) for reducing coupler "droop".
- DCC decoder and speaker (both optional)
- Light Emitting Diodes (LEDs), optional, 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
- Paint and decals, as desired.
For items above marked with #, Marbelup Models has a limited quantity available for sale. Other items will need to be purchased from local hobby shops or online sources.
UNDERFRAME PREPARATION
Remove the support structure from the 3D-printed underframe.
Take particular care around areas with delicate detail, including the vacuum hoses and the areas highlighted in the following images.
Remove and save the four horns printed at the front of the central motor cutout, leaving the spigots attached to the horns intact as much as possible. Only two are required, with two spares.
 |
| Underframe Details - Right Side, Front |
 |
| Underframe Details, Right Side, Rear |
 |
| Underframe Details, Left Side, Front |
 |
| Underframe Details - Left Side, Rear |
Clean out the indicated holes with a 1.8 mm drill bit and tap with 2-56 thread.
Note: Don't use an 8BA tap. Although the thread size is similar to 2-56, the supplied 2-56 screws will be very tight in the tapped holes and will damage the threads.
 |
| Underframe Holes to be Tapped 2-56 (viewed from below) |
Clean out the indicated holes with a 1.2 mm drill bit for later fitment of the motor mounts.
 |
| Underframe Holes to be Drilled 1.2 mm (viewed from above) |
Brass Reinforcing Strips
The underframe is reinforced by two brass strips, which must be cut to length and notched, as the diagram below, to fit snugly behind the end steps.
Note that the dimensions in the diagram are a guide. You may have to trim the ends and/or notches slightly in order for the brass strips to fit so don't force them if they seem too tight. Make sure you remove any rough edges from the brass.
 |
| Dimensions for Brass Strips (2 required) |
 |
| Brass Strip Placement |
With some prior planning, the brass strips can also serve as electrical busbars to carry power from the bogie pickups to the motor or via a DCC decoder. Contact Marbelup Models if you are interested in more details on this option. Note that it will require wires to be soldered to the brass strips and this must be done prior to gluing the strips in position.
Bogies and Drive Train
Remove and discard the brass cross-bearers from the North Yard drive bogies.
Fit a drive cup to the worm shaft on each bogie, so that the end of the shaft is flush with the inside of the drive cup.
3D printed bogie side frames are included, based on a design by Butlers Swamp Models, with a couple of cosmetic improvements by Marbelup Models. Install the bogie sideframes from the top of the North Yard bogies, and secure with the 2 mm screws provided. Don't overtighten the screws, as this could distort or split the ends of the bogie sideframes.
Install the bogies using the shouldered brass screws and springs provided, with the spring on top of the 3D printed underframe. As an option, one spring can be omitted which will allow one bogie to rock more easily to accommodate any track irregularities.
Note that it will be necessary to temporarily remove two of the tiny black screws securing the inner bearing for the worm shaft, to allow the worm shaft assembly to pivot upwards during the installation of the bogies. When replacing them, do not overtighten. The worm drive will run smoother if these are backed off approx. 1/2 turn from tight.
Marbelup Models has limited stock of spare screws M1.4 x 3 mm long, in case any go missing.
Fit the two 3D-printed motor mount brackets using four 1.5 x 6 mm self tapping screws.
Fit the two 3D-printed drive shafts into the drive cups in both the motor and bogie worm shafts, and gently guide the motor into the mounting brackets. Insert the motor slightly angled to the vertical at first, to allow the lower solder terminal to fit around the mounting bracket, then rotate the motor to the vertical position as it move into its proper position.
 |
| Mechanism Assembly |
When assembled on its bogies, the top surface of the "footplate" should be 25.5 mm above rail level.
Power Pickups and Motor Wiring
The North Yard bogies incorporate "split frame" power pickups which means that each of the black metal side frames is electrically connected to the wheels via the bronze bearing blocks. Although the axles are metal, each axle is electrically insulated inside the central gear to avoid a short circuit across the rails.
The gear towers include small fork-shaped tabs secured to each side plate by means of small (M1.4) screws. Internal wiring should be soldered to each of the small "forks" which can then be detached from the bogies to allow removal of the bogies without desoldering.
The Auscision motor is not specifically marked as to + and -, but it seems that the motor terminal which has a small, round hole adjacent to it is the + terminal.
For DC operation, the + terminal of the motor should be wired to the bogie sideplate on the right side as determined when the loco is moving forwards and the - terminal to the left sideplate. This will ensure the loco's direction is consistent with other DC locos,
For DCC operation, the + terminal of the motor should be wired to the orange wire and the - terminal to the grey wire. Refer to the instructions which accompanied your DCC decoder for full details of DCC wiring.
Couplers
The coupler height of the AB loco has been set at the correct scale height for WAGR/Westrail narrow gauge rollingstock, i.e. 12.0 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. 0.8 mm thick between the coupler box and mounting pad.
If intending to fit couplers at HO height, file out 0.8 mm from the bottom of the coupler mounting holes, as per diagram below. The headstock is only 0.5 mm thick in this region.
 |
| Headstock Modification for HO Coupler 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 #242 (supplied as standard with Whisker couplers). 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.
