Tuesday, 22 January 2019

Marbelup Models DB Loco Kit Project

Photo of completed model, built by Chris Andrews
The Marbelup Models project to produce a 3D-printed "kit" of the Westrail DB diesel locomotive in Sn3½* scale is complete! The 3D design is done and all ordered models still have been delivered.

Photo of Test Model

Basically, the "kit" consists of 3D-printed parts for loco body, underframe, fuel tank and bogie sideframes,   The general construction is similar to the Marbelup Models D and DA locos.

The model represents the DB in "as delivered" form.  As is common, some changes were made over the working life of the locos.  The most significant change is to the steps.  The steps at the ends were built out so as to be vertical, rather than inset on the original loco (to clear platforms).  Also the side steps behind the cab, which were originally attached to the front bogie, were replaced with longer steps hanging down from the underframe.

The "kit" cost is about $410 per loco.  This is a bit more than initially estimated, partly due to the fact that the DB is a large loco.  Also, i.Materialise have removed the discount for ordering multiple parts, which adds a bit to the cost of the smaller parts (bogies, fuel tank, etc.). (Actual cost subject to variation due to exchange rate variations against the Euro and/or prices increases in 3D printing.  Current pricing is based on AU$1.00 = 0.666 Euro.)

Due to ongoing quality issues with 3D prints from i.Materialise in Belgium, Marbelup Models is not accepting any new orders for 3D-printed models, for a while at least.  In general, small parts like bogies are printing very nicely, but some larger models are causing problems.  i.Materialise claim the problem is inherent with their Standard Resin material which was introduced about a year ago, although most early prints were very good.  Some prints are still very good, but the quality is quite variable.

Note that the majority of the 3D-printed parts will be printed in "Standard Resin" by i.Materialise.  Standard resin is a relatively new material and is translucent with a yellow tint.  The "Prime Gray" material, used for most previous Marbelup Models items, is still available but is about 30% more expensive than previously.  Initial indications are that the print quality of Standard Resin is equal to or better than Prime Gray, and the material specifications indicate that it is stronger and less brittle.

To complete the loco, the purchaser must also source a mechanism as well as some detail parts, screws, couplers, DCC decoder (if required), paint, decals, etc.  Assembly instructions are available online.

There are two options for the mechanism.  One is the "inline" drive bogies available from Hollywood Foundry, as have been used for the D and DA locos.  One or both bogies can be powered, depending on the modeller's preference.  Note that Hollywood Foundry are not accepting new orders as of early 2018 for an indeterminate time.

The second option is to use the motor and drive bogies from a ViTrains UK Class 47 loco.  The Vitrains motor is fitted with flywheels and the assembled mechanism is smooth and quiet.  The drive is to the outer 4 wheels of each bogie, the centre, free-rolling axles being lightly sprung.

See Summary of Mechanism Options for more information.

Marbelup Models has purchased several ViTrains locos from the UK.  These are available for purchase as a "donor" mechanism at a cost of $140 each.  This compares favourably with the Hollywood Foundry mechanisms which cost around $200 for single bogie drive and $250 for double bogie drive (including cost of NorthYard wheels.)

The 3D-printed underframe is available in two versions, to suit either the ViTrains or Hollywood Foundry mechanism.  The different mechanisms are not interchangeable.  The 3D-printed bogie sideframes are also specific to each mechanism.

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.  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.

Please note that complete ready to run locos will not be available from Marbelup Models, although it is possible that "third parties" may offer an assembly and/or painting service at additional cost.

* The DB loco kits proposed in HO and HOn3½ scale will not be produced due to lack of interest from HO modellers.