When assembled, the #242 draft gear box does have some excess vertical clearance for the coupler shank which allows for some undesirable "droop", which is more pronounced with the long shank couplers. The droop can be largely eliminated by gluing a strip of 0.25 mm styrene, say 2 mm wide (preferably black), across the front opening of the draft gear box. Prior to gluing, smooth off any rough edges from the styrene and use a minimum amount of liquid styrene cement. When the glue has dried, test fit the couplers in the draft gear boxes. If there is any restriction in side-to-side movement, lightly file the styrene strip to increase the clearance as needed.
DCC and Sound
The AB fuel tank is specially designed to accept an Auscision SP-58 speaker. These are available from Auscision or their Australian Modeller Shop as a spare part. The mounting tabs on the speaker should be tapped 2-56 and countersunk screws, e.g. 2-56 x 8 mm, inserted from the underside of the fuel tank.
Provision has been made for automatically connecting the speaker wires when the fuel tank is installed. If you wish to pursue this option, contact Marbelup Models for further information on the parts required.
Body Preparation and Details
Depending on the supplier of the 3D printed parts, the loco body may consist of either 2 pieces (white resin) or 3 pieces (clear resin).
Assembly of 3-Piece Body
 |
| 3-Piece Body (Clear Resin) |
The cab and short hood are printed as one piece, together with an attached part which is the end of the long hood. The end piece is printed sideways, in order to minimise stepping on the curved and angled surfaces from the 3D printing process.
The first step is to separate the end piece from the cab, by cutting the 4 round joining bars, e.g. with fine sidecutters. Trim the remains of the joining bars but they don't have to be perfectly flush.
Both ends of the long hood have projecting pins which locate in holes in the end walls of the cab and the inside of the end piece. The pins are nominally 1.8 mm in diameter, so use a 1.8 mm drill bit to gently clean out the mating holes. Avoid using a larger drill or the fit will be too sloppy.
Test fit the parts before gluing, making sure they fit together snugly with no gaps. Place the cab and long hood on a flat surface, such as a piece of glass, to ensure the bottom edge is straight. Once satisfied with the fit, secure the joins with superglue which can be applied from the inside to avoid glue traces on the outside surfaces.
Assembly of 2-Piece Body
 |
| 2-Piece Body (White Resin) |
With the 2-piece body, there is a single join behind the cab with interlocking tabs.
Test fit the parts before gluing, making sure they fit together snugly with no gaps. Place the 2 sections on a flat surface, such as a piece of glass, to ensure the bottom edge is straight. Once satisfied with the fit, secure the join with superglue which can be applied from the inside to avoid glue traces on the outside surfaces.
Body Clean up and Preparation
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. 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 2-piece body has an additional brace near the body join, which should also be removed.
The eight fixing holes in the body shell and nose should be tapped with a 2-56 thread (not 8-BA!). If necessary, clean out the holes prior to tapping using a 1.8 mm drill bit.
When assembling the body to the underframe, don't overtighten the screws as this can cause warping of the underframe.
Handrails
Refer to the following diagram and screenshots for handrail details. If you print the diagram, ensure you print at 100% size for accurate dimensions.
 |
| Front Handrails |
 |
| Rear Handrails |
 |
| Top Handrail |
 |
| Side Handrails - Note different shape for long handrail if air-con fitted. |
Use of A-Line Handrail Stanchions
The above screenshots are based on the use of A-Line preformed steel handrail stanchions, an alternative, which is potentially easier than soldering, 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 30 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 AB . The A-line part numbers are D1070 (extra long) and D1071 (long) - either will do. The stanchions should be trimmed at the bottom. After trimming, file off any rough edges from the cut end.
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.
If using A-line stanchions throughout, four different lengths/shapes are required, as designated A, B, C and D on the PDF diagram. Type A and B can be simply cut to length, whereas C and D both require a 90-degree bend as well. Brass wire can be used in place of Types B and D but soldering is required.
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 stanchions. It is suggested to orient all stanchions the same way, e.g. with the open side of the top loop inwards.
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.
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 stanchions. It is suggested to orient all stanchions the same way, e.g. with the open side of the top loop inwards.
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 front 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.
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 front 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.
Uncoupling Levers
Uncoupling levers can be formed from 0.4 mm brass wire and secured to the headstocks using turned brass handrail knobs, e.g. Markits "short" variety.
Refer the PDF Handrail Diagram for the required shape for bending.
Note that the double-sided uncoupling levers, as shown below, were a relatively late addition to the AB. They were delivered with chopper couplers, so no uncoupling levers were fitted. When fitted with automatic (knuckle) couplers, the uncoupling levers were only on the left, when viewed from each end of the loco. Also, on some locos, the shape of the left uncoupling lever was different from the right one, which was fitted later. Consult photos for the particular loco and era modelled.
 |
| Uncoupling Levers |
Horns
(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.
Headlights
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 AB 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:
- Cut heatshrink tubing to length, e.g. 8-10 mm.
- Hold 3 mm LED in a small vice by its legs, with the clear lens uppermost.
- Push the cut length of heatshrink tubing over the clear lens of the LED.
- Hold the shank of a 2 mm drill bit inside the heatshrink tubing while applying heat from a hot air gun.
- 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.
No comments:
New comments are not allowed.